key: cord-0035548-iyobzuud
authors: Popper, Helmut
title: Pneumonia
date: 2016-12-24
journal: Pathology of Lung Disease
DOI: 10.1007/978-3-662-50491-8_8
sha: d1c2bbf2e5d05e99bce59329cdd7c083b199302d
doc_id: 35548
cord_uid: iyobzuud

The lung is constantly exposed to airborne infectious agents due to the large surface area of approximately 100 m(2). Therefore pneumonia is one of the most common lung diseases. Understanding infection requires understanding the routes of infections, the way invading organisms infect epithelial cells, as well as defense mechanisms of the lung tissue acquired during evolution. Different variants of infectious and non-infectious pneumonias are discussed; special types of pneumonias such as granulomatous and fibrosing pneumonias are presented under separate sections. Causing organisms and other causes of pneumonias are included, and their mode of action is included as far as understood.

The lung is constantly exposed to airborne infectious agents due to the large surface area of approximately 100 m 2 . Therefore pneumonia is one of the most common lung diseases. Understanding infection requires understanding the routes of infections, the way invading organisms infect epithelial cells, as well as defense mechanisms of the lung tissue acquired during evolution.

By the double arterial supply via pulmonary and bronchial arteries, neutrophil granulocytes or lymphocytes and monocytes can be directed into an area of infection rapidly. In addition the diameter of the pulmonary capillaries of approximately 5-6 μm requires adaptation of leukocytes and thus also slows their passage time, providing more time for contact with adhesion molecules expressed on endothelial cells, required for migration into the infected tissue [ 1 ] .

Defense system: The mucociliary escalator system can remove infectious organisms before they might act on the epithelia. The more viscous layer of mucus is at the surface, the more liquid layer at the ciliary site. Bacteria, for example, stick within this viscous mucus and can be transported toward the larynx. The cough refl ex in addition helps to expel this material from the airways. An example how important this system works can be seen in patients with immotile cilia syndrome, where an inherent gene defect causes uncoordinated ciliary beating and results in defective clearance of mucus and subsequent recurrent infections [ 2 , 3 ] .

Innate immune system: The innate immune system consists of complement activation (often via alternative pathway), surfactant apoproteins capable of bacterial inactivation, and the cellular constituents such as macrophages, granulocytes, and epithelial cells. Here we will briefl y discuss this system. For more detailed information, the reader is referred to the vast amount of immunological reviews on this subject.

There are three known activation pathways for complement: the alternative, the classic, and the lectin pathway. Opsonization seems to be the most important function of complement C3. This leads to enhanced phagocytosis of bacteria. The system seems to be self-regulated as phagocytosis of apoptotic neutrophils by macrophages leads to less C3 activation and cytokine release by macrophages and consequently less infl ammation [ 4 ] .

Several surfactant apoproteins (SP) are produced by type II pneumocytes and secreted toward the alveolar surface. Two of them SPA and SPD are members of the collectin family proteins. At their C-terminal end, they have a lectin moiety, which is able to recognize bacterial oligosaccharides (galactosylceramide, glucosylceramide) present on the capsule of bacteria such as staphylococci. This binding causes aggregation and growth arrest of the bacteria and enhances phagocytosis by alveolar macrophages [ 5 , 6 ] .

Epithelial cells form a barrier for the entry of infectious organisms and thus protect the underlying mesenchymal structures, essential for lung function. Although many organisms have developed binding sites for respiratory epithelia, such as ICAM1 used by rhinoviruses, the epithelia have developed response mechanisms such as cytokine release, for example, proinfl ammatory interleukin 1β (IL1β), tumor necrosis factor α (TNFα), IL6, IL16, chemokines as IL8, macrophage infl ammatory protein (MIP1α), RANTES, granulocyte-macrophage colony-stimulating factor (GMCSF), and others [ 7 ] . By the release of these mediators, neutrophils, macrophages, lymphocytes, and especially also cytotoxic T and NK cells are attracted and might initially already kill the invading organisms.

Macrophages are the primary source of defense against any type of infectious organism. Macrophages constantly patrol throughout the lung, ingesting every inhaled foreign material. Macrophages in contrast to monocytes live longer due to a genetic shift toward antiapoptosis by downregulating PTEN [ 8 ] . Macrophages also express Toll-like receptors (TLR2, TLR4) and CD14 and interact with SPA and CD44 to exert different functions such as release of antibacterial proteins/peptides [ 9 ] . Granulocytes interact with macrophages: if large amount of bacteria are inhaled, macrophages direct neutrophils to the site of infection, whereas small amounts of bacteria might be cleared by macrophages alone. Removal of apoptotic neutrophils requires macrophages, and this in turn decreases the infl ammatory response and neutrophil infl ux [ 4 ] . Neutrophils are able to kill many phagocytosed bacteria by producing large amounts of oxygen radicals (superoxide anions) in their lysosomes and fusing them with the phagosomes. Neutrophils are produced in the bone marrow and released from there by cytokine stimuli. Once they enter the circulation, their apoptotic program is activated. They enter the infectious site using adhesion molecules on endothelia in due time and exert their function. This is facilitated by integrins and also other adhesins. Once within the interstitium, neutrophils move along gradients of chemokines and also acidic pH.

Eosinophils are specifi cally seen in parasitic infections. This is usually mediated by T lymphocytes and will be discussed below.

Adaptive immune system: The adaptive immune system is a late invention in evolution. It requires different types of lymphocytes, such as B lymphocytes for an antibody-mediated reaction and T lymphocytes and NK cells for a direct cellmediated toxic reaction. In addition this system also requires classical dendritic cells for antigen processing and antigen presentation; these cells get in contact with invading organisms at the site of fi rst contact or in lymph nodes.

Within the bronchial mucosa, IgA-producing B lymphocytes are found. Secreted IgA is a complex, where two molecules of IgA are joined by a secretory component. In combination with other molecules such as albumin, transferrin, ceruloplasmin, and IgG, these are antioxidants and have a mucosal defense function. These molecules are increased secreted in lung injury and infl ammation [ 10 ] . In cigarette smokers the immune barrier function is impaired by a decreased release of secretory component, which in turn also decreases the transcytosis of IgA [ 11 ] . One of the most important functions of IgA secreted at the lining fl uid is opsonization of different bacteria [ 12 ] .

Different types of dendritic cells can be found in the bronchial and alveolar system such as classical, follicular, Langerhans, and interdigitating reticulum cells. These cells are thought to play a role in antigen uptake and processing. Dendritic cells also direct the type of immune reaction by interacting with different Toll receptors. Under infl ammatory conditions a Thelper1 response is favored, whereas Thelper2 responses require another mechanism [ 13 ] . Dendritic cells, for example, confronted with mycobacteria will induce differentiation of CD4 + to CD4 + 17 + cells and also induce Toll receptor 9 expression resulting in granuloma formation [ 14 ] . Some subpopulations of dendritic cells can induce immune tolerance and exhaustion, which might play a role in certain diseases, but this will be discussed in another chapter.

There are some key features characterizing pneumonias, such as fever, cough, and fatigue. Fever will give some information about possible organisms: above 39.5 °C most likely this is caused by a viral infection, whereas bacterial pneumonias present with temperatures between 38 and 39 °C. Cough can be productive with either serous or purulent expectoration. Laboratory evaluation will show infl ammatory parameters, such as leukocytosis, etc.

Radiologically the lung will show ground glass opacities and consolidations, depending on the age of the infl ammatory infi ltrate. Clinically pneumonias are separated into typical and atypical pneumonia. Atypical pneumonia can have different meanings, either an atypical infi ltration pattern on CT scans or atypical presentation with rare infectious organisms.

Although infectious pneumonia is a common disease, biopsies and surgical resections are rarely seen in pathologic practice. Most of these cases are diagnosed clinically and treated accordingly by antibiotics. If biopsied or resected, these cases usually turn out as unusual pneumonia caused by unusual organisms. Pneumonias are commonly seen at autopsy. The evaluation of infectious organisms will be discussed after the granulomatous pneumonias.

Pneumonia develops in stages, starting with hemorrhage. The lung is dark red, consistency is fi rm, and on the cut surface, there is some granularity seen, corresponding to fi brin cloths out of the alveoli (Fig. 8.1 ). In the next stage, the color of the lung changes to gray and grayish yellow. This is induced by the infl ux of leukocytes, dying of leukocytes, and release of lipid substances ( Fig. 8.2 ). The consistency of the lung is comparable to liver tissue, hence the old name "hepatization." Finally in the best scenario, the exudate is reabsorbed, the alveoli are fi lled with air, and the lung changes back to normal (lysis). Most often these classical stages are not anymore seen, because pneumonia is immediately treated with antibiotics and therefore do not develop into the yellow "hepatization" stage but resolve out of the gray-red one. However, complications of bronchopneumonia can be seen such as abscess formation (Fig. 8.3 ) and pneumonia with infarcts due to infectious vasculitis (see below; Fig. 8.4 ). Histology and development of bronchopneumonia: Bronchopneumonia in the initial stages starts with an infl ux of macrophages from the interstitial cell pool as well as from the blood vessels (monocytoid cells; Fig. 8 .5 ). Capillaries are widened (hyperemia) and the endothelial gaps are opened. Fluid from the blood enters into the alveolar spaces (infl ammatory edema) and proteins start to coagulate (fi brin cloths). This initial stage is followed by an entry of red blood cells, which undergo lysis, contributing to fi brinogenesis. In this stage fi brin nets are seen mixed with red blood cells, scattered macrophages, and neutrophils. This corresponds to the macroscopic picture of hemorrhagic pneumonia (dark red cut surface, heavy lung, edematous fl uid rinsing from the cut surface). After 1 day dense infi ltrations by neutrophils appear, mixed with fi brin nets completely fi lling the alveolar spaces ( Fig. 8.6 ). Capillaries are still hyperemic and widened. Macroscopically the cut surface changes to a gray-red color, due to the massive infi ltration by granulocytes. Since the alveoli are completely fi lled by cells and fi brin, the consistency is similar to liver (hepatic consolidation or hepatization). Granulocytes ingesting and degrading bacteria also die because of liberation of toxic lysosomal enzymes accumulate lipids within their cytoplasm, which macroscopically gives the cut surface a yellow tone (usually by day 2-3; Fig. 8 .7 ). After 6-7 days clearance of the alveoli starts: neutrophils have degraded the bacteria, macrophages clear the debris from dying neutrophils, fi brin is lysed by the enzymes from macrophages and granulocytes, and fi nally the alveoli are fi lled by air again. Under normal condition the pneumonia resolves within 10-14 days without remnants of the infectious episode.

If for several reasons no resolution occurs, acute bronchopneumonia will undergo organization. The resulting morphologic picture is organizing pneumonia (see below). 

Lobar pneumonia is characterized by a uniform infl ammatory infi ltration of the lung. Bacteria are distributed early on by an edema within a whole lobe or several segments. The pneumonia therefore will show the same timely development in all areas involved. This means that the developmental stage of the infl ammation is identical in each area investigated. Most often biopsies or resection specimen will present with dense neutrophilic infi ltrations and fi brin cloths fi lling the alveoli. Bacteria can easily be identifi ed using a Gram stain (Fig. 8.7 ). Bronchopneumonia in contrast will show different developmental stages in different areas, depending on the amount of bacteria present in a given segment. This will result in a colorful picture on macroscopy with dark red, grayish, and even yellowish areas and the same on histology: areas of hemorrhage, areas of mixed fi brinous and granulocytic infi ltrations, areas of granulocytic debris, and macrophage infi ltration.

Pneumonias with abscess formation are another form of bronchopneumonia, which most often is seen in infections with certain species of bacteria. These abscesses are based on localized necrosis, either directly induced by the bacteria or by an interaction of bacteria with the coagulation system.

Clinically acute interstitial pneumonia (AIP, also adult respiratory distress syndrome (ARDS)) is characterized by an acute onset of severe hypoxia, with the radiological appearance of white lung. Histologically there is edema and fi brinous exudate, widened edematous alveolar septa (see also below acute fi brinous pneumonia). Later on hyaline membranes are formed -this was called diffuse alveolar damage (DAD) ( Fig. 8.8 ).

Depending on the cause of DAD, scattered neutrophilic and/or eosinophilic granulocytes can be found in bacterial, toxic, or drug-induced DAD, or few lymphocytes are seen in viral and rickettsia infections, respectively [ 15 , 16 ] . Infl ammatory infi ltrates may be even absent such as in various kinds of shock. Rarely cases of "idiopathic AIP" have been reported. Probably some of these cases represent cases of undiagnosed SLE or drug toxicity. In the author's experience in all cases sent for consultation and primarily labeled as idio- Hamman-Rich described an interstitial pneumonia with fulminant course leading to death in their six cases within 6 months. In the author's description, there was no hyaline membrane mentioned but a proliferation of fi broblasts. Since the tissues from these cases were all lost, this disease cannot be reconstructed and remains an enigma [ 18 ] .

