Targeting type 2 immunity and the future of food allergy treatment

Immune tolerance to foreign antigens in the intestine: mechanisms mediated by CD4＋ T cells

The immune system encounters a diverse array of antigens, both self and foreign, necessitating mechanisms to maintain tolerance and prevent harmful inflammatory responses. CD4＋ T cells, crucial in orchestrating immune responses, play a critical role in mediating tolerance to both self and foreign antigens. While the mechanisms of CD4＋ T cell-mediated tolerance to self-antigens are well-documented, the understanding of tolerance to foreign antigens, including those from commensal microbes and food, remains incomplete. This review discusses recent progress in the mechanisms underlying immune tolerance to foreign antigens, with a focus on the role of CD4＋ T cells. We explore how inflammatory and tolerogenic CD4＋ T cell subsets are developed and maintained. Moreover, we delve into the complexities of immune responses to commensal microbes and food antigens by reviewing recent findings, highlighting the immunological contexts that shape immune tolerance. Understanding these mechanisms enhances our comprehension of how immune tolerance is established and sustained, providing insights into potential therapeutic approaches for managing chronic inflammatory diseases resulting from a loss of immune tolerance to foreign antigens. [BMB Reports 2025; 58(4): 158-168].

The Etiology of IgE-Mediated Food Allergy: Potential Therapeutics and Challenges

Immunoglobulin E (IgE)-mediated food allergy has been dramatically increasing in incidence over the last few decades. The combinations of both genetic and environmental factors that affect the microbiome and immune system have demonstrated significant roles in its pathogenesis. The morbidity, and at times mortality, that occurs as the result of this specific, reproducible, but impaired immune response is due to the nature of the shift from a regulatory T (Treg) cellular response to a T helper 2 (Th2) cellular response. This imbalance caused by food allergens results in an interleukin (IL)-4 and IL-13 dominant environment that drives B cell activation and differentiation into IgE-producing plasma cells. The resulting symptoms can range from mild to more severe anaphylaxis, and even death. Current therapeutic strategies involve avoidance and broad symptom management upon accidental exposure; however, no definitive cure exists. This narrative review highlights how the elucidation of the pathogenesis of IgE-mediated food allergy resulted in the development of therapeutics that are more specific to these individual receptors and molecules which have been relatively successful in mitigating this potentially life-threatening allergic response. However, potential adverse effects and re-sensitization following the conclusion of treatment has urged the need for improved therapeutic methods. Therefore, given the understanding of their mechanism of action and the overlap with the mechanism of IgE-mediated food allergies, probiotics and small molecule natural compounds may provide novel therapeutic and preventative strategies. This is compelling, as they have demonstrated success in clinical trials and may provide hope to improve quality of life in allergy patients.

Egg allergen-specific T-cell and cytokine responses in healthy and egg-allergic children naturally tolerating baked egg

BACKGROUND

Type 1 regulatory T (Tr1) cells are critical players in maintaining peripheral tolerance, by producing high IL-10 levels in association with inducible T-cell co-stimulator (ICOS) expression. Whether these cells play a role in naturally acquired baked egg tolerance is unknown.

OBJECTIVES

Evaluate frequencies of egg-responsive Tr1 and Th2 cells in egg-allergic children that naturally acquired baked egg tolerance (BET) versus non-egg-allergic (NEA) children.

METHODS

Peripheral blood mononuclear cells from 70 natural BET and 15 NEA children were stimulated for 7 days with ovalbumin and ovomucoid. By flowcytometry, egg-responsive Tr1 cells were identified by co-expression of CD49b and LAG3, and Th2 cells by expression of CD49b but absence of LAG3. Seven-day cultured supernatant was analyzed for Th1, Th2, Tr1, and Th17 cytokines by MSD.

RESULTS

Natural BET children had a higher percentage of egg-responsive Th2 cells vs. NEA children (6.75% vs. 10.35%, p = .006). No significant difference was found in frequencies of egg-responsive Tr1 cells between NEA and natural BET children (11.40% vs. 12.55%, p = .42), although Tr1-related IL-10 and IL-21 production was higher in BET children. Interestingly, egg-responsive Tr1 cells from NEA children expressed higher ICOS levels vs. natural BET children (97.90 vs. 88.20, p < .0001). Supernatant from natural BET children showed elevated levels of Th2 cytokines IL-5, IL-9 and IL-13 and Th17 cytokine IL-17A.

