key: cord-0006221-gt3idqnj authors: Calandra, Thierry; Roger, Thierry title: Macrophage migration inhibitory factor: a regulator of innate immunity date: 2003 journal: Nat Rev Immunol DOI: 10.1038/nri1200 sha: ef314f100a7ceb2d848ccb8fc9d6ba13af460113 doc_id: 6221 cord_uid: gt3idqnj For more than a quarter of a century, macrophage migration inhibitory factor (MIF) has been a mysterious cytokine. In recent years, MIF has assumed an important role as a pivotal regulator of innate immunity. MIF is an integral component of the host antimicrobial alarm system and stress response that promotes the pro-inflammatory functions of immune cells. A rapidly increasing amount of literature indicates that MIF is implicated in the pathogenesis of sepsis, and inflammatory and autoimmune diseases, suggesting that MIF-directed therapies might offer new treatment opportunities for human diseases in the future. Among these effector molecules, cytokines have an essential role as they initiate the host inflammatory response and coordinate the cellular and humoral responses, which lead, within minutes to a few hours, to either the eradication or the containment of the invasive pathogen. The increased susceptibility to infection of animals in which genes encoding cytokines or cytokine receptors are mutated or deleted is strong evidence to support a crucial role for cytokine-or cytokine-receptor-dependent signalling pathways in regulating antimicrobial host defences. However, dysregulated production of pro-inflammatory mediators might also become life-threatening, as shown in patients with severe sepsis or septic shock, indicating that tight regulation of cytokine production is required. Discovered almost 40 years ago during studies of the DELAYED-TYPE HYPERSENSITIVITY reaction 4,5 , macrophage migration inhibitory factor (MIF) was one of the first cytokines to be identified (TIMELINE) . However, authentic biological activities of MIF remained ambiguous until the cloning of human MIF complementary DNA in 1989 (REF. 6 ). In 1991, a search for new regulators of inflammation led to the re-discovery of MIF as a molecule released, similar to a hormone, by cells of the anterior pituitary gland after exposure to the endotoxin lipopolysaccharide (LPS) 7 . This intriguing observation indicated that MIF could be a mediator that links the For more than a quarter of a century, macrophage migration inhibitory factor (MIF) has been a mysterious cytokine. In recent years, MIF has assumed an important role as a pivotal regulator of innate immunity. MIF is an integral component of the host antimicrobial alarm system and stress response that promotes the pro-inflammatory functions of immune cells. A rapidly increasing amount of literature indicates that MIF is implicated in the pathogenesis of sepsis, and inflammatory and autoimmune diseases, suggesting that MIF-directed therapies might offer new treatment opportunities for human diseases in the future. (TLRs). A family of receptors that recognize conserved products unique to microorganisms (such as lipopolysaccharide). Stimulation through TLRs induces dendriticcell maturation and activation, leading to optimal activation of the adaptive immune response. TLR-mediated events signal to the host that a microbial pathogen is present. DELAYED-TYPE HYPERSENSITIVITY (DTH). A T-cell-mediated immune response marked by monocyte/macrophage infiltration and activation. DTH skin tests have classically been used for the diagnosis of infection with intracellular pathogens, such as Mycobacterium tuberculosis, and as a measure of the vigour of the cellular immune system. Classical DTH responses to intracellular pathogens depend on CD4 + T cells producing a T helper 1-type profile of cytokines (interferon-γ and tumour-necrosis factor). Conserved synteny refers to the situation in which two linked loci in one species have homologues that are also linked in another species, indicating similarities in content and organization between chromosomes of different species. Genes encoding macrophage migration inhibitory factor, matrix metalloproteinase 11 and glutathione S-transferase θ2 are all positioned on human chromosome 22q11.2 and at 40.9 centimorgans on mouse chromosome 10. 792 | OCTOBER 2003 | VOLUME 3 www.nature.com/reviews/immunol R E V I E W S Crystallographic studies of human and rat MIFs indicate that MIF is a homotrimer (FIG. 2) . There is marked three-dimensional structural homology between MIF and three microbial enzymes -oxalocrotonate tautomerase, 5-carboxymethyl-2-hydroxymuconate isomerase and chorismate mutase [22] [23] [24] [25] [26] . MIF can mediate DTT, phenylpyruvate keto-enol isomerase and thiol-protein oxidoreductase activity [26] [27] [28] [29] [30] [31] [32] . The amino-terminal proline residue is crucial for the catalytic activity; however, it is unclear whether a functional enzyme activity of MIF is required for its biological function [33] [34] [35] [36] . It is possible that the enzyme activities of MIF represent vestigial signatures of the common ancestral origin of MIF and