Low colostral IgA associated with cow's milk allergy

The Role of IgA in the Manifestation and Prevention of Allergic Immune Responses

PURPOSE OF REVIEW

Immunoglobulin A (IgA) mediates immune exclusion of antigens in the gut. Notably, IgA plays also a role in the prevention of IgE-mediated allergies and induction of immune tolerance. The present review addresses the role of IgA in the manifestation of IgE-mediated allergies, including allergen-specific immunotherapy (AIT), the regulation of IgA production, and the mechanism of IgA in immune cell activation.

RECENT FINDINGS

The majority of studies report an association of IgA with the induction of immune tolerance in IgE-mediated allergies. However, reports on the involvement of humoral and mucosal IgA, IgA subtypes, monomeric and polymeric IgA, and the mechanism of IgA-mediated immune cell activation are confounding. Effects by IgA are likely mediated by alteration of microbiota, IgE-blocking capacity, or activation of inhibitory signaling pathways. However, the precise mechanism of IgA-regulation, the contribution of serum and/or mucosal IgA, and IgA1/2 subtypes, on the manifestation of IgE-mediated allergies, and the underlying immune modulatory mechanism are still elusive.

Cow's Milk Antigens Content in Human Milk: A Scoping Review

The functionality of breast milk in terms of immunity is well-known. Despite this, a significant proportion of breastfed infants exhibit sensitization to different potentially allergenic proteins and clinical reactivity (including anaphylaxis) early in life and before the introduction of complementary feeding for the first time. The potential induction of early oral tolerance to overcome early allergic sensitization through exposure to allergens in breast milk also remains controversial and not yet well-established. The objective of this scoping review is to provide a critical appraisal of knowledge about the content of cow’s milk antigens in human milk. The amount of dietary derived milk antigens found in human milk and the analytical methodologies used to detect and quantify these antigens, the allergic status of the mother, the stage of lactation, the time of sampling (before or after ingestion of food), and the impact of human milk allergen on the infant were the outcomes that were assessed. Allergy risk was explored in all reviewed studies and could help to better elucidate its role in the context of allergic disease development. According to the included literature, we can conclude that there are mainly fragments derived from bovine proteins in human milk, and the presence of potentially allergenic molecules is greater in the milk of mothers with an allergic tendency. A clear relationship between maternal diet and allergen content in breast milk could not be firmly concluded though. Also, infants receiving milk from human milk banks, where donor milk is pasteurized for preservation, may be subject to greater risk of allergy development, especially for β-lactoglobulin.

Food Proteins in Human Breast Milk and Probability of IgE-Mediated Allergic Reaction in Children During Breastfeeding: A Systematic Review

BACKGROUND

Previous reports suggested that food proteins present in human milk (HM) may trigger symptoms in allergic children during breastfeeding, but existing evidence has never been reviewed systematically.

OBJECTIVE

To assess the probability of food proteins in HM to trigger allergic reactions in infants with IgE-mediated food allergy.

METHODS

Electronic bibliographic databases (MEDLINE, EMBASE) were systematically searched from inception to November 3, 2021. The data regarding the levels of food proteins detected in HM were extracted and compared with data from the Voluntary Incidental Trace Allergen Labelling (VITAL 3.0) guide to assess the probability of food-allergic individuals to experience immediate type allergic reactions on ingesting HM.

RESULTS

A total of 32 studies were identified. Fourteen studies assessed excretion of cow's milk proteins into HM, 9 egg, 4 peanut, and 2 wheat; 3 measured levels of cow's milk and egg proteins simultaneously. We found that levels of all food proteins across the studies were much lower than the eliciting dose for 1% of allergic individuals (ED01) in most of the samples. The probability of an IgE-mediated allergic reaction in a food-allergic infant breastfed by a woman consuming the relevant food can be estimated as ≤1:1000 for cow's milk, egg, peanut, and wheat.

CONCLUSIONS

To our knowledge, this is the first systematic review that assesses and summarizes evidence on food proteins in HM and potential for IgE-mediated allergic reactions. Our data suggest that the probability of IgE-mediated allergic reactions to food proteins in HM is low.

Effects of Pre/Probiotic Supplementation on Breast Milk Levels of TGF-b1, TGF-b2, and IgA: A Systematic Review and Meta-Analysis of Randomized-Controlled Trial

Background: Previous studies have proposed that the maternal intake of pre/probiotics may affect the immune composition of breast milk. Nevertheless, the available findings are contradictory. This meta-analysis aimed to examine the impact of maternal supplementation with pre/probiotics on the levels of total immunoglobulin A (IgA), secretory IgA (SIgA), transforming growth factor beta 1 (TGF-β1), and TGF-2 in breast milk. Methods: PubMed and Scopus were systematically searched using a comprehensive search strategy for eligible randomized-controlled trials published up to February 2021. A random-effects model was applied to pool weighted mean difference and 95% confidence interval (CI) as effect size. Cochran's Q statistic and the I2 statistic were used to measure the between-study variance. Egger's regression test was used to assess publication bias. Results: A total of 12 different studies, with a total sample size of 1722 individuals (probiotic group: 858, placebo group: 864), were included in this meta-analysis. In the overall analysis, compared with placebo, maternal supplementation with pre/probiotics had no significant effect on concentrations of total IgA, SIgA, TGF-β1, and TGF-β2 in the breast milk. In the subgroup analysis, pre/probiotics did not affect total IgA, TGF-β1, and TGF-β2 in both colostrum/transitional and mature milk. However, a significant increase in SIgA was found in colostrum/transitional milk following pre/probiotic administration (WMD = 19.33, 95% CI: 0.83-37.83; p = 0.04), without evidence for remarkable heterogeneity (I² = 0.0, p = 0.57). Conclusions: Maternal supplementation with pre/probiotics may increase SIgA in colostrum/transitional milk, without any effect on total IgA, TGF-β1, and TGF-β2.