The sequence of events in DAD is largely dependent on the cause: Toxic metabolites of drugs or released collagenase and elastase from necrotizing pancreatitis will cause endothelial damage, followed by leakage of the small peripheral blood vessels. This causes edema, followed by pneumocyte cell death due to hypoxia. Serum proteins will pass into the alveolar lumina, coagulate there, and by the breathing movements are compressed into hyaline membranes (Figs. 8.9 and 8.10 ). In case of airborne disease, e.g., infection or inhaled toxins, pneumocytes type I die followed by type II. Due to the lack of surfactant lipids, the alveoli collapse. The basement membrane is either preserved or also destroyed (especially in viral infection). This again causes Drug-induced DAD (neuroleptic). In ( a ) areas of interstitial infi ltrations by lymphocytes and histiocytes are seen, as well as fi brin cloths in alveoli. There is also alveolar hemorrhage. In ( b ) there is endothelial damage and fi brin cloth, which points to the etiology (toxic sub-stance from circulation). In ( c ) fi brin cloths are seen within the septa as well as outside in alveoli, and in ( d ) there are hyaline membranes already in organization. H&E, bar 100 μm, and 20 μm in ( bd ) leakage of capillaries, edema with/without bleeding, protein extravasation into the alveoli, and fi nally formation of hyaline membranes.

The lethality of DAD is still high despite improvements, which have been made in the past decade. In some cases the progression of the disease might be blocked by antiprotease treatment [ 19 ] . In more recent time extracorporeal oxygenation or NO treatment has shown some benefi t. If the patient survives the acute phase, DAD will be organized, which is essentially an organizing pneumonia, by some authors also labeled organizing DAD: granulation tissue grows into the alveoli and hyaline membranes are incorporated into the plugs. Remnants of hyaline membranes can be demonstrated several weeks after the initial injury (Figs. 8.11 , 8.12 , and 8.13 ) . If a tissue biopsy or an autopsy specimen is available early on in the course of the disease, the etiology might be elaborated: in viral infection inclusion bodies can be seen, which can present either as nice large inclusion bodies (CMV, RSV) or by 12 DAD in organization, this is essentially an organizing pneumonia. Hyaline membranes are still visible but organized by granulation tissue, which grows within alveoli and fi nally will fi ll the lumina red-violet stained nucleic acids forming illdefi ned speckles in nuclei and/or cytoplasm (adenovirus) [ 20 ] . This is followed by atypical proliferation and transformation of pneumocytes type II (Fig. 8.14 ) . Typically the infected cell shows enlargement, an atypical large bizarre nucleus, and an accentuated nuclear membrane due to increased nucleic acid traffi c induced by the virus. These cellular features can last for several months. In contrast to atypical pneumocyte hyperplasia (AAH), these atypical cells are singles and do not form a continuous layer along the alveolar wall. Rickettsia infection results in less pronounced proliferation of pneumocytes. In shock and drug-induced DAD, the endothelia will undergo apoptosis and necrosis, and fi brin cloths might be seen in capillaries (Fig. 8.10 ). In these cases the alveolar septa are widened and edematous. Infl ammatory cells are scarce or absent. In later stages of drug pneumonia, scattered eosinophils are encountered -their function being completely unknown. What are the characteristics of DAD?

Edematous fl uid accumulation in alveoli and in the interstitium (depending on the time course) Fibrin cloths in alveoli with/without hyaline membranes Scarce infl ammatory infi ltrates (neutrophils and/or lymphocytes, etiology dependent) Minor diagnostic but etiologically important features are damage of pneumocytes, endo-thelial cells, fi brin thrombi in small blood vessels, and regeneration ± atypia Acute fi brinous and organizing pneumonia (AFOP) was recently described as a variant of DAD: the dominant pattern is accumulation of intra-alveolar fi brin and concomitant organizing pneumonia [ 21 ] . Also pneumocyte type II hyperplasia, edema, and infl ammatory infi ltrates were described. Clinically the symptoms were identi- cal to ARDS/AIP. The main difference stated by the author was the absence of hyaline membranes and the presence of fi brin cloths. The underlying causes were similar to classical DAD/AIP, so the author concluded that this might be a variant of DAD. However, some aspects have never been clarifi ed: Fibrin exudation and clothing is seen early in DAD (see also Fig. 8.9 ), so the earliest phase of DAD does not present with hyaline membranes -these are formed later on due to respiration, which compresses fi brin into hyaline membranes. Rarely DAD might also present with a multifocal pattern, which includes a timely heterogeneity: acute fi brinous exudation in one, organizing DAD in another area [ 22 ] . Within the underlying cause, similar diseases as in DAD were found, including rare cases of acute hypersensitivity pneumonia [ 21 , 23 ] .

LIP almost vanished from the literature in the last 5 years. The major problem is the separation from NSIP. When NSIP was described, it was never clearly separated from LIP [ 24 ] . When comparing my own cases and reports from the literature, it becomes evident that differences do exist: in LIP the lymphocytic and plasmacytic infi ltration is dense, hyperplasia of the bronchusassociated lymphoid tissue (BALT) is common, and within lymph follicles germinal centers are usually present [ 24 ] . The infi ltration in LIP is more diffuse, architectural distortion is common, and scarring does occur. Histiocytic and monocytic cellular infi ltrations are much less pronounced compared to NSIP. Lymphoepithelial lesions do occur similar to lymphomas, in some entities aggressively infi ltrating and destroying the epithelium; in other cases no epithelial disruption does occur. In contrast to NSIP, the architecture of the peripheral lung is remodeled, especially in later stages ( Fig. 8.15 ).

The clinical presentation depends on the underlying disease, and the CT scan usually shows ground glass opacities, in subacute and chronic stages, and also areas of fi brosis.

On gross morphology scattered areas of consolidations are seen.

Within the etiologic spectrum, similar diseases are found as in NSIP: autoimmune diseases especially collagen vascular diseases, allergic diseases as extrinsic allergic alveolitis/hypersensitivity pneumonia (EAA/HP) (acute and subacute), allergic drug reactions, HIV infection, and in children different types of immunodefi ciency (T-cell defect, NK-cell defect). The most important differential diagnoses, however, are extranodal marginal zone lymphoma of MALT/BALT type and lymphomatoid granulomatosis type I. In all cases the clonality has to be evaluated and a lymphoma needs to be excluded by proof of multiclonality.

LYG type I can be diffi cult to separate: large blasts are rare and can be obscured within a dense infi ltrate by small lymphocytes. The lymphocytic infi ltration is polyclonal, so this does not help in the separation. Therefore a search for EBV-positive blasts is essential. Also it is important to exclude posttransplant lymphoproliferative disease [ 25 ] , which can present in a similar pattern (large lymphoid cells usually EBV positive). However, it should be reminded that some of the autoimmune diseases have a high propensity of developing non-Hodgkin lymphomas later in the course [ 26 ] . Within the autoimmune diseases, Sjøgren's disease most often presents with LIP pattern [ 27 , 28 ] .

What are the morphologic characteristics?

Diffuse dense lymphoplasmocytic infi ltrates in alveolar septa and bronchial/bronchiolar walls. In some cases the lymphocytic infi ltration can form concentric rows encasing capillaries and venules. Hyperplasia of BALT with well-formed follicular centers. Focal fi brosis and scarring with distortion of the peripheral lung architecture. Lymphoepithelial lesions. Eccentric sclerosis of vessel walls with narrowing of lumina: this is usually a sign of deposition of immune complexes in the vessel walls and should prompt the search for diseases associated with the production of autoantibodies, such as Sjøgren's disease and systemic sclerosis.

Every case of LIP needs an evaluation for clonality using antibodies or in situ hybridization for kappa and lambda. As soon as a lymphoma is ruled out, further evaluation can be directed toward the underlying etiology. In a fi rst step, lymphocytes should be subtyped into B and T lymphocytes and furthermore into CD4+ and CD8+ T

lymphocytes. An evaluation of regulatory T cells using FOXP3 antibodies will also help in sorting the etiology. EAA/HP is dominated by CD8+ T lymphocytes at least in acute stages, whereas in autoimmune diseases the lymphocytic infi ltrate is usually mixed. The absence of Treg cells can be of help for the diagnosis of some of the autoimmune diseases, such as rheumatoid arthritis. 

GIP has a quite narrow etiologic spectrum either being caused by hard metal dust or by viral infection. The former will be discussed later. Several viruses can cause GIP, the classical one being measles virus. However, in contrast to pneumoconiosis in infections, the giant cells are mixed epithelial as well as macrophagocytic.

The epithelial giant cells (Hecht cells) are transformed pneumocytes type II in whom nuclear division was not followed by cell division giving rise to multinucleation [ 29 ] . The additional features are identical to DAD as described above.

Especially within the epithelial cells, viral inclusion bodies can be found ( Fig. 8.16 ). Besides measles, also respiratory syncytial virus (RSV) can present with this picture predominantly in children [ 30 ] . Alveolar and interstitial pneumonias can be induced by a wide variety of organisms. According to that they can be classifi ed as bacterial, viral, rickettsia, or parasitic. Parasitoses will be covered in eosinophilic pneumonias (Chap. 10 ).

Infectious pneumonias in childhood are quite common but are rarely biopsied. There are some differences in so far as the density of leukocytic infi ltrations is much less compared to the adult form.

Opportunistic infections as part of the infectious pneumonias in immunocompromised patients will be mentioned in the tables under the different organisms and in the chapter on transplantation pathology. Disorders related to therapeutic intervention, chemotherapeutic drug, and radiation injury will be discussed in toxic reaction due to drugs and inhalation.

Bacterial pneumonias are most often purulent; the dominant infl ammatory cell is the neutrophil. In early stages the infi ltration starts with macrophages and fi brin exudation followed by infi ltration by neutrophils. Abscess formation is common; cavitation is induced by some bacteria and most likely is induced by vasculitis and thrombosis. A few bacteria cause DAD and fi brinous pneumonia, other lymphocytic pneumonia -these tissue reactions can point to the underlying type of infection (Table 8 .1 ). A scattered type of neutrophilic infi ltration is seen in some infections such as Nocardia or Legionella In conditions where the fungi cannot be controlled, such as in bronchiectasis, the lung encases the infection by granulation tissue, starting as an organizing pneumonia, and later on a fi brous capsule separates the infectious focus from the normal lung -a mycetoma has been formed ( Fig. 8.21 ) . Normally there is a steady-state situation, i.e., no invasion of the fungus in deep areas of the lung occur, but the lung cannot get rid of the fungus. However, Fig. 8.19 ( a ) Purulent pneumonia due to fungal infection in a child being treated for leukemia. Note that the hyphae have already reached the blood vessels, which is a risk for developing sepsis. Although the size of the hyphae, the 45° angle of growth, and the septation would favor an Aspergillus type of fungus, be aware that many other fungi can look alike. In ( b ) the fungus could be identifi ed as Aspergillus niger , due to the presence of conidia. H&E, ×200, bar 20 μm there are rare conditions where invasion does occur and a chronic slowly progressing pneumonia develops -called chronic necrotizing mycosis. A few fungi pathogenic in humans can cause life-threatening infections: an example is mucormycosis. Again infection most often occurs in immunocompromised patients. The patients develop cough, occasionally mild hemorrhage, fever and shortness of breath is common. The major problem is that this fungus does not respond to many antifungal drugs therefore amphotericin B is applied, which has many toxic side effects. Pneumonia in Mucor infection presents with an infi ltration of macrophages and neutrophils, necrosis is widespread, pleura is often involved, or the infection can even enter the pleural cavity ( Fig. 8.22 , Table 8 .2 ).

Finally the reaction of the lung tissue against some specifi c forms of fungi can also be granulomatous. This reaction can be an innate immune reaction with histiocytes, macrophages, and foreign body giant cells or develop into a specifi c immune reaction with lymphocytes and epithelioid granuloma formation. However, this specifi c immune reaction depends on a functioning non-impaired immune system capable of producing different types of T lymphocytes (see below). Many fungi exhibit an angioinvasive growth behavior, i.e., their hyphae will grow toward arteries and veins directed by increase of pO 2 and immediately will invade through the vessels wall, resulting in sepsis. There exist also an allergic mycosis, called allergic bronchopulmonary mycosis (ABPA, ABPM), which is based on a sensitization against fungal proteins; this will be discussed in Chap. 10 .

Respirotropic viruses and Rickettsia cause viral and rickettsial pneumonias. One of the most common tissue reactions is DAD with hyaline membranes. In virus infections only scattered lymphocytes are seen in tissue sections, but in BAL there can be a lymphocytosis with up to 30 % of lymphocytes, predominantly CD8 + ones. Some viruses such as infl uenza type A strains can destroy the basal lamina of the epithelial layer and the capillaries by their enzymes. In these cases diffuse hemorrhage is seen with bleeding from capillaries, giving the macroscopic surface of the mucosa a dark red color. The distribution of infl ammatory changes is also important: infl uenza virus usually causes trachea-broncho-pneumonia, whereas adenovirus is more likely causing bronchiolo-pneumonia. In cases of less virulent types of strains of viruses, a lymphocytic interstitial pneumonia can be seen (Figs. 8.23 , 8.24 , and 8.25 ) . As a rule one should always try to fi nd viral inclusion bodies. They can be prominent and easily seen as in CMV or HSV infection, whereas in adenovirus infection this can be diffi cult, because of intracytoplasmic bodies. Since the virions are very small and invisible, the package is ill defi ned. Viral inclusion bodies are stained violet red due to their high content of either DNA or RNA, and viral inclusions change the internal structure of a nucleus: the nuclear membrane is less sharp, and the chromatin structure is blurred.

Clinically early pulmonary involvement appears as interstitial infi ltration with progression to nodular tumor masses obliterating the lung. As with other viral infections, mild diffuse alveolar damage to frank interstitial fi brosis is the prominent fi nding [ 31 ] . However, due to the specifi c attack of the virus toward CD4+ lymphocytes, concomitant infections are common. This also will change the histology of HIV-induced pneumonia. There can be an overlay by Pneumocystis jirovecii or cytomegalovirus pneumonia, a lymphoid interstitial pneumonia, and a desquamative interstitial pneumonia [ 32 ] . Children as well as adults can be involved. Early interstitial fi brosis and even complete resolution of the pulmonary changes can be seen early on in the disease development. Kaposi's sarcoma as a consequence of long-standing HIV infection is one of the most serious complications in these patients (this will be discussed in the tumor chapter) [ 33 ] (Table 8.3 ) .