DDT genes. Yet, the fact that the amino-terminal proline residue, for example, has been conserved through evolution is evidence against such an hypothesis. Expression patterns of MIF. At first, T cells were thought to be the main cellular source of MIF in the immune system. However, monocytes, macrophages, blood dendritic cells, B cells, neutrophils, eosinophils, mast cells and basophils have since been shown to express MIF [37] [38] [39] . In contrast to most cytokines, MIF is constitutively expressed and stored in intracellular pools, and therefore does not require de novo protein synthesis before secretion. Similar to interleukin-1 (IL-1), basic fibroblast growth factor and a secreted form of cyclophilin, MIF lacks an amino-terminal leader sequence, indicating that it is released from cells by a non-conventional protein-secretion pathway. Besides the immune system, MIF has a broad tissue distribution (FIG. 3) . Notably, MIF is expressed by cells and tissues that are in direct contact with the host's natural environment, such as the lung, the epithelial lining of the skin, and gastrointestinal and genitourinary tracts. Another distinctive feature of MIF is its high level of expression by several tissues of the endocrine system, especially by organs that are involved in stress responses (hypothalamus, pituitary and adrenal glands) 7,40-42 . Cytokines act by binding to cognate receptors expressed by target cells, thereby activating signal-transduction pathways, gene transcription and the expression of downstream effector molecules. In support of a mode of action mediated by the interaction endocrine and immune systems. Mif-knockout mice were generated in 1999, and reported to be healthy and devoid of any apparent deficit 8 . In this article, we review the main features and biological activities of MIF. Special emphasis is placed on the emerging concept that MIF has a central role as a regulator of innate immune and inflammatory responses, and the implications it might have for the development of new therapies for human sepsis and other inflammatory diseases. There is only one MIF gene in the human genome located on chromosome 22 (22q11.2), which is in SYNTENIC CONSERVATION with part of the mouse chromosome 10 that contains the Mif gene 6,9-13 . At least nine Mif pseudogenes have been found in the mouse genome 12,13 . Additional information on the structure of the human MIF gene is provided in FIG. 1. Searching of the human genome for homologues of MIF indicated that D-dopachrome tautomerase (DDT) was the only gene with marked homology to MIF 14 . As both genes are located relatively close on chromosome 22, it is tempting to speculate that the MIF and DDT genes are duplications of a common ancestral gene that have evolved to have different biological functions. Two polymorphisms of the human MIF gene have been linked to human diseases. One is a single-nucleotide mutation (a G-to-C transition at position -173) in the 5′ flanking region, which is associated with systemic-onset juvenile arthritis 15 . The other polymorphism is a CATT-tetranucleotide repeat at position -794, which correlates with disease severity in a cohort of patients with rheumatoid arthritis 16 . A single MIF messenger RNA species of~0.8 kb is found in humans, mice and rats. It encodes a 114amino-acid non-glycosylated protein of 12.5 kDa. All mammalian MIFs (human, mouse, rat and cattle) havẽ 90% homology. MIF, also known as glycosylationinhibiting factor (GIF), has been reported to suppress IgE synthesis and have antigen-specific suppressor activity 17 . Surprisingly, MIF does not seem to belong to any cytokine superfamily. Homologues of mammalian MIF have been found in chickens, both jawless and jawed fish, ticks, parasites, plants (Arabidopsis thaliana) and cyanobacteria 9, [18] [19] [20] [21] Timeline | The history of MIF downregulation of expression of TLR4 -the signaltransducing molecule of the LPS receptor complex 45, 46 . MIF upregulates the expression of TLR4 by acting on the ETS family of transcription factors, including PU.1, which are crucial for transcription of the mouse Tlr4 gene (FIG. 4a) . Therefore, MIF facilitates the detection of endotoxin-containing bacteria, enabling cells that are at the forefront of the host antimicrobial defence system, such as macrophages, to respond rapidly to invasive bacteria. Rapid production of pro-inflammatory cytokines is absolutely essential for mounting the host defensive response. Consistent with this concept, it was reported recently that Mif-deficient mice failed to control the growth of the intracellular pathogen Salmonella typhimurium and succumbed to infection 47 . Increased susceptibility of Mif-deficient mice to infection was associated with reduced plasma levels of the cytokines tumour-necrosis factor (TNF), IL-12 and interferon-γ (IFN-γ), but not of nitric oxide (NO), and with higher bacterial counts compared with wild-type mice. This indicates that MIF promotes a protective T HELPER 1 (T H 1)-CELL immune response against S. typhimurium. Taken together, these