The role of allergen-specific IgE, IgG and IgA in allergic disease

Immunoglobulin E (IgE)‐mediated allergy is the most common hypersensitivity disease affecting more than 30% of the population. Exposure to even minute quantities of allergens can lead to the production of IgE antibodies in atopic individuals. This is termed allergic sensitization, which occurs mainly in early childhood. Allergen‐specific IgE then binds to the high (FcεRI) and low‐affinity receptors (FcεRII, also called CD23) for IgE on effector cells and antigen‐presenting cells. Subsequent and repeated allergen exposure increases allergen‐specific IgE levels and, by receptor cross‐linking, triggers immediate release of inflammatory mediators from mast cells and basophils whereas IgE‐facilitated allergen presentation perpetuates T cell–mediated allergic inflammation. Due to engagement of receptors which are highly selective for IgE, even tiny amounts of allergens can induce massive inflammation. Naturally occurring allergen‐specific IgG and IgA antibodies usually recognize different epitopes on allergens compared with IgE and do not efficiently interfere with allergen‐induced inflammation. However, IgG and IgA antibodies to these important IgE epitopes can be induced by allergen‐specific immunotherapy or by passive immunization. These will lead to competition with IgE for binding with the allergen and prevent allergic responses. Similarly, anti‐IgE treatment does the same by preventing IgE from binding to its receptor on mast cells and basophils. Here, we review the complex interplay of allergen‐specific IgE, IgG and IgA and the corresponding cell receptors in allergic diseases and its relevance for diagnosis, treatment and prevention of allergy.

Traditional Farming Lifestyle in Old Older Mennonites Modulates Human Milk Composition

Background

In addition to farming exposures in childhood, maternal farming exposures provide strong protection against allergic disease in their children; however, the effect of farming lifestyle on human milk (HM) composition is unknown.

Objective

This study aims to characterize the maternal immune effects of Old Order Mennonite (OOM) traditional farming lifestyle when compared with Rochester (ROC) families at higher risk for asthma and allergic diseases using HM as a proxy.

Methods

HM samples collected at median 2 months of lactation from 52 OOM and 29 ROC mothers were assayed for IgA₁ and IgA₂ antibodies, cytokines, endotoxin, HM oligosaccharides (HMOs), and targeted fatty acid (FA) metabolites. Development of early childhood atopic diseases in children by 3 years of age was assessed. In addition to group comparisons, systems level network analysis was performed to identify communities of multiple HM factors in ROC and OOM lifestyle.

Results

HM contains IgA₁ and IgA₂ antibodies broadly recognizing food, inhalant, and bacterial antigens. OOM HM has significantly higher levels of IgA to peanut, ovalbumin, dust mites, and Streptococcus equii as well TGF-β2, and IFN-λ3. A strong correlation occurred between maternal antibiotic use and levels of several HMOs. Path-based analysis of HMOs shows lower activity in the path involving lactoneohexaose (LNH) in the OOM as well as higher levels of lacto-N-neotetraose (LNnT) and two long-chain FAs C-18OH (stearic acid) and C-23OH (tricosanoic acid) compared with Rochester HM. OOM and Rochester milk formed five different clusters, e.g., butyrate production was associated with Prevotellaceae, Veillonellaceae, and Micrococcaceae cluster. Development of atopic disease in early childhood was more common in Rochester and associated with lower levels of total IgA, IgA₂ to dust mite, as well as of TSLP.

Conclusion

Traditional, agrarian lifestyle, and antibiotic use are strong regulators of maternally derived immune and metabolic factors, which may have downstream implications for postnatal developmental programming of infant's gut microbiome and immune system.

The Breast Milk Immunoglobulinome

Breast milk components contribute to the infant’s immune development and protection, and among other immune factors, immunoglobulins (Igs) are the most studied. The presence of IgA in milk has been known for a long time; however, less information is available about the presence of other Igs such as IgM, IgG, and their subtypes (IgG1, IgG2, IgG3, and IgG4) or even IgE or IgD. The total Ig concentration and profile will change during the course of lactation; however, there is a great variability among studies due to several variables that limit establishing a clear pattern. In this context, the aim of this review was firstly to shed light on the Ig concentration in breast milk based on scientific evidence and secondly to study the main factors contributing to such variability. A search strategy provided only 75 studies with the prespecified eligibility criteria. The concentrations and proportions found have been established based on the intrinsic factors of the study—such as the sampling time and quantification technique—as well as participant-dependent factors, such as lifestyle and environment. All these factors contribute to the variability of the immunoglobulinome described in the literature and should be carefully addressed for further well-designed studies and data interpretation.

The multifaceted roles of breast milk antibodies

Neonates are born with an immature immune system and rely on the transfer of immunity from their mothers. Maternal antibodies are transferred via the placenta and breast milk. Although the role of placentally transferred immunoglobulin G (IgG) is established, less is known about the selection of antibodies transferred via breast milk and the mechanisms by which they provide protection against neonatal disease. Evidence suggests that breast milk antibodies play multifaceted roles, preventing infection and supporting the selection of commensals and tolerizing immunity during infancy. Here, we discuss emerging data related to the importance of breast milk antibodies in neonatal immunity and development.

Statistical Approaches in the Studies Assessing Associations between Human Milk Immune Composition and Allergic Diseases: A Scoping Review

A growing number of studies are focusing on the associations between human milk (HM) immunological composition and allergic diseases. This scoping review aims to identify statistical methods applied in the field and highlight pitfalls and unmet needs. A comprehensive literature search in MEDLINE and Embase retrieved 13,607 unique records. Following title/abstract screening, 29 studies met the selection criteria and were included in this review. We found that definitions of colostrum and mature milk varied across the studies. A total of 17 out of 29 (59%) studies collected samples longitudinally, but only 12% of these used serial (longitudinal) analyses. Multivariable analysis was used in 45% of the studies, but statistical approaches to modelling varied largely across the studies. Types of variables included as potential confounding factors differed considerably between models. Discrimination analysis was absent from all studies and only a single study reported classification measures. Outcomes of this scoping review highlight lack of standardization, both in data collection and handling, which remains one of the main challenges in the field. Improved standardization could be obtained by a consensus group of researchers and clinicians that could recommend appropriate methods to be applied in future prospective studies, as well as already existing datasets.

Immunomodulatory effects of breast milk on food allergy

OBJECTIVE

To summarize the literature on immunomodulatory effects of breast milk on sensitization and possible mechanisms of action.

DATA SOURCES

Animal and human studies in PubMed that assessed breastfeeding or breast milk composition in food allergy.

STUDY SELECTIONS

All recent studies and some older key publications focusing on this topic.

RESULTS

Human milk composition is highly variable among mothers, which can affect the developing infant immune system. Human milk also affects the infant gut microbiome, which is associated with food allergy. High levels of human milk immune factors (IgA, cytokines, oligosaccharides) are associated with reduced risk of food allergy in the infant; it remains uncertain whether these are directly protective or biomarkers of transferred protection. Animal studies highlight potential mechanisms of protection provided by antigens, transforming growth factor β, and immunocomplexes, yet their relevance is poorly understood in humans. The role of food antigens in human milk in initial sensitization or tolerance induction is unclear.

