IL-25 and CD4(+) TH2 cells enhance type 2 innate lymphoid cell-derived IL-13 production, which promotes IgE-mediated experimental food allergy

IL-9-producing cells in the development of IgE-mediated food allergy

Food allergy is a harmful immune reaction driven by uncontrolled type 2 immune responses. Considerable evidence demonstrates the key roles of mast cells, IgE, and TH2 cytokines in mediating food allergy. However, this evidence provides limited insight into why only some, rather than all, food allergic individuals are prone to develop life-threatening anaphylaxis. Clinical observations suggest that patients sensitized to food through the skin early in life may later develop severe food allergies. Aberrant epidermal thymic stromal lymphopoietin and interleukin (IL) 33 production and genetic predisposition can initiate an allergic immune response mediated by dendritic cells and CD4+TH2 cells in inflamed skin. After allergic sensitization, intestinal IL-25 and food ingestion enhance concerted interactions between type 2 innate lymphoid cells (ILC2s) and CD4+TH2 cells, which perpetuate allergic reactions from the skin to the gut. IL-4 and cross-linking of antigen/IgE/FcεR complexes induce emigrated mast cell progenitors to develop into the multi-functional IL-9-producing mucosal mast cells, which produce prodigious amounts of IL-9 and mast cell mediators to drive intestinal mastocytosis in an autocrine loop. ILC2s and TH9 cells may also serve as alternative cellular sources of IL-9 to augment the amplification of intestinal mastocytosis, which is the key cellular checkpoint in developing systemic anaphylaxis. These findings provide a plausible view of how food allergy develops and progresses in a stepwise manner and that atopic signals, dietary allergen ingestion, and inflammatory cues are fundamental in promoting life-threatening anaphylaxis. This information will aid in improving diagnosis and developing more effective therapies for food allergy-triggered anaphylaxis.

Global gene regulation during activation of immunoglobulin class switching in human B cells

Immunoglobulin class switch recombination (CSR) to IgE is a tightly regulated process central to atopic disease. To profile the B-cell transcriptional responses underlying the activation of the germinal centre activities leading to the generation of IgE, naïve human B-cells were stimulated with IL-4 and anti-CD40. Gene expression and alternative splicing were profiled over 12 days using the Affymetrix Human Exon 1.0 ST Array. A total of 1,399 genes, forming 13 temporal profiles were differentially expressed. CCL22 and CCL17 were dramatically induced but followed a temporal trajectory distinct from classical mediators of isotype switching. AICDA, NFIL3, IRF4, XBP1 and BATF3 shared a profile with several genes involved in innate immunity, but with no recognised role in CSR. A transcription factor BHLHE40 was identified at the core of this profile. B-cell activation was also accompanied by variation in exon retention affecting >200 genes including CCL17. The data indicate a circadian component and central roles for the Th2 chemokines CCL22 and CCL17 in the activation of CSR.

Developing food allergy: a potential immunologic pathway linking skin barrier to gut

Immunoglobulin E (IgE)-mediated food allergy is an adverse reaction to foods and is driven by uncontrolled type-2 immune responses. Current knowledge cannot explain why only some individuals among those with food allergy are prone to develop life-threatening anaphylaxis. It is increasingly evident that the immunologic mechanisms involved in developing IgE-mediated food allergy are far more complex than allergic sensitization. Clinical observations suggest that patients who develop severe allergic reactions to food are often sensitized through the skin in early infancy. Environmental insults trigger epidermal thymic stromal lymphopoietin and interleukin-33 (IL-33) production, which endows dendritic cells with the ability to induce CD4 ⁺TH2 cell-mediated allergic inflammation. Intestinal IL-25 propagates the allergic immune response by enhancing collaborative interactions between resident type-2 innate lymphoid cells and CD4 ⁺TH2 cells expanded by ingested antigens in the gastrointestinal tract. IL-4 signaling provided by CD4 ⁺TH2 cells induces emigrated mast cell progenitors to become multi-functional IL-9-producing mucosal mast cells, which then expand greatly after repeated food ingestions. Inflammatory cytokine IL-33 promotes the function and maturation of IL-9-producing mucosal mast cells, which amplify intestinal mastocytosis, resulting in increased clinical reactivity to ingested food allergens. These findings provide the plausible view that the combinatorial signals from atopic status, dietary allergen ingestions, and inflammatory cues may govern the perpetuation of allergic reactions from the skin to the gut and promote susceptibility to life-threatening anaphylaxis. Future in-depth studies of the molecular and cellular factors composing these stepwise pathways may facilitate the discovery of biomarkers and therapeutic targets for diagnosing, preventing, and treating food allergy.

