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

Recent advances in cellular and molecular mechanisms of IgE-mediated food allergy

Food allergy is a public health issue the prevalence of which is steadily increasing. New discoveries have contributed to the understanding of the molecular and cellular mechanisms that lead to IgE-mediated food allergy. Novel scientific findings have defined roles for specific cell types, such as T follicular helper cells, in induction of high-affinity IgE by B cells. Also, not only mast cells and basophils contribute to food anaphylaxis, but also other cell types, such as neutrophils and macrophages. Elucidation of mechanisms involved in sensitization to food allergens through organs including the skin is key to deepening our understanding of the "dual exposure" hypothesis, which suggests that allergic sensitization is mainly acquired through inflamed skin while the oral route induces tolerance. This review considers the latest scientific knowledge about the molecular and cellular mechanisms of IgE-mediated food allergy. It reveals crucial components involved in the sensitization and elicitation phases and emerging approaches in anaphylaxis pathophysiology.

Upregulated Expression of the IL-9 Receptor on TRAF3-Deficient B Lymphocytes Confers Ig Isotype Switching Responsiveness to IL-9 in the Presence of Antigen Receptor Engagement and IL-4

The pleiotropic cytokine IL-9 signals to target cells by binding to a heterodimeric receptor consisting of the unique subunit IL-9R and the common subunit γ-chain shared by multiple cytokines of the γ-chain family. In the current study, we found that the expression of IL-9R was strikingly upregulated in mouse naive follicular B cells genetically deficient in TNFR-associated factor 3 (TRAF3), a critical regulator of B cell survival and function. The highly upregulated IL-9R on Traf3-/- follicular B cells conferred responsiveness to IL-9, including IgM production and STAT3 phosphorylation. Interestingly, IL-9 significantly enhanced class switch recombination to IgG1 induced by BCR crosslinking plus IL-4 in Traf3-/- B cells, which was not observed in littermate control B cells. We further demonstrated that blocking the JAK-STAT3 signaling pathway abrogated the enhancing effect of IL-9 on class switch recombination to IgG1 induced by BCR crosslinking plus IL-4 in Traf3-/- B cells. Our study thus revealed, to our knowledge, a novel pathway that TRAF3 suppresses B cell activation and Ig isotype switching by inhibiting IL-9R-JAK-STAT3 signaling. Taken together, our findings provide (to our knowledge) new insights into the TRAF3-IL-9R axis in B cell function and have significant implications for the understanding and treatment of a variety of human diseases involving aberrant B cell activation such as autoimmune disorders.

Development of gastro-food allergy model in shrimp allergen extract-induced sensitized mice promotes mast cell degranulation

Background: Food allergies have become more common in the last decade. Shrimp is one of the most dominant food allergy triggers in Asian countries, including Indonesia. After ingesting allergens, B cells will produce allergen-specific Immunoglobin E (IgE). In the sensitization period, repeated allergen exposure promotes Mast Cell (MC) degranulation in intestinal tissue and releases several inflammatory mediators, thereby causing hypersensitivity reactions. Shrimp Allergen Extract (SAE) is an immunotherapy and diagnostic agent currently being developed in Indonesia. In this study, we investigated the effect of SAE administration on eliciting an MC immunological response. Methods: Mice were divided into a non-sensitized and sensitized group. The non-sensitized group only received 1 mg of alum (i.p), whereas the sensitized group received 1 mg of alum and 100 μg of SAE on days 0, 7, and 14. Then, both groups were challenged with 400 μg SAE (p.o) on days 21, 22, and 23 following systemic allergic symptom observation. Results: We showed that SAE was able to increase systemic allergic symptoms significantly in the sensitized mice through repeated challenge (1.33±0.21; 1.83±0.17; and 2.00±0.00), compared to non-sensitized mice (0.17±0.17). Moreover, histopathological analysis showed that the SAE administration causes an increase of MC degranulation in the ileum tissue of the sensitized mice (44.43%±0.01), compared to non-sensitized mice (35.45%±0.01) Conclusions: This study found that SAE could induce allergic reactions in mice by influencing critical effector cells, MCs.