observations provide a rationale for the constitutive expression of MIF by cells and tissues that are in close proximity to the external environment (FIG. 3) . Moreover, it offers a mechanism whereby Mif-deficient mice are resistant to lethal endotoxaemia 8 . MIF suppresses p53 activity. Primary tumours and numerous tumour-cell lines express high quantities of MIF 48 . A recent report indicating that MIF functions as a negative regulator of p53-mediated growth arrest and apoptosis has provided an interesting link between MIF, inflammation, cell growth and tumorigenesis 49 . Following this observation, it was reported that the proinflammatory function (that is, the production of TNF, IL-1β and PGE 2 ) and the viability of MIF-deficient macrophages were reduced compared with wild-type cells after challenge with LPS 50 . Despite the equal level of production of NO by MIF-deficient and wildtype macrophages, NO was thought to be a crucial mediator of increased apoptosis of MIF-deficient macrophages stimulated with LPS. Indeed, MIF was found to inhibit NO-induced intracellular accumulation of p53 and, therefore, p53-mediated apoptosis (FIG. 4b) . Inhibition of p53 by MIF required serial activation of ERK1/ERK2, PLA2, cyclooxygenase 2 (COX2) and PGE 2 . with a typical cytokine receptor, MIF was found to activate extracellular signal-regulated kinase 1 (ERK1)/ERK2 -members of the family of mitogen-activated protein kinases (MAPKs) (see next paragraph). MIF has been reported to bind to the extracellular domain of CD74the cell-surface form of the MHC class-II-associated invariant chain 43 (FIG. 4a) . Activation of ERK1/ERK2, cell proliferation and the production of prostaglandin E 2 (PGE 2 ) are activities of MIF that require the involvement of CD74. Whether CD74 is the long sought after MIF receptor or a docking molecule that is implicated in the presentation of MIF to its as-yet-unidentified receptor is unclear at present. The fact that the intracellular domain of CD74 does not seem to contain motifs that might interact with signal-transducing molecules would support the latter possibility. Studies of intracellular signalling events and proliferation of MIFstimulated quiescent fibroblasts showed that MIF induces rapid (within 30 minutes) and sustained (up to 24 hours) phosphorylation and activation of the ERK1−ERK2-MAPK pathway and cell proliferation 44 (FIG. 4a) . MIF-induced ERK1/ERK2 activation was protein kinase A dependent and associated with increased cytoplasmic phospholipase A2 (PLA2) enzyme activity. PLA2 is an important intracellular link in the activation of the pro-inflammatory cascade, resulting first in the production of arachidonic acid and then of prostaglandins and leukotrienes. PLA2 also is a key target of the anti-inflammatory effects of glucocorticoids, and the ERK1/ERK2-mediated induction of PLA2 is one mechanism whereby MIF could override the immunosuppressive effects of steroids 44 (see the section on MIF and inflammation). Constitutive expression of a cytokine by macrophages is unusual and intriguing, prompting the question of what kind of advantage does high baseline expression of MIF confer on macrophages? Studies carried out with macrophages transfected with antisense MIF constructs and macrophages that were isolated from Mif-deficient mice provided an answer to this question. Indeed, Mif-deficient macrophages were found to be hyporesponsive to LPS and Gram-negative bacteria, but not to other stimuli, as shown by reduced cytokine production due to the CD74 CD74, also known as the MHC class-II-associated invariant chain (Ii), is implicated in the transport of MHC class II proteins from the endoplasmic reticulum to the Golgi complex. About 5% of the cellular content of CD74 is expressed at the cell surface independently of MHC class II molecules. The intracellular domain of CD74 does not seem to contain sequences that are known to interact with signalling molecules. T HELPER 1/2 CELLS (T H 1/T H 2). Subsets of CD4 + T cells that are characterized by distinctive profiles of cytokine expression. T H 1 cells typically produce interleukin-2 (IL-2), IL-12 and interferon-γ that support macrophage activation and the development of a cellular-based immune response, whereas T H 2 cells typically produce IL-4, IL-5 and IL-13 that drive a humoral-based immune response. that endocytosis of MIF induces cell activation, whereas unprocessed intracellular MIF would not. At first glance, endocytosis would seem to be an atypical mode of action for a classic cytokine. However, it does not necessarily imply that endocytosis of MIF would bypass the requirement for a direct interaction with a membrane-bound receptor. In fact, there are examples of endosomes being implicated in signal transduction that is mediated by ligand-activated cytokine receptors. One such example is the transforming growth factor-β (TGF-β) receptor [55] [56] [57] . Second, the article by Kleemann et al. 53 assigns growth-inhibitory and anti-inflammatory functions to MIF that go against what were thought to be two