key: cord-0046178-h7c7fiv6
authors: Goldman, Armond S.; Chheda, Sadhana; Keeney, Susan E.; Schmalstieg, Frank C.
title: Immunology of Human Milk and Host Immunity
date: 2020-06-22
journal: Fetal and Neonatal Physiology
DOI: 10.1016/b978-1-4160-3479-7.10158-2
sha: 2f3c280b1a254e43463df01eac1dab19c807dce4
doc_id: 46178
cord_uid: h7c7fiv6

nan

In 1891, it was discovered that immunity could be transmitted through breast-feeding in experimental animals. 1 In the 1920s, 2-4 the incidence and severity of diarrheal diseases were found to be much lower in breast-fed than cow's milk-fed infants. Those clinical observations were confirmed repeatedly, [5] [6] [7] [8] and it was ascertained that breast-feeding protected against many bacterial and viral enteric pathogens. [7] [8] [9] [10] [11] [12] [13] Three explanations for the protection were advanced. The first explanation: Because human milk is less contaminated with enteropathogens than formula feedings, breast-fed infants are exposed to fewer infectious agents. The second: Increased birth-spacing as a result of the contraceptive effects of lactation decreases the number of children who transmit common contagious agents to susceptible siblings. 14 The third: Breast-fed infants are rarely in group-care facilities and are thus less exposed to communicable infections.

These propositions did not, however, entirely explain the protection provided by breast-feeding, for breast-fed infants are asymptomatic even when they are exposed to bacterial enteropathogens such as Shigella that contaminate the mother's nipples, colostrum, and milk. 5 Further, breast-fed infants are more resistant to common respiratory infections. [15] [16] [17] [18] Much of the protection is provided by a complex immunologic system in human milk. Furthermore, antimicrobial agents, which were the first parts of the immunological system to be recognized, [19] [20] [21] have certain shared features (Box 158-1). The inverse relationship between the quantities of many agents in human milk and the production of these agents by the infant suggested a relationship between the development of the infant's immune system and the ability of the lactating mammary gland to produce the immune factors. [22] [23] [24] After the concept of an immune system in human milk was formed, 19 antiinflammatory 21, 25, 26 and immunomodulating agents 21, 26 were discovered to be part of that system. Thereafter the evolutionary relationships between the immune system in human milk and the development of the immune system in the infant were appreciated. [22] [23] [24] 1. Certain postnatal developmental delays in the infant's immune system are compensated by the transmission of the same agents in human milk. 2. Other postnatal delays in components of the immune system in the infant are compensated by dissimilar agents in human milk. 3. Some agents in human milk initiate or augment functions poorly expressed in the infant. 4. Many antimicrobial agents in human milk act synergistically. 5. Some agents in human milk alter the physiological state of the alimentary tract from one suited for fetal life to one that is appropriate for extrauterine life. 6. Antibodies in human milk are produced by plasma cells that transformed from B cells that originate in the maternal intestines and bronchi. 7. Specialized living leukocytes are found in human milk. 8 . Defense agents in human milk protect against microbial pathogens without provoking inflammation in the infant. 9. Some agents in human milk inhibit inflammation. 10 . Some agents in human milk are immunoregulators. 11 . Some agents in human milk are antineoplastic. 12. Defense agents in human milk resist enzymatic digestion and thus function in the recipient's GI tract. 13 . Certain defense agents are created in the infant's GI tract by partial digestion of substrates in milk. 14. When defense agents in human milk interact with some pathogens, the infant develops specific adaptive immune responses but no symptomatic infections. Such a sheltered immunization is similar to immunizing with an attenuated microbial pathogen. 15 . Agents in human milk augment the growth of commensal enteric bacteria adapted to infants that produce compounds that protect against bacterial pathogens and convey other immunologic benefits. 27,28 16 . There is often a reciprocal relationship between the defense agents that are transmitted in milk and those transmitted during fetal life via the placenta.

The physical features, functions, and quantities of antimicrobial agents in human milk are summarized in Table 158 -1. The proteins will first be considered.

IgM, IgG, IgD, and IgA are in human milk. IgM concentrations are much lower in human milk than in serum. 29 IgM molecules in blood and milk are pentamers. However, unlike serum IgM, human milk IgM is bound to secretory component. The concentrations of IgG in human milk are lower than IgM in human milk and are much less than IgG in human serum. 29 All IgG subclasses are in human milk, 30 but the relative proportion of IgG4 is higher in human milk than serum. 30 Very little IgD is present in human milk. 31 IgE, the immunoglobulin responsible for immediate hypersensitivity, is essentially absent. 32 In contrast, IgA in the form of secretory IgA comprises more than 95% of human milk immunoglobulins. 29 Although some trimers and tetramers of IgA are in human milk, most secretory IgA consists of two identical IgA monomers united by a 15-kD polypeptide called the joining chain and complexed to a 75-kD glycoprotein, the secretory component. 33 receptors on the basolateral surface of epithelial cells. 35 The complex is internalized, the original cytoplasmic part of the receptor is cleaved off, and the remaining assembled protein is transported across the cell into milk. Secretory IgA antibodies in human milk are directed principally against enteric and respiratory pathogens (Table 158 -2). The precursors of the cells that generate those antibodies originated at those mucosal sites. In fact, those precursors are released from the maternal mucosal sites because of immunogen-triggered events. 36 Hormonal stimulation during lactation causes antigen-stimulated B cells from Peyer's patches of the lower small intestinal tract to switch from the IgM to the IgA isotype and migrate to the mammary gland. 37,38 A similar B-cell pathway links bronchial lymphoid tissues to the mammary gland. 39 The details are as follows.

After antigenic stimulation, cytokines from mononuclear leukocytes in Peyer's patches induce local B cells to switch from IgM to IgA. 40,41 The IgA + B cells then migrate sequentially into local intestinal lymphatic channels and lymph nodes, the cisterna chyli, the thoracic duct, and the vascular circulation. During lactation, they home to the stroma of the mammary gland. Experimental evidence suggests that the chemokine CCL28 and its receptor CCR10 are crucial to this process: (1) CCL28 is up-regulated in the murine mammary gland epithelium during lactation; 42 (2) most IgA + B cells in the enteromammary gland pathway display CCR10; 43 and (3) IgA + B cells that are CCR10 + move toward CCL28, which is expressed by mammary gland epithelium during lactation. 43 IgA + B cells in the mammary gland differentiate into IgAproducing plasma cells that remain in the lamina propria of the organ. IgA dimers produced by mammary gland plasma cells principally contain λ-light chains, whereas κ-light chains predominate in serum immunoglobulins. 44 IgA dimers released from those plasma cells bind to polymeric immunoglobulin receptors on the basolateral external membranes of mammary gland epithelial cells. 33, 34, 45, 46 The resultant receptor-dimeric IgA complex is transported to the apical side of the cell where the intracytoplasmic portion of the receptor is removed. The remaining molecule, secretory IgA, is secreted into milk. Thus enteromammary and bronchomammary pathways protect the immunologically immature infant against pathogens that the mother encounters (see Table 158 -2). This is important since secretory IgA antibodies and the antigen-binding repertoire of immunoglobulins are developmentally delayed during early infancy. 47 Also, some secretory IgA molecules in human milk are antiidiotypic antibodies that function as immunogens. 48 Certain secretory IgA antibodies in human milk are directed against the autoantigen CCR5, which is not only a chemokine receptor but is also the co-receptor for R5-tropic strains of HIV-1 that permits macrophages and immature dendritic cells to become infected with HIV-1. 49 The antibodies from uninfected as well as HIV-1 infected women bind to the second extracellular loop of CCR5 and thus block infection of macrophages and dendritic cells by HIV-1. In addition, secretory IgA antibodies to DNA enzymatically cleave DNA. 50,51 Therefore the DNA is recognized as an autoantigen and a substrate by the antibody enzyme and may hydrolyze free nucleic acids in the recipient's intestinal and respiratory tracts.