Pneumonia in children occurs in two peak ages: in early childhood and later in school children. Whereas pneumonia in school children is not much different from that in adults, pneumonia in early childhood is different. In small children the infi ltration by leukocytes is much less pronounced compared to adults; however, the symptoms are much more pronounced. When calculating the density of leukocytes in alveolar septa, a mild infi ltration by lymphocytes can be accompanied by dramatic shortness of breath and severe hypoxia, even requiring assisted ventilation. Infection in children in the fi rst 2 years of life can happen as intrauterine infection or as an infection shortly after birth ( Fig. 8.26 ).

Infections can occur in children already in the fetal period via transplacental infection. Some of these infections such as measles when occurring during the fi rst 3 months of gestation will cause developmental defects especially in the brain. Bacterial and fungal infections will not occur in this period, because for an infection a fully developed placenta is necessary. Whereas bacterial infections via the placenta will cause placentitis and amniitis [ 34 ] and cause premature delivery or intrauterine death, infections with viruses and Rickettsia will be transmitted to the fetus. Most common although in general rare infections are caused by ureaplasma (different serotypes), CMV, EBV, and Chlamydia trachomatis and pneumoniae [ 34 -40 ] . The disease is also known under the name of Wilson-Mikity syndrome ( Fig. 8 .27 ).

Bronchopulmonary dysplasia is a specifi c condition found in premature children. Infl ammation is a major contributor to the pathogenesis of BPD, which is often initiated by a respiratory distress response and exacerbated by mechanical ventilation and exposure to supplemental oxygen [ 41 ] . Similar to Wilson-Mikity syndrome, infectious organisms such as ureaplasma and CMV have been reported to cause BPD [ 34 , 42 , 43 ] . In BPD sometimes remnants of infant DAD can be seen (hyaline membranes; Fig. 8 .28 ), but the characteristic feature is interstitial fi brosis ( Fig. 8.29 ).

Aspiration in children can be seen in two different forms: meconium aspiration during delivery causing severe respiratory distress and postnatal aspiration, most often as silent nocturnal aspiration in breast-fed babies. Risk factors for severe meconium aspiration are fetal distress and birth asphyxia [ 44 , 45 ] . The diagnosis is most often made at autopsy. In addition to DAD, also a foreign body granulomatous reaction might be seen, depending on the time the child has survived. In silent nocturnal aspiration, children swallow milk from breast-feeding and aspirate small amounts. This causes scattered ground glass opacities on CT scan and lipid pneumonia on histology. However, the diagnosis can be made by bronchoalveolar lavage: macrophages laden with lipid droplets in their cytoplasm in more than 10 % are diagnostic in this setting ( Fig. 8.30 ).

HIV infection transmitted by HIV-positive mothers can cause also HIV in the child. It has been shown that HIV-infected women as well as HIV-infected family members coinfected with opportunistic pathogens might transmit these infections more likely to their infants than women without HIV infection, resulting in increased acquisition of such infections in the young child [ 46 ] . Otherwise HIV infection in children is morphologically similar to that in adults. Within the spectrum of opportunistic infections, Pneumocystis jirovecii is the most common.

The name granuloma is derived from the Latin word granulum, which means grain. The ending -oma is a Greek ending, used to designate a nodular swelling. Therefore granuloma is a nodular, well-circumscribed macroscopic lesion. With the invention of microscopy, this term has been extended to small nodular aggregates of cells.

Over the decades the defi nition has undergone different interpretations. Some use granuloma strictly for well-circumscribed lesions, whereas others also designate a more loose aggregate of infl ammatory cells as granuloma.

Epithelioid cell granulomas originally were recognized as a granulomatous infl ammatory reaction elicited by infectious organisms. The fi rst organisms identifi ed were Mycobacterium tuberculosis and bovis and Treponema pallidum [ 47 ] . In the nineteenth century, Schaumann, Besnier, and Boeck recognized another epithelioid cell granulomatosis, which, due to the macroscopic resemblance to dermal sarcoma, they called sarcoidosis [ 48 ] . In the following decades, various epithelioid cell granulomatoses have been added, and even in the 1990s, new diseases have been reported, like zirconiosis [ 49 -52 ] .

Formation? Why Necrosis?

The formation of epithelioid cell granulomas requires a combination of at least two different sets of stimulants: (a) stimulants for granuloma formation and (b) stimulants for epithelioid and Langhans cell differentiation. So what are the driving forces? Granuloma formation is an old phylogenetic process by which complex organisms protect themselves against invading organisms or toxic substances. The invader or a toxic substance is isolated by granulation tissue or is phagocytosed and degraded simply by macrophages as part of the innate immune system. If these cells can kill the invading organism, no further defense line is required. If the invader cannot be ingested and degraded by these cells, histiocytes and macrophages can form foreign body giant cells, which are more effi cient in phagocytosis and degradation. These cells together form foreign body granulomas. In every case the invading organism cannot be killed by phagocytosis, another defense line is activated, which includes immune mechanisms. This more powerful line of defense is the epithelioid cell granuloma. The driving forces, which induce granuloma formation, are the macrophages, the antigen-presenting cells, such as Langerhans and dendritic reticulum cells, and the T and B lymphocytes [ 53 -56 ] . Among the different cytokines released are interleukins 1β, 2, 3, 8, 10, 12, 17, macrophage migration inhibitory factor 1 (MIF1), IFNγ, and TNFα. How these factors act and interact is still not understood; however, macrophages and lymphocytes are activated and immobilized. This is followed by the cytokine-induced transformation of macrophages into epithelioid and foreign body giant cells [ 57 -62 ] . Giant cells can be either formed by fusion of macrophages or by nuclear division without cell division. Foreign body giant cells further on differentiate into Langhans giant cells. This process of transformation is maintained by the same secretory factors, which are produced in larger quantities by the epithelioid cells and by infi ltrating lymphocytes [ 63 ] .

But why do we fi nd non-necrotizing and necrotizing epithelioid cell granulomas even in the presence of the same organism? Different substances either actively liberated from mycobacteria or passively by degradation can induce granuloma formation. Among them are trehalose-6,6′-dimycolate, lipoarabinomannan, and 65 kDa antigen of mycobacterial capsule (a chaperonin) [ 61 , 62 ] . These products stimulate granuloma formation by the induction of cytokine gene expression, mainly IL1β or TNFα. In addition they have other effects, like induction of apoptosis, enhancing coagulation, and together release TNFα, which subsequently induce necrosis by occlusion of small blood vessels. The mycobacterial chaperonin also stimulates monocytes to express mRNA for TNFα and to release IL6 and IL8, cytokines which are chemoattractants for lymphocytes. In some patients necrotizing and non-necrotizing epithelioid cell granulomas, induced by M. tuberculosis , can be found side by side. The underlying mechanism is not completely understood. One possible explanation might be the mycobacterial burden: large amounts of mycobacteria release large quantities of coagulation factors and thus induce infarct-like necrosis. Another explanation is within the interaction of virulent stains of mycobacteria and host defense cells [ 63 ] .

When we go back to morphology, we can see three different settings, in which we encounter necrosis: M. tuberculosis escape the immune defense, multiply, invade vessel walls, and are in part degraded by leukocytes, and by this a massive liberation of capsule constituents occurs; epithelioid cell granulomas develop in vessels walls and obstruct or occlude the vessel lumen, and ischemic necrosis follows; an imbalance of the virulence of the mycobacteria and the immune defense capability of the host is in favor of the invading organism. These factors together might lead to higher concentration of TNFα, as well as trehalose-6,6′-dimycolate, lipoarabinomannan, and chaperonin. In addition vasculitis-associated and released thrombogenic factors may synergistically act together to induce this characteristic caseous necrosis (Fig. 8.31 ). When classifying granulomatous pneumonias, we will discern epithelioid from histiocytic granulomas and as a second step differentiate infectious from noninfectious forms.

Epithelioid cell granulomas are a specifi c form of granulomas, composed of epithelioid cells, giant cells, and lymphocytes (epithelioid: epithel = the stem of epithelium and oid = similar to). This type of granuloma can be induced by a variety of quite different stimuli. Epithelioid and giant cells are specialized members of the monocyte/macrophage lineage, the fi rst a differentiated secretory cell ( Fig. 8.32 ) and the second a specialized phagocytic cell ( Fig. 8.33 ). Giant cells can be either formed by cell fusion or by incomplete cell division (no cytoplasmic division). Both ways have been proven experimentally [ 56 , 64 , 65 ] . First foreign body giant cells are formed, which later reorganize into Langhans cells. These are characterized by a nuclear row opposite to the phagocytic pole of the cell. Lymphocytes are usually layered at the outer granuloma shell and can be numerous or sparse. Phenotypically these are T lymphocytes, whereas B lymphocytes are loosely arranged outside the granulomas. T-helper-1 and T-helper-2 and cytotoxic T lymphocytes (CD8 + ) can be present in the granulomas, with the composition depending on the type of underlying disease. This will be discussed later. We can encounter different stages of granuloma formation: fi rst we see a loose aggregation of macrophages, histiocytes, lymphocytes, and even neutrophils. During each step the granuloma becomes more compact, and the margins are better circumscribed. During aging, epithelioid cell granulomas might undergo fi brosis and hyalinization (Figs. 8.34 , 8.35 , and 8.36 ) . However, in some diseases like extrinsic allergic alveolitis, the epithelioid cell granulomas remain less well delineated and tend to be more loosely arranged. Also a spillover of lymphocytes into adjacent alveolar septa is seen.

A very important fi nding is central necrosis, defi ning the necrotizing epithelioid cell granuloma. Small necrobiotic foci or few apoptotic cells are not regarded as necrosis. The necrosis is either stained eosinophilic with minimal amounts of nuclear debris, or may contain larger amounts of nuclear debris, or stained blue violet by H&E. In early necrosis neutrophils can be found. The descriptive term caseous necrosis is often used; however, it should be reminded that this term was invented to describe these necroses macroscopically: a caseous necrosis is characterized by a yellowish color and soft, cheese-like consistency (Fig. 8.31 ).

Pathologists usually differentiate granulomatoses by their morphologic appearance: if there is an epithelioid cell granuloma with necrosis, primarily infectious diseases are to be discussed, whereas in non-necrotizing granulomas, other diagnoses are to be added. Although this rule will be true in most cases, it should be reminded that sometimes necrosis is not associated with infection, as in necrotizing sarcoid granulomatosis and some cases of bronchocentric granulomatosis. The distribution pattern of the granulomas may assist in sorting out specifi c diseases: the distribution of granulomas along lymphatic vessels is quite characteristic in sarcoidosis, whereas an airspace-oriented pattern is seen in most infectious epithelioid cell granulomatoses. However, the distribution pattern might not be apparent in transbronchial biopsies. Schema: The balance of the host's immune system capability and the virulence of the mycobacterial strain: extensive necrosis in tuberculosis associated with alveolar proteinosis points to impaired immune reaction, whereas a good functioning immune system and slowly growing mycobacteria will result in healing or scar.

A wide variety of responses and patterns can occur in tuberculosis. Infection in the European There is widespread necrosis and the granuloma formation is impaired. The granuloma wall is broken down at two areas in this section, and mycobacteria can escape the host's immune defense. H&E, ×100 population is frequent; up to 90 % of the population acquire a mycobacterial infection in early adulthood; however, only 1-3 % of this population will present with symptoms. In the majority of the population, this infection will cause tiny granulomas in the mid and upper portion of the lower lobes. These granulomas undergo fi brosis, and a scar is all what can be found quite frequently in this location at autopsies decades later.

Clinical symptoms are cough, night sweats, temperature around 38 °C, and fatigue. Radiologically tuberculosis presents with single or multinodular densities but also often simulates lung cancer. Even on CT scan, the differential diagnosis cannot be made with certainty.

In patients presenting with tuberculosis, the initial form is most often a multinodular disease with caseous necrosis but located in one of the lung lobes (usually lower lobes). Depending on the ability of the patient's immune system, vasculitis can occur. Under tuberculostatic treatment this type of tuberculosis usually heals leaving scars and bronchiectasis. These in later life can be the preformed cystic structures prone to mycetoma.

In rare instances the primary infection had destroyed large areas of the lung and the necrotic focus cannot be replaced by scar tissue. In this case the necrotic focus is encased by granulation tissue, which is subsequently replaced by scar tissue. In the center the necrotic focus is still present, and mycobacteria are viable. This lesion is called tuberculoma (Fig. 8.40 ) .

Secondary tuberculosis can occur in some patients in later life either as an exacerbation from a tuberculoma or by a secondary infection. In these cases the upper lobes are more often affected. Usually in this condition, miliary tuberculosis occurs: myco- Tuberculoma detected incidentally during X-ray and removed because clinically suspected for malignancy. Resection specimen formalin fi xed bacteria get access to the blood vessels causing vasculitis, and the organisms are disseminated within the lung but also to other organs (Fig. 8.41 ).

There are some complications from tuberculosis, such as hemorrhage, when the necrotizing granuloma destroys the wall of larger pulmonary arteries. This will cause diffuse bleeding and ultimately the death of the patient (Fig. 8.42 ). Another complication is access of the granulomas and their mycobacterial content to larger airways, which will result in aerogenous spreading of the organisms, but also infection of other humans within the patient's living area (Fig. 8.43 ) .