well-established properties of MIF -that is, its capacity to sustain cell growth and to induce proinflammatory responses. These apparently conflicting observations might be accounted for by differences in the concentrations of MIF or in the status (that is, quiescent or activated) of the cells that were used 39, 58 . Initially thought to be a T-cell cytokine of the adaptive immune system, MIF has emerged as a cytokine that has important functions in the innate immune system. Endotoxins are a main virulence factor of Gram-negative bacteria 59 . When stimulated with LPS, macrophages release MIF 40 . Other pro-inflammatory effector molecules of immune cells, such as TNF and IFN-γ, are also strong inducers of MIF production by macrophages 40 . After it is released in the tissue or in the systemic circulation, MIF acts as a classic pro-inflammatory cytokine promoting innate and adaptive immune responses through the activation of macrophages and T cells. Although MIF is required to combat infection (see the section on MIF and TLR4), high-level production of MIF is harmful during acute infections. Although MIF did not induce shock when injected alone, high doses of recombinant MIF exacerbated lethal endotoxaemia and Escherichia coli sepsis when co-injected with LPS or E. coli into mice 7,60 (BOX 1). High tissue and circulating levels of MIF were detected in mice with sepsis, and neutralizing antibodies specific for MIF reduced the production of TNF and protected the mice from lethal endotoxic shock or sepsis induced by E. coli or CAECAL LIGATION AND PUNCTURE (CLP), even when treatment with MIF-specific antibody was started after the onset of bacterial peritonitis 7,60 . The ability to rescue animals from sepsis when treatment is given therapeutically and not prophylactically is important, as anti-sepsis therapy, by definition, is always administered after the onset of infection in humans. Recapitulating some of these findings, Mif-deficient mice were reported to be resistant to endotoxic shock 8 . Although Mif-deficient mice that were produced using a different Mif gene-targeting approach were first reported to be as sensitive as wildtype mice to LPS 61 , additional experiments carried out by another group of investigators seem to indicate that these Mif-deficient mice are also resistant to LPS (J. Nishihira, personal communication). In agreement with these results, MIF was reported to interact with the E2F-p53 pathway to sustain normal and malignant cell growth 51 . Therefore, the upregulation of expression of TLR4 and sustained cell survival are two mechanisms whereby MIF promotes pro-inflammatory innate immune responses 50, 52 . MIF inhibits JAB1 activity. Using a YEAST TWO-HYBRID SYSTEM, an interaction between MIF and the protein known as JUN-activation domain-binding protein 1 (JAB1) or as COP9 signalosome subunit 5 (CSN5) was shown 53 . JAB1 activates JUN N-terminal kinase (JNK) to phosphorylate JUN and so functions as a co-activator of activator protein 1 (AP1) -a transcription factor that is implicated in cell growth, transformation and cell death 54 . Other functions ascribed to JAB1 include degradation of the cell-cycle inhibitor KIP1 and the tumour suppressor p53. MIF and JAB1 are co-localized in the cytoplasm and MIF inhibits the positive regulatory effects of JAB1 on the activity of JNK and AP1 (FIG. 4a) . This observation is intriguing for two other reasons. First, it indicates that cells can take up MIF by ENDOCYTOSIS. Given the abundant intracellular expression of MIF, it might be asked what advantage would the cell gain by using endocytosed MIF rather than intracellular MIF. Endocytosis of MIF might occur either in a receptor-dependent or receptor-independent manner. Therefore, one obvious difference might be YEAST TWO-HYBRID SYSTEM A screening system for protein-protein interactions, which results in the transcription of a reporter gene when a 'bait' protein that is attached to a DNA-binding domain comes into contact with a 'prey' protein bound to a transcriptional activator. ENDOCYTOSIS A process whereby extracellular material is internalized by a cell, which can occur either in a receptor-independent and often non-specific manner (for example, by pinocytosis) or in a receptor-dependent manner. Both clathrin-dependent endocytosis and clathrinindependent internalization triggered by lipid rafts can occur. toxin 1 (TSST1) or streptococcal pyrogenic exotoxin A (SPEA) induce the production of MIF by macrophages, which contributes to lethal pro-inflammatory responses. Mortality can be prevented by administration of neutralizing MIF-specific antibodies 66 (BOX 1) . Experiments carried out in Mif-deficient mice confirmed that a lack of Mif is associated with increased resistance to Grampositive shock caused by staphylococcal enterotoxin B 8 (BOX 1). MIF is also released by cells of whole blood stimulated with heat-killed Streptococcus pneumoniae, and MIF-specific antibody reduces cytokine production and increases survival in a mouse model of S. pneumoniaeinduced pneumonia (T.C. et