Secretory IgA in human milk also facilitates mucosal immunization against enteric microorganisms. 52 Secretory IgA adheres selectively to cells in Peyer's patches. Subsequently, the antibodies are transported to the underlying lymphoid tissue. There they bind to and are internalized by dendritic cells in the subepithelial dome region of Peyer's patches. If foreign enteric protein antigens are coupled to these antibodies, they will be processed by dendritic cells and then presented to T cells. Once the processed antigens are presented to TcRs on helper T cells, the T cells are activated. The activated T cells secrete cytokines that activate local cytotoxic T cells or stimulate local IgM + B cells to proliferate and switch their isotype to IgA. That eventually leads to the production of secretory IgA at mucosal sites.

The quantity of secretory IgA in human milk declines as lactation proceeds, but considerable secretory IgA is transmitted to the infant throughout breast-feeding. 54-57 Concentrations of secretory IgA in human milk are highest in colostrum 50 and gradually plateau later in lactation to about 1 mg/mL. 56 The approximate mean daily intake of secretory IgA in healthy full-term breast-fed infants is 125 mg/kg/day at 1 month and 75 mg/kg/ day by 4 months. 57 The pattern of immunoglobulins in human milk differs from the pattern in other mammals except closely related primates. 25 For example, the dominant immunoglobulin in bovine colostrum, IgG, is absorbed into the calf's blood. IgG production is developmentally delayed in those newborns. Without colostrum, they remain IgG-deficient and very susceptible to intestinal infections.

Secretory IgA resists intestinal proteases such as pancreatic trypsin. 58 Bacterial proteases attack the hinge region of IgA1, 59 but the second subclass, IgA2, is resistant to those proteases and is disproportionally increased in human milk. 30 Furthermore, secretory IgA antibodies against bacterial IgA proteases are present in human milk. 59 In that respect, the amount of secretory IgA excreted in stools of low birth weight infants fed human milk is about 30 times that in infants fed a cow's milk formula. 60 In addition, urinary excretion of secretory IgA rises in infants fed human milk. 61,62 It is unlikely that the antibodies are from human milk because there is no mechanism for the their transport from the gastrointestinal tract to the blood. Thus human milk may stimulate the infant to produce the antibodies and transport them into the urinary tract.

Free secretory component is also secreted into human milk, and this peptide inhibits the adherence of certain enterobacteria to epithelial cells. 63, 64 Lactoferrin Lactoferrin is a single-chain glycoprotein with two globular lobes, each of which displays a binding site for ferric iron. 65 In 90% of lactoferrin in human milk, 66 iron-binding sites are available to compete with siderophilic bacteria and fungal enterochelin for ferric iron. [67] [68] [69] The iron chelation disrupts the proliferation of those pathogens. Lactoferrin also kills by damaging outer membranes of many gram-positive and gram-negative bacteria. [70] [71] [72] This process is conducted by a peptide, lactoferricin, which is usually comprises 18 amino acid residues from the N-terminal region of lactoferrin that are formed by gastric pepsin digestion. 71, 72 Furthermore, lactoferrin inhibits certain viruses by a chelation-independent mechanism 73-76 and interferes with the adhesion of Escherichia coli to epithelial cells. 68 The mean concentration of lactoferrin in human colostrum is between 5 and 6 mg/mL. 54 As the volume of milk production increases, the concentration falls to about 1 mg/mL at 2 to 3 months of lactation. 55 The mean intake of milk lactoferrin in healthy breast-fed full-term infants is about 260 mg/kg/day at 1 month and 125 mg/kg/day by 4 months. 57 Because human lactoferrin resists proteolysis 77 and the concentration of lactoferrin is much greater in human than bovine milk, 25 the excretion of lactoferrin in the stools is higher in infants fed human milk than in those fed a cow's milk formula. 60, 78 The quantity of lactoferrin excreted in stools of low-birth-weight infants fed human milk is approximately 185 times that excreted by infants fed a cow's milk formula. 60 That estimate, however, may be too high because of immunoreactive fragments of lactoferrin in the stools of human milk-fed infants. 79 There is also a significant increment in urinary excretion of intact and fragmented lactoferrin as a result of human milk feedings. 62, 79 Although the transport mechanism is unknown, the increase is a result of absorbed human milk lactoferrin and it fragments. 80 Lysozyme Lysozyme, a 15-kD single chain protein, lyses susceptible bacteria by hydrolyzing β-1,4 linkages between N-acetylmuramic acid and 2-acetylamino-2-deoxy-d-glucose residues in cell walls. 81 High concentrations of lysozyme are in human milk throughout lactation. 54-56 Longitudinal changes in lysozyme during lactation are unlike most other immune factors in human milk. The mean concentration of lysozyme is about 70 μg/mL in colostrum, 54 20 μg/mL at 1 month and 250 μg/mL by 6 months of lactation. 55 The high content of lysozyme in human milk and its resistance to proteolysis lead to an eightfold increase in lysozyme in the stools of low-birth-weight infants fed human milk. 60 The urinary excretion of this protein is not increased in infants fed human milk. 62

α-Lactalbumin is expressed only in the lactating mammary gland. A folding variant of the protein kills Streptococcus pneumoniae in vitro. 82 Furthermore, a molecular complex consisting of partially unfolded α-lactalbumin and oleic acid kills many types of tumor cells in vitro by several mechanisms including apoptosis and macroautophagy. 83, 84 The protein invades tumor cells, depolarizes mitochondrial membranes, releases cytochrome c, exposes phosphatidyl serine, reduces caspase responses, and activates 20S proteasomes. α-Lactalbumin also translocates to tumor cell nuclei to cause chromatin disruption, loss of transcription, and nuclear condensation. The protein also kills certain skin papillomas and bladder cancers in situ. However, the in vivo antineoplastic action of the protein in human milk upon the recipient infant is undetermined.

CCL28 is not only a chemokine; it also kills Candida albicans and many gram-positive and gram-negative bacteria. The killing is mediated by the 28 amino acid C-terminus of the molecule. 85 

Macrophage inhibitory factor (MIF), a constituent of human milk, 86 is a proinflammatory cytokine that also up-regulates TLR-4 87 and aids in killing Mycobacterium tuberculosis in human macrophages. 88 

Fibronectin facilitates the uptake of many particulates by mononuclear phagocytes. The in vivo effects of this opsonin in human milk 89 are unknown.

All components of the classical and alternative pathways of complement are in human milk, but their concentrations are much lower than those in serum. [90] [91] [92] Based upon in vitro experiments, 93 degradation products of C3 (C3b or C3bi) in human milk may augment phagocytosis of microbial pathogens in the infant's gastrointestinal or respiratory tracts.

Milk mucins are high-molecular-weight, highly glycosylated proteins. 94 Two thirds of mucin in human milk is bound to milk fat globule membranes. The concentration of mucin in human milk ranges between 50 and 90 mg/mL. Human milk fat globules and mucin from their membranes inhibit the binding of S-fimbriated E. coli to human epithelial cells. 94 The most prominent mucin, MUC1, resists intragastric digestion in preterm infants. 95 Major fragments of MUC1 are in feces of breast-fed infants, 96 and mucins from such feces inhibit the adhesion of S-fimbriated E. coli to epithelial cells. 97 

Human milk mucin was thought to defend against rotavirus in experimental mice, 98 but the protection turned out to be lactadherin, 99 a 49-kDa glycoprotein on milk fat globules that resists intragastric digestion. 95 A protein analogous to human lactadherin, MFG-E8, is found on murine milk fat globules. 100 MFG-E8 on murine macrophages binds to phosphatidyl serine exposed on the outer membranes of apoptotic cells. 101, 102 It also binds to α1β3 and α1β5 integrins on macrophages in the spleen and lymph nodes and elicited peritoneal macrophages via a tripeptide (RDG) motif within the second of its two EGF repeats. Because of the double linkage, apoptotic cells are phagocytized without inducing inflammation. Human lactadherin may have similar effects.

