Group 2 Innate Lymphoid Cells Promote Development of T Follicular Helper Cells and Initiate Allergic Sensitization to Peanuts

IL-33 protects from recurrent C. difficile infection by restoration of humoral immunity

Clostridioides difficile infection (CDI) recurs in 1 of 5 patients. Monoclonal antibodies targeting the virulence factor TcdB reduce disease recurrence, suggesting that an inadequate anti-TcdB response to CDI leads to recurrence. In patients with CDI, we discovered that IL-33 measured at diagnosis predicts future recurrence, leading us to test the role of IL-33 signaling in the induction of humoral immunity during CDI. Using a mouse recurrence model, IL-33 was demonstrated to be integral for anti-TcdB antibody production. IL-33 acted via ST2+ ILC2 cells, facilitating germinal center T follicular helper (GC-Tfh) cell generation of antibodies. IL-33 protection from reinfection was antibody-dependent, as μMT KO mice and mice treated with anti-CD20 mAb were not protected. These findings demonstrate the critical role of IL-33 in generating humoral immunity to prevent recurrent CDI.

Atopic skin inflammation promotes systemic anaphylactic responses via IL-13 signaling in conventional dendritic cells

Cutaneous allergen sensitization (CAS) underlies atopic dermatitis (AD) and leads to various allergic symptoms, including food allergy and anaphylaxis. IL-13 expression by T follicular helper T (TFH) has been reported to be involved in generating high-affinity IgE antibodies and causing systemic anaphylaxis.1, 2 However, the mechanisms by which IL-13 triggers IgE-mediated allergic responses remain poorly defined. In the present study, we elucidate the role of IL-13 in the CAS-mediated mechanism by which high-affinity IgE antibodies are produced when the same allergen is introduced at a distal site in the secondary sensitization. The CAS model system using mice lacking the cell lineage-specific IL-13 receptor (IL-13R) demonstrated that dendritic cells (DCs), but not T or B cells, are critical in the high-affinity IgE-mediated anaphylactic response. The IL-13 signal in type 2 conventional DCs (cDC2s) enhanced the expression of MHC class II and CD301b, which was essential for the recall of type 2 responses, inducing the production of high-affinity IgE antibodies. Similar IL-13R-expressing DCs were identified in allergic rhinitis and food allergy patients with a history of AD. These findings strongly suggest the importance of DC-specific IL-13 signaling in CAS-induced allergic reactions associated with the atopic march, which is common in human AD patients.

T follicular helper cells in food allergy

T follicular helper (Tfh) cells help direct the production of antibodies by B cells. In addition to promoting antibody responses to vaccination and infection, Tfh cells have been found to mediate antibody production to food antigens. Work over the past decade has delineated the specific phenotypes of Tfh cells that induce antibodies to food while also clarifying the divergent Tfh cell requirement for different food-specific antibody isotypes. Furthermore, Tfh and antibody responses to food can occur at multiple barrier sites - namely, skin, airway, and gut. Depending on the context of food antigen exposure, the immune response to food at these sites can be protective, as in the case of tolerance or immunotherapy, or pathogenic, as in the case of allergy. This review will highlight recent advances in our understanding of how Tfh cells promote antibodies to food as well as future avenues for continued discovery.

IL-33 protects from recurrent C. difficile infection by restoration of humoral immunity

Clostridioides difficile infection (CDI) recurs in one of five patients. Monoclonal antibodies targeting the virulence factor TcdB reduce disease recurrence, suggesting that an inadequate anti-TcdB response to CDI leads to recurrence. In patients with CDI, we discovered that IL-33 measured at diagnosis predicts future recurrence, leading us to test the role of IL-33 signaling in the induction of humoral immunity during CDI. Using a mouse recurrence model, IL-33 was demonstrated to be integral for anti-TcdB antibody production. IL-33 acted via ST2+ ILC2 cells, facilitating germinal center T follicular helper (GC-Tfh) cell generation of antibodies. IL-33 protection from reinfection was antibody-dependent, as μMT KO mice and mice treated with anti-CD20 mAb were not protected. These findings demonstrate the critical role of IL-33 in generating humoral immunity to prevent recurrent CDI.