al., unpublished observations). Together with the observations obtained in experimental models of endotoxaemia and Gramnegative sepsis, these data indicate that MIF has an important role in the pathogenesis of bacterial infections. In addition to bacterial sepsis, MIF has been implicated in the pathogenesis of parasitic (malaria, cysticercosis and leishmaniasis) and viral (cytomegalovirus and influenza virus) infections. MIF is produced in the lymph nodes of mice infected with Leishmania major, and in vivo administration of recombinant MIF reduced the severity of infection 67 . Mice that lack Mif were more susceptible to leishmaniasis and cysticercosis than wild-type mice 68, 69 . Phagocytosis of erythrocytes infected with Plasmodium chabaudi or uptake of malarial pigment (hemozoin) by macrophages induced the release of MIF 70 . MIF inhibits erythroid, multipotential and granulocyte-macrophage progenitor-derived colony formation, indicating that it could be implicated in the pathophysiology of malarial anaemia. In pregnant women with placental malaria, the production of MIF by intervillous blood mononuclear cells is markedly upregulated 71 . A rapidly growing amount of evidence supports the notion that MIF is an integral component of host inflammatory responses. As summarized earlier, MIF is rapidly released by immune cells that are exposed to microbial products or to pro-inflammatory cytokines, or during antigen-specific activation, and has potent autocrine and paracrine effects that promote cell growth and survival. Using MIF-deficient cells, MIF-specific antibodies or recombinant MIF, investigators have provided evidence that MIF directly or indirectly promotes the production or expression of a large panel of proinflammatory molecules, including cytokines (such as TNF, IFN-γ, IL-1β, IL-2, IL-6, IL-8 and macrophage inflammatory protein 2) 40,72-75 , nitric oxide 8,11 , COX2 and products of the arachidonic acid pathway (such as PGE 2 ) 44, 50 , and several matrix metalloproteinases and their inhibitors 76, 77 . A surprising observation, which at first seemed to be incompatible with the pro-inflammatory features of this cytokine, was that MIF secretion was induced rather than inhibited by glucocorticoid hormones 72 . However, this paradoxical finding assisted in determining an circulating concentrations of MIF are increased during inflammation, infection and stress 60, 72, 79 . Analysis of the molecular mechanisms of MIF and glucocorticoid interactions have shown that MIF does interfere with glucocorticoids at a transcriptional and post-transcriptional level (FIG. 4c) . Daun and Cannon 80 showed that MIF antagonizes the effect of hydrocortisone on the nuclear factor-κB (NF-κB)−inhibitor of NF-κB (IκB) signal-transduction pathway by counteracting the steroid-mediated induction of cytosolic IκBα. important feature of the biology of MIF. Indeed, MIF was found to override the immunosuppressive effects of glucocorticoids (FIG. 4c) . In vitro, MIF was observed to reverse glucocorticoid-induced inhibition of TNF, IL-1, IL-6 and IL-8 synthesis by peripheral-blood mononuclear cells 72 , of cytosolic PLA2 activity, of arachidonicacid release by fibroblasts 44 and of proliferation by T cells 73 . This counter-regulatory effect of MIF was confirmed in mouse models of endotoxaemia 72 and antigen-induced arthritis 78 glucocorticoid activity, and that MIF and glucocorticoids function together to modulate innate and acquired immune responses. This concept has been further exemplified by recent studies implicating MIF in the pathogenesis of acute and chronic inflammatory and autoimmune diseases in humans and in experimental models (BOX 2). Although MIF was discovered as a factor that is released by activated lymphocytes, so far little is known about its role in adaptive immunity. T cells constitutively express MIF 73 . Mitogens, tetanus toxoid, CD3-specific antibody, TSST1 and glucocorticoids have been reported to stimulate the release of MIF from T cells or from mouse splenocytes 66, 73, 82 . Although MIF is mainly thought to be produced by T H 2 cells 73 , it is also produced by T H 0 and T H 1 cells (T.C., unpublished observations). Possibly acting through an autocrine loop, MIF supports the activation and proliferation of T cells, and the production of IL-2 (REF. 73 ). MIF-specific antibodies prevented superantigen-induced activation and proliferation of splenocytes 66 , lending further support to the concept that MIF is also a lymphotropic cytokine. Moreover, MIF inhibits regulatory effects on cytotoxic CD8 + T cells and regulates lymphocyte trafficking 82 . So, MIF also has important immunomodulatory functions in the adaptive immune system. MIF has been shown to be implicated in the pathogenesis of numerous acute and chronic inflammatory diseases 39 , including sepsis, acute respiratory distress syndrome (ARDS), asthma, arthritis, glomerulonephritis, inflammatory bowel diseases, atopic dermatitis, allograft rejection and most recently atherosclerosis (BOX 2) . As the focus of this article is on innate