Bacterial Metabolites: A Link between Gut Microbiota and Dermatological Diseases

Dysbiosis has been identified in many dermatological conditions (e.g., psoriasis, atopic dermatitis, systemic lupus erythematosus). One of the ways by which the microbiota affect homeostasis is through microbiota-derived molecules (metabolites). There are three main groups of metabolites: short-chain fatty acids (SCFAs), tryptophan metabolites, and amine derivatives including trimethylamine N-oxide (TMAO). Each group has its own uptake and specific receptors through which these metabolites can exert their systemic function. This review provides up-to-date knowledge about the impact that these groups of gut microbiota metabolites may have in dermatological conditions. Special attention is paid to the effect of microbial metabolites on the immune system, including changes in the profile of the immune cells and cytokine disbalance, which are characteristic of several dermatological diseases, especially psoriasis and atopic dermatitis. Targeting the production of microbiota metabolites may serve as a novel therapeutic approach in several immune-mediated dermatological diseases.

Ovalbumin-Induced Epithelial Activation Directs Monocyte-Derived Dendritic Cells to Instruct Type 2 Inflammation in T Cells Which Is Differentially Modulated by 2'-Fucosyllactose and 3-Fucosyllactose

Allergic sensitization starts with epithelial cell activation driving dendritic cells (DCs) to instruct T helper 2 (Th2) cell polarization. Food allergens trigger intestinal epithelial cell (IEC) activation. Human milk oligosaccharides may temper the allergic phenotype by shaping mucosal immune responses.We investigated in vitro mucosal immune development after allergen exposure by combining ovalbumin (OVA)-preexposed IEC with monocyte-derived DCs (OVA-IEC-DCs) and subsequent coculture of OVA-IEC-DCs with Th cells. IECs were additionally preincubated with 2'FL or 3FL.OVA activation increased IEC cytokine secretion. OVA-IEC-DCs instructed both IL13 (p < 0.05) and IFNγ (p < 0.05) secretion from Th cells. 2'FL and 3FL permitted OVA-induced epithelial activation, but 2'FL-OVA-IEC-DCs boosted inflammatory and regulatory T-cell development. 3FL-OVA-IEC lowered IL12p70 and IL23 in DCs and suppressed IL13 (p < 0.005) in T cells, while enhancing IL17 (p < 0.001) and IL10 (p < 0.005).These results show that OVA drives Th2- and Th1-type immune responses via activation of IECs in this model. 2'FL and 3FL differentially affect OVA-IEC-driven immune effects. 2'FL boosted overall T-cell OVA-IEC immunity via DC enhancing inflammatory and regulatory responses. 3FL-OVA-IEC-DCs silenced IL13, shifting the balance towards IL17 and IL10.This model demonstrates the contribution of IEC to OVA Th2-type immunity. 2'FL and 3FL modulate the OVA-induced activation in this novel model to study allergic sensitization.

The rationale for development of ligelizumab in food allergy

Food allergy (FA) is a growing healthcare problem worldwide and the rising prevalence in many countries can be attributed to lifestyle, environmental, and nutritional changes. Immunoglobulin E (IgE)-mediated FA is the most common form of FA affecting approximately 3%-10% of adults and 8% of children across the globe. Food allergen-induced immediate hypersensitivity reactions mediated by IgE and high-affinity IgE receptor (FcεRI) complexes on mast cells and basophils are a major hallmark of the disease. FA can affect several aspects of health-related quality of life and impose a substantial financial burden on patients and healthcare systems. Although currently there is one United States Food and Drug Administration (FDA) and European Medicines Agency (EMA)-approved treatment for peanut allergy (Palforzia), the main treatment approaches are based on allergen avoidance and symptom management. Thus, there is an urgent need for more effective and ideally disease-modifying strategies. Given the crucial role of IgE in FA, anti-IgE monoclonal antibodies are considered promising therapeutic agents. Talizumab was the first humanized anti-IgE antibody to demonstrate substantial protection against allergic reactions from accidental peanut exposure by substantially increasing the peanut reactivity threshold on oral food challenge. However, development of talizumab was discontinued and further trials were performed using omalizumab. In double-blind, Phase 2, placebo-controlled trials in patients with multi-FAs, sustained dosing with omalizumab, or omalizumab in combination with oral immunotherapy, enabled rapid desensitization to multiple trigger foods. In this review, we describe the development of ligelizumab (a derivative of talizumab), a next generation, humanized monoclonal anti-IgE antibody, its existing clinical evidence, and its potential in the management of FA. When compared with omalizumab, ligelizumab binds with ∼88-fold higher affinity for human IgE and recognizes a different epitope that substantially overlaps with the binding site of FcεRI. These properties translate into a high potency to block IgE/FcεRI signaling in both in vitro and in vivo studies. Given its efficient suppression of IgE levels, good safety and pharmacokinetic/pharmacodynamic profile, ligelizumab clearly warrants further studies for the potential management of FA.