Innate lymphoid cells in immunoglobulin E-mediated food allergy

PURPOSE OF REVIEW

Recognition of the importance of innate lymphoid cells (ILCs) in the immune mechanisms of food allergy has grown in recent years. This review summarizes recent findings of ILCs in immunoglobulin E (IgE)-mediated food allergy. New research on ILCs in the context of the microbiome and other atopic diseases are also considered with respect to how they can inform understanding of the role of ILCs in food allergy.

RECENT FINDINGS

ILCs can mediate allergic and tolerogenic responses through multiple pathways. A novel subset of interleukin (IL)-10 producing ILC2s are associated with tolerance following immunotherapy to grass pollen, house dust mite allergy and lipid transfer protein allergy. ILC2s can drive food allergen-specific T cell responses in an antigen-specific manner. A memory subset of ILC2s has been identified through studies of other atopic diseases and is associated with effectiveness of response to therapy.

SUMMARY

The role of ILCs in food allergy and oral tolerance is relatively understudied compared to other diseases. ILCs can modulate immune responses through several mechanisms, and it is likely that these are of importance in the context of food allergy. Better understanding of theses pathways may help to answer fundamental questions regarding the development of food allergy and lead to novel therapeutic targets and treatment.

The role of Interleukin-21 (IL-21) in allergic disorders: Biological insights and regulatory mechanisms

In recent decades, allergic diseases subsequent from an IgE-mediated response to specific allergens have become a progressively public chronic disease worldwide. They have shaped an important medical and socio-economic burden. A significant proportion of allergic disorders are branded via a form 2 immune response relating Th2 cells, type 2 natural lymphoid cells, mast cells and eosinophils. Interleukin-21 (IL-21) is a participant of the type-I cytokine family manufactured through numerous subsets of stimulated CD4+ T cells and uses controlling properties on a diversity of immune cells. Increasingly, experimental sign suggests a character for IL-21 in the pathogenesis of numerous allergic disorders. The purpose of this review is to discuss the biological properties of IL-21 and to summaries current developments in its role in the regulation of allergic disorders.

Regulatory ILC2-Role of IL-10 Producing ILC2 in Asthma

Over the past two decades, a growing body of evidence observations have shown group two innate lymphoid cells (ILC2) to be critical drivers of Type 2 (T2) inflammatory responses associated with allergic inflammatory conditions such as asthma. ILC2 releases copious amounts of pro-inflammatory T2 cytokines-interleukin (IL)-4, IL-5, IL-9, and IL-13. This review provides a comprehensive overview of the newly discovered regulatory subtype of ILC2 described in murine and human mucosal tissue and blood. These KLRG1+ILC2 have the capacity to produce the anti-inflammatory cytokine IL-10. Papers compiled in this review were based on queries of PubMed and Google Scholar for articles published from 2000 to 2023 using keywords "IL-10" and "ILC2". Studies with topical relevance to IL-10 production by ILC2 were included. ILC2 responds to microenvironmental cues, including retinoic acid (RA), IL-2, IL-4, IL-10, and IL-33, as well as neuropeptide mediators such as neuromedin-U (NMU), prompting a shift towards IL-10 and away from T2 cytokine production. In contrast, TGF-β attenuates IL-10 production by ILC2. Immune regulation provided by IL-10+ILC2s holds potential significance for the management of T2 inflammatory conditions. The observation of context-specific cues that alter the phenotype of ILC warrants examining characteristics of ILC subsets to determine the extent of plasticity or whether the current classification of ILCs requires refinement.

