Oliver T. Burton

A microbiota signature associated with experimental food allergy promotes allergic sensitization and anaphylaxis

BACKGROUND Commensal microbiota play a critical role in maintaining oral tolerance. The effect of food allergy on the gut microbial ecology remains unknown. OBJECTIVE We sought to establish the composition of the gut microbiota in experimental food allergy and its role in disease pathogenesis. METHODS Food allergy-prone mice with a gain-of-function mutation in the IL-4 receptor α chain (Il4raF709) and wild-type (WT) control animals were subjected to oral sensitization with chicken egg ovalbumin (OVA). Enforced tolerance was achieved by using allergen-specific regulatory T (Treg) cells. Community structure analysis of gut microbiota was performed by using a high-density 16S rDNA oligonucleotide microarrays (PhyloChip) and massively parallel pyrosequencing of 16S rDNA amplicons. RESULTS OVA-sensitized Il4raF709 mice exhibited a specific microbiota signature characterized by coordinate changes in the abundance of taxa of several bacterial families, including the Lachnospiraceae, Lactobacillaceae, Rikenellaceae, and Porphyromonadaceae. This signature was not shared by similarly sensitized WT mice, which did not exhibit an OVA-induced allergic response. Treatment of OVA-sensitized Il4raF709 mice with OVA-specific Treg cells led to a distinct tolerance-associated signature coincident with the suppression of the allergic response. The microbiota of allergen-sensitized Il4raF709 mice differentially promoted OVA-specific IgE responses and anaphylaxis when reconstituted in WT germ-free mice. CONCLUSION Mice with food allergy exhibit a specific gut microbiota signature capable of transmitting disease susceptibility and subject to reprogramming by enforced tolerance. Disease-associated microbiota may thus play a pathogenic role in food allergy.

Regulatory T Cell Reprogramming toward a Th2-Cell-like Lineage Impairs Oral Tolerance and Promotes Food Allergy

Oral immunotherapy has had limited success in establishing tolerance in food allergy, reflecting failure to elicit an effective regulatory T (Treg) cell response. We show that disease-susceptible (Il4ra(F709)) mice with enhanced interleukin-4 receptor (IL-4R) signaling exhibited STAT6-dependent impaired generation and function of mucosal allergen-specific Treg cells. This failure was associated with the acquisition by Treg cells of a T helper 2 (Th2)-cell-like phenotype, also found in peripheral-blood allergen-specific Treg cells of food-allergic children. Selective augmentation of IL-4R signaling in Treg cells induced their reprogramming into Th2-like cells and disease susceptibility, whereas Treg-cell-lineage-specific deletion of Il4 and Il13 was protective. IL-4R signaling impaired the capacity of Treg cells to suppress mast cell activation and expansion, which in turn drove Th2 cell reprogramming of Treg cells. Interruption of Th2 cell reprogramming of Treg cells might thus provide candidate therapeutic strategies in food allergy.

Beyond immediate hypersensitivity: evolving roles for IgE antibodies in immune homeostasis and allergic diseases

Summary:  Immunoglobulin E (IgE) antibodies have long been recognized as the antigen‐specific triggers of allergic reactions. This review briefly introduces the established functions of IgE in immediate hypersensitivity and then focuses on emerging evidence from our own investigations as well as those of others that IgE plays important roles in protective immunity against parasites and exerts regulatory influences in the expression of its own receptors, FcεRI and CD23, as well as controlling mast cell homeostasis. We provide an overview of the multifaceted ways in which IgE antibodies contribute to the pathology of food allergy and speculate regarding potential mechanisms of action of IgE blockade.

Oral immunotherapy induces IgG antibodies that act through FcγRIIb to suppress IgE-mediated hypersensitivity.