CONCLUSION

The protection against allergy development provided by human milk may be attributable to the effect on the infant gut microbiome or direct effects on immune system. Studies evaluating the effect of breastfeeding and human milk composition on food allergy are needed.

Immunologically Active Components in Human Milk and Development of Atopic Disease, With Emphasis on Food Allergy, in the Pediatric Population

Breast-feeding is currently recommended to prevent the development of allergic diseases; however, data are conflicting and mechanisms are unclear. The immunomodulatory composition of human milk is poorly characterized and varies between mothers. We and others have shown that high levels of human milk IgA and certain cytokines and human milk oligosaccharides are associated with protection against food allergy in the infant, but it is unclear whether they are responsible for or simply biomarkers of the vertical transfer of protection. Because human milk has pre- and probiotic properties, the anti-allergy protection afforded by human milk may be due to its control on the developing gut microbiome. In mice, murine milk IgA supports gut homeostasis and shapes the microbiota, which in turn diversifies the intestinal IgA repertoire that reciprocally promotes the diversity of gut microbiome; these mechanisms are poorly understood in humans. In addition, several human milk bioactives are immunostimulatory, which may in part provide protection against allergic diseases. The regulation of immunologically active components in human milk is incompletely understood, although accumulating evidence suggests that IgA and cytokines in human milk reflect maternal exposures. This review summarizes the current literature on human milk components that have been associated with protection against food allergy and related allergic disorders in early childhood and discusses the work relating to regulation of these levels in human milk and possible mechanisms of action.

Breast milk IgA to foods has different epitope specificity than serum IgA-Evidence for entero-mammary link for food-specific IgA?

BACKGROUND

We have previously shown that maternal cow's milk (CM) elimination results in downregulation of CM-specific IgA antibody levels in BM, but not in serum, suggesting that an entero-mammary link may exist for food-specific antibody-secreting cells.

OBJECTIVE

We sought to investigate whether food-specific IgA epitope profiles differ intra-individually between mother's serum and BM. We also examined how infants' food epitope-specific IgA develops in early infancy and the relationship of IgA epitope recognition with development of cow's milk allergy (CMA).

METHODS

We measured specific IgA to a series of overlapping peptides in major CM allergens (α_s1 -, α_s2 -, β- and κ-caseins and β-lactoglobulin) in paired maternal and infant serum as well as BM samples in 31 mother-infant dyads within the first 15 post-partum months utilizing peptide microarray.

RESULTS

There was significant discordance in epitope specificity between BM and maternal sera ranging from only 13% of sample pairs sharing at least one epitope in α_s1 -casein to 73% in κ-casein. Epitope-specific IgA was detectable in infants' sera starting at less than 3 months of age. Sera of mothers with a CMA infant had increased binding of epitope-specific IgA to CM proteins compared to those with a non-CMA infant.

CONCLUSION & CLINICAL RELEVANCE

These findings support the concept that mother's milk has a distinct antifood antibody repertoire when compared to the antibody repertoire of the peripheral blood. Increased binding of serum epitope-specific IgA to CM in mothers of infants with CMA may reflect inherited systemic immunogenicity of CM proteins in these families, although specific IgA in breast milk was not proportionally up-regulated.

Role of Maternal Allergy on Immune Markers in Colostrum and Secretory Immunoglobulin A in Stools of Breastfed Infants

BACKGROUND

Although protection against infectious diseases has been observed among breastfed infants as compared to formula-fed infants, possible benefits of breastfeeding by allergic mothers for allergy prevention remain controversial.

OBJECTIVES

The aims of this study were to determine whether maternal allergy would influence immune markers (secretory immunoglobulin A [sIgA], interleukin-8 [IL-8], soluble CD14 [sCD14]) in colostrum and the associations between maternal allergy and fecal sIgA levels in breastfed infants.

METHODS

Study subjects were enrolled from the Prediction of Allergies in Taiwanese Children (PATCH) birth cohort study. Colostrum samples were obtained from 98 lactating mothers. Stool samples were collected from 108 infants within 5 days after birth and at 2 and 4 months of age. We compared concentrations of sIgA, IL-8, and sCD14 in colostrum between mothers with and without a history of allergic disease and allergic sensitization. We also compared fecal sIgA levels between breastfed and formula-fed infants and between infants with allergic and nonallergic mothers.

RESULTS

The sIgA concentrations were significantly higher in colostrum from allergic mothers than from nonallergic mothers (P = .01) and from allergic mothers who were immunoglobulin E (IgE) sensitized compared to nonallergic mothers who were not IgE sensitized (P = .023). Breastfed infants had significantly higher fecal sIgA levels as compared to formula-fed infants, regardless of whether their lactating mothers had an allergy (P < .05).

CONCLUSION

We found that breastfeeding is associated with increased infants' fecal sIgA levels and may have potential protective effects to the infants during the first 4 months of life, regardless of whether their lactating mothers have allergies.

Role of maternal elimination diets and human milk IgA in the development of cow's milk allergy in the infants

BACKGROUND

The role of maternal avoidance diets in the prevention of food allergies is currently under debate. Little is known regarding the effects of such diets on human milk (HM) composition or induction of infant humoral responses.

OBJECTIVE

To assess the association of maternal cow's milk (CM) avoidance during breastfeeding with specific IgA levels in HM and development of cow's milk allergy (CMA) in infants.

METHODS

We utilized HM and infant serum samples from a prospective birth cohort of 145 dyads. Maternal serum and HM samples were assessed for casein and beta-lactoglobulin (BLG)-specific IgA and IgG by ELISA; 21 mothers prophylactically initiated a strict maternal CM avoidance diet due to a sibling's history of food allergy and 16 due to atopic eczema or regurgitation/vomiting seen in their infants within the first 3 months of life. Infants' sera were assessed for casein and BLG-specific IgG, IgA and IgE; CMA was confirmed by an oral food challenge. The impact of HM on BLG uptake was assessed in transcytosis assays utilizing Caco-2 intestinal epithelial cell line.

RESULTS

Mothers avoiding CM had lower casein- and BLG-specific IgA in HM than mothers with no CM restriction (P = 0.019 and P = 0.047). Their infants had lower serum casein- and BLG-specific IgG(1) (P = 0.025 and P < 0.001) and BLG-specific IgG(4) levels (P = 0.037), and their casein- and BLG-specific IgA levels were less often detectable than those with no CM elimination diet (P = 0.003 and P = 0.007). Lower CM-specific IgG4 and IgA levels in turn were associated with infant CMA. Transcytosis of BLG was impaired by HM with high, but not low levels of specific IgA.