CONCLUSION

Natural BET children maintain increased egg-specific Th2 responses, along with comparable proportions of egg-responsive Tr1 cells exhibiting higher IL-10 but lower ICOS expression in comparison with NEA children.

IgE versus IgG and IgA: Differential roles of allergen-specific antibodies in sensitization, tolerization, and treatment of allergies

The prevalence of asthma, rhinitis, and food allergies has increased dramatically over the last few decades. This increase originally started in western countries, but is now also evident in many other regions of the world. Given the fact that the increase is so quick, the noted increase cannot be linked to a genetic effect, and many environmental factors have been identified that are associated with increased or reduced prevalence of allergies, like changing dietary habits, increased urbanization, pollution, exposure to microorganisms and LPS, and the farming environment and raw milk consumption. Although the key role of allergen-specific IgE in allergies is well known, the role of allergen-specific IgG and IgA antibodies is less well defined. This review will provide an overview of the functions of allergen-specific IgE in allergy, the role of allergen-specific antibodies (IgG (4) and IgA) in allergen immunotherapy (AIT), the possibility to use allergen-specific antibodies for treatment of ongoing allergies, and the potential role of allergen-specific antibodies in tolerance induction to allergens in a preventive setting. In the last, more speculative, section we will present novel hypotheses on the potential role of allergen-specific non-IgE antibodies in allergies by directing antigen presentation, Th2 development, and innate immune training.

Structural characterization and mast cell stabilizing activity of Red-edge tea polysaccharide

The potential anti-allergic properties of tea have been demonstrated in studies supporting theanine and catechin. However, research on tea polysaccharides' anti-allergic properties has been limited. In this study, we extracted red-edge tea crude polysaccharide (RETPS) and evaluated its anti-allergic activity using the mast cell, passive cutaneous anaphylaxis, and passive systemic anaphylaxis models. We purified RETPS using the DEAE-52 cellulose column, analyzed its composition and structural characteristics, and compared the anti-allergic properties of different polysaccharide fractions. The purified components RETPS-3 and RETPS-4 displayed higher galacturonic acid content and lower molecular weight (106.61 kDa and 53.95 kDa, respectively) compared to RETPS (310.54 kDa). In addition, RETPS-3 and RETPS-4 demonstrated superior anti-allergic activity than RETPS in mice's passive cutaneous and systemic allergic reactions. Our findings provide evidence of the anti-allergic potential of tea polysaccharides and offer a theoretical foundation for developing tea polysaccharides as a functional anti-allergic food product.

The Role of Food Allergy in Atopic Dermatitis

Atopic dermatitis (AD) and food allergies are 2 atopic conditions that tend to develop early in life. Their interrelationship has been a topic of controversy and many studies. The presence of atopic dermatitis in infancy and early childhood, particularly if severe, is a risk factor for the development of immunoglobulin E (IgE) -mediated food allergies. While it is common for children with AD to demonstrate extensive sensitization to foods, serum IgE testing is not always indicative of clinical allergy.

Decoding food reactions: a detailed exploration of food allergies vs. intolerances and sensitivities

The food matrix is a complex system encompassing all constituent elements in food production. It influences the digestibility of these elements through direct interactions and affects the digestive environment. Furthermore, the gastrointestinal system possesses precise mechanisms that efficiently process dietary components into essential nutrients, effectively preventing the onset of abnormal immune responses or dysfunctional host reactions in most instances. However, the incidence of adverse food reactions is constantly increasing, and evidence indicates that this process is environmental. Adverse reactions can be categorized as toxic or nontoxic. Toxic reactions are dose-dependent and can result from natural compounds, processing-induced substances, or contaminants. Nontoxic reactions like food intolerance and hypersensitivity depend on individual susceptibility and evoke specific pathological and physiological responses. This review aims to elucidate the mechanisms underlying the occurrence of immune- (food allergies and sensitivities) and non-immune-mediated (food intolerance) reactions, emphasizing the fundamental distinctions between these two categories. Enhanced comprehension and distinction of these mechanisms will significantly contribute to advancing preventive and therapeutic approaches and establishing guidelines for food labeling concerning immune-mediated reactions.