BACKGROUND Food-induced anaphylaxis is triggered by specific IgE antibodies. Paradoxically, some subjects with significant IgE levels can ingest allergenic foods without incident. Similarly, subjects completing oral immunotherapy (OIT) tolerate food challenges despite persistent high-titer food-specific IgE. OBJECTIVE We sought to test whether IgG antibodies induced by food immunotherapy prevent food-induced anaphylaxis and whether this occurs through the inhibitory receptor FcγRIIb. METHODS Food allergy-susceptible Il4raF709 mice were enterally sensitized to ovalbumin (OVA). Similarly sensitized IgE-deficient (IgE(-/-)) Il4raF709 mice, which can ingest OVA without anaphylaxis, were subjected to a high-dose enteral OVA desensitization protocol (OIT). Sera from both groups were tested for the ability to activate or inhibit bone marrow mast cells (BMMCs) exposed to allergen or to passively transfer allergy to naive hosts. In parallel experiments sera obtained from patients with peanut allergy before and after undergoing OIT were interrogated for their ability to enhance or suppress peanut-induced activation in an indirect assay by using basophils from nonallergic donors. RESULTS Il4raF709 mice exhibited strong OVA-specific IgE responses. Their sera efficiently sensitized BMMCs for activation by antigen challenge. Sera from Il4raF709/IgE(-/-) mice subjected to OVA OIT suppressed BMMC responses. This inhibition was IgG mediated and FcγRIIb dependent. Similarly, pre-OIT but not post-OIT sera from patients efficiently sensitized basophils for peanut-induced activation. IgG antibodies in post-OIT sera suppressed basophil activation by pre-OIT sera. This inhibition was blocked by antibodies against FcγRII. CONCLUSION Food-specific IgG antibodies, such as those induced during OIT, inhibit IgE-mediated reactions. Strategies that favor IgG responses might prove useful in the management of food allergy.

Immunoglobulin E signal inhibition during allergen ingestion leads to reversal of established food allergy and induction of regulatory T cells.

Immunoglobulin E (IgE) antibodies are known for triggering immediate hypersensitivity reactions such as food anaphylaxis. In this study, we tested whether they might additionally function to amplify nascent antibody and T helper 2 (Th2) cell-mediated responses to ingested proteins and whether blocking IgE would modify sensitization. By using mice harboring a disinhibited form of the IL-4 receptor, we developed an adjuvant-free model of peanut allergy. Mast cells and IgE were required for induction of antibody and Th2-cell-mediated responses to peanut ingestion and they impaired regulatory T (Treg) cell induction. Mast-cell-targeted genetic deletion of the FcεRI signaling kinase Syk or Syk blockade also prevented peanut sensitization. In mice with established allergy, Syk blockade facilitated desensitization and induction of Treg cells, which suppressed allergy when transferred to naive recipients. Our study suggests a key role for IgE in driving Th2 cell and IgE responses while suppressing Treg cells in food allergy.

Direct effects of IL-4 on mast cells drive their intestinal expansion and increase susceptibility to anaphylaxis in a murine model of food allergy

Interleukin (IL)-4 has critical roles in allergic disorders, including food hypersensitivity. The direct effects of the cytokine on the survival and function of mast cells, the key effectors of food anaphylaxis, have not been established. In this study, we demonstrate that IL-4 induces a marked intestinal mastocytosis in mice. This phenotype is reproduced in animals expressing Il4rαF709, an activating variant of the IL-4 receptor α-chain (IL-4Rα). Il4rαF709 mice exhibit enhanced anaphylactic reactions but unaltered physiological responses to vasoactive mediators. IL-4 induces Bcl-2 and Bcl-XL and enhances survival and stimulates proliferation in cultured bone marrow–derived mast cells (BMMC). These effects are STAT6 (signal transducer and activator of transcription factor 6)-dependent and are amplified in Il4rαF709 BMMC. In competitive bone marrow chimeras, Il4rαF709 mast cells display a substantial competitive advantage over wild-type mast cells, which, in turn, prevail over IL-4Rα−/− mast cells in populating the intestine, establishing a cell-intrinsic effect of IL-4 in intestinal mast cell homeostasis. Our results demonstrate that IL-4-signaling is a key determinant of mast cell expansion in food allergy.

The S. mansoni glycoprotein ω-1 induces Foxp3 expression in NOD mouse CD4+ T cells

Immunization with Schistosoma mansoni soluble antigen preparations protects non‐obese diabetic (NOD) mice against the development of type 1 diabetes. These preparations have long been known to induce Th2 responses in vitro and in vivo. Recently, two separate groups have reported that ω‐1, a well‐characterized glycoprotein in S. mansoni soluble egg antigens (SEA), which with IL‐4 inducing principle of S. mansoni eggs (IPSE/α‐1) is one of the two major glycoproteins secreted by live eggs, is a major SEA component responsible for this effect. We found that ω‐1 induces Foxp3 as well as IL‐4 expression when injected in vivo. We confirmed that ω‐1 conditions DCs to drive Th2 responses and further demonstrated that ω‐1 induces Foxp3+ T cells from NOD mouse naïve T cells. In contrast, IPSE/α‐1 did not drive Foxp3 responses. The in vitro development of Foxp3‐expressing T cells by ω‐1 was TGF‐β‐ and retinoic acid‐dependent. Our work, therefore, identifies ω‐1 as an important factor for the induction of Foxp3+ T cells by SEA in NOD mice.