In addition to antimicrobial peptides generated by partial digestion of lactoferrin, cysteine-rich, cationic low-molecular-weight peptides are in human milk including β-defensin-1, 103 which disrupts E. coli, and the α-defensins -1,-2, and -3 (HNP -1, -2, and -3) 104 and α-defensins, which inhibit HIV-1 replication and may interfere with postpartum transmission of HIV-1. 104 

Oligosaccharides in human milk are produced by mammary gland glycosyltransferases. Their concentrations in colostrum and mature milk are about 20 mg/dL and 12 mg/dL, respectively. 105 Many oligosaccharides are in human milk, 106 and they differ from those found in cow's milk. Although the quantities of total gangliosides in human and bovine milk are similar, the frequencies of each type of ganglioside in the milk of the two species are different. For example, greater amounts of monosialoganglioside 3 and GM 1 are found in human than in bovine milk. 106, 107 Because these agents resist enzymatic digestion, it was predicted that they would have nonnutritional functions. Indeed, some are receptor analogues that inhibit the in vitro binding of certain enteric or respiratory bacterial pathogens and their toxins to epithelial cells. 106, 108, 109 The chemistry of these compounds dictates the specificity of their binding. For example, GM 1 gangliosides are receptor analogues for Vibrio cholerae and E. coli toxins, 109 whereas the globotriaosylceramide Gb3 binds to b subunits of shigatoxin. 110 A fucosyloligosaccharide inhibits the stable toxin of E. coli, 111 whereas a different one inhibits Campylobacter jejuni. 112 Human milk oligosaccharides interfere with the attachment of Haemophilus influenzae and S. pneumoniae to respiratory epithelium, 113 and G1cNAc(β1-3) Gal-disaccharide subunits block attachment of S. pneumoniae to respiratory epithelium. 113 The severity of Campylobacter or calcivirus enteritis in breast-fed infants is inversely proportional to concentrations of oligosaccharides in maternal milk that consist mainly of α-(1→2) oligosaccharides. 114 It is unclear whether the risk to other enteropathogens is related to quantitative variations in other oligosaccharides in human milk.

In addition, sulfated glycolipids, glycosaminoglycans, 115 and Lewis X component 116 in human milk inhibit in vitro infection by HIV-1. Polymers of Lewis X component interact with a dendritic cell-specific ICAM3-grabbing nonintegrin that facilitates the transfer of HIV-1 from dendritic cells to CD4 + T cells. Consequently, gp120 on the envelope of HIV-1 is unable to bind to those T cells.

Animal experiments suggest that oligosaccharides and glycoconjugates in human milk protect against certain enteric bacterial infections. 117 In that regard, certain human milk oligosaccharides survive passage through the alimentary tract 118 and some are absorbed and then excreted into the urinary tract. 119 This may account for some protection by human milk against urinary tract infections. 120 Sugars in the glycoconjugates mucins, lactadherin, and secretory IgA also interfere with binding of bacterial pathogens to epithelial cells. 93, 94, 121 In addition to the direct antibacterial effects of the carbohydrates in human milk, nitrogen-containing oligosaccharides, glycoproteins, and glycopeptides in human milk are growth promoters for lactobacilli and bifidobacilli. 122, 123 For example, the growth-promoter activity associated with caseins may reside in the oligosaccharide moiety of those complex molecules. 123 These factors are responsible for the predominance of lactobacilli and bifidobacilli in the bacterial flora of the large intestine of breastfed infants. The commensal bacteria produce large amounts of acetic acid, which suppress the multiplication of enteropathogens. The Lactobacillus strain GG may also aid in the recovery from acute rotavirus infections 124 and may enhance the formation of specific circulating antibodies during enteric infections. 29 In addition, enteric commensal bacteria may stimulate the production of IL-12 125 and low-molecular-weight antibacterial peptides such as defensins. 126 These latter defense mechanisms may contribute to the comparative paucity in stools of breast-fed infants of bacterial pathogens most often found in urinary tract infections such as P-fimbriated E. coli. 127 Lipids Fatty acids and monoglycerides generated by the enzymatic digestion of lipid substrates in human milk disrupt enveloped viruses. 128, 129 These antiviral lipids may aid to prevent coronavirus infections of the intestinal tract 130 and defend against intestinal parasites such as Giardia lamblia and Entameoba histolytica. 131, 132 Monoglycerides from milk lipid hydrolysis also inactivate certain gram-positive and gram-negative bacteria. 133 These lipids may act synergistically with one another and with antibacterial peptides. 134 Hydrolysis of milk lipids occurs in infants because of lingual lipase and the activation of human milk bile-salt stimulated lipase in the duodenum. Thus the products of lipid digestion may help defend breast-fed infants against enteric infections in the proximal gastrointestinal tract.

Living leukocytes are found in human milk, 135 and virtually all of them are activated. 136, 137 In contrast to B cells that transform into plasma cells that remain sessile in the mammary gland, other leukocytes attracted to the site traverse the mammary epithelium and become part of milk secretions. The highest concentrations of leukocytes in human milk occur in the first few days of lactation (1-3 × 10 6 /mL). The several types of leukocytes and their major features are as follows.

The relative frequencies of T cells and B cells among lymphocytes in early human milk secretions are 83% and 6%, respectively. 136 The small number of natural killer cells in human milk 136 is in keeping with the low cytotoxic activity of human milk leukocytes. 138 The numbers of B cells in human milk are small because most B cells that enter the lamina propria of the mammary gland transform into sessile plasma cells.

Both CD4 + (helper) and CD8 + (cytotoxic/suppressor) T-cell subpopulations are present in human milk. 136 But compared with human blood T cells, the proportion of CD8 + T cells in human milk is greater. 136 CD4 + and CD8 + T cells in human milk bear markers of cellular activation including CD45RO and HLA-DR. 136 Moreover, a greater percentage of human milk CD8 + T cells express the intestinal homing receptor, CD103, and the mucosal homing receptor, CCR9, than those found in blood. 139 T cells in human milk produce certain cytokines such as interferon-γ. 140 Additional cytokines are produced by human milk leukocytes, 141 but the extent of their production and secretion is undetermined.

Neutrophils and macrophages are the dominant leukocytes in human milk. Both types of cells are laden with milk fat globules and other membranes that have been phagocytized. Because of these intracytoplasmic bodies, they are difficult to recognize by common staining methods. They can be identified however by the presence of myeloperoxidase in neutrophils), 141,142 nonspecific esterase in macrophages, 141, 142 or CD14 or MHC class II molecules in macrophages. 141 Both types of cells in human milk are phagocytic. A respiratory burst occurs in milk macrophages after stimulation. 142, 143 Superoxide anion generation by those cells is more marked after exposure to mannose-receptor ligands. 143 The macrophages also process and present antigens to T cells. 144 In contrast to blood neutrophils, human milk neutrophils do not increase adherence, polarity, directed migration, 145 or deformability after exposure to chemoattractants. 146 These alterations may be due to agents in human milk. For example, the decreased calcium influx found in human milk neutrophils is duplicated by incubating blood neutrophils in human milk. 147 Unlike human milk neutrophils, the motility of macrophages in human milk is increased compared with blood monocytes. 148 The features of these cells in human milk are likely due to cellular activation, because they display phenotypic features of activation, including an increased expression of CD11b/CD18 and a decreased expression of CD62L. 137 The activation may be due in part to ingestion of milk fat globules or other membranous materials in human milk. 137 

The in vivo fate and role of human milk leukocytes in the infant are poorly understood. Only a small numbers of memory T cells are detected in infancy 149 ; thus maternal memory T cells in milk may compensate for that developmental delay in the infant. There is evidence from experimental animal studies that milk lymphocytes enter tissues of the neonate, 141 but that has not been demonstrated in humans. In addition, cellular immunity may be transferred by breast-feeding. 150 

Inflammatory agents and systems that give rise to them are poorly represented in human milk. 25, 26 These include (1) the coagulation system; (2) the kallikrein-kininogen system; (3) most complement components; (4) IgE; (5) basophils, mast cells, eosinophils; and (6) cytotoxic lymphocytes. Certain proinflammatory cytokines (see subsequent discussion) are found in human milk, but there is no clinical evidence that they generate inflammation in the recipient.