Diagnosis is established fi rst by the demonstration of an epithelioid granulomatous reaction, followed by the proof of mycobacteria within the granuloma or in cytological material (BAL, smear) and by culture or PCR. This will be discussed in detail at the end.

This is an infection with atypical mycobacteria (other than M. tuberculosis complex (MOTT)). It was once a rare disease, causing epithelioid cell granulomas in newborn and young children. It now has become a well-recognized disease in patients suffering from AIDS, or in otherwise immunocompromised patients. Many different mycobacteria can induce predominantly non-necrotizing epithelioid cell granulomas, among them M. avium -intracellulare, M. fortuitum , M. gordonae , M. kansasii , and M. xenopi , to name just the more common species. Some cause local disease, like skin lesions by M. marinum , whereas others cause systemic disease, like M. avium (Fig. 8.44 ). The diagnosis of mycobacteriosis can be made by acid-fast stains but in most instances requires culture or molecular biology techniques for species defi nition. In cases of severe immunodefi ciency, the host's reaction might be impaired, which results in the inability to form epithelioid cell granulomas. In these cases macrophage granulomas are found, similar to granulomas in lepromatous lepra.

The reproductive cycle of MOTT species is quite variable: M. avium -intracellulare is a very slow-growing organism, which requires a culture for up to 11 weeks until the organism can be identifi ed, whereas M. fortuitum is a fast-growing organism, which can be identifi ed within 2 weeks. Necrotizing granulomas are usually found in these fast-growing species.

Recently a new disease was described as hot tub lung disease. Mycobacteria of the MOTT complex were identifi ed as the causing agent [ 66 , 67 ] . If this is an infectious disease caused by slow-growing MOTT, species in otherwise immunocompetent patients or a hypersensitivity reaction is not clear. An answer to this question is complicated as a hyperreactivity or allergic reaction can occur in mycobacterial infections as part of the immune defense and thus is not a proof of an allergy (Fig. 8.45 ). Biopsies from patients suffering from this type of disease will show exposure-related symptoms, i.e., increase of symptoms during the weekend (exposure to mycobacteria in hot tub) and relief of symptoms during the week. Morphologically the lesions present as non-necrotizing epithelioid cell granulomas, similar to classical mycobacteriosis with slow-growing mycobacteria such as M. avium -intracellulare (Table 8 .5 ).

In certain areas of the world, M. leprae is still widespread and infection due to bad hygiene conditions does occur. Areas with still high prevalence are in tropical Africa and Asia, less frequently South and Central America. Predilections are found in skin, upper respiratory tract, nerves, and testes. Lung lesions and involvement of other organ systems are rarely encountered; however, they do occur in end-stage disease (personal communication). Whereas in lepromatous leprosy, there is an unspecifi ed macrophage-dominated host reaction, in granulomatous leprosy the host is able to mount an epithelioid cell reaction. Necrosis in these granulomas is uncommon; in most instances the granulomas resemble those seen in sarcoidosis. In cases of borderline tuberculoid reaction (mixture of tuberculoid and lepromatous leprosy), the granulomas tend to be more loose than those in tuberculosis (Fig. 8.46 ). The differentiation of macrophages and histiocytes into epithelioid 

There are a few bacteria, other than mycobacteria, which can induce the formation of epithelioid cell granulomas. Among these Treponema pallidum is the best known. Treponema pallidum , the causative agent of syphilitic gumma, still exists, although rare in Western countries. In recent years a rise of syphilis is seen in Asian and South American countries, and new cases appear in Europe due to "sex tourism." In most instances it might be diffi cult to get the proper information from the patients. The primary infection sites are the external genitalia, where a granulomatous and ulcerating infl ammation starts. After bacteremia the organisms can enter the lungs. Infl ammation is characterized by necrotizing epithelioid cell granulomas with numerous neutrophils within the central necrosis (Figs. 8.47 , 8.48 , and 8.49 ). Vasculitis is commonly seen in this granulomas causing vascular obstruction. The name gumma, used for these granulomas, is derived from their macroscopic appearance: the central necrosis is not caseous as in tuberculosis but has a gumlike consistency, hence the name (gummi arabicum). The Treponema organisms can be stained by silver impregnation (modifi ed Warthin-Starry stain, Fig. 8 .50 ) or immunohistochemically by specifi c antibodies.

Other bacteria able to mount an epithelioid granulomatous reaction are other members of the Spirochaetae family, like Leptospirochaetae .

In rare instances atypical bacteria form a histiocytic granulomatous infl ammation. Some of these were initially included in malakoplakia. However, infectious organisms have been identifi ed in some of these, such as Rhodococcus equi and Tropheryma whipplei , the causing organism of Whipple's disease (Fig. 8.51 ). Actinomyces another rare bacterium can cause either purulent pneumonia with abscess formation or also a histiocytic granulomatous reaction (Fig. 8.52 ). 

Most often fungi cause either a localized mycetoma or a diffuse bronchopneumonia. Rarely they will cause a granulomatous reaction. However there are species, such as Histoplasma , which more often induce granuloma formation. Information on the epidemiology, the distribution, reproduction cycles, and much more can be found at the website of the Center for Disease Control and Prevention (CDC: www.cdc.gov ). Clinical symptoms are similar to tuberculosis. On X-ray and CT scan, nodules of different size can be seen, often in both lungs. Based on the different forms of cysts and sporozoites, and with the aid of additional stains, the following mycoses can be differentiated:

Histoplasma organisms are found in wet lowland areas. H. capsulatum is widespread in the soil of North American river valleys, especially in valleys fl ooded annually, for example, the Mississippi river and its main tributaries. For reproduction this organism requires periodic fl ooding, after which spores are produced. These spores will resist deterioration for a long time and are the source for infection. In certain areas of Mesoamerica, animals such as bats are another source of infections, and outbreaks have been reported [ 68 ] . Its occurrence in Europe has been described in humans (Fig. 8.53 ) but also in animals. Histoplasma capsulatum is a yeastlike uni-nucleate organism, 2-4 μm in diameter. It reproduces by budding or by endospores. The organisms are usually found within macrophages and histiocytes but also in the necrotic debris.

Capsules of Histoplasma can be stained by GMS and by PAS, leaving the center unstained. With Giemsa the nuclei of the sporozoites are stained, leaving the capsule more or less unstained. The African variant is Histoplasma duboisii , which is larger than H. capsulatum. H. duboisii similar to H. capsulatum exists in the soil of river valleys, along the large African rivers, like the Niger. Lung lesions in African histoplasmosis are less frequent than with the North American form. Acute histoplasmosis presents with bronchopneumonia and abscess formation; the reaction is dominated by neutrophils and macrophages. In chronic forms epithelioid cell granulomas are seen in both; however, necrotizing granulomas are more frequent in H. capsulatum -induced lesions. This form of histoplasmosis can look identical to necrotizing tuberculosis; only the stain for the organisms will tell the difference.

Cryptococcus neoformans and C. gattii are distributed worldwide, except the arctic and antarctic circles. The organisms are found in the soil or in the droppings from pigeons. Airborne spores are inhaled but usually cause infection in patients with weakened immune system. The organisms are 4-7 μm in diameter, their cell walls can be stained by H&E, but the mucinous capsule is usually unstained. Mucicarmine or PAS stains are helpful in highlighting the capsule. The organisms reproduce by budding. The small or large yeastlike organisms are found side by side, and buds might be small or large and show prominent fragmentation, which distinguish them from Histoplasma and Blastomyces . In the acute setting, cryptococcosis causes a bronchopneumonia with abscess formation but also accumulations of macrophages within their cytoplasm, the organisms can be demonstrated. In the subacute and chronic form, epithelioid granulomas are formed [ 69 ] . The organisms are usually found within Langhans giant cells, but may also be found lying free within necrosis ( Fig. 8.54 ).

Blastomyces dermatitidis can be found in North America and Africa. The fungus lives in moist soil where decomposing organic matter supplies its nutrients. It is a thick-walled round 8-15 μm organism, which reproduces by budding. The buds are numerous and are broad based attached to the parent yeast. The fungus has many nuclei, which distinguish it from Cryptococcus and the Coccidioides organisms. GMS stain the whole yeast; the capsule can be highlighted by PAS or mucicarmine stains. Infection occurs by inhalation of airborne spores. The symptoms of acute blastomycosis are similar to fl u. Blastomyces regularly induce a granulomatous reaction with and without necrosis; however, the necroses are not of the classical caseous type: they contain cellular debris and many neutrophils. 

Coccidioides immitis is found in the soil of dry, desertlike areas in the southwestern parts of the USA, but also in Central and South America. It is also known as valley fever and is a common cause of pneumonias in these endemic areas. It is characterized by large sporangia, 30-60 μm in diameter, the endospores are each 1-5 μm. They can be identifi ed in H&E-stained sections; however, GMS and PAS also stain them (Fig. 8.55 ). The sporangia can be found within giant cells or free within necrosis. In some cases an acute bronchopneumonia with a dominant neutrophilic and macrophagocytic infi ltration is seen; in other cases classic epithelioid cell granulomas are developed.

Paracoccidioides brasiliensis -found in South America -is characterized by multiple buds growing out of one organism. The single fungus is 5-15 μm in diameter but by budding may approach 20-40 μm (Fig. 8.56 ). The fungus is uninucleate and the buds are of varying size Other fungi causing deep mycosis rarely induce epithelioid cell granulomas. In most instances organisms, like Aspergillus , Candida , Pneumocystis , and others, cause a localized mycetoma, or a diffuse invasive mycosis, or an allergic reaction (allergic bronchopulmonary aspergillosis/mycosis). The cause for organisms like Aspergillus or Pneumocystis to induce an epithelioid cell granulomatous infl ammation is largely unknown (Figs. 8.57 and 8.58 ).

These granulomas are characterized by the absence of central necrosis; however, necrobiotic foci can occur. It is important to rule out neutrophilic, eosinophilic, and mixed granulocytic and lymphocytic vasculitis, which is the hallmark of a 

The diagnosis is based on the exclusion of cultivable and/or stainable organisms. Important are the clinical picture and the radiological data, like bilateral hilar lymphadenopathy on X-ray. The granulomas are most frequently found along bronchovascular bundles, pulmonary veins, and lymphatics. High-resolution CT scans are useful to highlight this distribution pattern ( Fig. 8.59 ).

In sarcoidosis the earliest lesion is characterized by an accumulation of macrophages/monocytes and lymphocytes within alveolar septa and underneath the bronchial mucosa (Fig. 8.60 ). These monocytoid cells differentiate into epithelioid and giant cells. Early on foreign body as well as Langhans giant cells can be seen. Later on lymphocytes become scarce, and the granulomas stick out from an otherwise not infl amed parenchyma (Figs. 8.61 , 8.62 , and 8.63 ). Well-formed granulomas undergo fi brosis, which usually starts from the outside of the granuloma in a concentric fashion. Finally a hyalinized granuloma remains, which will show an occasional epithelioid cell (Fig. 8.36 ). In fully developed granulomas, lymphatic vessels can be seen transversing the granuloma, sometimes also capillaries. A granulomatous vasculitis pattern can be seen in some cases (Fig. 8.64 ). Granulomas are usually within the interstitium and do not show any association with the airway epithelium. Some features have been regarded as specifi c, like asteroid, Schaumann, and conchoid bodies in the Langhans cells. However, these structures can be seen in all Langhans cell containing granulomas of diverse etiology and are of no help in making the diagnosis of sarcoidosis. Calcium oxalate, carbonate, and pyrophosphate crystals can be found in granulomas and in Schaumann bodies; however, they are not diagnostic too (Fig. 8.65 ) . A T-helper lymphocyte (CD3 + CD4 + )-dominated alveolitis in the BAL might supplement the histologic diagnosis.

Diagnosis on small biopsies and cytological specimen is easy in sarcoidosis. Due to the predominant distribution pattern along the bronchovascular bundles, transbronchial biopsies are most often diagnostic (Fig. 8.66 ). Since sarcoidosis also involves the hilar lymph nodes, EBUSderived fi ne needle aspiration is also most often diagnostic (Fig. 8.67 ) .

A variant of sarcoidosis has been described as nodular sarcoidosis . In this form of sarcoidosis, the granulomas coalesce forming large aggregates, which can reach a diameter of up to 3 cm (Fig. 8.68 ) [ 70 , 71 ] . Clinically nodular sarcoidosis does not behave different from common sarcoidosis. Also the therapy and prognosis is similar.

Another variant of sarcoidosis is necrotizing sarcoid granulomatosis (NSG). In NSG non-caseating epithelioid cell granulomas are found. The distribution is similar to sarcoidosis with a dominant involvement of the bronchovascular bundle. In addition there is an epithelioid granulomatous vasculitis causing ischemic infarcts. The granulomas can usually confl uent, forming large nodules identical to nodular sarcoidosis; the lymphocytic rim is usually prominent (Figs. 8.69 and 8.70 ). Liebow originally described this disease as a separate entity [ 72 ] , because he assumed that it has features in between Wegener's granulomatosis (vasculitis, ischemic necrosis) and sarcoidosis (nodular aggregates of epithelioid cell granulomas). Based on our own observation and research, we proposed NSG as a variant of sarcoidosis, characterized by nodular aggregates of epithelioid cell granulomas, granulomatous vasculitis, and ischemic infarcts [ 73 , 74 ] : granulomatous vasculitis is a feature in NSG and sarcoidosis, ischemic necrosis in NSG is due to lumen obstruction induced by vasculitis, and fi nally like sarcoidosis NSG is also a systemic disease involving several organs (liver, spleen, ocular adnexa, lymph nodes, etc.).