CD45 alleviates airway inflammation and lung fibrosis by limiting expansion and activation of ILC2s

Group 2 innate lymphoid cells (ILC2s) are critical for the immune response against parasite infection and tissue homeostasis and involved in the pathogenesis of allergy and inflammatory diseases. Although multiple molecules positively regulating ILC2 development and activation have been extensively investigated, the factors limiting their population size and response remain poorly studied. Here, we found that CD45, a membrane-bound tyrosine phosphatase essential for T cell development, negatively regulated ILC2s in a cell-intrinsic manner. ILC2s in CD45-deficient mice exhibited enhanced proliferation and maturation in the bone marrow and hyperactivated phenotypes in the lung with high glycolytic capacity. Furthermore, CD45 signaling suppressed the type 2 inflammatory response by lung ILC2s and alleviated airway inflammation and pulmonary fibrosis. Finally, the interaction with galectin-9 influenced CD45 signaling in ILC2s. These results demonstrate that CD45 is a cell-intrinsic negative regulator of ILC2s and prevents lung inflammation and fibrosis via ILC2s.

An update on recent developments and highlights in food allergy

While both the incidence and general awareness of food allergies is increasing, the variety and clinical availability of therapeutics remain limited. Therefore, investigations into the potential factors contributing to the development of food allergy (FA) and the mechanisms of natural tolerance or induced desensitization are required. In addition, a detailed understanding of the pathophysiology of food allergies is needed to generate compelling, enduring, and safe treatment options. New findings regarding the contribution of barrier function, the effect of emollient interventions, mechanisms of allergen recognition, and the contributions of specific immune cell subsets through rodent models and human clinical studies provide novel insights. With the first approved treatment for peanut allergy, the clinical management of FA is evolving toward less intensive, alternative approaches involving fixed doses, lower maintenance dose targets, coadministration of biologicals, adjuvants, and tolerance-inducing formulations. The ultimate goal is to improve immunotherapy and develop precision-based medicine via risk phenotyping allowing optimal treatment for each food-allergic patient.

Androgen receptor signaling protects male mice from the development of immune response to peanut

OBJECTIVES

Peanut (PN) allergy is a major public health concern. Recent research has brought clarity about how individuals become sensitized to PN allergen with routes known through the skin, as well as the airway. Still unclear, however, is the role of sex hormones on the development of allergic immune responses to PN. This study examines the role of androgen receptor (AR) signaling in regulating PN-specific immune responses.

METHODS

We utilized a 4-week inhalation mouse model of PN allergy that is known to drive the production of PN-specific antibodies and elicit systemic anaphylaxis following PN challenge. Wildtype (WT) male, female, and androgen receptor-deficient testicular feminization mutant (ARTfm) male mice were examined using this model to document sex differences in PN allergy. To determine if sex differences also existed in the cellular immune response, this study utilized a 3-day inhalation mouse model of PN to examine the response of group 2 innate lymphoid cells (ILC2s). WT male and female mice were examined using this model to document sex differences in ILC2 response within the lungs.

RESULTS

AR use is critical in regulating PN-specific antibody levels. We found that ARTfm males have a higher antibody response and significantly worse anaphylactic response following PN challenge relative to WT males. WT males also exhibit a less severe anaphylactic response compared to ARTfm male and female mice. Lastly, we discovered that lung ILC2s from female mice respond more robustly to PN compared to ILC2s within WT male mice.

CONCLUSIONS

Taken together, this study suggests that male sex hormones, namely androgens, negatively regulate allergic immune responses to PN.

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.

Understanding sex differences in the allergic immune response to food

Food allergies are of great public health concern due to their rising prevalence. Our understanding of how the immune system reacts to food remains incomplete. Allergic responses vary between individuals with food allergies. This variability could be caused by genetic, environmental, hormonal, or metabolic factors that impact immune responses mounted against allergens found in foods. Peanut (PN) allergy is one of the most severe and persistent of food allergies, warranting examination into how sensitization occurs to drive IgE-mediated allergic reactions. In recent years, much has been learned about the mechanisms behind the initiation of IgE-mediated food allergies, but additional questions remain. One unresolved issue is whether sex hormones impact the development of food allergies. Sex differences are known to exist in other allergic diseases, so this poses the question about whether the same phenomenon is occurring in food allergies. Studies show that females exhibit a higher prevalence of atopic conditions, such as allergic asthma and eczema, relative to males. Discovering such sex differences in allergic diseases provide a basis for investigating the mechanisms of how hormones influence the development of IgE-mediated reactions to foods. Analysis of existing food allergy demographics found that they occur more frequently in male children and adult females, which is comparable to allergic asthma. This paper reviews existing allergic mechanisms, sensitization routes, as well as how sex hormones may play a role in how the immune system reacts to common food allergens such as PN.