CONCLUSIONS

Maternal CM avoidance was associated with lower levels of mucosal-specific IgA levels and the development of CMA in infants.

CLINICAL RELEVANCE

HM IgA may play a role in preventing excessive, uncontrolled food antigen uptake in the gut lumen and thereby in the prevention of CMA.

Relationship between breast milk sCD14, TGF-β1 and total IgA in the first month and development of eczema during infancy

INTRODUCTION

The overall beneficial effects of breastfeeding for infants have been well documented, but its role in allergy prevention is controversial.

OBJECTIVE

We investigated the relationship between breast milk immunomodulatory factors and subsequent development of eczema and atopic sensitization in the first year of life.

METHODS

Day 7 and 28 breast milk samples were collected from mothers carrying infants at high risk of allergic disease. Aqueous-phase breast milk samples were assayed for TGF-β1, sCD14 and total IgA. Infants were assessed for the presence of eczema and atopic sensitization at 12 months of age. The levels of breast milk TGF-β1, sCD14 and total IgA were compared in infants who subsequently developed eczema and sensitization in the first year and those who did not.

RESULTS

The levels of breast milk sCD14, total IgA, and TGF-β1 at either day 7 or 28 were not associated with subsequent development of eczema or atopic sensitization during the first year of life.

CONCLUSION

Levels of breast milk immune parameters were not associated with eczema outcomes or sensitization in infants at 12 months. This suggests that apparent immunological effects on breast milk immunomodulatory factors may not necessarily lead to clinical benefits, and these immune markers may not be critical determinants of allergic disease in infancy.

Development of natural tolerance and induced desensitization in cow's milk allergy

Cow's milk allergy (CMA) affects 2-3% of infants. It resolves in the great majority spontaneously during childhood. CMA encompasses a spectrum of clinical and immunologic characteristics. Non-IgE-mediated allergy typically resolves earlier than IgE-mediated allergy. The most documented prognostic characteristic is that intense-specific IgE response predicts persistence of CMA. Low serum levels of cow's milk (CM)-specific IgG4 are also associated with persistent CMA. Natural development of tolerance involves an immunologic shift where Th2 responses diminish, and Th1 as well as T regulatory cell responses strengthen. Accordingly, specific IgE levels decrease and specific IgG4, possibly also IgA, levels increase in serum. Specific oral immunotherapy (OIT) with CM induces desensitization in most cases where spontaneous recovery has not yet occurred. Data on long-term tolerance induction are still scarce. According to current research data, the immunologic changes induced by OIT resemble those seen during natural development of tolerance.

Colostrum of healthy mothers contains broad spectrum of secretory IgA autoantibodies

PURPOSE

Human colostrum and milk provide a newborn with immunomodulatory components, ensuring protection and proper development of the immune system. Secretory IgA antibodies in colostrum represent the first line of defence against harmful substances, but their potential spectra of reactivity with autoantigens remains unclear. Here, we characterised the repertoire of natural sectretory IgA autoantibodies in colostrum of healthy mothers.

METHODS

The human colostrum samples from 39 healthy mothers were analyzed for autoantibodies by indirect immunofluorescence, dot blots, immunoblots and ELISA.

RESULTS

We found that there is high diversity in reactivities of colostral IgA antibodies to autoantigens among individual samples. Using tissue sections and biochips commonly used for autoimmunity testing, we found that most samples reacted with monkey ovary (79.3%), monkey pancreatic tissue (78.6%), human HEp-2 cells (69%) and monkey adrenal gland (69.0%), fewer samples reacted with monkey liver tissue (47.2%), rat stomach (42.9%), monkey testicular tissue (41.4%), monkey salivary gland (39.3%), rat kidney (32.1%) and monkey cerebellar tissue (17.9%). At the protein level, we detected reactivity of IgA with 21 out of 25 (auto) antigens. The majority of the samples reacted with the pyruvate dehydrogenase complex, E3 ubiquitin ligase, cytosolic liver antigen, promyelocytic leukemia protein and nuclear pore glycoprotein-210. Using ELISA, we found reactivity of colostral IgA antibodies against examined extractable nuclear antigens, double stranded DNA, phospholipids and neutrophil cytoplasm.

CONCLUSIONS

The broad spectrum of polyreactive natural autoantibodies present in human colostrum may contribute to proper development of mucosal immune system of the breastfed infant.

Mother to child transfer of IgG and IgA antibodies against Dermatophagoides pteronyssinus

There is strong evidence from animal models that placental and/or breast milk-mediated transfer of maternal allergen-specific IgG prevents allergic immune responses in the progeny. Both human and animal data also point to IgA as having an important regulatory role. In contrast, little is known about maternal transfer of IgG and IgA specific for respiratory allergens in humans. Dermatophagoides pteronyssinus (Der p) is an indoor allergen that is a major cause of asthma worldwide. We analysed maternal to child Der p-specific IgG and IgA transfer in a cohort of 77 paired maternal and child samples. We found Der p-specific IgG and its IgG1, IgG2 and IgG4 subclasses in all cord blood samples. Except for IgG1, cord levels were higher in newborns from atopic mothers (n = 29) compared to non-atopic mothers (n = 48). Der p-specific IgA was found in all colostrum samples and levels were independent of maternal atopic status. Notably, anti-Der p IgG was also found in colostrum and levels were higher in atopic mothers. We believe that our work is a critical first step in the identification of early factors that may impact asthma development and should guide the development of clinical studies that assess whether Der p-specific IgG and IgA protect children from allergy as demonstrated in animal models.

Oral tolerance in neonates: from basics to potential prevention of allergic disease

Oral tolerance refers to the observation that prior feeding of an antigen induces local and systemic immune tolerance to that antigen. Physiologically, this process is probably of central importance for preventing inflammatory responses to the numerous dietary and microbial antigens present in the gut. Defective oral tolerance can lead to gut inflammatory disease, food allergies, and celiac disease. In the last two cases, the diseases develop early in life, stressing the necessity of understanding how oral tolerance is set up in neonates. This article reviews the parameters that have been outlined in adult animal models as necessary for tolerance induction and assesses whether these factors operate in neonates. In addition, we highlight the factors that are specific for this period of life and discuss how they could have an impact on oral tolerance. We pay particular attention to maternal influence on early oral tolerance induction through breast-feeding and outline the major parameters that could be modified to optimize tolerance induction in early life and possibly prevent allergic diseases.