The etiology of sarcoidosis is presently a matter of debate. It has been shown that in some cases, mycobacteria could be cultured from sarcoidosis granulomas of the skin after subculture [ 75 , 76 ] . Different investigators succeeded in demonstrating mycobacterial DNA and RNA in sarcoidosis. We have found mycobacterial DNA other than tuberculosis complex (MOTT-DNA) in one third of sarcoidosis cases. Others could demonstrate DNA of Propionibacterium acnes [ 77 -83 ] . Neither mycobacteria nor propionibacteria could be cultured directly from the granulomas. So how to interpret this? Is the fi nding of bacterial DNA in sarcoidosis granulomas incidental? Could it be causative for It has been speculated that cell wall-defi cient mycobacteria, unable to grow, might induce sarcoidosis. We have shown that in some cases, DNA insertion sequences, characteristic for M. avium , could be amplifi ed from granulomas. In three cases of recurrent sarcoidosis in lung transplants, mycobacterial DNA other than tuberculosis complex could be found [ 84 ] . Other recent reports have demonstrated that naked mycobacterial DNA is capable of inducing a strong immune response [ 85 -87 ] . And it is known that mycobacteria can preferentially persist in macrophages. In a working hypothesis, we assume that slow-growing members of mycobacteria might elicit an allergic reaction, in the background of a host's hyperergic predisposition. Via circulation these allergens could be distributed to different organ systems, elicit-ing the well-known perivascular granulomatous reaction.

By gene profiling we have identified genetic deregulation of proliferation and apoptosis. In sarcoidosis patients with active disease, proliferation pathways involving the phosphoinositol-3-kinase-Akt2 pathway, including Src kinase, and crk-oncogene, as well as fatty acid-binding proteins 4 and 5 together with PPARβδ, induce proliferation of macrophages and lymphocytes of Th1 lineage. In addition the apoptosis pathway is downregulated by protein 14-3-3. So probably the underlying defect in sarcoidosis might be a prolonged proliferation of lymphocytes and macrophages and a longer survival of these activated cells, which then causes disease [ 88 ] . The mechanism by which mycobacteria or propionibacteria can trigger this inflammatory reaction is still unclear, but the answer might be found in the mechanisms of antigen processing and presentation. Other theories are focusing on polymorphisms of different genes such as TNFβ and HSP70 [ 89 ] . A lot of research has focused on polymorphisms within the HLA system. HLADRB1*0301/ DQB1*0201 has been linked to good prognosis and Lofgren syndrome; a linkage study found genetic alterations on chromosome 5 in African American sarcoidosis patients, whereas another linkage to chromosome 6 (identified as BTNL2 gene) was found in a German population [ 90 ] . Finally studies have focused on the Toll-like receptor (TLR) family, which are responsible for the processing of antigens and also dictate the type of immune reactions. Modifications within the TLR4 might be associated with the susceptibility for sarcoidosis [ 91 ] .

The proof of mycobacterial DNA in sarcoid granulomas has serious diagnostic implications: molecular proof of mycobacterial DNA does neither rule out sarcoidosis nor confi rm mycobacteriosis. The clinical setting, the radiological data, and the histological and microbiological proof of stainable/viable mycobacteria are required. In recurrent sarcoidosis in lung transplants, even DNA sequencing is necessary, to discern MOTT-DNA positive cases of sarcoidosis from secondary mycobacterial infection in the transplant.

Chronic berylliosis is an allergic epithelioid cell granulomatosis. The granulomas tend to be larger than in EAA/HP or sarcoidosis; however, it is impossible to differentiate them morphologically from sarcoidosis. The granuloma itself is identical to the granuloma in sarcoidosis (Fig. 8.71 ). As in sarcoidosis no infectious organisms can be demonstrated in the granulomas. No larger series of BAL have been reported in berylliosis so far. However, in an experimental investigation, a predominance of T-helper lymphocytes has been reported, making BAL an unsuitable tool for the differentiation of berylliosis and sarcoidosis. For the diagnosis a lymphocyte transformation test is usually recommended, and an exposure history is necessary. The exact cause of berylliosis is still unclear. Beryllium oxide is a molecule, too small to induce an allergic reaction. Berylliumprotein complexes most probable induce this reaction. Beryllium might form tetrameric complexes with amino acids and alter the tertiary structure of proteins, subsequently eliciting an allergic reaction [ 92 , 93 ] . A genetic predisposition for chronic allergic berylliosis has been proven [ 94 ] , and recently tetramers of beryllium-loaded HLADP2-mimotope and HLADP2plexin A4 have been detected in patients. This tetramers bind specifi cally to CD4 + T cells and might elicit the allergic reaction [ 95 ] . By electron microscopy and EDAX analysis, beryllium oxide can be proven in the granulomas. It should be reminded that in routinely processed specimen, the beryllium oxide is often leached out from the tissue by the solvents used for fi xation, dehydration, and embedding. The same is true for an analysis, using laser-assisted mass spectrophotometry (LAMA) in paraffi n-embedded tissues.

Another rare occupational allergic granulomatous reaction against metal compounds was reported for zirconium. Zirconium dust can induce non-necrotizing epithelioid cell granulomas, similar to beryllium oxide, probably based on a similar mechanism.

This is a granulomatous lung disease, induced by an allergic reaction against different fungi, plant pollen and proteins, and also animal proteins. In open lung biopsies, epithelioid cell granulomas are frequently seen in EAA/HP, whereas they are quite rare in transbronchial biopsies. This might be a technical and distribution phenomenon: whereas granulomas in sarcoidosis are easily found in the bronchial mucosa, in EAA/HP the granulomas are more frequent in the periphery of the lung, usually distributed along small blood vessels (venules, capillaries; Fig. 8.72 ). Granulomas are, however, not the diagnostic requirement of EAA/ HP: a dense lymphocytic interstitial infi ltration centered upon small blood vessels alone raises the differential diagnosis of EAA/HP (Fig. 8.72a ) . As in sarcoidosis all special stains for infectious organisms are negative. In contrast to sarcoidosis, the granulomas in EAA/ HP are more loosely organized; they have usually a broader rim of lymphocytes, and the lymphocytic infi ltration spills over into the adjacent alveolar septa. In active disease there may be a lymphocytic interstitial infi ltration with or without lymph follicle hyperplasia. Very helpful is the BAL: in EAA/HP there is a lymphocytic alveolitis with a predominance of cytotoxic T lymphocytes (CD8 + , CD11a + ). The CD4/CD8 ratio should be <0.8. However, it should be mentioned that a few exceptions to this rule have been reported. There is also a time effect: under antigen restriction the helper-suppressor ratio normalizes within a week and in some cases may even become >1.0 within a few days (unpublished personal observations).

In chronic EAA/HP a variety of other forms of pneumonia have been reported: NSIP, UIP, and OP can be seen; however, in my experience a lymphocytic infi ltration is usually present even in these late stages (Fig. 8.73 ). In contrast to acute HP/EAA, CD4 + lymphocytes can dominate the infi ltration, which might cause concerns about the differentiation from sarcoidosis. But the combination of epithelioid cell granulomas with fi brosing types of pneumonia such as UIP, NSIP, or OP rules out sarcoidosis. In sar-coidosis fi brosis starts from the granulomas in a concentric fashion and in my experience is never combined with fi brosing pneumonia.

Not infrequently an epithelioid cell granulomatous infl ammation in the lung and hilar lymph nodes in the setting of a bronchial carcinoma or lymphoma is found. The granulomas are indistinguishable from those in sarcoidosis. The distribution of lymphocyte subsets is similar to sarcoidosis. Lymphocytes in the granulomas are predominantly CD4 + helper cells, whereas CD8 + and B lymphocytes are found in the surrounding areas (unpublished personal observations). Within the lungs sarcoid granulomas are found along the draining lymphatics, a pattern also seen in sarcoidosis. A careful examination of all available data is necessary to separate this reaction from sarcoidosis: If we are dealing with lymph nodes, we usually end up with a differential diagnosis of epithelioid cell granulomatous lymphadenitis, sarcoidosis vs. sarcoid reaction. The cause of these sarcoid granulomas has never been elucidated. The most reliable assumption is that cytokines released from lymphocytes and macrophages together with mediators liberated by tumor cell death induce this type of reaction.

We will briefl y mention GPA and parasitic granulomas. GPA besides other features is characterized by a granulocytic vasculitis and by necrosis (ischemic infarct). Epithelioid cell granulomas can be found in approximately 30 % of cases; however, since the changes in the vasculitis classifi cation, those cases without granulomas might fall into microscopic polyangiitis. Also parasitic infections can present with epithelioid cell granulomas. However, in parasitic infections eosinophils are the hallmark, not seen in this quantity in the diseases discussed above (this will be discussed in chapter on eosinophilic diseases).

In cases of a negative AFS, GMS, and PAS stain, one should think of rheumatoid arthritis involving the lung and pleura. Although in the majority of cases lung involvement is usually associated with one of the variants of interstitial pneumonia, rarely a granulomatous reaction can be found. This might take the appearance of a classic rheumatoid granuloma with palisading histiocytes or an epithelioid cell granuloma without central necrosis, associated with seropositivity (Figs. 8.74 and 8.75 ). Both types of granulomas can be found side by side. For confi rmation immunohistochemical stains for immunoglobulins and complement components can be used. Central necrosis very often contains remnants of destroyed collagen fi bers (visible under polarized light), unusual in other variants of granulomatoses. It should be mentioned that rare cases of coincident rheumatoid arthritis and tuberculosis do exist; therefore mycobacteria should be excluded in these epithelioid cell granulomas. A more detailed discussion of common patterns in rheumatoid arthritis with lung involvement will follow in another chapter.

The hallmark is a necrotizing bronchiolitis with peribronchiolar extension of the infl ammatory infi ltrates. In the lumina necrotic debris can be seen, and remnants of fungi should be demonstrated. Within the bronchiolar walls, epithelioid cell granulomas and/or palisading histiocytic granulomas are found. In addition there is usually a dense infi ltrate of eosinophils. In this classic variant, BCG is induced by an allergic reaction against different types of fungi, most often members of the Aspergillus family ( Fig. 8.76 ). However, AFS and GMS stains should always be performed to exclude mycobacteria, especially when the infl ammatory infi ltrates contain many neutrophils (Fig. 8.76d ) . Another organism Actinomyces can present with bronchocentric granulomatosis, again with neutrophils in the necrotic center. In all these cases, BCG is an infectious disease, not allergic. If AFS is negative, fungal remnants are proven by GMS or PAS stains, and eosinophils are admixed to the granulomas, a diagnosis of bronchocentric granulomatosis as a variant of allergic bronchopulmonary mycosis/aspergillosis (ABPM/A) can be made. In my experience, it is often necessary to perform serial sections to demonstrate the fungus. The clinical information about positive allergy tests might be helpful. Combinations of type 1 and 4 immune reactions can be seen in this form of ABPM. In rare cases bronchocentric, necrotizing granulomatosis might also be seen in the setting of Wegener's disease. Therefore ANCA tests can be helpful in this differential diagnosis.

Both colitis ulcerosa and Crohn's disease can involve the lung (Fig. 8.77 ). In Crohn's disease a variety of patterns can be found; in most cases these are nonspecifi c. Without the knowledge of Crohn's disease, it might be impossible to make the correct association. Fortunately in about 84 % of cases, the bowel precedes lung involvement (Table 8 .6 ). Within the necrosis remnants of collagen fi bers can be seen by polarization. This will help identifying the underlying disease. H&E, ×200 In Colitis ulcerosa the pattern is more restricted. Acute bronchiolitis with ulceration, NSIP, and organizing pneumonia are most often found. The differential diagnosis is complicated by the fact that sulfasalazine can cause a druginduced pneumonia, such as NSIP, DIP, eosinophilic pneumonia, and DAD [ 97 -99 ] .

Foreign body granulomatosis is a response of the innate immune system toward inhaled substances, which cannot be removed by macrophages or granulocytes. Most often this occur in aspiration of material from the digestive tract. Usually these are patients hospitalized because of CNS diseases or patients after an accident. The inhaled material can be identifi ed in early granulomas, because the substances are not fully disintegrated by the giant cells. In later stages fi brosis can occur and the identifi cation of the foreign material might be impossible (Fig. 8.78 ) .

Although lipid pneumonia is not a granulomatous pneumonia, we will briefl y discuss this here, because the cause is inhalation of lipid material, and a giant cell reaction can occur. This is a diffuse pneumonia sometimes involving several lobes. The reason in many instances is an inhalation of nasal droplets rich in paraffi n oil or other substances as vitamin A dissolved in oil. A chronic use might result in inhalation and accumulation of signifi cant amounts of these slowly degradable lipids, which ultimately results in lipid pneumonia. Another cause of lipid pneumonia is seen sometimes in the vicinity of squamous cell carcinomas. Most likely this lipids are derived from dying keratinized tumor cells. Lipid pneumonia is characterized by an accumulation of macrophages, which have ingested lipids and appear as foam or clear cells. These macrophages also can be seen in the interstitium; some foreign body giant cells are encountered within the alveoli (Fig. 8.79 ) .