Maintenance of caecal homeostasis by diverse adaptive immune cells in the rhesus macaque

Objectives

The caecum bridges the small and large intestine and plays a front-line role in discriminating gastrointestinal antigens. Although dysregulated in acute and chronic conditions, the tissue is often overlooked immunologically.

Methods

To address this issue, we applied single-cell transcriptomic-V(D)J sequencing to FACS-isolated CD45+ caecal patch/lamina propria leukocytes from a healthy (5-year-old) female rhesus macaque ex vivo and coupled these data to VDJ deep sequencing reads from haematopoietic tissues.

Results

We found caecal NK cells and ILC3s to co-exist with a spectrum of effector T cells partially derived from SOX4 + recent thymic emigrants. Tolerogenic Vγ8Vδ1-T cells, plastic CD4+ T helper cells and GZMK + EOMES + and TMIGD2 + tissue-resident memory CD8+ T cells were present and differed metabolically. An IL13 + GATA3 + Th2 subset expressing eicosanoid pathway enzymes was accompanied by IL1RL1 + GATA3 + regulatory T cells and a minor proportion of IgE+ plasma cells (PCs), illustrating tightly regulated type 2 immunity devoid of ILC2s. In terms of B lymphocyte lineages, caecal patch antigen-presenting memory B cells sat alongside germinal centre cells undergoing somatic hypermutation and differentiation into IGF1 + PCs. Prototypic gene expression signatures decreased across PC clusters, and notably, expanded IgA clonotypes could be traced in VDJ deep sequencing reads from additional compartments, including the bone marrow, supporting that these cells contribute a steady stream of systemic antibodies.

Conclusions

The data advance our understanding of caecal immunological function, revealing processes involved in barrier maintenance and molecular networks relevant to disease.

Current state and advances in desensitization for peanut allergy in pediatric age

Peanut allergy affects about 1%-3% of the pediatric population in the world, with an important increase in the last decades. Nowadays, international guidelines recommend the early introduction of peanuts in the infant diet, with poor information about the quantity and the frequency of the intake. Allergen immunotherapy may represent the only therapeutic strategy able to modify the natural history of peanut allergy. In particular, oral immunotherapy showed the most promising results in terms of efficacy, but with significant rates of adverse reactions, mostly gastrointestinal. In 2020, the Food and Drug Administration and the European Medicines Agency approved Palforzia®, an oral drug for patients aged 4-17 years. Several studies are ongoing to improve the tolerability of oral immunotherapy and standardize the desensitization protocols. Sublingual immunotherapy permits to offer much lower doses than oral immunotherapy, but fewer adverse events are shown. Subcutaneous immunotherapy is associated with the greatest systemic adverse effects. Epicutaneous immunotherapy, for which Viaskin® patch was approved, has the highest safety profile. Innovative studies are evaluating the use of biological drugs, such as omalizumab or dupilumab, and probiotics, such as Lactobacillus rhamnosus, in monotherapy or associated with oral immunotherapy. Therapy for peanut allergy is constantly evolving, and new perspectives are ongoing to develop.

The B Cell Response and Formation of Allergenic and Anti-Allergenic Antibodies in Food Allergy

Food allergies are a growing public health concern worldwide, especially in children and young adults. Allergen-specific IgE plays a central role in the pathogenesis of food allergies, but their titers poorly correlate with allergy development. Host immune systems yield allergen-specific immunoglobulin (Ig)A, IgE and IgG subclasses with low or high affinities and differential Fc N-glycosylation patterns that can affect the allergic reaction to food in multiple ways. High-affinity IgE is required to induce strong mast cell activation eventually leading to allergic anaphylaxis, while low-affinity IgE can even inhibit the development of clinically relevant allergic symptoms. IgA and IgG antibodies can inhibit IgE-mediated mast cell activation through various mechanisms, thereby protecting IgE-positive individuals from allergy development. The production of IgE and IgG with differential allergenic potential seems to be affected by the signaling strength of individual B cell receptors, and by cytokines from T cells. This review provides an overview of the diversity of the B cell response and the diverse roles of antibodies in food allergy.