Food allergy: separating the science from the mythology

Numerous genes are involved in innate and adaptive immunity and these have been modified over millions of years. During this evolution, the mucosal immune system has developed two anti-inflammatory strategies: immune exclusion by the use of secretory antibodies to control epithelial colonization of microorganisms and to inhibit the penetration of potentially harmful agents; and immunosuppression to counteract local and peripheral hypersensitivity against innocuous antigens, such as food proteins. The latter strategy is called oral tolerance when induced via the gut. Homeostatic mechanisms also dampen immune responses to commensal bacteria. The mucosal epithelial barrier and immunoregulatory network are poorly developed in newborns. The perinatal period is, therefore, critical with regard to the induction of food allergy. The development of immune homeostasis depends on windows of opportunity during which innate and adaptive immunity are coordinated by antigen-presenting cells. The function of these cells is not only orchestrated by microbial products but also by dietary constituents, including vitamin A and lipids, such as polyunsaturated omega-3 fatty acids. These factors may in various ways exert beneficial effects on the immunophenotype of the infant. The same is true for breast milk, which provides immune-inducing factors and secretory immunoglobulin A, which reinforces the gut epithelial barrier. It is not easy to dissect the immunoregulatory network and identify variables that lead to food allergy. This Review discusses efforts to this end and outlines the scientific basis for future food allergy prevention.

High intestinal IgA associates with reduced risk of IgE-associated allergic diseases

Development of oral tolerance and its stimulation by probiotics are still incomprehensible. Microbial stimulation of the gut may induce a subtle inflammation and induce secretion of mucosal IgA, which participates in antigen elimination. In a cohort of allergy-prone infants receiving probiotics and prebiotics or placebo we studied intestinal IgA and inflammation in the development of eczema, food allergy, asthma, and rhinitis (allergic diseases). We performed a nested unmatched case-control study of 237 infants participating in a randomized double-blind placebo-controlled allergy-prevention trial using a combination of four probiotic strains pre-natally and during 6 months form birth. We measured faecal IgA, alpha1-antitrypsin (alpha1-AT), tumour necrosis factor-alpha (TNF-alpha), and calprotectin at the age of 3 and 6 months. By age 2 yr, 124 infants had developed allergic disease or IgE-sensitization (cases) and 113 had not (controls). In infants with high faecal IgA concentration at the age of 6 months, the risk of having any allergic disease before the age of 2 yr tended to reduce [odds ratio (OR: 0.52)] and the risk for any IgE-associated (atopic) disease reduced significantly (OR: 0.49). High faecal calprotectin at the age of 6 months associated also with lower risk for IgE-associated diseases up to age 2 yr (OR: 0.49). All faecal inflammation markers (alpha1-AT, TNF-alpha, and calprotectin) correlated positively with faecal IgA (p < 0.001). Probiotics tended to augment faecal IgA (p = 0.085) and significantly increased faecal alpha1-AT (p = 0.001). High intestinal IgA in early life associates with minimal intestinal inflammation and indicates reduced risk for IgE-associated allergic diseases.

Multiple T cell epitope peptides suppress allergic responses in an egg allergy mouse model by the elicitation of forkhead box transcription factor 3- and transforming growth factor-beta-associated mechanisms

BACKGROUND

Peptide-based immunotherapy (PIT) represents an attractive approach for targeted interventions in immunological disorders, but has not been widely explored in the context of food allergy.

OBJECTIVE

In this study, we built on the information obtained from the recent identification of three immunodominant T cell epitopes of hen ovalbumin (OVA), a major egg allergen, to assess the therapeutic potential of PIT for food allergy, using the BALB/c mouse model.

METHODS

Groups of mice were sensitized to OVA by repeated oral gavages, and subsequently administered with single or multiple synthetic peptides containing OVA T cell epitopes. Following the peptide administration period, all mice were orally challenged with high doses of OVA to elicit active anaphylaxis. Serum, spleen, and intestinal tissues were collected for the determination of immunoglobulin levels, cytokine secretions, and intestinal gene expression.

RESULTS

Significantly lower anaphylactic scores were exhibited by mice that received multiple epitope-containing peptides, accompanied by lower serum histamine and OVA-specific IgE levels, compared with placebo-treated mice. Mechanistically, the quantification of cytokine secretions in splenocyte cultures revealed a T helper type 1-biased response (IFN-gamma) in all peptide-treated mice to the detriment of a T helper type 2-response (IL-4). Interestingly, a similar cytokine expression profile was determined in intestinal tissues, accompanied by a pronounced mRNA expression of regulatory molecules TGF-beta and forkhead box transcription factor 3 (FOXP3). These data suggest the activation of local repressive mechanisms mediated by subsets of regulatory T cells.

CONCLUSION

We demonstrated the therapeutic potential of PIT in a mouse model of food allergy model and provided evidence that mechanistic pathways entailing regulatory molecules TGF-beta and FOXP3, stand as promising trails for the further understanding of peptide-based strategies for food allergy.

Low breast milk TGF-beta2 is induced by Lactobacillus reuteri supplementation and associates with reduced risk of sensitization during infancy

The immunological composition of breast milk differs between mothers. The reasons for these differences and the consequences for the breast-fed infants are poorly understood. The aim of this study was to evaluate the effect of probiotic Lactobacillus reuteri supplementation on the immunological composition of breast milk in relation to sensitization and eczema in the babies. Total IgA, secretory IgA (SIgA), TGF-beta1, TGF-beta2, IL-10, TNF, soluble CD14 (sCD14), and Na/K ratios were analyzed in colostrum and mature milk obtained from women treated with L. reuteri (n = 54) or placebo (n = 55) from gestational week 36 until delivery. Bacteriological analyses of L. reuteri were performed in faecal samples of the mothers. The infants were followed prospectively for 2 yr regarding development of eczema and sensitization as defined by a positive skin prick test and/or circulating allergen-specific IgE antibodies at 6, 12, and 24 months of age. Supplementation of L. reuteri during pregnancy was associated with low levels of TGF-beta2 and slightly increased levels of IL-10 in colostrum. For TGF-beta2, this association was most pronounced in mothers with detectable L. reuteri in faeces. Infants receiving breast milk with low levels of TGF-beta2 were less likely to become sensitized during their first 2 yr of life. A similar trend was observed for development of IgE-associated eczema. The levels of total IgA, SIgA, TGF-beta1, TNF, sCD14, and Na/K ratios in breast milk were not affected by the intake of L. reuteri. None of these parameters correlated with sensitization or development of eczema in the infant, except for high Na/K ratios that associated with increased risk of sensitization. Supplementation with L. reuteri during late pregnancy reduces breast milk levels of TGF-beta2, and low levels of this cytokine are associated with less sensitization and possibly less IgE-associated eczema in breast-fed infants.