Human milk also contains many antiinflammatory agents 25,26 including (1) factors that promote epithelial growth and thus strengthen mucosal barriers; (2) antioxidants; (3) agents such as lactoferrin that interfere with some complement components 26, 151 ; (4) enzymes that degrade mediators of inflammation; (5) protease inhibitors 152 ; (6) agents that bind to substrates such as lysozyme to elastin 153 and lactoferrin to the toxic moiety of lipopolysaccharide, lipid A 154 ; (7) cytoprotective agents such as prostaglandins E 1 , E 2 , and F 2 α, 155, 156 ; and (8) agents that inhibit the functions of inflammatory leukocytes 26 such as binding of LPS to CD14 by lactoferrin 154 and the down-regulation by lactoferrin of LPS-induced cytokine production by mononuclear phagocytes via NFκB 157 (Table 158-3) . Furthermore, many antiinflammatory agents in human milk are adapted to survive in the alimentary tract.

The main antioxidants in human milk include an ascor batelike compound, 158 uric acid, 158 α-tocopherol, 159,160 and β-caro tene. 159, 160 Blood levels of α-tocopherol and β-carotene are higher in breast-fed than formula-fed infants not supplemented with those agents. 160 The in vivo action of those agents in human milk is unknown.

Mucosal growth factors in human milk include epithelial growth factor, 161 lactoferrin, 162 cortisol, 163 polyamines, 164, 165 and peptides produced from α-lactalbumin and lysozyme. 166 Other hormones and growth factors in human milk 167 also affect the growth and differentiation of epithelium and thus limit the penetration of antigens and pathogens into the intestines. In that respect, the biophysical and biochemical organization and functions of mucosal barriers in adults and neonates are different. 168, 169 Furthermore, their maturation may be accelerated by human milk. 170, 171 Enzymes in human milk degrade inflammatory mediators. Platelet-activating factor (PAF) plays a role in an intestinal injury in rats induced by endotoxin and hypoxia. 172 Human milk, however, contains an acetylhydrolase that degrades PAF, 173 whereas the production of human PAF-acetylhydrolase is developmentally delayed. 174 As a result of these agents in human milk, intestinal permeability is lessened in breast-fed infants. [175] [176] [177] 

Observations suggest that immunomodulating agents in human milk are important: 1. Epidemiologic investigations suggest that older children who are breast-fed during infancy may be at less risk for developing certain chronic diseases mediated by immunologic, inflammatory, or oncogenic mechanisms. The diseases are type 1 diabetes mellitus, 178-180 type 2 diabetes mellitus, 181 lymphomas, 182,183 acute lymphocytic leukemia, 183, 184 and Crohn's disease. 185,186 2. Increased levels of certain immune factors in breast-fed infants cannot be accounted for by passive transfer of those substances from human milk. Breast-feeding primes the recipient to produce higher blood levels of interferon-α in response to respiratory syncytial virus (RSV) infections. 187 In addition, increments in blood levels of fibronectin achieved by breastfeeding cannot be accounted for by the amounts of that protein in human milk. Moreover, breast-feeding leads to a more rapid development of systemic 188 and secretory 188, 189 antibody responses and of secretory IgA in external secretions 60-62 including urine, 61,62 which are far removed from the route of ingestion. There is no evidence that those increments are caused by absorption of those same factors from human milk. 3. Thymic growth, 190 T-cell emigration from the thymus possibly caused by increased IL-7 in human milk, 191 T-cell maturation, and IL-10 production 192 are increased in breast-fed infants compared with infants who are not breast-fed. 4. All leukocytes in human milk are activated.

After it was ascertained that human milk leukocytes were activated, activating agents in human milk were sought. It was found that human milk enhances the movement of blood monocytes in vitro and that much of that motility was abrogated by antibodies to tumor necrosis factor-α (TNF-α). 193 Subsequently, TNF-α in human milk was detected immunochemically. 194 Since then, many cytokines have since been found in human milk (Table  158 -4). They include the following: 1. IL-7, which promotes intrathymic development of T cells and maintenance of mature T cells in the peripheral lymphoid system. 192 2. IL-2 with IL-7, which promotes the proliferation of recent thymic immigrants. 195 3. Th1 (interferon-γ, 196 197 and IL-18 198 ) and Th2 (IL- 10 199,200 and IL-4 201 ) cytokines. 4. Macrophage-stimulating cytokines including IL-1β, 202 IL-6, 203 and MIF. 86 5. Chemotaxins including IL-8, 204 RANTES, 201 CCL28, 85 and eotaxin. 201 6. Interferon-inducible proteins IP-10 and MIG. 205 7. Antiinflammatory agents such as Il-4, 201 TGF-β1, 206 TGF -β2 207 and IL-10 199,200 8. Growth factors EGF, 161,167 granulocyte colony-stimulating factor, 208 macrophage-CSF, 209 hepatic growth factor, 210 Il-4 196 and erythropoietin. 211 It should be pointed out that the in vivo fate, action, and interactions of these cytokines in human milk are complex and largely unexplored. For example, IL-2 greatly decreases the expression of IL-7 receptor α-chains (IL-7Rα). 212 Because IL-7Rα is a component of receptors for IL-7 and thymic stromal lymphopoietin, IL-2 may negatively regulate signals by each of these cytokines. It is unclear whether the in vitro actions pertain to the in vivo effects upon the infant.

Other immunomodulating agents in human milk include β-casomorphins, 213 prolactin, 167, 214 antiidiotypic antibodies, 48 α-tocopherol, 159, 160 nucleotides that enhance NK-cell, macrophage, and Th1 activities, 215 cell adhesion molecules ICAM-1, VCAM-1, E-and L-selectin, 216 mannan-binding lectin-which activates complement by the lectin pathway after recognizing surface saccharide motifs on microorganisms 217 and soluble CD14, a B-cell mitogen. 218 Toll-like receptors (TLR) in human milk are being investigated. Soluble TLR-2 is present in human milk. 219 Furthermore, a protein of approximately 80 kD in human milk enhances the response of TLR4 and TLR5 receptors on umbilical cord blood mononuclear leukocytes. 220 In addition to the antimicrobial and antiinflammatory functions of lactoferrin, this single-chain glycoprotein also promotes the differentiation of dendritic cells from monocytes. 221 It will be important to establish whether lactoferrin in human milk has a similar in vivo effect in the recipient infant.