Hyaline granulomatosis is characterized by single or multiple nodules with a hyaline center surrounded by infi ltrates composed of lymphocytes and plasma cells (Fig. 8.80 ). Many different diseases might result in such morphology. Infections can show such pictures, especially mycobacterial infections; however, there will be remnants of epithelioid cell granulomas, and the lymphocytic reaction is not as dense. Non-Hodgkin lymphomas especially plasmacytic variants should be excluded in cases with multiple nodules; fi nally IgG4-associated fi brosis and infl ammatory myofi broblastic tumor need to be excluded. The latter ones will present with proliferating myofi broblasts or infi ltrates of histiocytes; however, in old lesions the center can be hyalinized. 

All available materials (biopsies, BAL, sputum, secretions, etc.) from patients can be used for detection of infectious organisms. In most cases satisfactory results will be obtained. In our hands a combination of biopsy and BAL is superior.

The organisms can be detected, either in BAL or biopsy, and the host's reaction can be evaluated. BAL and biopsy can predict even prognostic outcome. An identifi cation of M. tuberculosis in an immunocompromised patient and nonnecrotizing epithelioid cell granulomas as the reaction of the host can be interpreted as a good prognostic sign, because the host can mount an immune reaction against these mycobacteria. In sarcoidosis CD4/CD8 ratios >3.5 are usually good prognostic indicators. Fibrosis in the biopsy and mediators of fi broblast stimulation like PDGF in BAL fl uid might predict endstage lung disease (Popper, unpublished observations) .

Special stains are necessary: First an acidfast stain (AFS, either auramine-rhodamine fl uorescence or Ziehl-Neelsen), a silver impregnation (GMS, methenamine silver impregnation according to Grocott), a Giemsa stain, and a periodic acid-Schiff stain (PAS) should be done simultaneously. We prefer the auramine-rhodamine stain, because in paucibacillary tuberculosis the mycobacteria are easier detected: they are orange fl uorescent in a black background (Fig. 8.81 ). Based on these reactions, a differential diagnosis of tuberculosis or mycobacteriosis Fig. 8.79 Lipid pneumonia due to chronic inhalation of paraffi n oil from nasal droplets. In the lung numerous macrophages have accumulated in the alveoli but also the interstitium. In the inset some brownish material is also seen in the cytoplasm of the macrophages, representing insoluble lipids not dissolved by the tissue processing. H&E, ×50 and 150 Clinically there was a diagnosis of adrenogenitale syndrome established. If hyaline granulomatosis is associated with this disease cannot be answered. H&E, bar 500 μm can be made. It should be noted that mycobacteria can also be silver impregnated by the GMS stain ( Fig. 8.82 ). The nontuberculous mycobacteria are sometimes described as having a shorter and thicker appearance in AFS; however, this should always be proven by PCR and culture. In every case of purulent pneumonia, a Gram stain should be added to the panel of special stains. Although an identifi cation of a species is not possible, the information about gram-positive or gram-negative cocci or bacilli will already help the clinician to select possible antibiotics for treatment, until the organism has been identifi ed by either culture or PCR. In all cases where a BAL is submitted together with the biopsy, this material is even better to fi nd and identify the organisms, either bacteria, fungi, or parasites ( Fig. 8.83 ).

Fungi can easily be identifi ed by GMS and PAS stains. A tentative diagnosis can be made in many cases. However, in rare infections culture might be required to subtype the fungus. For many fungi also antibodies are available and can be used for immunohistochemical identifi cation. In addition fungi can also be typed by PCR for specifi c gene sequences. Rare bacteria like Treponema can be stained by silver impregnation (Warthin-Starry stain) or immunohistochemically using specifi c antibodies. Unicellular parasites such as malaria, Toxoplasma , and Trypanosoma are usually diffi cult to identify in tissue section, but they are more easily identifi ed in fl uids either BAL or blood (Figs. 8.83 and 8.84 ).

A PCR-based characterization of slow-growing mycobacteria is recommended. For example, a culture of M. avium can be very time consuming (up to 11 weeks), whereas a PCR result can be reported within 2 days. We prefer a PCR for the mycobacterial chaperonin (65 kDa antigen coding gene), and for specifi c insertion sequences, unique for different mycobacteria. Other sequences, which characterize mycobacteria in general, are the DNA coding for the 16S rRNA and the 32 kDa protein. The insertion sequence IS 6110 can be used to demonstrate DNA of M. tuberculosis , M. bovis , M. africanum , and all members of the M. tuberculosis complex (Fig. 8.85 ). For the demonstration of MOTT, different strategies are available: either a multiplex PCR using unique sequences for different mycobacteria in one PCR run ( Fig. 8.86 ) or the more time-consuming amplifi cation of the 16S rRNA coding gene and sequencing of the amplicon can be done. The base exchanges characteristic for different mycobacteria can then be used for species typing. Alternatively amplicons can also be digested by restriction enzymes and the species identifi ed by the length of the fragments [ 78 , 100 , 101 ] .

The proof of chronic berylliosis and zirconiosis requires element analysis in tissue granulomas. This can be done under certain circumstances. The biopsy should be sent frozen to the pathology laboratory. The biopsy can be freeze dried, fi xed in formalin vapor, and embedded in Epon. Ultrathin sections can be analyzed in the electron microscope using EDAX, and the elements of interest can be identifi ed. By this procedure leaching of BeO or ZrO can be reduced.

Culture of infectious organisms is still the ultimate proof and should always be done. But new methods are emerging, which might not only shorten the time until a specifi c organism is identifi ed but also subtyping by strains will be possible. Next-generation sequencing or shotgun whole genome sequencing (WGS) can be used to simultaneously evaluate the microbiome in tissue sections and BAL [ 102 , 103 ] .

Fibrosing Pneumonias (Interstitial Pneumonias)

Originally Liebow [ 104 ] proposed a classifi cation based on morphological descriptions, with the following entities: UIP (usual interstitial pneumonia), BIP (bronchiolitis obliteransinterstitial pneumonia), diffuse alveolar damage (DAD, also acute interstitial pneumonia, clinically corresponding to acute respiratory distress syndrome (ARDS)), LIP (lymphocytic interstitial pneumonia), DIP (desquamative interstitial pneumonia), and GIP (giant cell interstitial pneumonia). He did not divide them into idiopathic or those with known etiology but recognized that there can be different etiology present behind each of these entities. Katzenstein's updates from 1993 to 1998 [ 105 , 106 ] was the next major step, adding NSIP (nonspecifi c interstitial pneumonia) to the list of UIP, DIP, BIP, and AIP/DAD, and following the debate at that time structured the classifi cation into idiopathic and non-idiopathic (=known etiology). Therefore she removed LIP and GIP, because an etiology could be assigned to them. The original BIP was renamed into bronchiolitis obliterans-organizing pneumonia (BOOP) [ 107 ] , a term which was long before known as "pneumonia with carnifi cation" (karnifi zierende Pneumonie) in the German literature. Later on Mueller and Colby showed a radiologicpathologic correlation and used the previously created name BOOP (bronchiolitis obliteransorganizing pneumonia) [ 108 , 109 ] instead of BIP.

When these entities were combined with clinical data, it was apparent that there was a major difference between idiopathic UIP and the "rest": patients with UIP had a worse prognosis and most of them died within 5 years after diagnosis [ 110 ] . And there was no treatment for those patients: a hope of an effective treatment by interferon γ could not be proven [ 111 ] . At this time clinicians recognized that idiopathic pulmonary fi brosis (IPF or cryptogenic fi brosing alveolitis (CFA)) was not a rare disease. Therefore it seemed logical to separate idiopathic interstitial pneumonias from those with known cause and thus to provide prognostic and therapeutic information for the clinicians: no response of patients with UIP/IPF toward corticosteroids and immunosuppressive drugs and dismal prognosis, whereas responsiveness of patients with NSIP to corticosteroids and immunosuppressive drugs and a better prognosis.

The next step happened when UIP and the fi brosing variant of NSIP were compared to each other showing that the initial difference vanished especially when evaluated for a 10-year survival [ 110 ] . But it became clear more and more that the underlying etiology largely predicts the outcome: autoimmune diseases would respond to immunosuppressive regimen, whereas idiopathic IPs would not. Following this aspect DIP and RBILD were next excluded from idiopathic interstitial pneumonias, because in both entities cigarette smoking was identifi ed as the main cause of the disorder. LIP was also skipped, probably because of a clearly defi ned etiology in almost all cases, either lymphoma, allergic, or autoimmune diseases. GIP was skipped, since it either is induced by hard metal inhalation or viral infection (measles, respiratory syncytial virus, and others) [ 112 , 113 ] .

What makes the present-day classifi cation complicated is the combination of radiology, pathology, and pulmonology resulting in provisional diagnoses or divergent names for pathology and clinics. And different views came into the classifi cation: clinicians introduced symptoms, lung function data, and age of the patient, and radiologists introduced their terminology in what correlates to UIP. Finally the ATS/ERS/ JRS/ALAT societies recommended that these three disciplines should together make the fi nal diagnosis of IIPs [ 114 ] .

There are examples which support such a perspective: organizing pneumonia has a wide variety of etiologic causes, and the idiopathic form COP needs exclusion of all other causes, which on several occasions can be done by pathologists, but in other cases only by combining morphology with clinical information. Furthermore radiology has gained a major impact on the diagnosis of IIPs, which resulted in decreasing numbers of patients for whom a pathologic diagnosis is required.

Based on recommendations from a joint committee established by the ERS, ATS, JRS, and ALAT, pathologists, radiologists, and pulmonologists proposed a new classifi cation and also a diagnostic algorithm for ILD and IPF [ 114 , 115 ] (Tables 8.7 and 8.8 ).

UIP/IPF is a chronic progressive fi brosing disease of the lung, which leads to death of the patient usually within 3-5 years after the diagnosis is made [ 116 ] . It affects predominantly patients in their four to fi fth decade of life; however, lesions may occur much earlier and remain undetected until they will cause impaired lung function by their increasing number. Due to increased awareness and increased resolution of CT scans, UIP/IPF might be seen more often in younger-aged patients. Characteristically lesions are found in both lower lobes with a predominance of subpleural regions. The involvement of both lobes is most often symmetrical.

UIP/IPF is the most common interstitial pneumonia, accounting for approximately 55 % [ 114 , Organizing pneumonia (OP) Acute interstitial pneumonia Diffuse alveolar damage (DAD) * *We will not discuss DAD within the fi brosing pneumonias, as this is an acute pneumonia, and in those cases with DAD undergoing organization, this is organizing pneumonia 117 ]. The disease predominantly occurs in an older age group, usually >50 years [ 117 ] . Disease prevalence has been estimated for the EU to be around 1:120,000. However, this could change, because UIP/IPF most often is diagnosed at a late stage. If our diagnostic capabilities can be refi ned, it might be reasonable that the disease could be diagnosed in a younger-aged group, since we know from the pathogenesis that fi brosis starts much earlier.

The clinical symptoms are characterized by insidious onset of dyspnea on exertion, duration of disease ≥3 months, and bibasilar inspiratory dry crackles. These clinical symptoms are quite unspecifi c and therefore need a further confi rmation by high-resolution computed tomography (HRCT). There should be subpleural predominantly basal abnormalities, reticular changes and scars, honeycombing with or without traction bronchiectasis (Fig. 8.87 ) , and the absence of middle fi eld predominance, micronodules, diffuse mosaic attenuation and air trapping, or consolidations in segments [ 118 ] .

Macroscopically the pleura show multiple retractions giving the surface a cobblestone appearance, but pleuritis is not seen. On cut surface cystic lesions, consolidations and scars are found (Fig. 8.88 ). [ 115 ] This schema includes also a stepwise algorithm for the diagnosis starting with the clinical examination, followed by the interpretation of the HRCT picture. If the clinical history and presentation, and the CT scan presents with classical features, a lung biopsy might not be required, as stated by the consensus conference. However, in my personal experience based on many consultation cases many so-called typical ones turned out to be other diseases as suspected 

The cause and the etiology of IPF/UIP are not well understood. There is a working hypothesis, which can explain some of the features. The disease starts with an as yet unidentifi ed epithelial injury causing apoptosis of pneumocytes [ 119 -122 ] . Infl ammatory signals released by the dying pneumocytes cause transformation and proliferation of fi broblasts and myofi broblasts in a myxoid stroma and repair [ 123 ] (so-called fi broblastic focus). Genetic abnormalities may underlie these apoptotic response: in the recent years, research in familial forms of IPF has highlighted the importance of surfactant apoproteins in maintaining a homeostasis between injury and repair and that mutations in the surfactant apoprotein C gene might be causally related to the development of familial IPF [ 124 ] . In these familial IPF, mutations in genes encoding surfactant apoprotein C and A2 increase endoplasmic stress reactions in pneumocytes type II, and in addition mutations in the telomerase genes TERT and TERC are responsible for telomere shortening probably decreasing the pool of peripheral lung stem cells and thus impairing repair and regeneration [ 125 ] . This later defects are also found in sporadic IPF cases. Therefore inhalation of any kind of toxic material from the environment might cause an overwhelming oxidative stress reaction leading to increased apoptosis of pneumocytes and impaired regeneration [ 126 ] . This fi ts quite well into the epidemiology of IPF patients: the majority are smokers; some have a history of environmental dust exposure [ 127 , 128 ] . There is also evidence of epithelialmesenchymal transition (EMT) of pneumocytes into myofi broblasts, but also scattered bone marrow-derived mesenchymal stem cells seem to move into these foci [ 129 -131 ] (Fig. 8.89 ). These foci undergo maturation with collagen deposition, and fi nally the process results in fi brosis of alveolar septa and bronchiolar walls [ 121 ] . This in turn causes obstruction of the terminal airways resulting in cystic destruction of the remaining peripheral lobules, giving rise to honeycombing and remodeling of the lung parenchyma [ 122 , 132 , 133 ] . Recently additional mutations have been identifi ed in IPF: a mutation of MUC5B gene promoter was shown to be associated with risk for IPF and also fi brosing NSIP [ 134 ] , and another gene mutation in dyskerin (DKC1) was associated with familial IPF [ 135 ] . Whereas the function of MUC5B is not explored, dyskerin cooperates with hTERT and thus may be another variant of this complex scenario. IPF develops stepwise, which means there are lung lobules not affected yet looking normal, whereas others are destroyed or even completely lost to fi brosis and scarring. This is meant by the term "timely heterogeneity" (Fig. 8.90 ).