A humanized mouse model of anaphylactic peanut allergy

Background: Food allergy is a growing health problem with very limited treatment options. Investigation of the immunologic pathways underlying allergic sensitization to foods in humans has been greatly constrained by the limited availability of intestinal tissue and gut‐resident immune cells. Although mouse models have offered insights into pathways of food sensitization, differences between rodent and human immune physiology limit the extension of these findings to our understanding of human disease. Objective: We sought to develop a strategy for the generation of mice with humanized adaptive immune systems, complete with tissue engraftment by human mast cells that are competent to mount specific IgE‐mediated responses and drive systemic anaphylaxis on ingestion challenge. Methods: Nonobese diabetic severe combined immunodeficient mice lacking the cytokine receptor common gamma chain (&ggr;c−/−) and carrying a human stem cell factor transgene were engrafted with human hematopoietic stem cells. The impact of peanut (PN) feeding and IgE neutralization on the development of immune responses, mast cell homeostasis, and anaphylactic food allergy was assessed in these animals. Results: Humanized nonobese diabetic severe combined immunodeficient common gamma chain–deficient stem cell factor (huNSG) mice exhibited robust engraftment with functional human T and B lymphocytes and human mast cells were found in significant numbers in their tissues, including the intestinal mucosa. Following gavage feeding with PN, they mounted specific antibody responses, including PN‐specific IgE. When enterally challenged with PN, they exhibited mast‐cell–mediated systemic anaphylaxis, as indicated by hypothermia and increases in plasma tryptase levels. Anti‐IgE (omalizumab) treatment ablated this anaphylactic response. Conclusions: huNSG mice provide a novel tool for studying food allergy and IgE‐mediated anaphylaxis.

Allergen-specific IgG antibody signaling through FcγRIIb promotes food tolerance

Background: Patients with food allergy produce high‐titer IgE antibodies that bind to mast cells through Fc&egr;RI and trigger immediate hypersensitivity reactions on antigen encounter. Food‐specific IgG antibodies arise in the setting of naturally resolving food allergy and accompany the acquisition of food allergen unresponsiveness in oral immunotherapy. Objective: In this study we sought to delineate the effects of IgG and its inhibitory Fc receptor, Fc&ggr;RIIb, on both de novo allergen sensitization in naive animals and on established immune responses in the setting of pre‐existing food allergy. Methods: Allergen‐specific IgG was administered to mice undergoing sensitization and desensitization to the model food allergen ovalbumin. Cellular and molecular mechanisms were interrogated by using mast cell– and Fc&ggr;RIIb‐deficient mice. The requirement for Fc&ggr;RII in IgG‐mediated inhibition of human mast cells was investigated by using a neutralizing antibody. Results: Administration of specific IgG to food allergy–prone IL4raF709 mice during initial food exposure prevented the development of IgE antibodies, TH2 responses, and anaphylactic responses on challenge. When given as an adjunct to oral desensitization in mice with established IgE‐mediated hypersensitivity, IgG facilitated tolerance restoration, favoring expansion of forkhead box protein 3–positive regulatory T cells along with suppression of existing TH2 and IgE responses. IgG and Fc&ggr;RIIb suppress adaptive allergic responses through effects on mast cell function. Conclusion: These findings suggest that allergen‐specific IgG antibodies can act to induce and sustain immunologic tolerance to foods.

IgE receptor signaling in food allergy pathogenesis

The pathogenesis of food allergy remains poorly understood. Recent advances in the use of murine models have led to discoveries that mast cells and IgE receptor signaling not only drive immediate hypersensitivity reactions but also exert an immunoregulatory function, promoting the development of allergic sensitivity to foods. We review the evidence that IgE, IgE receptors, key signaling kinases and mast cells impair oral tolerance to ingested foods, preventing the induction of regulatory T cells (Treg) and promoting the acquisition of pro-allergic T helper (Th) 2 responses. We discuss innovative strategies that that could be implemented to counteract these immunoregulatory effects of IgE-mediated mast cell activation, and potentially reverse established sensitization, curing food allergy.