Long-term reduction in food allergy susceptibility in mice by combining breastfeeding-induced tolerance and TGF-β-enriched formula after weaning

Antibodies in breast milk: Pro-bodies designed for healthy newborn development

This manuscript sheds light on the impact of maternal breast milk antibodies on infant health. Milk antibodies prepare and protect the newborn against environmental exposure, guide and regulate the offspring's immune system, and promote transgenerational adaptation of the immune system to its environment. While the transfer of IgG across the placenta ceases at birth, milk antibodies are continuously replenished by the maternal immune system. They reflect the mother's real-time adaptation to the environment to which the infant is exposed. They cover the infant's upper respiratory and digestive mucosa and are perfectly positioned to control responses to environmental antigens and might also reach their circulation. Maternal antibodies in breast milk play a key role in the immune defense of the developing child, with a major impact on infectious disease susceptibility in both HIC and LMIC. They also influence the development of another major health burden in children-allergies. Finally, emerging evidence shows that milk antibodies also actively shape immune development. Much of this is likely to be mediated by their effect on the seeding, composition and function of the microbiota, but not only. Further understanding of the bridge that maternal antibodies provide between the child and its environment should enable the best interventions to promote healthy development.

Maternal influences on offspring food allergy

The prevalence of allergies has been globally escalating. While allergies could appear at any age, they often develop in early life. However, the significant knowledge gap in the field is the mechanisms by which allergies affect certain people but not others. Investigating early factors and events in neonatal life that have a lasting impact on determining the susceptibilities of children to develop allergies is a significant area of the investigation as it promotes the understanding of neonatal immune system that mediates tolerance versus allergies. This review focuses on the research over the recent 10 years regarding the potential maternal factors that influence offspring allergies with a view to food allergy, a potentially life-threatening cause of anaphylaxis. The role of breast milk, maternal diet, maternal antibodies, and microbiota that have been suggested as key maternal factors regulating offspring allergies are discussed here. We also suggest future research area to expand our knowledge of maternal-offspring interactions on the pathogenesis of food allergy.

A newborn's perspective on immune responses to food

In this review, we will highlight infants' immune responses to food, emphasizing the unique aspects of early-life immunity and the critical role of breast milk as a food dedicated to infants. Infants are susceptible to inflammatory responses rather than immune tolerance at the mucosal and skin barriers, necessitating strategies to promote oral tolerance that consider this susceptibility. Breast milk provides nutrients for growth and cell metabolism, including immune cells. The content of breast milk, influenced by maternal genetics and environmental exposures, prepares the infant's immune system for the outside world, including solid foods. To do this, breast milk promotes immune system development through antigen-specific and non-antigen-specific immune education by exposing the newborn to food and respiratory allergens and acting on three key targets for food allergy prevention: the gut microbiota, epithelial cells, and immune cells. Building knowledge of how the maternal exposome and human milk composition influence offspring's healthy immune development will lead to recommendations that meet the specific needs of the developing immune system and increase the chances of promoting an appropriate immune response to food in the long term.

Milk: A Natural Guardian for the Gut Barrier

The gut barrier plays an important role in health maintenance by preventing the invasion of dietary pathogens and toxins. Disruption of the gut barrier can cause severe intestinal inflammation. As a natural source, milk is enriched with many active constituents that contribute to numerous beneficial functions, including immune regulation. These components collectively serve as a shield for the gut barrier, protecting against various threats such as biological, chemical, mechanical, and immunological threats. This comprehensive review delves into the active ingredients in milk, encompassing casein, α-lactalbumin, β-lactoglobulin, lactoferrin, the milk fat globular membrane, lactose, transforming growth factor, and glycopeptides. The primary focus is to elucidate their impact on the integrity and function of the gut barrier. Furthermore, the implications of different processing methods of dairy products on the gut barrier protection are discussed. In conclusion, this study aimed to underscore the vital role of milk and dairy products in sustaining gut barrier health, potentially contributing to broader perspectives in nutritional sciences and public health.