IgA antibodies, TGF-beta1 and -beta2, and soluble CD14 in the colostrum and development of atopy by age 4

Specific defense factors in breast milk together with length of breast-feeding and genetic predisposition may modulate the development of allergy. We studied whether IgA, soluble CD14 (sCD14), or transforming growth factor (TGF)-beta in colostrum could affect the development of atopy in children up to age 4. From a cohort of 4676, we selected four groups of children with either long or short exclusive breast-feeding (>3.5 or <0.5 mo); these groups further differed in the presence or absence of atopic heredity. In colostrum from mothers, we measured total IgA, IgA antibodies to cow's milk (CM) and casein, sCD14, and TGF-beta1 and -beta2. The children were divided into three groups: those with no atopic symptoms or IgE, those with allergic symptoms, and those with both outcomes. Mothers of infants later showing atopic symptoms or, in addition, having IgE sensitization (verified atopy) had a lower concentration of IgA casein antibodies in their colostrum than did mothers of infants with no indication of atopy at age 4. Low concentration of IgA casein antibodies was a significant risk for verified atopy. sCD14 levels were lower in colostrum of mothers with infants developing atopic symptoms and IgE sensitization than of those of infants with no atopy. Specific IgA antibodies to CM antigens and sCD14 in colostrum significantly associated with the appearance of both symptomatic and verified atopy by age 4.

Cytokine, chemokine and secretory IgA levels in human milk in relation to atopic disease and IgA production in infants

The relationship between breast-feeding, IgA production and development of atopic disease in children is a matter of controversy. Some of this controversy might be due to individual differences in the composition of breast milk. The aim of this study was to relate the levels of cytokines, chemokines and secretory (S)-IgA antibodies in breast milk to the development of atopic manifestation and salivary IgA production in infants. Cytokine, chemokine and SIgA levels, as measured with enzyme-linked immunosorbent assay (ELISA), in colostrum and mature milk were analyzed in relation to the development of positive skin-prick tests (SPT), allergic symptoms and salivary IgA antibody production during the first 2 years of life in 53 infants. There was no association between levels of IL-4, -5, -6, -8, -10, -13, -16, IFN-gamma, TGF-beta1, -beta2, RANTES, eotaxin or SIgA levels in the breast milk with either SPT-positivity, development of allergic symptoms or salivary IgA levels during the first 2 years of life in the infants. Thus, differences in the composition of cytokines, chemokines and SIgA in breast milk did not, to any major degree, affect the development of a positive SPT, atopic symptoms, nor salivary IgA antibody production during the first 2 years of life.

Current understanding of gastrointestinal immunoregulation and its relation to food allergy

Tolerance to food antigens induced via the gut ("oral tolerance") appears to be a rather robust adaptive immune mechanism. However, the neonatal period is particularly critical in terms of mucosal defense, with regard to infections and priming for allergic disease. This is so because the intestinal barrier function provided by secretory antibodies, as well as the immunoregulatory network, is poorly developed for a variable period after birth. Notably, the postnatal development of mucosal immune homeostasis depends on the establishment of a normal commensal microbial flora and also on adequate timing and dose of dietary antigens when first introduced. In this context, breastfeeding appears to exert both shielding and positive regulatory effects. Altogether, the intestinal immune system normally seems rather fit for tolerance induction against innocuous antigens because most children with food allergy "outgrow" their problems, whereas airway allergy tends to persist.

Breast-feeding and the development of cows' milk protein allergy

Early feeding with cows' milk (CM) may cause cows' milk allergy (CMA). Breast milk contains many immune factors which compensate for the undeveloped defence mechanisms of the gut of the newborn infant. We studied the effect of supplementary CM feeding at the maternity hospital on the subsequent incidence of CMA, the effects of formula and breast feeding on the subsequent immunologic types of CMA, and the importance of immune factors present in colostrum in the immune responses of infants with CMA. In a cohort of 6209 infants, 824 were exclusively breast-fed and 87% required supplementary milk while in the maternity hospital: 1789 received CM formula, 1859 pasteurized human milk, and 1737 whey hydrolysate formula. The cumulative incidence of CMA, verified by a CM elimination-challenge test, was 2.4% in the CM, 1.7% in the pasteurized human milk and 1.5% in the whey hydrolysate group. Among these infants, exposure to CM at hospital and a positive atopic heredity increased the risk of CMA. Of the exclusively breast-fed infants, 2.1% had CMA. Risk factors for the development of IgE-mediated CMA were: exposure to CM at hospital, breast-feeding during the first 8 weeks at home either exclusively or combined with infrequent exposure to small amounts of CM and long breast-feeding. The content of transforming growth factor-beta1 (TGF-beta1) in colostrum from mothers of infants with IgE-mediated CMA was lower than from mothers of infants with non-IgE-mediated CMA. In infants with CMA, TGF-beta1 in colostrum negatively correlated with the result of skin prick test and the stimulation of peripheral blood mononuclear cells to CM, but positively with infants' IgA and IgG antibodies to CM proteins. Feeding of CM formula at maternity hospital increases the risk of CMA, but exclusive breast-feeding does not eliminate the risk. Prolonged breast-feeding exclusively or combined with infrequent exposure to small amounts of CM during the first 8 weeks induces the development of IgE-mediated CMA. Colostral TGF-beta1 may inhibit IgE- and cell mediated reactions and promote IgG-IgA antibody production to CM in infants prone to developing CMA.

Does low IgA in human milk predispose the infant to development of cow's milk allergy?