In addition to their antimicrobial properties, some oligosaccharides are immunomodulatory. Lacto-N-fucopentaose III and lacto-N-neotetraose increase the production of murine IL-10. 222 Furthermore, human milk acidic oligosaccharides increase the number of interferon-producing CD4 + and CD8 + T cells and IL-13 production by CD8 + T cells. 223 In addition, more CD25 is expressed on CD4 + T cells after exposure to those oligosaccharides. 223 

Several evolutionary outcomes concerning the relationships between the immune status of infants and defense agents in human milk have been recognized. In respect to one of the main evolutionary outcomes, many aspects of the human immune system are incompletely developed at birth, and the immaturity is most marked in very-low-birth-weight infants. They include (1) the mobilization and function of neutrophils, [224] [225] [226] (2) the maturation of dendritic cells, 227, 228 (3) the recognition by monocytes and macrophages to bacterial agents by toll-like receptors TLR2 and TLR4, 229 (4) the production of lysozyme 230 and secretory IgA, 231 (5) memory T cells that bear CD45RO, 149 (6) the full expression of the antibody repertoire, 232 and (7) the production of certain cytokines including TNF-α, [233] [234] [235] 236, 237 interferon-γ, 237-239 IL-6, 234,240 IL-10, 233,241 IL-12, 242,243 IL-18, 243 G-CSF, 244 GM-CSF, 245 IL-3, 244 and RANTES. 246 Many developmentally delayed defense agents are present in human milk (Table 158-5) . For instance, secretory IgA antibodies in milk compensate for low production of secretory IgA during early infancy. 248 Human milk antibodies are polyclonal and directed against protein and polysaccharide antigens. This is important because infants display a more restricted antibody clonality 248 and do not produce IgG antibodies to polysaccharides. 249 Conjugate vaccines have been introduced, but antibody responses to them are higher in breast-fed than cow's milk-fed infants. 250 An additional example is the interrelationship between the production of lysozyme by the infant and the mammary gland. High lysozyme levels in human milk 54-56 are coupled to low production of the protein by tracheo-bronchial mucosal cells during infancy. 230 Indeed, normal intraluminal concentrations of lysozyme in infancy may depend on breast-feeding. This is in keeping with higher lysozyme activities in stools of breast-fed infants than in infants who are not breast-fed. 60 The functions of immune factors in human milk in the recipient infant depend on their survival in the infant. The following are germane: (1) Proteins may affect the epithelium, leukocytes, or other cells of the proximal GI or respiratory tracts where proteolytic enzymes are not produced. (2) Some proteins are inherently resistant to proteolysis. (3) Ingested proteins may escape Types  Examples   T-cell production augmentation  IL-7  Cellular immunity enhancement  Interferon-γ, TNF-α, IL-12, and IL-18  Humoral immunity enhancement TGF-β2, IL-4, IL-10  Macrophage stimulation  IL-1β, IL-6 

Antimicrobial SIgA Lactoferrin Lysozyme Antiinflammatory IL-10 PAF-acetylhydrolase Lactoferrin Lysozyme Immunomodulatory

Memory T cells IL-4 IL-10 IL-12 G-CSF TNF-α Interferon-γ RANTES digestion because of developmental delays in production of gastric HCl and pancreatic proteases. 251 This resistance to digestion may be augmented by (1) the buffering capacity of human milk that shields some acid-labile components of milk, (2) antiproteases in human milk, 152 (3) the inherent resistance of many defense agents in human milk to digestive processes, and (4) the compartmentalization of some defense agents in human milk. 86, 94, 95 In that respect, much of the TNF-α in human milk is bound to soluble receptors. 252 

Maturational delays of the immune system are generally more profound in premature infants. Furthermore, the problem is compounded by the shortened duration of placental transfer of IgG to the fetus, 253 medical problems during the newborn period, 254 nutritional imbalances, and invasive clinical procedures that increase the risks to infections.

Milk from women who deliver prematurely contains many of the same antimicrobial factors that are found in milk from women who have delivered after a full-term pregnancy. These include secretory Ig, lactoferrin, and lysozyme. 255 The concentrations of some defense agents are higher in preterm than term milk. Those higher concentrations may be in large part due to a lower production of milk by women who deliver prematurely. However, that may not be the total explanation for the higher concentrations in that patterns of the concentrations of some antimicrobial agents in preterm and term milk are not the same. 255 

In addition to the protection against enteric infections and respiratory infections, there are several indications that human milk feedings protect premature infants against systemic infections that are prone to occur in such infants. [256] [257] [258] Necrotizing Enterocolitis

Human milk protects against necrotizing enterocolitis (NEC). 259 Human and experimental animal studies suggest that IgA, 260 erythropoietin, 261,262 PAF-acetylhydrolase, [172] [173] [174] 200, 263, 264 protect against NEC. These possibilities are in keeping with two important findings: 1) each of these defense agents is well represented in human milk and not in artificial feedings, and 2) the production of each agent in human infants is developmentally delayed.

One animal model suggests that IL-10 in human milk may prevent intestinal inflammation. Mice homozygous for IL-10 null genes develop a fatal enterocolitis that begins soon after weaning and is dependent on an enteric bacterial flora. 263, 264 The enterocolitis had some features of Crohn's disease and NEC. Much of the enterocolitis in those animals is prevented by intraperitoneal injections of IL-10 given at the start of weaning. 263 One study suggests that variations in the concentrations of IL-10 in human milk may be responsible for some of the risk of NEC in premature infants. 200 Two distinct populations of women were found in respect to the concentrations of IL-10 in their milk-72% were high producers, and 28% were very low producers. 200 In women whose infants developed NEC while receiving their own mother's milk, IL-10 was barely detected or undetected in milk from more than 90% of them. 200 The study awaits verification.

Although it is unknown whether human milk protects against pulmonary and vascular effects of hyperoxia, α 1 -antitrypsin prevents many of the features observed in hyperoxic neonatal rats including elevated pulmonary elastolytic activity. 265 Furthermore, a murine model suggests that TGF-β1 in human milk protects against certain pulmonary inflammatory diseases. Mice homozygous for the TGF-β1 null gene display infiltrations of macrophages and T cells in many organ sites, particularly the lungs, heart, and salivary glands. [266] [267] [268] Further, the effects of TGF-β1 deficiency are mitigated by ingestion of TGF-β1 in murine milk. 268 Furthermore, one study suggests that greater exposure to human milk TGF-β1 lessens the risk of asthma in the first year of life. 206 

Some studies suggest that human milk protects against atopic dermatitis 269 and asthma 206, 270 and that some of the protection against asthma is mediated by TGF-β1 206 and soluble CD14 in human milk. 270 However, there is no consensus whether as to whether breast-feeding protects against atopic diseases. 271 Much of the disagreement may be due to confounding variables including variations in genetic predisposition to atopic disorders, the sufficiency of breast-feeding, unappreciated dietary exposures, and exposures to inhaled allergens or irritants. Further, increased exposures to infectious diseases facilitate Th1 responses that lead to cellular immunity, whereas lower exposures engender Th2 responses that lead to antibody formation and hence to possible IgE-mediated hypersensitivity. Thus, the effect of breast-feeding on atopic diseases may depend on factors that are not equally represented in all investigated populations.

Moreover, the question is complicated by foreign food antigens in human milk 272 and the triggering of allergic reactions by those antigens in some infants. 273 To test whether a breast-fed infant reacts to a foreign food antigen in human milk, dietary elimination and oral challenge with the food in question in the breast-feeding mother are needed. 273 If the infant reacts to a foreign food antigen in human milk, then the food should be eliminated from the maternal diet. If the allergen is a basic food, the elimination diet should contain the correct types and quantities of nutrients to meet the needs of the mother. 20 If dietary elimination is impractical, breast-feeding may be stopped and a hypoallergenic formula instituted. In addition, allergic disease in breast-fed infants may be due to alterations in fatty acids in human milk. [273] [274] [275] 

Evidence for induction of immunologic tolerance by breastfeeding comes from studies of alloreactivity. Maternal renal allografts are better tolerated in children from women who breast-feed transplant recipients than those who do not. 276, 277 The difference in alloreactivity is also shown with blood lymphocytes from mothers and their children. Less alloreactivity occurs when lymphocytes from the mother (stimulators) are cocultured with her breast-fed child's cells (reactors). 278 The tolerance may be induced by HLA-DR antigens on fat globules 279, 280 and macrophages 137, 141, 144 in human milk.