Blocking the inhibitory receptor programmed cell death 1 prevents allergic immune response and anaphylaxis in mice

BACKGROUND

Food allergy and acute anaphylaxis can be life-threatening. While T follicular helper (Tfh) cells play a pivotal role in the allergic immune responses, the immunologic mechanisms that regulate the production of antibodies (Abs) that mediate anaphylaxis are not fully understood.

OBJECTIVE

The aim of this study was to investigate the role of the inhibitory receptor programmed cell death protein 1 (PD-1), which is highly expressed on Tfh cells, in allergic immune responses using an animal model of peanut allergy and anaphylaxis.

METHODS

Naive wild-type mice were exposed to peanut flour intranasally and then challenged with peanut extract to induce systemic anaphylaxis. The roles of PD-1 were examined by blocking Abs and using gene-deficient animals. A hapten model and passive cutaneous anaphylaxis were used to characterize allergen-specific Abs.

RESULTS

Treatment with anti-PD-1 enhanced development of Tfh cells and germinal center B cells in mice exposed to peanut flour. Nonetheless, anti-PD-1 or its ligand fully protected mice from developing anaphylaxis. Anti-PD-1 treatment or genetic deficiency of PD-1 in CD4⁺ T cells inhibited production of peanut-specific IgE and increased the levels of IgG. The passive cutaneous anaphylaxis showed that peanut-specific Abs generated in anti-PD-1-treated animals prevented, rather than provoked, anaphylaxis when transferred to naive animals. Anti-PD-1 promoted production of Abs with low affinity for an antigen in the hapten model.

CONCLUSION

Blockade of the pathway between PD-1 and its ligand is protective against allergic immune responses. The direct interaction between Tfh cells and B cells may play a pivotal role in controlling Ab quality and clinical manifestation of allergic diseases.

Group 2 innate lymphoid cells promote TNBC lung metastasis via the IL-13-MDSC axis in a murine tumor model

Group 2 innate lymphoid cells (ILC2s) are reportedly associated with the progression of many tumors. However, the role of ILC2s in triple-negative breast cancer (TNBC) lung metastasis remains unclear. In this study, we found that ILC2s may be a key element in the process of TNBC lung metastasis since the adoptive transfer of pulmonary ILC2s increased the numbers of metastatic lung nodules and reduced the survival of tumor-bearing mice. ILC2-promoted 4 T1 lung metastasis appears to be related to ILC2-derived IL-13. An expansion of IL-13-producing ILC2s and an elevated expression of IL-13 mRNA in pulmonary ILC2s were determined in tumor-bearing mice, in parallel with an increase in the levels of local IL-13 by ILC2 transfer. The neutralization of IL-13 reduced the increased pulmonary metastatic nodules and improved the decreased survival rate caused by ILC2-adoptive transfer. Interestingly, adoptive transfer of ILC2s elevated IL-13Ra1 expression in myeloid-derived suppressor cells (MDSCs). Treatment of ILC2-transferred tumor-bearing mice with anti-IL-13 antibodies significantly diminished the number of pulmonary MDSCs and inhibited MDSC activation. Moreover, when pulmonary MDSCs were cocultured with ILC2s in the presence of an anti-IL-13 mAb, the number and activation of MDSCs were reduced. Depletion of MDSCs may promote the proliferation of CD4+ T cells and CD8+ T cells, but reduce the expansion of regulatory T cells (Tregs) in the lungs of ILC2-transferred tumor-bearing mice. Our results suggest that pulmonary ILC2s may promote TNBC lung metastasis via the ILC2-derived IL-13-activated MDSC pathway.