immunity, we limit our discussion of the potential therapeutic implications of MIF to sepsis and ARDS. Severe sepsis and septic shock are acute clinical manifestations of dysregulated innate immune responses. These life-threatening complications are the tenth most common cause of death in the United States and the second most common cause of death in noncoronary intensive-care units 62 . Over the past 20 years, considerable progress has been made in our understanding of the pathogenesis of sepsis 65 . Although a recent survey in the United States on the epidemiology of sepsis indicated that mortality is decreasing 62 , identification of new treatments is still a priority as death rates of severe sepsis (20-35%) and septic shock (50-60%) remain high. The intrinsic pro-inflammatory properties of MIF, the fact that it is highly expressed by innate immune cells, and that it has a crucial role in macrophage responses against microbial products provide compelling evidence in support of a role for MIF in sepsis. This hypothesis has been tested in several experimental models of toxic shock and live bacterial sepsis, which have shown that excessive production of MIF is harmful in the acute Confirming and extending these observations, we recently found evidence that MIF inhibits both the transcriptional and post-transcriptional regulation of cytokine production by glucocorticoids (T.C. and T.R., unpublished observations). Supported by increasing amounts of literature 42, 44, 74, 80, 81 , a concept has emerged that MIF acts as a physiological antagonist of Therefore, in contrast to many other anti-cytokine therapies, treatment with MIF-specific antibody fulfills an important prerequisite for any anti-sepsis agent, that is the ability to rescue mice from death when treatment is given in a therapeutic manner (that is, once sepsis has developed). MIF-specific antibody also protects TNF-deficient mice from CLP, arguing for an intrinsic contribution of MIF to the pathogenesis of sepsis. phase of sepsis. Increased levels of MIF have been detected in the blood of patients with severe sepsis or septic shock 60, 79, 83, 84 . A correlation between levels of MIF in the blood and the severity of sepsis, levels of stress hormones (cortisol) and cytokines (IL-6), acute lung injury and a fatal outcome was found. Human pathologies associated with increased MIF expression by organs or systems • Immune system: sepsis, septic shock and allograft rejection 60, 79, 83, 84, 103, 104 • Lung: adult respiratory distress syndrome, asthma, tuberculosis and Wegener's granulomatosis 4, [85] [86] [87] 105 • Kidney: glomerulonephritis 106, 107 • Bones and joints: rheumatoid arthritis, systemic-onset juvenile idiopathic arthritis and polychondritis 6,81,108-110 • Gastrointestinal tract: colitis and Crohn's disease 96, 111 • Skin: atopic dermatitis, psoriasis and systemic sclerosis [112] [113] [114] • Endocrine system: type-2 diabetes and pancreatitis 99, 115 • Brain: multiple sclerosis and neuro-Behcet's disease 116 • Eye: uveitis and iridocyclitis 117, 118 • Heart and vasculature: atherosclerosis 119 Structural characterization and chromosomal location of the mouse macrophage migration inhibitory factor gene and pseudogenes Conserved gene structure and genomic linkage for D-dopachrome tautomerase (DDT) and MIF A novel 5′-flanking region polymorphism of macrophage migration inhibitory factor is associated with systemic-onset juvenile idiopathic arthritis A functional promoter polymorphism in the macrophage migration inhibitory factor (MIF) gene associated with disease severity in rheumatoid arthritis Biochemical basis of antigen-specific suppressor T cell factors: controversies and possible answers Macrophage migration inhibitory factor (MIF) of jawed and jawless fishes: implications for its evolutionary origin Identification and characterization of a homologue of the pro-inflammatory cytokine macrophage migration inhibitory factor in the tick Filarial nematode parasites secrete a homologue of the human cytokine macrophage migration inhibitory factor Conservation of long-range synteny and microsynteny between the genomes of two distantly related nematodes Crystal structure at 2. 6Å resolution of human macrophage migration inhibitory factor Crystal structure of the macrophage migration inhibitory factor from rat liver References 22 and 23 provided the first description of the three-dimensional structure of MIF, implying that MIF is a trimer with structural homology to bacterial isomerases Enzymatic ketonization of 2-hydroxymuconate: specificity and mechanism investigated by the crystal structures of two isomerases Crystal structure of human D-dopachrome tautomerase, a homologue of macrophage migration inhibitory factor, at 1. 