Although much has been learned, there is much to be discovered. This includes: 1) other defense agents present in human milk, 2) regulation of production of the agents during lactation, 3) the precise molecular form of each defense agent in human milk, 4) where compartmentalized and soluble-receptor bound agents in human milk are released, 5) whether other defense agents are created in the infant's gastrointestinal tract by partial digestion of substrates in human milk, 6) mechanisms responsible for activating leukocytes in human milk, 7) in vivo fate and action of the defense agents in human milk, 8) effects of commensal bacterial flora induced by breast-feeding upon the immune system of the recipient, 9) tolerogenic effects of human milk, and 10) long-term effects of antiinflammatory, immunomodulating, and antineoplastic agents in human milk. Like the skin and gastrointestinal (GI) tract, the lungs are a mucosal organ with a large surface area exposed to the external environment. Unlike the skin and GI tract, the lung is considered to be largely sterile below the glottis whereas the skin and GI tract are colonized with bacteria termed "commensal flora." Despite the lower airway being sterile, the upper airway becomes rapidly colonized with bacteria that can be aspirated into the lower airway, thus the lung has evolved an array of host defense mechanisms to prevent development of infection in the air space. This robust development of pulmonary host defense mechanisms was an essential step in the evolution of air-breathing animals. The major physiologic aspect of the lung is to perform gas exchange, namely the exchange of oxygen and carbon dioxide across the alveolar capillary membrane.

To maintain this function, the lungs must have buffering capacity in the airway and alveolar space to neutralize potentially injurious agents including pathogens. In a 3.5-kg neonate with a typical minute ventilation ranging from 100 to 150 mL/ (kg•min), the lungs are required to filter approximately 30 L of inhaled air hourly. This is a problematic task in that the alveolar surface area requiring protection is 20 times the average neonatal body surface area. 1 In addition to normal tidal breathing or gas exchange the lung must be able to handle larger insults because of what may occur upon aspiration of oropharyngeal or gastric contents. Available pulmonary host defenses can be broadly categorized as either structural or immunologic. Examples of structural defenses include the larynx and epiglottis (which are 

Über Immunität, Durch Verebung Un Säugung

The relation between breast and artificial feeding and infant mortality

Breast and artificially feeding of infants. Influence on morbidity and mortality of twenty thousand infants

Breast and artificially fed infants. A study of the age incidence in the morbidity and mortality in twenty thousand cases

Bacteria in colostrum and milk of Guatemalan Indian women

Diarrhoeal disease in a cohort of Guatemalan village children observed from birth to age two years

Shigella infection in breast-fed Guatemalan Indian neonates

The protective effect of human milk against diarrhea: A review of studies from Bangladesh

Breast-feeding as a determinant of severity in shigellosis: Evidence for protection throughout the first three years of life in Bangladeshi children

Protection against cholera in breast-fed children by antibodies in breast milk

Rotavirus infection in a maternity unit

Effects of antibodies, trypsin and trypsin inhibitors on susceptibility of neonates to rotavirus infections

Modulation of rotavirus enteritis during breastfeeding. Implications on alterations in the intestinal bacterial flora

Breast feeding, birth spacing and their effects on child survival

Breast-feeding protects against respiratory syncytial virus infections

Breast-feeding and respiratory syncytial virus infection

Protective effect of breastfeeding against infection

Infant outcomes. Institute of Medicine. Subcommittee on Nutrition During Lactation

Host resistance factors in human milk

The immunological system in human milk: the past-a pathway to the future

The immune system in human milk and the developing infant

Evolution of immunologic functions of the mammary gland and the postnatal development of immunity

Modulation of the gastrointestinal tract of infants by human milk. Interfaces and interactions. An evolutionary perspective

Evolution of the mammary gland defense system and ontogeny of the immune system

Anti-inflammatory properties of human milk

Expression of functional immunomodulatory and antiinflammatory factors in human milk

Enhancement of the circulating antibody secreting cell response in human diarrhea by a human Lactobacillus strain

Protective nutrients and functional foods for the gastrointestinal tract

Immunoglobulins in human milk

Local production of IgG4 in human colostrum

Lactoferrin and free secretory component of human milk inhibit the adhesion of enteropathogenic Escherichia coli to HeLa cells

Human milk glycoproteins inhibit the adherence Salmonella typhimurium to HeLa cells

Structure of human lactoferrin at 3.2-Å resolution

Iron in human milk

Iron-binding proteins in milk and resistance of Escherichia coli infection in infants

Differences in inhibition of the growth of commensal and enteropathogenic strains of Escherichia coli by lactoferrin and secretoryimmunoglobulin A isolated from human milk

Kinetic effect of human lactoferrin on the growth of Escherichia coli 0111

A bactericidial effect for human lactoferrin

Antibacterial activity of lactoferrin and apepsin-derived lactoferrin peptide fragment

A review: the active peptide of lactoferrin

Multiple molecular forms of human lactoferrin. Identification of a class of lactoferrins that possess ribonuclease activity and lacks iron binding capacity

Lactoferrin and cyclic lactoferricin inhibit the entry of human cytomegalovirus into human fibroblasts

A milk protein lactoferrin enhances human T cell leukemia virus type I and suppresses HIV-1 infection

Antiadenovirus activity of milk proteins: lactoferrin prevents viral infection

The effect of trypsin and chymotrypsin on the in vitro antimicrobial and iron-binding properties of lactoferrin in human milk and bovine colostrum. Unusual resistance of human apolactoferrin to proteolytic digestion

Characterization and properties of the human and bovine lactotransferrins extracted from the faeces of newborn infants

Molecular forms of lactoferrin in stool and urine from infants fed human milk

Origin of intact lactoferrin and its DNA-binding fragments found in the urine of human milk-fed preterm infants. Evaluation of stable isotopic enrichment

Mechanism of lysozyme action

A folding variant of alphalactalbumin with bactericidal activity against Streptococcus pneumoniae

Multimeric α-lactalbumin from human milk induces apoptosis through a direct effect on cell nuclei

Apoptosis and tumor cell death in response to HAMLET (human alpha-lactalbumin made lethal to tumor cells)

CCL28 has dual roles in mucosal immunity as a chemokine with broad-spectrum antimicrobial activity

Presence of macrophage migration inhibitory factor in human milk: evidence in the aqueous phase and milk fat globules

Role of MIF in acute lung injury in mice with acute pancreatitis complicated by endotoxemia

Macrophage migration Inhibitory factor reduces the growth of virulent Mycobacterium tuberculosis in human macrophages

Plasma fibronectin concentrations in breast fed and formula fed neonates

Developmental aspects of complement components in the newborn. The presence of complement components and C3 proactivator (properdin factor B) in human colostrum

Complement system in human colostrum: presence of nine complement components and factors of alternative pathway in human colostrum

C3/C4 concentration ratio reverses between colostrum and mature milk in human lactation

Activation and deposition of human breast-milk complement C3 opsonins on serum sensitive Escherichia coli 0111

Chemistry of milk mucins and their anti-microbial action

Milk fat globule glycoproteins in human milk and in gastric aspirates of mother's milk-fed preterm infants

Detection of large fragments of the human milk mucin MUC-1 in feces of breast-fed infants

Inhibition of adhesion of S-fimbriated Escherichia coli to epithelial cells by meconium and feces of breast-fed and formula-fed newborns: mucins are the major inhibitory component

Human milk mucin inhibits rotavirus replication and prevents experimental gastroenteritis