We sought a relationship between total and cow's milk-specific IgA levels in colostrum and human milk and subsequent development of cow's milk allergy (CMA) in the breast-fed infant. The study included 87 nursing mothers and their infants (age, 2 d to 7 mo), followed prospectively up to 1 y. At 1 y, 48 mothers (69% with an atopic constitution) had an infant with CMA, verified by clinical cow's milk challenge, eight (38% with an atopic constitution) had a baby who had had protracted infantile colic but no CMA (disease control group), and 31 (23% with an atopic constitution) had a healthy infant. Total breast-milk IgA was measured by radial immunodiffusion, and IgA antibodies to cow's milk were measured by ELISA during the breast-feeding period. The levels of total and cow's milk-specific IgA antibodies in colostrum and human milk were significantly lower in the mothers whose baby later developed CMA [estimated third day value, 0.38 g/L (95% confidence interval, 0. 24-0.82)] than in the ones whose infant remained healthy or had had infantile colic but not CMA [0.82 g/L (95% confidence interval, 0. 99-1.51); p < 0.05]. The infants developed CMA significantly more often if the concentration of total IgA antibodies in milk was <0.25 g/L, when measured between 6 d and 4 wk postpartum [sensitivity, 0. 55; specificity, 0.92; odds ratio, 14.7 (95% confidence interval, 3. 1-70.2); p < 0.001]. The levels of cow's milk-specific IgA positively correlated with the levels of total IgA but not with the development of CMA in the infant. The levels of total or cow's milk-specific IgA did not correlate with maternal atopy. IgA antibodies in colostrum and human milk may prevent antigen entry at the intestinal surface of the breast-fed infant. A low IgA content in human milk may lead to defective exclusion of food antigens and thus predispose an offspring to develop food allergies.

Gliadin-specific IgA antibodies in breast milk

Breast-feeding helps to protect against coeliac disease because of the presence of antigliadin-IgA antibodies (AGA-IgA) in breast milk. The aim of this study was to assess the concentrations of AGA-IgA in breast milk during lactation, and whether these concentrations vary with the socioeconomic status of the women. Samples of serum for determination of IgA albumin and AGA-IgA, and samples of breast-milk for AGA-IgA were collected from 105 healthy mothers (aged 17 - 36 years). Women were divided into two groups: group 1 were of low and group 2 were of high socioeconomic status. No differences were observed between the study parameters in the two groups. Serum AGA-IgA in both groups was, however, significantly lower than that in colostrum. AGA-IgA concentrations in both groups gradually decreased during 45 days of lactation; the difference between colostrum and the samples taken at days 10 and 30 - 45 of lactation was significant. The encouragement of sufficient and long-term (e.g. 4 - 6 months) breast-feeding seems likely to be beneficial in preventing coeliac disease.

Detection of IgA antibodies to cat, beta-lactoglobulin, and ovalbumin allergens in human milk

BACKGROUND

The relationship between the development of allergy during infancy and breast-feeding remains controversial. This controversy may be due to individual variations in the composition of human milk. Antibodies to food antigens to which the mother is commonly exposed are present in the milk, but their relationship to allergy is still unknown. IgA antibodies to inhalant allergens have not been previously detected.

OBJECTIVE

Our purpose was to analyze secretory IgA antibody levels to cat, beta-lactoglobulin, and ovalbumin allergens in colostrum and mature milk in relation to maternal allergy.

METHODS

Colostrum and samples of mature milk were obtained after 1 and 3 months of lactation from 53 nursing mothers (17 allergic and 36 nonallergic mothers) and were analyzed for total secretory IgA levels by ELISA and secretory IgA antibodies to cat, beta-lactoglobulin, and ovalbumin by an enzyme-amplified ELISA. The specificity of the assays was confirmed by inhibition experiments.

RESULTS

Secretory IgA to cat, beta-lactoglobulin, and ovalbumin allergens were detected in colostrum as well as mature milk. The levels of secretory IgA to ovalbumin were lower in colostrum from allergic mothers with P =.016, whereas the levels to beta-lactoglobulin and cat were similar in the 2 groups. IgA antibodies to ovalbumin were detected in 94% of the colostrum samples from allergic and in all samples from nonallergic mothers, in 82% and 96%, respectively at 1 month, and 53% and 65% at 3 months. Fewer samples had detectable secretory IgA antibodies to beta-lactoglobulin than to ovalbumin and cat, and only 33% and 10% of the samples from the allergic and nonallergic mothers, respectively, remained positive at 3 months. All the allergic mothers had detectable IgA to cat in colostrum, whereas 83% and 73% of the samples were positive at 1 and 3 months. The corresponding numbers were 93%, 81%, and 81% in the nonallergic mothers (not significant).

CONCLUSION

Even a low level of exposure of the mucosa (eg, by inhalant allergens) can induce antibody secretion into the milk, both in allergic and nonallergic mothers.

Human milk polyunsaturated long-chain fatty acids and secretory immunoglobulin A antibodies and early childhood allergy

The possible protective effect of breast milk against atopic manifestations in infancy, i.e. atopic eczema and food allergy, has been controversial for the last decades. Besides the methodological problems, differences in the composition of human milk could explain these controversies. The aim of this study was to investigate the composition of polyunsaturated fatty acids (PUFA) and secretory immunoglobulin A (S-IgA) levels to food proteins (ovalbumin and beta-lactoglobulin) and an inhalant allergen (cat) in milk from mothers of allergic and non-allergic children. Blood samples were obtained at birth and at 3 months from 120 children. Skin prick tests were performed at 6, 12 and 18 months, and the development of atopic diseases was assessed in the children. Breast milk samples were collected from their mothers at birth and monthly during the lactation period. Milk PUFA composition was measured by gas chromatography, and enzyme-linked immunosorbent assay (ELISA) was used to measure total S-IgA, anti-cat S-IgA, anti-ovalbumin S-IgA, and anti-beta-lactoglobulin S-IgA. Allergic disease developed in 44/120 children (22/63 children of allergic mothers and 22/57 children of non-allergic mothers). Lower levels of eicosapentaenoic acid, C20:5 n-3 (EPA), docosapentaenoic acid C22:5 n-3 (DPA), and docosatetraenoic acid C22:4 n-6 (DHA) (p < 0.05 for all) were found in mature milk from mothers of allergic as compared to milk from mothers of non-allergic children. The total n-6:total n-3 and the arachidonic acid, C20:4 n-6 (AA):EPA ratios were significantly lower in transitional and mature milk from mothers of allergic children, as compared to milk from mothers of non-allergic children. The PUFA levels in serum of allergic and non-allergic children were largely similar, except for higher levels of C22:4 n-6 and C22:5 n-6 (p < 0.05 for both) and a higher AA:EPA ratio in serum phospholipids in the former group (p < 0.05). Changes in the levels of milk PUFA were reflected in changes in PUFA serum phospholipids, particularly for the n-6 PUFA. The AA: EPA ratio in maternal milk was related, however, to the AA:EPA only in serum from non-allergic children, while this was not the case in allergic children. The levels of total S-IgA, anti-cat S-IgA, anti-ovalbumin S-IgA, and anti-beta-lactoglobulin S-IgA in milk from mothers of allergic, as compared to non-allergic, children were similar through the first 3 months of lactation. Low levels of n-3 PUFA in human milk, and particularly a high AA:EPA ratio in maternal milk and serum phospholipids in the infants, were related to the development of symptoms of allergic disease at 18 months of age. The milk PUFA composition influenced the composition of PUFA in serum phospholipids of the children. We also showed that the lower levels of colostral anti-ovalbumin S-IgA and lower total S-IgA in mature milk from atopic mothers did not influence the development of allergic disease in the children up to 18 months of age. The findings indicate that low alpha-linolenic acid, C18:3 n-3 (LNA) and n-3 long-chain polyunsaturated fatty acids (LCP) 20-22 carbon chains, but not the levels of S-IgA antibodies to allergens, are related to the development of atopy in children.