54 A resolution Macrophage migration inhibitory factor: cytokine, hormone, or enzyme? The macrophage migration inhibitory factor MIF is a phenylpyruvate tautomerase The immunoregulatory mediator macrophage migration inhibitory factor (MIF) catalyzes a tautomerization reaction Disulfide analysis reveals a role for macrophage migration inhibitory factor (MIF) as thiol-protein oxidoreductase Characterization of catalytic centre mutants of macrophage migration inhibitory factor (MIF) and comparison to Cys81Ser MIF The cytokine macrophage migration inhibitory factor reduces pro-oxidative stress-induced apoptosis Macrophage migration inhibitory factor Biochemical and mutational investigations of the enzymatic activity of macrophage migration inhibitory factor Enzymatically inactive macrophage migration inhibitory factor inhibits monocyte chemotaxis and random migration Dissection of the enzymatic and immunologic functions of macrophage migration inhibitory factor. Full immunologic activity of N-terminally truncated mutants The tautomerase activity of MIF is a potential target for discovery of novel anti-inflammatory agents Evolving Concepts in Sepsis and Septic Shock Macrophage migration inhibitory factor Macrophage migration inhibitory factor (MIF): mechanisms of action and role in disease The macrophage is an important and previously unrecognized source of macrophage migration inhibitory factor Migration inhibitory factor expression in experimentally induced endotoxemia Regulation of macrophage migration inhibitory factor expression by glucocorticoids in vivo The authors describe the binding of MIF to the extracellular domain of CD74, also known as MHC class-II-associated invariant chain, leading to activation of the extracellular signal Sustained mitogen-activated protein kinase (MAPK) and cytoplasmic phopholipase A2 activation by macrophage migration inhibitory factor (MIF) MIF regulates innate immune responses through modulation of Toll-like receptor 4 Macrophage migration inhibitory factor (MIF) regulates host responses to endotoxin through modulation of Toll-like receptor 4 (TLR4) Macrophage migration inhibitory factor (MIF) plays a pivotal role in immunity against Salmonella typhimurium Tumor growth-promoting properties of macrophage migration inhibitory factor (MIF) A proinflammatory cytokine inhibits p53 tumor suppressor activity A report indicating that MIF functions as a negative regulator of p53-mediated growth arrest and apoptosis, providing an interesting link between MIF, inflammation Macrophage migration inhibitory factor (MIF) sustains macrophage proinflammatory function by inhibiting p53: regulatory role in the innate immune response Macrophage migration inhibitory factor deficiency is associated with altered cell growth and reduced susceptibility to Ras-mediated transformation Macrophage migration inhibitory factor (MIF) modulates innate immune responses induced by endotoxin and Gram-negative bacteria Report of a two-hybrid screen indicating the interaction between MIF and JUN-activation domainbinding protein 1 (JAB1) -a transcription factor implicated in cell growth AP-1 as a regulator of cell life and death SARA, a FYVE domain protein that recruits Smad2 to the TGF-β receptor Early endosomal regulation of Smaddependent signaling in endothelial cells Mechanisms of TGF-β signaling from cell membrane to the nucleus Signal transduction. A most interesting factor Innate immune sensing and its roots: the story of endotoxin Protection from septic shock by neutralization of macrophage migration inhibitory factor Deficiency of the macrophage migration inhibitory factor gene has no significant effect on endotoxaemia The epidemiology of sepsis in the United States from Induction of interleukin-1 by a product of Staphylococcus aureus associated with toxic shock syndrome The staphylococcal enterotoxins and their relatives Pathogenesis of sepsis: new concepts and implications for future treatment Macrophage migration inhibitory factor is a critical mediator of the activation of immune cells by exotoxins of Grampositive bacteria Migration inhibitory factor induces killing of Leishmania major by macrophages: dependence on reactive nitrogen intermediates and endogenous TNF-α Migration-inhibitory factor gene-deficient mice are susceptible to cutaneous Leishmania major infection Macrophage migration inhibitory factor plays a critical role in mediating protection against the helminth parasite Taenia crassiceps Macrophage migration inhibitory factor release by macrophages after ingestion of Plasmodium chabaudi-infected erythrocytes: possible role in the pathogenesis of malarial anemia Immunity to placental malaria. IV. Placental malaria is associated with upregulation of macrophage migration inhibitory factor in intervillous blood This paper describes the existence of a MIF-glucocorticoid counter-regulatory system that controls inflammatory and immune responses An essential regulatory role for macrophage migration inhibitory factor in T-cell activation Regulatory role for macrophage migration inhibitory factor in acute respiratory distress syndrome Effect of anti-macrophage migration inhibitory factor antibody on lipopolysaccharide-induced pulmonary neutrophil accumulation High expression of macrophage migration inhibitory factor in the synovial tissues of rheumatoid joints Macrophage migration