The histological hallmarks are fi broblastic foci, scars and diffuse fi brosis, honeycomb areas, and uninvolved areas in between (heterogeneity). In the author's experience, a diagnosis of UIP/IPF can be established in some cases even without clinical information when the following features are given: fi broblastic foci, timely heterogeneity (involved and uninvolved peripheral lobules), cystic and fi brotic destruction resulting in honeycombing, and most important the absence of infl ammatory infi ltrates in areas of fi broblastic foci, absence of granulomas, or features of other interstitial infl ammation. Let us briefl y characterize the main morphologic features, since this still causes confusion and misunderstanding:

The fi broblastic focus lies within the walls of alveolar and interlobular septa, as well as bronchioles. They do not project into the alveolar lumen. In early stages they are composed of myofi broblasts and fi broblasts in an immature myxoid matrix. This matrix will stain for immature collagen and reticulin fi bers. The overlaying surface is either denuded (no pneumocytes) or can show pneumocyte regeneration with a lot of reactive changes of the nuclei, even epithelial giant cells can be present (Figs. 8.91 , 8.92 , and 8.93 ) . When the focus get's older, mature collagen appears and the cells look more like fi brocytes. The overlaying epithelium looks reactive and usually has a type II or bronchiolar cell appearance. The honeycomb lesion was originally defi ned by radiologists as a single or multicystic lesion within a fi brotic lung area [ 136 ] . Given the differences in resolution between HRCT and histology, there is a substantial difference in size between the two. Pathologically a so-called honeycomb lesion is a cystic lung lesion involving a secondary lobule. This lobule has lost most of the peripheral alveoli, shows a cystic central area composed of bronchioles and centroacinar structures, covered by a cuboidal and cylindrical epithelium, resembling bronchiolar epithelium and transformed pneumocytes type II (Fig. 8.94 ) . In some cases a [ 114 ] In some cases the diagnosis of IPF can be based on clinical and CT fi ndings alone. Whenever pathologic evaluation is involved, a diagnosis of UIP is mandatory for the diagnosis of IPF. However, it should be noted that even among specialists in interstitial lung diseases, Fig. 8.97 Myofi broblastic focus in a patient with rheumatoid arthritis. In this case there is a dense lymphocytic infi ltration extending into the foci and thus pointing to an underlying immune mechanism. H&E, bar 50 μm radiologists and pulmonologists had low kappa statistics, when evaluating UIP/IPF cases. It was always the pathologic diagnosis of UIP, which solved many cases [ 114 , 137 -139 ] . In addition in a study by Morell, many cases diagnosed as being IPF were retrospectively corrected as chronic hypersensitivity pneumonia [ 140 ] . This points to the importance of a pathological diagnosis.

Acute exacerbation of UIP/IPF is clinically characterized by rapid worsening of the patient's symptoms and severe hypoxia most often requiring mechanical ventilation and oxygen supply. Many patients will die under this condition. Histologically two types of acute exacerbations can be seen examining autopsy cases: secondary infection with infectious pneumonia in the background of UIP or multiple fi broblastic foci and severe fi brosis leaving not much lung parenchyma for ventilation. In these latter cases, there is usually severe lung edema present. If a viral infection is present, the histological pattern is diffuse alveolar damage (DAD) [ 20 ] overlaying UIP; if bacterial or fungal infection causes exacerbation, a purulent bronchopneumonia is found. Another complication is severe stenosis of pulmonary arteries and hypertension ( Fig. 8.99 ) .

Besides in IPF a UIP pattern can occur in many other diseases, such as autoimmune diseases, allergic diseases, toxic inhalation, drug-induced pneumonias, and many more. This still causes a lot of confusion, because the term UIP is not used uniformly: some authors use UIP strictly in the sense of IPF, others do not care about etiology and simply diagnose UIP as a pattern, and a third group discerns UIP and UIP-like tissue reactions. The same happens with clinicians: most think a UIP diagnosis already means IPF and are confused to learn that UIP can present in chronic EAA/HP as well as drug reactions, for example. We will discuss these in Chap. 9 .

Cryobiopsy is a new technology to evaluate cancer but is also used to provide tissues for interstitial lung disease diagnosis. The diagnosis of UIP by the pathologist is often possible but an etiology-based diagnosis most often not. So in those patients where the clinical and radiological diagnosis is in favor of UIP/IPF, cryobiopsy might add the missing piece in confi rming the diagnosis (Fig. 8.100 ).

The morphology of FIPF shows more heterogeneity than seen in sporadic IPF. Maybe this refl ects the different underlying mechanisms such as defects in the telomere reconstruction or defects in the surfactant system. There are myofi broblastic foci, cystic remodeling of the alveolar tissue, fi brosis, and normal areas of alveolar tissue -all criteria like sporadic IPF. However, in some cases dense infl ammatory infi ltrates and even aggregates of lymphocytes can be seen (Figs. 8.101 , 8.102 , and 8.103 ). In cases under the age of 15, fi brosing NSIP might also be found [ 141 ] . In a case series by Leslie et al., UIP was found in less than 50 % of patients with FIPF. In the other cases, unclassifi able parenchymal fi brosis and smooth muscle proliferations in fi brosis was noted. The survival for the entire cohort was poor, with an estimated mortality of 93 % and a median age at death of 60.9 years [ 142 ] . 

NSIP is a diffuse interstitial pneumonia, characterized by loose lymphocytic, macrophagocytic, and histiocytic cell infi ltration within alveolar septa combined with mild fi brosis. There is no timely heterogeneity, meaning that the lesions seem to have appeared at the same time.

Hyperplasia of the bronchus-associated lymphoid tissue (BALT) is usually not present [ 116 , 143 ] . The lung architecture is preserved in contrast to UIP, and cystic destruction is absent. Two forms are discerned, which in some cases might represent timely sequences of the disease: the cellular and fi brotic type (Figs. 8.104 , 8.105 , 8.106 , and 8.107 ). Both behave different; the cellular type has a better prognosis, whereas the fi brotic variant is more close to UIP [ 110 ] . In the etiologic background, NSIP is most often associated with autoimmune diseases, especially with collagen vascular diseases [ 28 , 144 -147 ]. An association with drug-induced pneumonia and also with allergic diseases such as extrinsic allergic alveolitis/hypersensitivity pneumonia (EAA/HP) has also been reported [ 148 , 149 ] . Only those cases without an identifi able etiology are labeled as idiopathic NSIP. However, the morphologic pattern is identical; therefore in most instances, idiopathic NSIP remains a clinical diagnosis. There are some exceptions: in cases where additional features such as epithelioid cell granulomas are identifi ed, this will favor EAA/HP; an additional pathology of endothelia could point to drug-induced disease. Clinically NSIP shows diffuse infi ltrations, corresponding to ground glass opacities on HRCT. Symptoms as in the other interstitial lung diseases are quite unspecifi c. Many patients with NSIP will respond to corticosteroid and/or immunosuppressive drug treatment, but also spontaneous resolution of the disease has been reported [ 150 , 151 ] . So far no genetic factors leading to NSIP have been identifi ed.

So what makes this diagnosis?

• The lung architecture is preserved. On low power the alveolar walls, interlobular septa, and primary as well as secondary lobules can be outlined (draw lines along alveolar walls on a digitized photograph, this helps in understanding). • Diffuse infi ltrates composed of lymphocytes macrophages and histiocytic cells, usually few plasma cells. • If fi brosis is present, this usually causes no distortion of the lung architecture. • Fibrosis is diffuse, not merging with scars.

Infl ammatory infi ltrates in cases of fi brosing NSIP are usually scarce. • Non-necrotizing granulomas can be present in certain cases (EAA/HP); however they should not be encountered in idiopathic NSIP. • Hyperplasia of BALT is absent.

Organizing Pneumonia (OP, COP)

Cryptogenic organizing pneumonia (COP) is a diagnosis of exclusion, based on the morphology of organizing pneumonia (OP, formerly bronchiolitis obliterans-organizing pneumonia (BOOP)).

On HRCT OP/COP shows a pattern with combinations of ground glass opacities and consolidations and the almost diagnostic tree-in-bud pattern, sometimes also reticulonodular pattern [ 152 ] (Fig. 8.108 ). In rare cases the consolidation can mimic a tumor [ 153 ] . Histologically the hallmark of OP is an intra-alveolar granulation tissue, the so-called Masson body ( Fig. 8.109 ). It consists of proliferating fi broblasts and myofi broblasts with infl ammatory cells like neutrophils, lymphocytes, histiocytes, and macrophages. Hemosiderin-laden macrophages are often present. The granulation tissue can start from the wall of bronchi, bronchioles, and alveoli. There is usually a defect of the epithelial layer and also the basal lamina. Fibroblasts and myofi broblasts grow into the defect; however, in contrast to normal repair, the granulation tissue does not stop but continuously grows into the airspaces, fi lling these completely or incompletely. In later stages pneumocytes will grow over these granulation tissue plugs and therefore a slit-like airspace can be formed (Fig. 8.110 ) [ 153 ] . The amount of infl ammatory cells within the granulation tissue depends on the cause of OP. The morphologic pattern of organizing pneumonia (OP) has a very wide range of etiologies (Table 8 .9 ). In some cases of OP, the etiologic cause can be determined, for example, by hyaline membranes in DAD or by viral inclusion bodies in post-viral OP or by endothelial cell reactions in drug-induced OP. In some cases an additional pathologic tissue reaction besides OP can also point to the underlying etiology. If looking for the etiology, one should also closely investigate the small blood vessels and the regenerating pneumocytes: viral inclusion bodies might be still visible, scattered neutrophilic granulocytes can be found in the granulation tissue in cases of bacterial or fungal infection, and eosinophils might be seen pointing to a previous druginduced pneumonia. In virus-induced pneumonias another feature can be found, even after several months: single transformed pneumocytes showing atypical nuclei and a homogenously stained smudged chromatin pattern Fig. 8.108 CT scan of a patient with organizing pneumonia. The reticulonodular pattern and the tree-in-bud pattern are nicely shown. There are also some nodular densities in the peripheral lung and ground glass opacities ( Fig. 8.111 ). In drug-induced and metabolic as well as in autoimmune diseases, the vascular walls can show various structural changes making an etiology-based diagnosis probable: eccentric vasculopathy with scattered lymphocytes and without endothelial damage might point to deposition of idiotypic-anti-idiotypic immune complexes (without complement activation; Fig. 8 .112 ) and endothelial damage with fi brosis and repair can point toward druginduced damage (Fig. 8.113 ).

So what are the diagnostic features?

• Granulation tissue growing into bronchi, bronchioles, and alveoli, usually with remnants of infl ammatory cells • Fibrotic occlusion of whole lobules or remaining slit-like spaces covered by pneumocytes • A mixture of infl ammatory cells within these granulation tissue plugs depending on the cause of previous damage COP as a CRP diagnosis is a diagnosis of exclusion: if all possible underlying diseases are excluded, COP can be diagnosed (Fig. 8.114 ). This has some importance, since COP responds well to corticosteroid treatment.

ACIF has already been described in the airway chapter, so it is only mentioned briefl y here. It affects patients with a history of environmental exposure to toxic or allergic substances. Also cocaine abuse was found in one [ 156 ] . The morphology is characterized by fi brosis along the small bronchi extending into the peripheral lung following a lobular distribution. In some cases fi broblastic foci can occur, however, always associated with this distribution pattern. Cystic lung remodeling is absent; instead a whole lobule or subsegment is destroyed by fi brosis. Metaplastic epithelium is common in the affected lobules and also hyperplasia of smooth muscle cells (muscular cirrhosis). The disease rapidly progresses and in the reported series almost half of the patients died of disease. Corticosteroid treatment was effective in some patients. 