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Breastfeeding and Allergy Effect Modified by Genetic, Environmental, Dietary, and Immunological Factors

Breastfeeding (BF) is the most natural mode of nutrition. Its beneficial effect has been revealed in terms of both the neonatal period and those of lifelong effects. However, as for protection against allergy, there is not enough data. In the current narrative review, the literature within the last five years from clinical trials and population-based studies on breastfeeding and allergy from different aspects was explored. The aim of this review was to explain how different factors could contribute to the overall effect of BF. Special consideration was given to accompanying exposure to cow milk, supplement use, the introduction of solid foods, microbiota changes, and the epigenetic function of BF. Those factors seem to be modifying the impact of BF. We also identified studies regarding BF in atopic mothers, with SCFA as a main player explaining differences according to this status. Conclusion: Based on the population-based studies, breastfeeding could be protective against some allergic phenotypes, but the results differ within different study groups. According to the new research in that matter, the effect of BF could be modified by different genetic (HMO composition), environmental (cesarean section, allergen exposure), dietary (SCFA, introduction of solid food), and immunologic factors (IgG, IgE), thus partially explaining the variance.

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.

Characteristics of Exogenous Allergen in Breast Milk and Their Impact on Oral Tolerance Induction

Food allergy is a common health problem in childhood since its prevalence was estimated to range from 6. 5 to 24.6% in European countries. Recently, a lot of research has focused on the impact of breastfeeding on oral tolerance induction. Since it was found that breast milk contains immunologically active food antigens, it would be very helpful to clarify the factors of antigen shedding that promotes oral tolerance. This narrative review aimed to summarize the latest evidence from experimental and human studies regarding allergen characteristics in human milk that may influence oral tolerance induction. A literature search in PubMed, MEDLINE, and Google Scholar was conducted. The diet of the mother was found to have a direct impact on allergen amount in the breastmilk, while antigens had different kinetics in human milk between women and depending on the antigen. The mode of antigen consumption, such as the cooking of an antigen, may also affect the allergenicity of the antigen in human milk. The dose of the antigen in human milk is in the range of nanograms per milliliter; however, it was found to have a tolerogenic effect. Furthermore, the presence of antigen-specific immunoglobulins, forming immune complexes with antigens, was found more tolerogenic compared to free allergens in experimental studies, and this is related to the immune status of the mother. While examining available data, this review highlights gaps in knowledge regarding allergen characteristics that may influence oral tolerance.

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.

Allergen shedding in human milk: Could it be key for immune system education and allergy prevention?

In addition to being a source of nutrients for the developing newborn, human milk contains thousands of bioactive compounds, which influence infant health in the short-term as exemplified by its major benefits on infectious disease prevention. Many of the human milk compounds also have the required characteristics to instruct immune development and guide long-term health. Prebiotics, probiotics, and varied antimicrobial molecules all have the potential to shape the composition and function of the establishing gut microbiota, which is known to be a major determinant of immune function. Another and less explored way human milk can instruct long-term immunity is through antigen shedding. Here, we will review the evidence that antigens from maternal environment and more specifically from allergen sources are found in human milk. We will discuss data from rodent models and birth cohorts showing that allergen shedding in breast milk may influence long-term allergy risk. We will uncover the variables that may underlie heterogeneity in oral tolerance induction and allergy prevention in children breast-fed by allergen-exposed mothers. We will focus on the parameters that control antigen transfer to breast milk, on the unique biological characteristics of allergens in breast milk, and on the milk bioactive compounds that were found to influence immune response in offspring. We propose this understanding is fundamental to guide maternal interventions leading to lifelong allergen tolerance.

Regulation of oral antigen delivery early in life: Implications for oral tolerance and food allergy

The increasing incidence of food allergy remains a significant public health concern. Food allergy is partially due to a lack, or loss of tolerance to food allergens. Clinical outcomes surrounding early life practices, such as breastfeeding, antibiotic use and food allergen exposure, indicate the first year of life in children represents a unique time for shaping the immune system to reduce allergic outcomes. Animal models have identified distinctive aspects of when and where dietary antigens are delivered within the intestinal tract to promote oral tolerance prior to weaning. Additionally, animal models have identified contributions from maternal proteins from breast milk and bacterial products from the gut microbiota in regulating dietary antigen exposure and promoting oral tolerance, thus connecting decades of clinical observations on the benefits of breastfeeding, early food allergen introduction and antibiotic avoidance in the first year of life in reducing allergic outcomes. Here, we discuss how exposure to gut luminal antigens, including food allergens, is regulated in early life to generate protective tolerance and the implications of this process for preventing and treating food allergies.