Lycopene intake induces colonic regulatory T cells in mice and suppresses food allergy symptoms

BACKGROUND

Food allergy (FA) is a common disease in children; thus, a high level of safety is required for its prevention and treatment. Colonic regulatory T cells (Tregs) have been suggested to attenuate FA. We investigated the Treg-inducing ability and anti-FA effects of carotenoids, a pigment contained in vegetables and fruits.

METHODS

C57BL/6N mice were fed a diet containing 0.01% (w/w) of lycopene, β-carotene, astaxanthin or lutein for 4 weeks, and the population of colonic Tregs was assessed. Subsequently, to evaluate the Treg-inducing ability of lycopene, splenic naïve CD4⁺ T cells from BALB/c mice were cultured with anti-CD3/CD28 antibody, TGF-β and lycopene, and the frequencies of Tregs were examined. The effect of 0.1% (w/w) lycopene containing diet on FA was investigated in OVA-induced FA model BALB/c mice.

RESULTS

In screening, only lycopene significantly increased the frequency and number of colonic Tregs. Lycopene also increased Treg differentiation in splenic naïve CD4⁺ T cells. In FA mice, lycopene feeding significantly increased the number of colonic Tregs and attenuated allergic symptoms. The expression levels of IL-4, IL-9 and IL-13 mRNA in colonic mucosa were also significantly reduced by lycopene. IL-9 is known to induce proliferation of mast cells, and we found that lycopene feeding significantly reduced the number of mast cells in the colonic mucosa of FA mice.

CONCLUSION

Our results suggest that lycopene, a carotenoid present in many common foods on the market, may have the potential to induce colonic Tregs and suppress FA symptoms.

Innate lymphoid cells: The missing part of a puzzle in food allergy

Food allergy is an increasingly prevalent disease driven by uncontrolled type 2 immune response. Currently, knowledge about the underlying mechanisms that initiate and promote the immune response to dietary allergens is limited. Patients with food allergy are commonly sensitized through the skin in their early life, later on developing allergy symptoms within the gastrointestinal tract. Food allergy results from a dysregulated type 2 response to food allergens, characterized by enhanced levels of IgE, IL-4, IL-5, and IL-13 with infiltration of mast cells, eosinophils, and basophils. Recent studies raised a possible role for the involvement of innate lymphoid cells (ILCs) in driving food allergy. Unlike lymphocytes, ILCs lack They represent a group of lymphocytes that lack specific antigen receptors. ILCs contribute to immune responses not only by releasing cytokines and other mediators but also by responding to cytokines produced by activated cells in their local microenvironment. Due to their localization at barrier surfaces of the airways, gut, and skin, ILCs form a link between the innate and adaptive immunity. This review summarizes recent evidence on how skin and gastrointestinal mucosal immune system contribute to both homeostasis and the development of food allergy, as well as the involvement of ILCs toward inflammatory processes and regulatory mechanisms.

Crosstalk between the Producers and Immune Targets of IL-9

IL-9 has been reported to play dual roles in the pathogenesis of autoimmune disorders and cancers. The collaboration of IL-9 with microenvironmental factors including the broader cytokine milieu and other cellular components may provide important keys to explain its conflicting effects in chronic conditions. In this review, we summarize recent findings on the cellular sources of, and immunological responders to IL-9, in order to interpret the role of IL-9 in the regulation of immune responses. This knowledge will provide new perspectives to improve clinical benefits and limit adverse effects of IL-9 when treating pathologic conditions.

Exploring the Molecular Mechanisms Underlying the Protective Effects of Microbial SCFAs on Intestinal Tolerance and Food Allergy

A body of evidence suggests that food allergy (FA) has increased in prevalence over the past few decades. Novel findings support the hypothesis that some commensal bacteria and particularly microbial metabolites might contribute to development of oral tolerance and prevention from FA. Recently, beneficial effects of short-chain fatty acids (SCFAs), the main class of gut microbiota-derived metabolites, on FA have been proposed. The intestinal SCFAs are major end products during bacterial fermentation of complex and non-digestible carbohydrates such as dietary fiber. The multifaceted mechanisms underlying beneficial effects of SCFAs on the mucosal immune system comprise the regulation of diverse cellular pathways in epithelial, dendritic, and T cells, as well as the impact on the immunometabolism and epigenetic status of regulatory lymphocytes. Of note, SCFAs are effective inhibitors of histone deacetylases (HDACs). As a consequence, SCFAs appear to be implicated in attenuation of intestinal inflammation and autoimmune diseases. In this review, we will discuss the recent development in this research area by highlighting the role of the individual SCFAs acetate, propionate, butyrate, and pentanoate in promoting the differentiation of regulatory T and B cells and their potential beneficial effects on the prevention of FA. In this context, targeted alterations in the gut microbiota in favor of SCFA producers or supplementation of medicinal food enriched in SCFAs could be a novel therapeutic concept for FA.