The airway as a route of sensitization to peanut: An update to the dual allergen exposure hypothesis

Food allergies have increased at an alarming rate over the past 2 decades, indicating that environmental factors are driving disease progression. It has been postulated that sensitization to foods, in particular, peanut, occurs through impaired skin. Peanut allergens have been quantified in household dust and may be the culprit source. Indeed, T_H2 cell-skewing innate cytokines can be driven by application of food antigens on both intact and impaired skin of mice, resulting in antigen-specific IgE production and anaphylaxis following allergen exposure. However, allergy induction through the skin can be prevented by induction of oral tolerance before skin exposure. These observations led to the dual allergen exposure hypothesis, according to which oral exposure to food antigens leads to tolerance and antigen exposure on impaired skin leads to allergy. Here, we propose the airway as an alternative route of sensitization in the dual allergen exposure hypothesis that leads to food allergy. Specifically, we will provide evidence from mouse models and human cell-based studies that together implicate the airway as a plausible route of sensitization.

Roles of innate lymphoid cells (ILCs) in allergic diseases: The 10-year anniversary for ILC2s

In the 12 years since the discovery of innate lymphoid cells (ILCs), our knowledge of their immunobiology has expanded rapidly. Group 2 ILCs (ILC2s) respond rapidly to allergen exposure and environmental insults in mucosal organs, producing type 2 cytokines. Early studies showed that epithelium-derived cytokines activate ILC2s, resulting in eosinophilia, mucus hypersecretion, and remodeling of mucosal tissues. We now know that ILC2s are regulated by other cytokines, eicosanoids, and neuropeptides as well, and interact with both immune and stromal cells. Furthermore, ILC2s exhibit plasticity by adjusting their functions depending on their tissue environment and may consist of several heterogeneous subpopulations. Clinical studies show that ILC2s are involved in asthma, allergic rhinitis, chronic rhinosinusitis, food allergy, and eosinophilic esophagitis. However, much remains unknown about the immunologic mechanisms involved. Beneficial functions of ILCs in maintenance or restoration of tissue well-being and human health also need to be clarified. As our understanding of the crucial functions ILCs play in both homeostasis and disease pathology expands, we are poised to make tremendous strides in diagnostic and therapeutic options for patients with allergic diseases. This review summarizes discoveries in immunobiology of ILCs and their roles in allergic diseases in the past 5 years, discusses controversies and gaps in our knowledge, and suggests future research directions.

Food Allergies: An Example of Translational Research

Food allergies have been rising in prevalence since the 1990s, imposing substantial physical, psychosocial, and economic burdens on affected patients and their families. Until recently, the only therapy for food allergy was strict avoidance of the allergenic food. Recent advances in translational studies, however, have led to insights into allergic sensitization and tolerance. This article provides an overview of cutting-edge research into food allergy and immune tolerance mechanisms utilizing mouse models, human studies, and systems biology approaches. This research is being translated and implemented in the clinical setting to improve diagnosis and reduce food allergy's public health burden.

Allergic sensitization to peanuts is enhanced in mice fed a high-fat diet

The incidence of peanut (PN) allergy is on the rise. As peanut allergy rates have continued to climb over the past few decades, obesity rates have increased to record highs, suggesting a link between obesity and the development of peanut allergy. While progress has been made, much remains to be learned about the mechanisms driving the development of allergic immune responses to peanut. Remaining unclear is whether consuming a Western diet, a diet characterized by overeating foods rich in saturated fat, salt, and refined sugars, supports the development of PN allergy. To address this, we fed mice a high fat diet to induce obesity. Once diet-induced obesity was established, mice were exposed to PN flour via the airways using our 4-week inhalation model. Mice were subsequently challenged with PN extract to induce anaphylaxis. Mice fed a high-fat diet developed significantly higher titers of PN-specific IgE, as well as stronger anaphylactic responses, when compared to their low-fat diet fed counterparts. These results suggest that obesity linked to eating a high-fat diet promotes the development of allergic immune responses to PN in mice. Such knowledge is critical to advance our growing understanding of the immunology of PN allergy.