The Gut‒Breast Axis: Programming Health for Life

The gut is a pivotal organ in health and disease. The events that take place in the gut during early life contribute to the programming, shaping and tuning of distant organs, having lifelong consequences. In this context, the maternal gut plays a quintessence in programming the mammary gland to face the nutritional, microbiological, immunological, and neuroendocrine requirements of the growing infant. Subsequently, human colostrum and milk provides the infant with an impressive array of nutrients and bioactive components, including microbes, immune cells, and stem cells. Therefore, the axis linking the maternal gut, the breast, and the infant gut seems crucial for a correct infant growth and development. The aim of this article is not to perform a systematic review of the human milk components but to provide an insight of their extremely complex interactions, which render human milk a unique functional food and explain why this biological fluid still truly remains as a scientific enigma.

Administration of Extensive Hydrolysates From Caseins and Lactobacillus rhamnosus GG Probiotic Does Not Prevent Cow's Milk Proteins Allergy in a Mouse Model

Background

Early nutrition may influence the development of food allergies later in life. In the absence of breastfeeding, hydrolysates from cow's milk proteins (CMP) were indicated as a prevention strategy in at risk infants, but their proof of effectiveness in clinical and pre-clinical studies is still insufficient. Thanks to a validated mouse model, we then assessed specific and nonspecific preventive effects of administration of extensive hydrolysates from caseins (eHC) on the development of food allergy to CMP. The additional nonspecific effect of the probiotic Lactobacillus GG (LGG), commonly used in infant formula, was also assessed.

Methods

Groups of young BALB/cByJ female mice were pretreated by repeated gavage either with PBS (control mice), or with PBS solution containing non-hydrolyzed milk protein isolate (MPI), eHC or eHC+LGG (eq. of 10 mg of protein/gavage). All mice were then experimentally sensitized to CMP by gavage with whole CM mixed with the Th2 mucosal adjuvant Cholera toxin. All mice were further chronically exposed to cow's milk. A group of mice was kept naïve. Sensitization to both caseins and to the non-related whey protein β-lactoglobulin (BLG) was evaluated by measuring specific antibodies in plasma and specific ex vivo Th2/Th1/Th17 cytokine secretion. Elicitation of the allergic reaction was assessed by measuring mMCP1 in plasma obtained after oral food challenge (OFC) with CMP. Th/Treg cell frequencies in gut-associated lymphoid tissue and spleen were analyzed by flow cytometry at the end of the protocol. Robust statistical procedure combining non-supervised and supervised multivariate analyses and univariate analyses, was conducted to reveal any effect of the pretreatments.

Results

PBS pretreated mice were efficiently sensitized and demonstrated elicitation of allergic reaction after OFC, whereas mice pretreated with MPI were durably protected from allergy to CMP. eHC+/-LGG pretreatments had no protective effect on sensitization to casein (specific) or BLG (non-specific), nor on CMP-induced allergic reactions. Surprisingly, eHC+LGG mice demonstrated significantly enhanced humoral and cellular immune responses after sensitization with CMP. Only some subtle changes were evidenced by flow cytometry.

Conclusion

Neither specific nor nonspecific preventive effects of administration of casein-derived peptides on the development of CMP food allergy were evidenced in our experimental setup. Further studies should be conducted to delineate the mechanisms involved in the immunostimulatory potential of LGG and to clarify its significance in clinical use.

Prevention of Allergy to a Major Cow's Milk Allergen by Breastfeeding in Mice Depends on Maternal Immune Status and Oral Exposure During Lactation

Background: The high incidence of food allergy in childhood points to the need of elucidating early life factors dictating allergy susceptibility. Here, we aim to address in a mouse model how the exposure to a major cow's milk allergen through breastmilk of mothers with different immune status influences food allergy outcome in offspring.