inhibitory factor upregulates matrix metalloproteinase-9 and -13 in rat osteoblasts. Relevance to intracellular signaling pathways Regulation of macrophage migration inhibitory factor by endogenous glucocorticoids in rat adjuvant-induced arthritis Macrophage migration inhibitory factor and hypothalamo-pituitary-adrenal function during critical illness Macrophage migration inhibitory factor antagonizes hydrocortisone-induced increases in cytosolic IκBα Macrophage migration inhibitory factor in rheumatoid arthritis: evidence of proinflammatory function and regulation by glucocorticoids Regulation of the CTL response by macrophage migration inhibitory factor Plasma levels of macrophage migration inhibitory factor are elevated in patients with severe sepsis Macrophage migration inhibitory factor is a critical mediator of systemic inflammatory response syndrome Role for macrophage migration inhibitory factor in acute respiratory distress syndrome Human circulating eosinophils secrete macrophage migration inhibitory factor (MIF) Macrophage migration inhibitory factor (MIF) in bronchial asthma An essential role for macrophage migration inhibitory factor in the tuberculin delayed-type hypersensitivity reaction Macrophage migration inhibitory factor is involved in the pathogenesis of collagen type II-induced arthritis in mice Involvement of macrophage migration inhibitory factor in the evolution of rat adjuvant arthritis De novo renal expression of macrophage migration inhibitory factor during the development of rat crescentic glomerulonephritis The pathogenic role of macrophage migration inhibitory factor in immunologically induced kidney disease in the rat TNF-α upregulates renal MIF expression in rat crescentic glomerulonephritis Reversal of established rat crescentic glomerulonephritis by blockade of macrophage migration inhibitory factor (MIF): potential role of MIF in regulating glucocorticoid production Upregulation of macrophage migration inhibitory factor in acute renal allograft rejection in the rat Development of chronic colitis is dependent on the cytokine MIF Amelioration of dextran sulfate sodiuminduced colitis by anti-macrophage migration inhibitory factor antibody in mice Macrophage migration inhibitory factor is an important mediator in the pathogenesis of gastric inflammation in rats Macrophage migration inhibitory factor is a critical mediator of severe acute pancreatitis De novo expression of macrophage migration inhibitory factor in atherogenesis in rabbits In vivo blockade of macrophage migration inhibitory factor ameliorates acute experimental autoimmune encephalomyelitis by impairing the homing of encephalitogenic T cells to the central nervous system Inhibition of experimental autoimmune uveoretinitis with anti-macrophage migration inhibitory factor antibodies Trauma patients with positive cultures have higher levels of circulating macrophage migration inhibitory factor (MIF) Macrophage migration inhibitory factor expression in human renal allograft rejection Elevated levels of serum macrophage migration inhibitory factor in patients with pulmonary tuberculosis Expression of macrophage migration inhibitory factor in human glomerulonephritis Increased production of macrophage migration inhibitory factor by T cells in patients with IgA nephropathy Macrophage migration inhibitory factor in rheumatoid arthritis: clinical correlations Macrophage migration inhibitory factor in patients with juvenile idiopathic arthritis Serum level of macrophage migration inhibitory factor as a useful parameter of clinical course in patients with Wegener's granulomatosis and relapsing polychondritis Macrophage migration inhibitory factor in the sera and at the colonic mucosa in patients with ulcerative colitis: clinical implications and pathogenic significance Macrophage migration inhibitory factor is an essential immunoregulatory cytokine in atopic dermatitis Evidence for a role of macrophage migration inhibitory factor in psoriatic skin disease Expression of macrophage migration inhibitory factor in diffuse systemic sclerosis Elevated serum content of macrophage migration inhibitory factor in patients with type 2 diabetes Macrophage migration inhibitory factor in the cerebrospinal fluid of patients with conventional and optic-spinal forms of multiple sclerosis and neuro-Behcet's disease Prominent increase of macrophage migration inhibitory factor in the sera of patients with uveitis Increase of macrophage migration inhibitory factor in sera of patients with iridocyclitis Expression of macrophage migration inhibitory factor in different stages of human atherosclerosis Role of macrophage migration inhibitory factor in otitis media with effusion in adults We thank M. Pagni for preparing figure 2 and J. Bernhagen for critical reading of the manuscript. The work was supported by the Swiss National Science Foundation, the Leenaards Foundation, the Santos Suarez Foundation and the Bristol-Myers Squibb Foundation. T. C. and T. R. are recipients of career and research awards of the Leenaards Foundation.