Siglec-8 antibody reduces eosinophils and mast cells in a transgenic mouse model of eosinophilic gastroenteritis

Aberrant accumulation and activation of eosinophils and potentially mast cells (MCs) contribute to the pathogenesis of eosinophilic gastrointestinal diseases (EGIDs), including eosinophilic esophagitis (EoE), gastritis (EG), and gastroenteritis (EGE). Current treatment options, such as diet restriction and corticosteroids, have limited efficacy and are often inappropriate for chronic use. One promising new approach is to deplete eosinophils and inhibit MCs with a monoclonal antibody (mAb) against sialic acid-binding immunoglobulin-like lectin 8 (Siglec-8), an inhibitory receptor selectively expressed on MCs and eosinophils. Here, we characterize MCs and eosinophils from human EG and EoE biopsies using flow cytometry and evaluate the effects of an anti-Siglec-8 mAb using a potentially novel Siglec-8-transgenic mouse model in which EG/EGE was induced by ovalbumin sensitization and intragastric challenge. MCs and eosinophils were significantly increased and activated in human EG and EoE biopsies compared with healthy controls. Similar observations were made in EG/EGE mice. In Siglec-8-transgenic mice, anti-Siglec-8 mAb administration significantly reduced eosinophils and MCs in the stomach, small intestine, and mesenteric lymph nodes and decreased levels of inflammatory mediators. In summary, these findings suggest a role for both MCs and eosinophils in EGID pathogenesis and support the evaluation of anti-Siglec-8 as a therapeutic approach that targets both eosinophils and MCs.

Elaeocarpusin Inhibits Mast Cell-Mediated Allergic Inflammation

Mast cells are major effector cells for allergic responses that act by releasing inflammatory mediators, such as histamine and pro-inflammatory cytokines. Accordingly, different strategies have been pursued to develop anti-allergic and anti-inflammatory candidates by regulating the function of mast cells. The purpose of this study was to determine the effectiveness of elaeocarpusin (EL) on mast cell-mediated allergic inflammation. We isolated EL from Elaeocarpus sylvestris L. (Elaeocarpaceae), which is known to possess anti-inflammatory properties. For this study, various sources of mast cells and mouse anaphylaxis models were used. EL suppressed the induction of markers for mast cell degranulation, such as histamine and β-hexosaminidase, by reducing intracellular calcium levels. Expression of pro-inflammatory cytokines, such as tumor necrosis factor-α and IL-4, was significantly decreased in activated mast cells by EL. This inhibitory effect was related to inhibition of the phosphorylation of Fyn, Lyn, Syk, and Akt, and the nuclear translocation of nuclear factor-κB. To confirm the effect of EL in vivo, immunoglobulin E-mediated passive cutaneous anaphylaxis (PCA) and ovalbumin-induced active systemic anaphylaxis (ASA) models were induced. EL reduced the PCA reaction in a dose dependent manner. In addition, EL attenuated ASA reactions such as hypothemia, histamine release, and IgE production. Our results suggest that EL is a potential therapeutic candidate for allergic inflammatory diseases that acts via the inhibition of mast cell degranulation and expression of proinflammatory cytokines.

The Initiation of Th2 Immunity Towards Food Allergens

In contrast with Th1 immune responses against pathogenic viruses and bacteria, the incipient events that generate Th2 responses remain less understood. One difficulty in the identification of universal operating principles stems from the diversity of entities against which cellular and molecular Th2 responses are produced. Such responses are launched against harmful macroscopic parasites and noxious substances, such as venoms, but also against largely innocuous allergens. This suggests that the established understanding about sense and recognition applied to Th1 responses may not be translatable to Th2 responses. This review will discuss processes and signals known to occur in Th2 responses, particularly in the context of food allergy. We propose that perturbations of homeostasis at barrier sites induced by external or internal subverters, which can activate or lower the threshold activation of the immune system, are the major requirement for allergic sensitization. Innate signals produced in the tissue under these conditions equip dendritic cells with a program that forms an adaptive Th2 response.