Role of human-milk lactadherin in protection against symptomatic rotavirus infection

The major fat-globule membrane proteins, bovine components 15/16 and guinea-pig GP 55, are homologous to MGF-E8, a murine glycoproteincontaining epidermal growth factor-like and factor V/VIII-like sequences

Autoimmune disease and impaired uptake of apoptotic cells in MFG-E8-deficient mice

MFG-E8-dependent clearance of apoptotic cells, and autoimmunity caused by its failure

Abundant human beta-defensin-1 expression in milk and mammary gland epithelium

Defensins in innate antiviral immunity

Oligosaccharides in human milk during different phases of lactation

Oligosaccharides and glycoconjugates in human milk

Human and bovine milk: comparison of ganglioside composition and enterotoxin-inhibitory activity

Inhibition of bacterial adhesion and toxin binding by glycoconjugate and oligosaccharide receptor analogues in human milk

AB: Trace amounts of ganglioside GM1 in human milk inhibit enterotoxins from Vibrio cholerae and Escherichia coli

Human milk contains the Shiga toxin and Shiga-like toxin receptor glycolipid Gb3

Fucosylated oligosaccharides of human milk protect suckling mice from heat-stable enterotoxin of Escherichia coli

Human milk glycoconjugates that inhibit pathogens

Inhibition of attachment of Streptococcus pneumoniae and Haemophilus influenzae by human milk and receptor oligosaccharides

Human milk oligosaccharides are associated with protection against diarrhea in breast-fed infants

Inhibition of HIV-1 infection in vitro by human milk sulfated glycolipids and glycosaminoglycans

Lewis X component in human milk binds DC-SIGN and inhibits HIV-1 transfer to CD4+ T lymphocytes

Do the binding properties of oligosaccharides in milk protect human infants from gastrointestinal bacteria?

Survival of human milk oligosaccharides in the intestine of infants

Urinary excretion of lactose and complex oligosaccharides in preterm infants fed human milk or infant formulas

Protective effect of breastfeeding against urinary tract infection

Secretory immunoglobulin A carries oligosaccharides for Escherichia coli type 1 fimbrial lectin

Undialyzable growth factors for Lactobacillus bifidus var. pennsylvanicus. Protective effect of sialic acid bound to glycoproteins and oligosaccharides against bacterial degredation

Bifidobacterium bifidus var. Pennsylvanicus growth promoting activity of human milk casein and its derivates

A human Lactobacillus strain (Lactobacillus casei sp strain GG) promotes recovery from acute diarrhea in children

Lactobacilli from human gastrointestinal mucosa are strong stimulators of IL-12 production

Inducible expression of human β defensin 2 by Fusobacterium nucleatum in oral epithelial cells: multiple signaling pathways and role of commensal bacteria in innate immunity and the epithelial barrier

Adhesion and entry of uropathogenic Escherichia coli

Membrane-disruptive effect of human milk: inactivation of enveloped viruses

Inactivation of enveloped viruses and killing of cells by fatty acids and monoglycerides

Isolation and propagation of a human enteric coronavirus

Human milk kills parasitic protozoa

Cholate-dependent killing of Giardia lamblia by human milk

Antimicrobial activity of lipids added to human milk, infant formula, and bovine milk

Human milk inactivates pathogens individually, additively, and synergistically

The cells of human colostrum. I. In vitro studies of morphology and functions

Activated and memory T lymphocytes in human milk

Activated neutrophils and neutrophil activators in human milk -increased expression of CD11b and decreased expression of L-selectin

Human colostral cytotoxicity. II. Relative defects in colostral leukocyte cytotoxicity and inhibition of peripheral blood leukocyte cytotoxicity by colostrum

Breast milk-derived antigenspecific CD8+ T cells: an extralymphoid effector memory cell population in humans

Lymphokine production by human milk lymphocytes

Transfer of maternal leukocytes to the infant by human milk

Oxygen metabolism of human colostral macrophages: Comparison with monocytes and polymorphonuclear leukocytes

Superoxide anion generation in human milk macrophages: opsonin-dependent versus opsonin-independent stimulation compared with blood monocytes

Cellular immunity in human milk

Decreased response of human milk leukocytes to chemoattractant peptides

The effects of colostrum on neutrophil function: decreased deformability with increased cytoskeletal-associated actin

Human milk effects on neutrophil calcium metabolism: blockade of calcium influx after agonist stimulation

The motility of human milk macrophages in collagen gels

Deficient quantitative expression of CD45 isoforms on CD4 + and CD8 + T-cell subpopulations and subsets of CD45RA low CD45RO low T cells in newborn blood

Differential modulation of the immune response by breast-or formula-feeding of infants

Modulation of classical C3 convertase of complement by tear lactoferrin

Protease inhibitors and their relation to protease activity in human milk

Lysozyme binds to elastin and protects elastin from elastase-mediated degradation

Antimicrobial and immunoregulatory functions of lactoferrin and its potential therapeutic application

Prostaglandin E1, E2, and F2 alpha in human milk and plasma

Prostaglandin concentrations in human milk

Lactoferrin downregulates the LPS-induced cytokine production in monocytic cells via NFκB

Colostral antioxidants: separation and characterization of two activities in human colostrum

Vitamin A and E content of human milk at early stages of lactation

Influence of breast-feeding on the restoration of the low serum concentration of vitamin E and β-carotene in the newborn infant

Epidermal growth factor is a major growth-promoting agent in human milk

Human lactoferrin stimulates thymidine incorporation into DNA of rat crypt cells

Changes in the concentration of cortisol in milk during different stages of human lactation

Polyamines in human and cow's milk

Polyamine concentration in rat milk and food, human milk, and infant formula

Growth-active peptides are produced from alpha-lactalbumin and lysozyme

Hormones and growth factors in human milk

Development of the gastrointestinal mucosal barrier. Evidence for structural differences in microvillus membranes from newborn and adult rabbits

Developmental changes in the activities of sialyland fucosyltransferases in the rat small intestine

Development of the neonatal rat small intestinal barrier to nonspecific macromolecular absorption. II. Role of dietary corticosterone

Colostrum-induced enteric mucosal growth in beagle puppies

Endotoxin and hypoxia-induced intestinal necrosis in rats: the role of platelet activating factor

Presence of platelet-activating factor-acetylhydrolase in milk

Serum PAF acetylhydrolase increases during neonatal maturation

Early feeding, antenatal glucocorticoids, and human milk decrease intestinal permeability in preterm infants

Development of gastrointestinal mucosal barrier. II. The effect of natural versus artificial feeding on intestinal permeability to macromolecules

Intestinal permeability changes during the first month: effect of natural versus artificial feeding

A meta-analysis of infant diet and insulin-dependent diabetes mellitus: do biases play a role

Early infant feeding and risk of developing type 1 diabetes-associated autoantibodies

Longer breastfeeding is an independent protective factor against development of type 1 diabetes mellitus in childhood

Breastfeeding and the incidence of non-insulin-dependent diabetes mellitus in Pima Indians

Infant feeding and childhood cancer

Longer breast-feeding and protection against childhood leukaemia and lymphomas

Breast-feeding and risk of childhood acute leukemia

Role of infant feeding practices in development of Crohn's disease in childhood

Risk of inflammatory bowel disease attributable to smoking, oral contraception and breastfeeding in Italy: a nationwide case-control study

Effect of breast feeding on responses of systemic interferon and virus-specific lymphocyte transformation in infants with respiratory syncytial virus infection

In-vivo immune responses of breastand bottle-fed infants to tetanus toxoid antigen and to normal gut flora

Development of secretory immunity in breast fed and bottle fed infants

Breast-feeding influences thymic size in late infancy

Improved thymic function in exclusively breastfed infants is associated with higher interleukin 7 concentrations in their mothers' breast milk