Detection and characterization of antibodies specific to food antigens (gliadin, ovalbumin and beta-lactoglobulin) in human serum, saliva, colostrum and milk

Antibodies against food antigens are usually produced in healthy people. This humoral response can be detected both in serum and secretions. The characterization of this response can be useful for a better understanding of food-related immunological alterations. In this study, IgA and IgG antibodies specific to ovalbumin, beta-lactoglobulin or gliadin were measured in serum, saliva, colostrum and milk from 40 healthy breast-feeding women. Specific IgA and IgG to the three antigens were measured by indirect ELISA. Specific IgG levels were highest in serum and very low in the other biological fluids. No correlation between the IgG specific to the different antigens was found. Specific IgA reactivity was found in all the samples analysed. Levels observed were higher in colostrum and milk than in serum and saliva. In spite of being three different unrelated food antigens, a correlation between the levels of specific IgA was found in saliva, colostrum and milk samples of all subjects studied. The specificity of IgA anti-gliadin antibodies from serum, saliva and colostrum was analysed by immunoblotting of SDS-PAGE-separated wheat proteins. Each sample presented a unique pattern of recognition. No common pattern of recognition was found either among the same biological fluids of the different subjects tested, or among the different samples--either serum, colostrum or saliva--of the same individual. Different degrees of specificity to wheat proteins among IgA from colostrum, saliva or serum were observed, suggesting that the local IgA-producing populations are functionally different in the different tissues of the organism.

Mechanisms of gastrointestinal reactions to food

Much of the genetic information that modulates mucosal immune responses was encoded several million years ago and has subsequently been subjected to modifications selected by the impact of microorganisms and food antigens. Confronted with these challenges, the intestinal immune system has developed two arms: (1) immune exclusion performed mainly by secretory IgA antibodies to inhibit colonization of pathogenic microorganisms and penetration of harmful antigens; and (2) down-regulatory mechanisms to avoid local and peripheral overreaction (hypersensitivity) towards innocuous substances. The latter phenomenon is called oral tolerance and apparently explains why most individuals show no adverse immune reactions food. When the mucosal barrier function is insufficient, tolerance to dietary antigens is abrogated in genetically susceptible individuals. This is most likely to occur during the vulnerable period after birth before the immunoregulatory network has been established. Breast-feeding appears to be immunologically important during this period, not only to substitute for the infant's lacking secretory antibodies but also because of its immune-modulating effects.

Dietary factors influencing levels of food antibodies and antigens in breast milk

The effect of a milk-free diet during late pregnancy and lactation, on levels of cows' milk specific antibodies and antigens in breast milk, was examined. Women with an allergic condition (defined as atopic) were randomly allocated to a milk-free diet (n = 10) or an unrestricted diet (n = 12). Twelve non-atopic women followed an unrestricted diet. A significant reduction (p < 0.001) in beta-lactoglobulin-specific immunoglobulin A and alpha-casein-specific immunoglobulin A levels was observed over the first 5 days in all groups. The mean level of beta-lactoglobulin antigens in breast milk from women who adhered strictly to the milk-free diet was significantly lower than the levels of the atopic group on the unrestricted diet (p < 0.02). The allergy incidence in the infants born in the atopic diet group was significantly lower compared with that of the atopic group on the unrestricted diet.

Human alpha-lactalbumin and bovine beta-lactoglobulin absorption in infants

We investigated gut permeability to human alpha-lactalbumin (ALA) and bovine beta-lactoglobulin (BLG) in 20 infants from birth to 8 months or until weaning, before which they were on a strictly cow's-milk-free diet. We measured the proteins with a sensitive, solid-phase, double-sandwich immunofluorometric assay. Median (range) levels of serum ALA on days 3-4 after birth, and at 1 and 2 months of age were 31 (12-225), 6 (0-55), and 2 (0-16) micrograms/l serum per g ALA given per kg body weight, respectively. At 3, 5, and 8 months of age, only trace amounts of ALA were found. One week after weaning, serum BLG was found in 5/13 infants (38%) and at 2 weeks in 3/14 infants (21%), with median concentrations of 7 and 4 micrograms/l serum per g BLG given per kg body weight, respectively. No ALA could be detected in any of these samples. In absorption of ALA, the four infants who had allergic symptoms did not differ from those without symptoms. Thus, systemic absorption of ALA and BLG does occur in infants. Absorption of ALA is greatest after birth, when 3 x 10(-4) (median) of the given antigens are absorbed, but absorption decreases rapidly. The gut may often be transiently permeable to BLG when cow's-milk-based formula is started.

Allergenicity of cow milk proteins

The allergenicity and antigenicity of cow milk proteins are age dependent. Because the nonspecific and specific factors inhibiting the passage of cow milk proteins through the epithelial layer of the intestine are deficient at birth, although developing during early infancy, allergy to cow milk may be acquired during the first year of life. Allergic reactivity to cow milk is lost during childhood in the vast majority of cases. This change may depend at least partly on the development of the local immune system of the gut producing antigen-specific IgA antibodies. Circulating IgG antibodies to cow milk proteins are always produced when an infant has cow milk in the diet but are not associated with allergy; their titer is reduced with age. Clinical challenge tests show that most cow milk-allergic patients react to several protein fractions of cow milk. A patient may have IgE antibodies to several fractions of cow milk, measured either by skin testing or by radioallergosorbent test. Likewise, various tests for cell-mediated immunity may show positive reactions to several fractions. No single major allergen is apparent in cow milk, according to either the challenge tests or laboratory procedures: casein, alpha-lactalbumin, and beta-lactoglobulin all show a high proportion of positive reactions.