Methods: BALB/cJ future dams were either kept naïve, or sensitized through the oral route using cholera toxin (“orally sensitized”) or through the i.p. route using alum (“i.p. sensitized”), or rendered fully tolerant (oral gavage without any adjuvant) to bovine β-lactoglobulin (BLG). After mating with naïve males and delivery, mothers were orally exposed or not to BLG during the whole lactation. Then, eight groups of lactating mothers were considered: naïve, i.p. sensitized, orally sensitized, or tolerant, each exposed or not during lactation. In order to specifically address breastmilk effects on their allergy susceptibility, pups from naïve-synchronized mothers were cross-fostered by the different groups of treated dams and lactating mothers at delivery. In some experiments, mothers kept their own pups to address a possible in utero effect. BLG antigen, BLG-specific antibodies, and BLG-immune complexes were measured in breastmilk from the different lactating mother groups. Allergic sensitization was monitored in 5-weeks old female offspring (n = 7–8/group of lactating mothers) by determining BLG-specific antibodies in plasma and splenocytes cytokine secretion after i.p. injections of BLG/alum. Allergic reaction to oral BLG challenge was evaluated by measuring mMCP1 in plasma.

Results: Offspring was protected from one allergic i.p. sensitization when nursed by i.p. sensitized mothers, independently of BLG exposure during lactation. Orally sensitized dams conferred protection in offspring solely when exposed to BLG during lactation, while naïve mothers did not provide any protection upon BLG exposure. The levels of protection correlated with the levels of BLG-specific antibodies and BLG-immune complex in breastmilk. There was a trend for decreased sensitization in offspring breastfed by tolerant and exposed mothers, which was not associated with transfer of specific antibodies through breastmilk. Protection provided by nursing by treated/exposed mothers was not persistent after a boost i.p. injection of the progeny and then did not protect them from an allergic reaction induced at this time point. No additional in utero effects were evidenced.

Conclusion: Our study demonstrates the strong potential of breastmilk to modulate immune response to a major cow's milk allergen in the progeny. It highlights the importance of maternal immune status and of her consumption of the allergen during lactation in dictating the outcomes in offspring. This opens perspectives where modulating maternal immune status might increase the chance of cow's milk allergy prevention in breastfed children.

A role for early oral exposure to house dust mite allergens through breast milk in IgE-mediated food allergy susceptibility

BACKGROUND

Successful prevention of food allergy requires the identification of the factors adversely affecting the capacity to develop oral tolerance to food antigen in early life.

OBJECTIVES

This study sought to determine whether oral exposure to Dermatophagoides pteronyssinus through breast milk affects gut mucosal immunity with long-term effects on IgE-mediated food allergy susceptibility.

METHODS

Gut immunity was explored in 2-week-old mice breast-fed by mothers exposed to D pteronyssinus, protease-inactivated D pteronyssinus, or to PBS during lactation. We further analyzed oral tolerance to a bystander food allergen, ovalbumin (OVA). In a proof-of-concept study, Der p 1 and OVA levels were determined in 100 human breast milk samples and the association with prevalence of IgE-mediated egg allergy at 1 year was assessed.

RESULTS

Increased permeability, IL-33 levels, type 2 innate lymphoid cell activation, and T_h2 cell differentiation were found in gut mucosa of mice nursed by mothers exposed to D pteronyssinus compared with PBS. This pro-T_h2 gut mucosal environment inhibited the induction of antigen-specific FoxP3 regulatory T cells and the prevention of food allergy by OVA exposure through breast milk. In contrast, protease-inactivated D pteronyssinus had no effect on offspring gut mucosal immunity. Based on the presence of Der p 1 and/or OVA in human breast milk, we identified groups of lactating mothers, which mirror the ones found in mice to be responsible for different egg allergy risk.

CONCLUSIONS

This study highlights an unpredicted potential risk factor for the development of food allergy, that is, D pteronyssinus allergens in breast milk, which disrupt gut immune homeostasis and prevents oral tolerance induction to bystander food antigen through their protease activity.

Developments in the field of allergy in 2017 through the eyes of Clinical and Experimental Allergy

In this article, we described the development in the field of allergy as described by Clinical and Experimental Allergy in 2017. Experimental models of allergic disease, basic mechanisms, clinical mechanisms, allergens, asthma and rhinitis and clinical allergy are all covered.