Lower proportion of CD45R0+ cells and deficient interleukin-10 production by formula-fed infants, compared with human-fed, is corrected with supplementation of long-chain polyunsaturated fatty acids

Chemokinetic agents for monocytes in human milk: possible role of tumor necrosis factor-alpha

Tumor necrosis factor-α in human milk

Interleukin-2 in human milk: a potential modulator of lymphocyte development in the breastfed infant

Presence of interferon-gamma and interleukin-6 in colostrum of normal women

Interleukin-12 in human milk

Interleukin-18 in human milk

Interleukin-10 (IL-10) in human milk

Concentrations of IL-10 in preterm human milk and in milk from mothers of infants with necrotizing enterocolitis

Chemoattractant factors in breast milk from allergic and nonallergic mothers

Interleukin-1β in human colostrum

Interleukin-6 in human milk

Production of interleukin-6 and interleukin-8 by human mammary gland epithelial cells

Detection of interferon-gammainducible chemokines in human milk

TGF-beta in human milk is associated with wheeze in infancy

Transforming growth factor-beta (TGF-β) in human milk

Human milk contains granulocyte colony stimulating factor (G-CSF)

Identification of macrophage colony-stimulating factor in human milk and mammary epithelial cells

Hepatocyte growth factor in human milk and reproductive tract fluids

Origin and fate of erythropoietin in human milk

IL-2 negatively regulates IL-7 receptor alpha chain expression in activated T lymphocytes

Novel opioid peptides derived from human β-casein: human β-casomorphins

Milk-borne prolactin and neonatal development

Dietary nucleotide effects upon murine natural killer cell activity and macrophage activation

Soluble form of ICAM-1, VCAM-1, E-and L-selectin in human milk

Changes in the mannan binding lectin (MBL) concentration in human milk during lactation

Soluble CD14 enriched in colostrum and milk induces B cell growth and differentiation

Soluble forms of toll-like receptor (TLR)2 capable of modulating TLR2 signaling are present in human plasma and breast milk

Modulation of neonatal microbial recognition: TLR-mediated innate immune responses are specifically and differentially modulated by human milk

Lactoferrin acts as an alarmin to promote the recruitment and activation of APCs and antigen-specific immune responses

Oligosaccharide-specific induction of interleukin 10 production by B220+ cells from schistosome-infected mice: a mechanism for regulation of CD4+ T-cell subsets

Human milk-derived oligosaccharides and plant-derived oligosaccharides stimulate cytokine production of cord blood T-cells in vitro

Diminished lectin-, epidermal growth factor-, complement binding domain-cell adhesion molecule-1 on neonatal neutrophils underlies their impaired CD18-independent adhesion to endothelial cells in vitro

Decreased superoxide production, degranulation, tumor necrosis factor alpha secretion, and CD11b/ CD18 receptor expression by adherent monocytes from preterm infants

Decreased mRNA expression of G-CSF receptor in cord blood neutrophils of term newborns: regulation of expression by G-CSF and TNF-alpha

Blood plasmacytoid dendritic cell responses to CpG oligodeoxynucleotides are impaired in human newborns

Dendritic cell immaturity during infancy restricts the capacity to express vaccine-specific T-cell memory

Immaturity of infection control in preterm and term newborns is associated with impaired Toll-like receptor signaling

Human tracheobronchial secretions: development of mucous glycoprotein and lysozyme-secreting systems

Development of intestinal mucosal immunity in fetal life and the first postnatal months

Development of the human antibody repertoire

Decreased interleukin-10 production by neonatal monocytes and T cells: relationship to decreased production and expression of tumour necrosis factor-alpha and its receptors

Neonatal interleukin-1β, interleukin-6, and tumor necrosis factor: cord blood levels and cellular production

Role of MyD88 in diminished tumor necrosis factor alpha production by newborn mononuclear cells in response to lipopolysaccharide

Cellular and molecular mechanisms for reduced interleukin 4 and interferon-gamma production by neonatal T cells

Maternal and neonatal IL-4 and IFN-gamma production at delivery and 3 months after birth

Decreased production of interferongamma by human neonatal cells. Intrinsic and regulatory deficiencies

Differential patterns of methylation of the IFN-γ promoter at CpG and non-CpG sites underlie differences in IFN-γ gene expression between human neonatal and adult CD45RO-T Cells

Differential development of type 1 and type 2 cytokines and beta-chemokines in the ontogeny of healthy newborns

Decreased interleukin-10 in tracheal aspirates from preterm infants developing chronic lung disease

Development of interleukin-12-producing capacity throughout childhood

Defective production of IL-18 and IL-12 by cord blood mononuclear cells influences the T helper-1 interferon gamma response to group B Streptococci

Decreased G-CSF and IL-3 production and gene expression from mononuclear cells of newborn infants

Decreased stimulated GM-CSF expression and GM-CSF gene production but normal numbers of GM-CSF receptors in human term newborns as compared with adults

C-C chemokine profile of cord blood mononuclear cells: selective defect in RANTES production

Mucosal immunity: integration between mother and the breast-fed infant

Human cord blood antibody repertoire. Mixed population of V H gene segments and CDR3 distribution in the expressed Calpha and Cgamma repertoires

Prevention of Haemophilus influenzae type b bacteremic infections with the capsular polysaccharide vaccine

Effect of breast-feeding on antibody response to conjugate vaccine

Digestive-absorptive functions in fetuses, infants, and children

Soluble tumor necrosis factor-alpha (TNF-alpha) receptors in human colostrum and milk bind to TNF-alpha and neutralize TNF-alpha bioactivity

Immunoglobulins in human fetal sera at different stages of gestation

Acute respiratory failure and bronchopulmonary dysplasia

Effects of prematurity on the immunologic system in human milk

Does breast milk protect against septicaemia in the newborn?

Breast milk feeding in very low birthweight infants

Partial supplementation with expressed breast-milk for prevention of infection in low-birth-weight infants

Breast milk and neonatal necrotising enterocolitis

Prevention of necrotizing enterocolitis in low-birth -weight-infants by IgA-IgG feeding

Human milk as a potential enteral source of erythropoietin

Erythropoietin and the incidence of necrotizing enterocolitis in infants with very low birth weight

Interleukin-10-deficient mice develop chronic enterocolitis

Enterocolitis and colon cancer in interleukin-10-deficient mice are associated with aberrant cytokine production and CD4(+) TH1-like responses

Alpha 1-antitrypsin protects neonatal rats from pulmonary vascular and parenchymal effects of oxygen toxicity

Targeted disruption of the mouse transforming growth factor-β1 gene results in multifocal inflammatory disease

Transforming growth factor beta 1 null mutation in mice causes excessive inflammatory response and early death

Maternal rescue of transforming growth factor-β1 null mice

Promotion of Breastfeeding Intervention Trial (PROBIT): a randomized trial in the Republic of Belarus

Breastfeeding, soluble CD14 concentration in breast milk and risk of atopic dermatitis and asthma in early childhood: birth cohort study

Maturation of immunocompetence in breast-fed vs. formula-fed infants

The passage of maternal dietary proteins in human breast milk

Association of atopic diseases with breast-feeding: food allergens, fatty acids, and evolution

Breast milk fatty acids in mothers of children with atopic eczema

Atopic sensitization during the first year of life in relation to long chain polyunsaturated acid levels in human milk

Maternal donor-related transplants: influence of breast feeding on reactivity to the allograft

Influence of breast feeding on subsequent reactivity to a related renal allograft

Influence of breast feeding on the cytotoxic T cell allorepertoire in man

Demonstration of HLA-DR-like antigens on milk fat globule membranes

The presence of HLA-DR antigens on lactating human breast epithelium and milk fat globule membranes