Regulation of Allergic Immune Responses by Microbial Metabolites

Emerging evidence demonstrates that the microbiota plays an essential role in shaping the development and function of host immune responses. A variety of environmental stimuli, including foods and commensals, are recognized by the host through the epithelium, acting as a physical barrier. Two allergic diseases, atopic dermatitis and food allergy, are closely linked to the microbiota, because inflammatory responses occur on the epidermal border. The microbiota generates metabolites such as short-chain fatty acids and poly-γ-glutamic acid (γPGA), which can modulate host immune responses. Here, we review how microbial metabolites can regulate allergic immune responses. Furthermore, we focus on the effect of γPGA on allergic T helper (Th) 2 responses and its therapeutic application.

Diospyros kaki calyx inhibits immediate-type hypersensitivity via the reduction of mast cell activation

CONTEXT

Diospyros kaki L. (Ebenaceae) fruit is widely distributed in Asia and is known to exert anti-inflammatory and antithrombotic effects.

OBJECTIVE

We evaluated the inhibitory effect of aqueous extract of D. kaki calyx (AEDKC) on mast cell-mediated immediate-type hypersensitivity and underlying mechanism of action.

MATERIALS AND METHODS

For in vivo, ovalbumin (OVA)-induced active systemic anaphylaxis (ASA) and immunoglobulin (Ig) E-mediated passive cutaneous anaphylaxis (PCA) models were used. In the ASA, AEDKC (1-100 mg/kg) was orally administered 3 times during 14 days. In the PCA, AEDKC was orally treated 1 h before the antigen challenge. The control drug dexamethasone was used to compare the effectiveness of AEDKC. For in vitro, IgE-stimulated RBL-2H3 cells and primary cultured peritoneal mast cells were used to determine the role of AEDKC (0.01-1 mg/mL).

RESULTS

Oral administration of AEDKC dose dependently suppressed rectal temperature decrease and increases in serum histamine, total IgE, OVA-specific IgE, and interleukin (IL)-4 in the ASA. In the PCA, AEDKC reduced Evans blue pigmentation. Compared to dexamethasone (10 mg/kg), AEDKC (100 mg/kg) showed similar inhibitory effects in vivo. AEDKC concentration dependently suppressed the release of histamine and β-hexosaminidase through the reduction of intracellular calcium in mast cells. In addition, AEDKC decreased the expression and secretion of tumour necrosis factor-α and IL-4 by the reduction of nuclear factor-κB. The inhibitory potential of AEDKC (1 mg/mL) was similar with dexamethasone (10 μM) in vitro.

CONCLUSIONS

We suggest that AEDKC may be a potential candidate for the treatment of mast cell-mediated allergic diseases.

Innate lymphoid cell-derived cytokines in autoimmune diseases

The most recently recognized types of immune cells, the innate lymphoid cells (ILCs), have been sub-divided according to respective distinct expression profiles of regulatory factors or/and cytokines. ILCs have also been shown to participate in a variety of beneficial immune responses, including participation in attack against pathogens and mediation of the pre-inflammatory and inflammatory responses through their production of pro-inflammatory cytokines. As such, while the ILCs exert protective effects they may also become detrimental upon dysregulation. Indeed, recent studies of the ILCs have revealed a strong association with the advent and pathogenesis of several common autoimmune diseases, including psoriasis, inflammatory bowel disease (IBD) and multiple sclerosis (MS). Though the ILCs belong to lineage negative cells that are distinctive from the Th cells, the profiles of secreted cytokines from the ILCs overlap with those of the corresponding Th subsets. Nevertheless, considering that the ILCs belong to the innate immune system and the Th cells belong to the adaptive immune system, it is expected that the ILCs should function at the early stage of diseases and the Th cells should exert predominant effects at the late stage of diseases. Therefore, it is intriguing to consider targeting of ILCs for therapy by targeting the corresponding cytokines at the early stage of diseases, with the late stage cytokine targeting mainly influencing the Th cells' function. Here, we review the knowledge to date on the roles of ILCs in various autoimmune diseases and discuss their potential as new therapeutic targets.

Beyond Hygiene: Commensal Microbiota and Allergic Diseases

Complex communities of microorganisms, termed commensal microbiota, inhabit mucosal surfaces and profoundly influence host physiology as well as occurrence of allergic diseases. Perturbing factors such as the mode of delivery, dietary fibers and antibiotics can influence allergic diseases by altering commensal microbiota in affected tissues as well as in intestine. Here, we review current findings on the relationship between commensal microbiota and allergic diseases, and discuss the underlying mechanisms that contribute to the regulation of allergic responses by commensal microbiota.