The Microbiome, Timing, and Barrier Function in the Context of Allergic Disease

Allergic disease affects millions. Despite many advances in our understanding of the immune system in the past century, the physiologic underpinning for the existence of allergy remains largely mysterious. Food allergies, in particular, have increased dramatically in recent years, adding a new sense of urgency to unraveling this mystery. The concurrence of significant lifestyle changes in Western societies with increasing disease prevalence implies a causal link. Demographic variables that influence the composition and function of the commensal microbiota early in life seem to be most important. Identifying the evolutionary and physiologic foundations of allergic disease and defining what about our modern environment is responsible for its increased incidence will provide insights critical to the development of new approaches to prevention and treatment.

Regulation of IgE-Mediated Food Allergy by IL-9 Producing Mucosal Mast Cells and Type 2 Innate Lymphoid Cells

Due to the increasing prevalence and number of life-threatening cases, food allergy has emerged as a major health concern. The classic immune response seen during food allergy is allergen-specific IgE sensitization and hypersensitivity reactions to foods occur in the effector phase with often severe and deleterious outcomes. Recent research has advanced understanding of the immunological mechanisms occurring during the effector phase of allergic reactions to ingested food. Therefore, this review will not only cover the mucosal immune system of the gastrointestinal tract and the immunological mechanisms underlying IgE-mediated food allergy, but will also introduce cells recently identified to have a role in the hypersensitivity reaction to food allergens. These include IL-9 producing mucosal mast cells (MMC9s) and type 2 innate lymphoid cells (ILC2s). The involvement of these cell types in potentiating the type 2 immune response and developing the anaphylactic response to food allergens will be discussed. In addition, it has become apparent that there is a collaboration between these cells that contributes to an individual's susceptibility to IgE-mediated food allergy.

Roles of basophils and mast cells in cutaneous inflammation

Mast cells and basophils are associated with T helper 2 (Th2) immune responses. Newly developed mast cell-deficient mice have provided evidence that mast cells initiate contact hypersensitivity via activating dendritic cells. Studies using basophil-deficient mice have also revealed that basophils are responsible for cutaneous Th2 skewing to haptens and peptide antigens but not to protein antigens. Recently, several studies reported the existence of innate lymphoid cells (ILCs), which differ from classic T cells in that they lack the T cell receptor. Mast cells and basophils can interact with ILCs and play some roles in the pathogenesis of Th2 responses. Basophil-derived interleukin (IL)-4 enhances the expression of the chemokine CCL11, as well as IL-5, IL-9, and IL-13 in ILC2s, leading to the accumulation of eosinophils in allergic reactions. IL-33-stimulated mast cells can play a regulatory role in the development of ILC2-mediated non-antigen-specific protease-induced acute inflammation. In this review, we discuss the recent advances in our understanding of mast cells and basophils in immunity and inflammation.

IL-4 production by group 2 innate lymphoid cells promotes food allergy by blocking regulatory T-cell function

BACKGROUND

Food allergy is a major health issue, but its pathogenesis remains obscure. Group 2 innate lymphoid cells (ILC2s) promote allergic inflammation. However their role in food allergy is largely unknown.

OBJECTIVE

We sought to investigate the role of ILC2s in food allergy.

METHODS

Food allergy-prone mice with a gain-of-function mutation in the IL-4 receptor α chain (Il4raF709) were orally sensitized with food allergens, and the ILC2 compartment was analyzed. The requirement for ILC2s in food allergy was investigated by using Il4raF709, IL-33 receptor-deficient (Il1rl1(-/-)), IL-13-deficient (Il13(-/-)), and IL-4-deficient (Il4(-/-)) mice and by adoptive transfer of in vitro-expanded ILC2s. Direct effects of ILC2s on regulatory T (Treg) cells and mast cells were analyzed in coculture experiments. Treg cell control of ILC2s was assessed in vitro and in vivo.

RESULTS

Il4raF709 mice with food allergy exhibit increased numbers of ILC2s. IL-4 secretion by ILC2s contributes to the allergic response by reducing allergen-specific Treg cell and activating mast cell counts. IL-33 receptor deficiency in Il4raF709 Il1rl1(-/-) mice protects against allergen sensitization and anaphylaxis while reducing ILC2 induction. Adoptive transfer of wild-type and Il13(-/-) but not Il4(-/-) ILC2s restored sensitization in Il4raF709 Il1rl1(-/-) mice. Treg cells suppress ILC2s in vitro and in vivo.

CONCLUSION

IL-4 production by IL-33-stimulated ILC2s blocks the generation of allergen-specific Treg cells and favors food allergy. Strategies to block ILC2 activation or the IL-33/IL-33 receptor pathway can lead to innovative therapies in the treatment of food allergy.