Oral Tolerance Induction to Newly Introduced Allergen is Favored by a Transforming Growth Factor-β-Enriched Formula

Food allergies have become a major healthcare concern, hence preventive efforts to ensure oral tolerance induction to newly introduced antigens are particularly relevant. Given that transforming growth factor-β (TGF-β) plays a key role in immune tolerance, we tested whether an infant formula enriched with TGF-β would improve oral tolerance induction. A partially hydrolyzed whey protein-based formula was enriched with cow's-milk-derived TGF-β (TGF-β-enriched formula) by adding a specific whey protein isolate (WPI). The manufacturing process was optimized to achieve a concentration of TGF-β within the range of human breast milk concentrations. Protection from allergic sensitization and immune response was assessed in a mouse model. Adult mice received the TGF-β-enriched formula, a control non-enriched formula, or water ad libitum for 13 days before sensitization and suboptimal tolerization to ovalbumin (OVA). When compared to non-tolerized mice, suboptimally-tolerized mice supplemented with the TGF-β-enriched formula showed significantly lower levels of total immunoglobulin-E (IgE) and OVA-specific (IgG1). Mouse mast-cell protease-1 (mMCP-1) and cytokine levels were also significantly decreased in suboptimally-tolerized mice fed the TGF-β-enriched formula. In conclusion, oral supplementation with cow's-milk-derived TGF-β decreased allergic responses to newly introduced allergens and thus reduced the risk of developing food allergy.

Influences of Maternal Factors Over Offspring Allergies and the Application for Food Allergy

The prevalence of food allergy has been steadily rising worldwide with the highest incidence noted among younger children, and increasingly recognized as a growing public concern. The first known ingestion of foods often causes allergic reaction, suggesting that sensitization of offspring with food allergens may occur during pregnancy and/or through breastfeeding. This creates a milieu that shapes the neonatal immune responses to these allergens. However, the effects of maternal allergen exposure and maternal sensitization with allergens on development of allergies in offspring remain controversial. This review discusses recent advances from human data in our understanding of how maternal factors, namely, food allergens, allergen-specific immunoglobulins, cytokines, genetics, and environmental factors transferred during pregnancy or breastfeeding influence offspring allergies and how such effects may be applicable to food allergy. Based on information obtained from mouse models of asthma and food allergy, the review also dissects the mechanisms by which maternal factors, including the impact of immune complexes, transforming growth factor-β, vitamin A, and regulatory T-cell responses, contribute to the induction of neonatal tolerance vs. development of allergic responses to maternally transferred allergens.

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.

Mechanisms of gastrointestinal allergic disorders

Gastrointestinal (GI) allergic disease is an umbrella term used to describe a variety of adverse, food antigen-driven, immune-mediated diseases. Although these diseases vary mechanistically, common elements include a breakdown of immunologic tolerance, a biased type 2 immune response, and an impaired mucosal barrier. These pathways are influenced by diverse factors such as diet, infections, exposure to antibiotics and chemicals, GI microbiome composition, and genetic and epigenetic elements. Early childhood has emerged as a critical period when these factors have a dramatic impact on shaping the immune system and therefore triggering or protecting against the onset of GI allergic diseases. In this Review, we will discuss the latest findings on the molecular and cellular mechanisms that govern GI allergic diseases and how these findings have set the stage for emerging preventative and treatment strategies.

Mechanisms of Oral Tolerance

Oral tolerance is a state of systemic unresponsiveness that is the default response to food antigens in the gastrointestinal tract, although immune tolerance can also be induced by other routes, such as the skin or inhalation. Antigen can be acquired directly by intestinal phagocytes, or pass through enterocytes or goblet cell-associated passages prior to capture by dendritic cells (DCs) in the lamina propria. Mucin from goblet cells acts on DCs to render them more tolerogenic. A subset of regulatory DCs expressing CD103 is responsible for delivery of antigen to the draining lymph node and induction of Tregs. These DCs also imprint gastrointestinal homing capacity, allowing the recently primed Tregs to home back to the lamina propria where they interact with macrophages that produce IL-10 and expand. Tregs induced by dietary antigen include Foxp3⁺ Tregs and Foxp3^- Tregs. In addition to Tregs, T cell anergy can also contribute to oral tolerance. The microbiota plays a key role in the development of oral tolerance, through regulation of macrophages and innate lymphoid cells that contribute to the regulatory phenotype of gastrointestinal dendritic cells. Absence of microbiota is associated with a susceptibility to food allergy, while presence of Clostridia strains can suppress development of food allergy through enhancement of Tregs and intestinal barrier function. It is not clear if feeding of antigens can also induce true immune tolerance after a memory immune response has been generated, but mechanistic studies of oral immunotherapy trials demonstrate shared pathways in oral tolerance and oral immunotherapy, with a role for Tregs and anergy. An important role for IgA and IgG antibodies in development of immune tolerance is also supported by studies of oral tolerance in humans. The elucidation of key pathways in oral tolerance could identify new strategies to increase efficacy of immunotherapy treatments for food allergy.