Toll-like receptor 2 plays a role in the early infl ammatory response to murine pneumococcal pneumonia but does not contribute to antibacterial defense

Problems in the differential diagnosis of Kartagener's syndrome and ATPase defi ciency

Physiology of airway mucus clearance mucus clearance as a primary innate defense mechanism for mammalian airways

The scavenger receptor CD36 downmodulates the early infl ammatory response while enhancing bacterial phagocytosis during pneumococcal pneumonia

The immunology of virus infection in asthma

Pulmonary surfactant protein A enhances the host-defense mechanism of rat alveolar macrophages

Co-ordinated role of TLR3, RIG-I and MDA5 in the innate response to rhinovirus in bronchial epithelium

Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response

Impact of micropapillary histologic subtype in selecting limited resection vs lobectomy for lung adenocarcinoma of 2cm or smaller

Protein transport across the lung epithelial barrier

Cigarette smoke decreases the expression of secretory component in human bronchial epithelial cells, in vitro

Host defense function of the airway epithelium in health and disease: clinical background

The innate pulmonary granuloma: characterization and demonstration of dendritic cell recruitment and function

TLR9 regulates the mycobacteria-elicited pulmonary granulomatous immune response in mice through DC-derived Notch ligand delta-like 4

Lymphomatoid granulomatosis and diffuse alveolar damage associated with methotrexate therapy in a patient with rheumatoid arthritis

Diffuse alveolar damage: uncommon manifestation of pulmonary involvement in patients with connective tissue diseases

Histopathological approach to patterns of interstitial pneumonia in patient with connective tissue disorders

Fulminating diffuse interstitial fi brosis of the lungs

The gastric juice aspiration syndrome (Mendelson syndrome). Aspects of pathogenesis and treatment in the pig

Viral infection in acute exacerbation of idiopathic pulmonary fi brosis

Acute fi brinous and organizing pneumonia: a histological pattern of lung injury and possible variant of diffuse alveolar damage

Regional alveolar damage (RAD). A localized counterpart of diffuse alveolar damage

Distinct histopathology of acute onset or abrupt exacerbation of hypersensitivity pneumonitis

Facts and controversies in the classifi cation of idiopathic interstitial pneumonias

Epstein-Barr virus-associated pneumonia in patients with post-transplant lymphoproliferative disease after hematopoietic stem cell transplantation

Lymphoproliferation in autoimmunity and Sjogren's syndrome

Interstitial lung disease in primary Sjogren syndrome

Variations in histological patterns of interstitial pneumonia between connective tissue disorders and their relationship to prognosis

Cell-cell fusion induced by measles virus amplifi es the type I interferon response

Giant cell pneumonia due to respiratory syncytial virus. Occurrence in severe combined immunodefi ciency syndrome

Diffuse alveolar damage and interstitial fi brosis in acquired immunodefi ciency syndrome patients without concurrent pulmonary infection

Pathologic pulmonary fi ndings in children with the acquired immunodefi ciency syndrome: a study of ten cases

Pathologic features of the lung in the acquired immune defi ciency syndrome (AIDS): an autopsy study of seventeen homosexual males

Ureaplasma infections in pre-term infants: recent information regarding the role of ureaplasma species as neonatal pathogens

Cytomegalovirus associated neonatal pneumonia and Wilson-Mikity syndrome: a causal relationship?

Wilson-Mikity syndrome: a pulmonary disorder of premature infants

Mikity syndrome: updated diagnostic criteria based on nine cases and a review of the literature

Chlamydial pneumonia of infancy vs Wilson-Mikity syndrome

Chronic lung disease of prematurity: a short history

Chronic respiratory disease in premature infants caused by Chlamydia trachomatis

Bronchopulmonary dysplasia and infl ammatory biomarkers in the premature neonate

Risk factors for bronchopulmonary dysplasia in neonates born at </= 1500 g

Congenital and perinatal cytomegalovirus lung infection

Meconium aspiration syndrome -a 21-years' experience from a tertiary care center and analysis of risk factors for predicting disease severity

Respiratory distress in the newborn

Guidelines for the Prevention and Treatment of Opportunistic Infections among HIV-exposed and HIV-infected children: recommendations from CDC, the National Institutes of Health, the HIV Medicine Association of the Infectious Diseases Society of America, the Pediatric Infectious Diseases Society, and the American Academy of Pediatrics

Differential diagnosis and etiology of epithelioid cell granulomatosis of the lung

Multiple benign sarcoid of the skin

Metals that cause sarcoidosis

Sarcoid granulomatosis after zirconium exposure with multiple organ involvement

Interstitial lung granulomas as a possible consequence of exposure to zirconium dust

Hypersensitivity pneumonitis and exposure to zirconium silicate in a young ceramic tile worker

Expression of granulocyte-macrophage colony-stimulating factor mRNA by infl ammatory cells in the sarcoid lung

The macrophage in sarcoid granuloma formation

Macrophage differentiation and granulomatous infl ammation in osteopetrotic mice (op/op) defective in the production of CSF-1

Properties of multinucleated giant cells in a new in vitro model for human granuloma formation

Epithelioid cell granulomatosis of the lung: new insights and concepts. Sarcoidosis Vasc Diffuse Lung Dis

Pulmonary granulomatous infl ammation: from sarcoidosis to tuberculosis

Regulation of macrophage activation

Identifying control mechanisms of granuloma formation during M. tuberculosis infection using an agent-based model

Interferon-gamma independent formation of pulmonary granuloma in mice by injections with trehalose dimycolate (cord factor), lipoarabinomannan and phosphatidylinositol mannosides isolated from Mycobacterium tuberculosis

Mycobacterial lipomannan induces granuloma macrophage fusion via a TLR2-dependent, ADAM9-and beta1 integrinmediated pathway

Langhans giant cells from M. tuberculosisinduced human granulomas cannot mediate mycobacterial uptake

An in vitro dual model of mycobacterial granulomas to investigate the molecular interactions between mycobacteria and human host cells

Construction of novel in vitro epithelioid cell granuloma model from mouse macrophage cell line

Hypersensitivity pneumonitis associated with mycobacterium avium complex and hot tub use

Diffuse pulmonary disease caused by nontuberculous mycobacteria in immunocompetent people (hot tub lung)

Mycobacteria-induced granuloma necrosis depends on IRF-1

Persistent Cryptococcus neoformans pulmonary infection in the rat is associated with intracellular parasitism, decreased inducible nitric oxide synthase expression, and altered antibody responsiveness to cryptococcal polysaccharide

Sarcoidosis with large nodular lesions simulating pulmonary metastases. An analysis of 126 cases of intrathoracic sarcoidosis

Images in clinical medicine. Nodular sarcoidosis

Burns Amberson lecture -pulmonary angiitis and granulomatosis

Necrotizing sarcoid granulomatosis

Necrotizing sarcoid granulomatosis -is it different from nodular sarcoidosis?

Detection of mycobacterial rRNA in sarcoidosis with liquidphase hybridisation

Detection of mycobacterial DNA in sarcoidosis and tuberculosis with polymerase chain reaction

Mycobacterium tuberculosis DNA in tissue affected by sarcoidosis

DNA of mycobacterium tuberculosis in formalin-fi xed, paraffi nembedded tissue in tuberculosis and sarcoidosis detected by polymerase chain reaction

Detection of mycobacterium tuberculosis DNA in tissue samples of children with sarcoidosis

Proliferative response of peripheral blood mononuclear cells and levels of antibody to recombinant protein from propionibacterium acnes DNA expression library in Japanese patients with sarcoidosis

Quantitative PCR of mycobacterial and propionibacterial DNA in lymph nodes of Japanese patients with sarcoidosis

Propionibacterium acnes in sarcoidosis

Indigenous pulmonary propionibacterium acnes primes the host in the development of sarcoid-like pulmonary granulomatosis in mice

Mycobacterial DNA in recurrent sarcoidosis in the transplanted lung -a PCR-based study on four cases

Mycobacterial catalase-peroxidase is a tissue antigen and target of the adaptive immune response in systemic sarcoidosis

Spectrum of chronic lung disease in a population of newborns with extremely low gestational age

A polymorphism in the toll-like receptor 2 is associated with IL-12 production from monocyte in lepromatous leprosy

Enhanced proliferation and decreased apoptosis in lung lavage cells of sarcoidosis patients

Genetic polymorphisms of the TNFB and HSP70 genes located in the human major histocompatibility complex in sarcoidosis

Genetics of sarcoidosis. Semin Respir Crit Care Med

Study of toll-like receptor gene loci in sarcoidosis

Immunology of chronic beryllium disease

Recent advances in understanding the biomolecular basis of chronic beryllium disease: a review

Structural basis of chronic beryllium disease: linking allergic hypersensitivity and autoimmunity

Identifi cation of beryllium-dependent peptides recognized by CD4+ T cells in chronic beryllium disease

Noninfectious lung pathology in patients with Crohn's disease

The lung in infl ammatory bowel disease

Desquamative interstitial pneumonitis complicating infl ammatory bowel disease of childhood

Idiopathic non-specifi c interstitial pneumonia: as an 'autoimmune interstitial pneumonia'

Multiplex polymerase chain reaction for rapid detection of atypical mycobacteria and mycobacterium tuberculosis complex

Presence of mycobacterial DNA in sarcoidosis

Making the leap from research laboratory to clinic: challenges and opportunities for next-generation sequencing in infectious disease diagnostics

Analysis of the microbiome: advantages of whole genome shotgun versus 16S amplicon sequencing

The interstitial pneumonias

Idiopathic interstitial pneumonia: classifi cation and diagnosis

Idiopathic pulmonary fi brosis: clinical relevance of pathologic classifi cation

Lung biopsy in rheumatoid arthritis

Radiologic fi ndings are strongly associated with a pathologic diagnosis of usual interstitial pneumonia

Nonspecifi c interstitial pneumonia: correlation between thin-section CT fi ndings and pathologic subgroups in 55 patients

Idiopathic nonspecifi c interstitial pneumonia: prognostic signifi cance of cellular and fi brosing patterns: survival comparison with usual interstitial pneumonia and desquamative interstitial pneumonia

A preliminary study of long-term treatment with interferon gamma-1b and low-dose prednisolone in patients with idiopathic pulmonary fi brosis

Chronic granulomatous disease of childhood: respiratory cytology

Giant cell interstitial pneumonia in a hard-metal worker. Cytologic, histologic and analytical electron microscopic investigation

An offi cial ATS/ ERS/JRS/ALAT statement: idiopathic pulmonary fi brosis: evidence-based guidelines for diagnosis and management

American Thoracic Society/European International Multidisciplinary consensus classifi cation of the idiopathic interstitial pneumonias. ATS/ERS joint statement adopted by the ATS board of directors

Prognostic signifi cance of histopathologic subsets in idiopathic pulmonary fi brosis

Idiopathic pulmonary fi brosis

Idiopathic pulmonary fi brosis: guidelines for diagnosis and clinical management have advanced from consensus-based in 2000 to evidencebased in 2011

The pathogenesis of idiopathic pulmonary fi brosis

Compartmentalized expression of c-FLIP in lung tissues of patients with idiopathic pulmonary fi brosis

Usual interstitial pneumonia

Pathogenetic mechanisms in usual interstitial pneumonia/idiopathic pulmonary fi brosis

Transcription factor GATA-6 is expressed in quiescent myofi broblasts in idiopathic pulmonary fi brosis

Nonspecifi c interstitial pneumonia and usual interstitial pneumonia with mutation in surfactant protein C in familial pulmonary fi brosis

Idiopathic pulmonary fi brosis: update on genetic discoveries

Reactive oxygen species are required for maintenance and differentiation of primary lung fi broblasts in idiopathic pulmonary fi brosis

Prognostic factors for idiopathic pulmonary fi brosis: clinical, physiologic, pathologic, and molecular aspects

Is idiopathic pulmonary fi brosis an environmental disease?

Circulating fi brocytes are an indicator of poor prognosis in idiopathic pulmonary fi brosis

Migratory marker expression in fi broblast foci of idiopathic pulmonary fi brosis

Repetitive intratracheal bleomycin models several features of idiopathic pulmonary fi brosis

TNFalpha sensitizes normal and fi brotic human lung fi broblasts to Fas-induced apoptosis

Extracellular superoxide dismutase has a highly specifi c localization in idiopathic pulmonary fi brosis/usual interstitial pneumonia

Genome sequencing of idiopathic pulmonary fi brosis in conjunction with a medical school human anatomy course

A novel dyskerin (DKC1) mutation is associated with familial interstitial pneumonia

Diagnosing fi brotic lung disease: when is high-resolution computed tomography suffi cient to make a diagnosis of idiopathic pulmonary fi brosis?

Radiological versus histological diagnosis in UIP and NSIP: survival implications

Idiopathic interstitial pneumonia: do community and academic physicians agree on diagnosis?

Idiopathic interstitial pneumonia: what is the effect of a multidisciplinary approach to diagnosis?

Chronic hypersensitivity pneumonitis in patients diagnosed with idiopathic pulmonary fi brosis: a prospective casecohort study

Familial idiopathic pulmonary fi brosis: clinical features and outcome

Familial idiopathic interstitial pneumonia: histopathology and survival in 30 patients

Nonspecifi c interstitial pneumonia

Individualization of a clinicopathologic entity in a series of 12 patients

Nonspecifi c interstitial pneumonia associated with polymyositis and dermatomyositis: serial high-resolution CT fi ndings and functional correlation

Histopathologic subsets of fi brosing alveolitis in patients with systemic sclerosis and their relationship to outcome

The major histopathologic pattern of pulmonary fi brosis in scleroderma is nonspecifi c interstitial pneumonia

Nonspecifi c interstitial pneumonia pattern as pulmonary involvement of rheumatoid arthritis

The pathogenesis of chronic hypersensitivity pneumonitis in common with idiopathic pulmonary fi brosis: expression of apoptotic markers

Hypersensitivity pneumonitis associated with lefl unomide therapy

A histologic pattern of nonspecifi c interstitial pneumonia is associated with a better prognosis than usual interstitial pneumonia in patients with cryptogenic fi brosing alveolitis

Differences in clinical features and prognosis of interstitial lung diseases between polymyositis and dermatomyositis

Collagen vascular disease-related lung disease: high-resolution computed tomography fi ndings based on the pathologic classifi cation

Bronchiolitis obliterans. Organizing pneumonia

Ultrastructural evidence of alveolar epithelial injury in idiopathic bronchiolitis obliterans-organizing pneumonia

Bronchiolitis obliterans-organizing pneumonia (BOOP)-like variant of Wegener's granulomatosis. A clinicopathologic study of 16 cases

Airway-centered interstitial fi brosis: a distinct form of aggressive diffuse lung disease