IL-10 Receptor or TGF-β Neutralization Abrogates the Protective Effect of a Specific Nondigestible Oligosaccharide Mixture in Cow-Milk-Allergic Mice

Background

Dietary nondigestible, short-chain galacto-, long-chain fructo-, and pectin-derived acidic oligosaccharides (GFAs) lower the effector response in cow-milk-allergic (CMA) mice; and forkhead box P3 (Foxp3)-positive regulatory T cells (Tregs) were shown to contribute to this.

Objective

The aim of this study was to assess the contribution of interleukin 10 (IL-10) and transforming growth factor β (TGF-β) to the protective effect of the GFA diet in CMA mice.

Methods

Female C3H/HeOuJ mice, 3-4 wk old, were orally sensitized with cholera toxin (Sham) or whey and cholera toxin (Whey) 1 time/wk for 5 consecutive weeks and challenged with whey 1 wk later. The mice were fed a control or 1% GFA (9:2:1) (Whey+GFA) diet starting 2 wk before the first sensitization. In a second experiment, the mice were also injected with αIL-10 receptor (αIL-10r), αTGF-β, or isotype control antibodies 24 h before each sensitization. The acute allergic skin response, anaphylaxis score, whey-specific IgE, mucosal mast cell protease 1 (mMCP-1), and Treg frequency in the mesenteric lymph nodes (MLNs) and intestinal Foxp3, Il10, and Tgfb mRNA expression were determined.

Results

In Whey+GFA mice, intestinal Il10, Tgfb, or Foxp3 mRNA expression was 2-10 times higher (P < 0.05) and the MLN Treg frequency was 25% higher compared with Whey mice (P < 0.05). The acute allergic skin response was 50% lower in Whey+GFA mice compared with Whey mice (P < 0.01), and IL-10 receptor (IL-10r) or TGF-β neutralizing antibodies prevented this protective effect (P < 0.001). The Whey mice had higher serum mMCP-1 concentrations and whey-immunoglobulin E (-IgE) levels than Sham mice (P < 0.01), whereas these were not higher in Whey+GFA mice, and neutralizing antibodies partially interfered with these responses.

Conclusions

Dietary GFAs enhance the Treg frequency in the MLNs and mucosal IL-10 and TGF-β transcription while suppressing the allergic effector response. Neutralizing antibodies showed that the allergy-protective effect of the GFA diet was mediated by IL-10 and TGF-β in CMA mice.

Maternal IgG immune complexes induce food allergen-specific tolerance in offspring

The role of maternal immune responses in tolerance induction is poorly understood. To study whether maternal allergen sensitization affects offspring susceptibility to food allergy, we epicutaneously sensitized female mice with ovalbumin (OVA) followed by epicutaneous sensitization and oral challenge of their offspring with OVA. Maternal OVA sensitization prevented food anaphylaxis, OVA-specific IgE production, and intestinal mast cell expansion in offspring. This protection was mediated by neonatal crystallizable fragment receptor (FcRn)-dependent transfer of maternal IgG and OVA immune complexes (IgG-IC) via breast milk and induction of allergen-specific regulatory T (T reg) cells in offspring. Breastfeeding by OVA-sensitized mothers or maternal supplementation with IgG-IC was sufficient to induce neonatal tolerance. FcRn-dependent antigen presentation by CD11c⁺ dendritic cells (DCs) in offspring was required for oral tolerance. Human breast milk containing OVA-IgG-IC induced tolerance in humanized FcRn mice. Collectively, we demonstrate that interactions of maternal IgG-IC and offspring FcRn are critical for induction of T reg cell responses and control of food-specific tolerance in neonates.