Basophils and mast cells are crucial for reactions due to epicutaneous sensitization to ovalbumin

The potential of orally exposed risk factors and constituents aggravating food allergy: Possible mechanism and target cells

Food allergy is a significant concern for the health of humans worldwide. In addition to dietary exposure of food allergens, genetic and environmental factors also play an important role in the development of food allergy. However, only the tip of the iceberg of risk factors in food allergy has been identified. The importance of food allergy caused by orally exposed risk factors and constituents, including veterinary drugs, pesticides, processed foods/derivatives, nanoparticles, microplastics, pathogens, toxins, food additives, dietary intake of salt/sugar/total fat, vitamin D, and therapeutic drugs, are highlighted and discussed in this review. Moreover, the epithelial barrier hypothesis, which is closely associated with the occurrence of food allergy, is also introduced. Additionally, several orally exposed risk factors and constituents that have been reported to disrupt the epithelial barrier are elucidated. Finally, the possible mechanisms and key immune cells of orally exposed risk factors and constituents in aggravating food allergy are overviewed. Further work should be conducted to define the specific mechanism by which these risk factors and constituents are driving food allergy, which will be of central importance to the targeted therapy of food allergy.

Animal Models of IgE Anaphylaxis

Allergies and atopy have emerged as significant public health concerns, with a progressively increasing incidence over the last two decades. Anaphylaxis is the most severe form of allergic reactions, characterized by a rapid onset and potentially fatal outcome, even in healthy individuals. Due to the unpredictable nature and potential lethality of anaphylaxis and the wide range of allergens involved, clinical studies in human patients have proven to be challenging. Diagnosis is further complicated by the lack of reliable laboratory biomarkers to confirm clinical suspicion. Thus, animal models have been developed to replicate human anaphylaxis and explore its pathophysiology. Whereas results obtained from animal models may not always be directly translatable to humans, they serve as a foundation for understanding the underlying mechanisms. Animal models are an essential tool for investigating new biomarkers that could be incorporated into the allergy workup for patients, as well as for the development of novel treatments. Two primary pathways have been described in animals and humans: classic, predominantly involving IgE and histamine, and alternative, reliant on IgG and the platelet-activating factor. This review will focus essentially on the former and aims to describe the most utilized IgE-mediated anaphylaxis animal models, including their respective advantages and limitations.

Topical Administration of a Novel Acetylated Tetrapeptide Suppresses Vascular Permeability and Immune Responses and Alleviates Atopic Dermatitis in a Murine Model

Although the pathogenesis of atopic dermatitis (AD) remains to be fully deciphered, skin barrier abnormality and immune dysregulation are known to be involved. Recently, the vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) system has also been implicated in the pathogenesis of this multifactorial chronic inflammatory skin disorder. Previously, we showed that a novel tetrapeptide, N-acetyl-Arg-Leu-Tyr-Glu (Ac-RLYE), inhibits angiogenesis and vascular permeability effectively by selectively antagonizing VEGFR-2. The current study aimed to investigate the pharmacological effect of Ac-RLYE on AD in vitro and in vivo. The in vitro experiments demonstrated that Ac-RLYE inhibited VEGF-induced vascular permeability in endothelial cells. Moreover, in an in vivo animal model of AD, Ac-RLYE relieved AD-like symptoms such as ear thickness and dermatitis severity scores and infiltration of immune cells, including mast cells and eosinophils. Ac-RLYE inhibited IgE secretion, restored the skin barrier protein filaggrin level, and markedly downregulated gene expression of AD-related Th1, Th2, and Th17 cytokines. Collectively, these findings suggest that Ac-RLYE would be useful for the treatment of AD and associated inflammatory skin disorders.

Dendritic cell immunoreceptor drives atopic dermatitis by modulating oxidized CaMKII-involved mast cell activation

Allergens have been identified as potential triggers in patients with atopic dermatitis (AD). AD patients are highly sensitive to cockroach allergen. The underlying mechanism, however, remains undetermined. Here, we established a cockroach allergen-induced AD-like mouse model and demonstrated that repeated exposure to cockroach allergen led to aggravated mouse skin inflammation, characterized by increased type 2 immunity, type 2 innate lymphoid cells (ILC2s), and mast cells. Increased skin mast cells were also observed in AD patients. AD mice with mast cell-deficient mice (kitW-sh/W-sh) showed diminished skin inflammation, suggesting that mast cells are required in allergen-induced skin inflammation. Furthermore, dendritic cell immuno-receptor (DCIR) is up-regulated in skin mast cells of AD patients and mediates allergen binding and uptake. DCIR-/- mice or reconstituted kitW-sh/W-sh mice with DCIR-/- mast cells showed a significant reduction in AD-like inflammation. Both in vitro and in vivo analyses demonstrated that DCIR-/- mast cells had reduced IgE-mediated mast cell activation and passive cutaneous anaphylaxis. Mechanistically, DCIR regulates allergen-induced IgE-mediated mast cell ROS generation and oxidation of calmodulin kinase II (ox-CaMKII). ROS-resistant CaMKII (MM-VVδ) prevents allergen-induced mast cell activation and inflammatory mediator release. Our study reveals a previously unrecognized DCIR-ROS-CaMKII axis that controls allergen-induced mast cell activation and AD-like inflammation.

Epicutaneously sensitized food-induced anaphylaxis is ameliorated with "oral tolerance" to antigen

Food allergy is an antigen-specific immunological adverse reaction after exposure to a given food. Multiple clinical studies showed that oral immunotherapy (OIT) is effective for the prevention and treatment for food allergy that is developed in infants and children. However, the effectiveness of OIT for epicutaneously sensitized food allergy remains unclear. Previously, we established a mouse model of epicutaneous-sensitized food allergy. In this model, systemic allergic reaction including intestinal and skin symptoms, such as anaphylaxis, was observed. We treated this model with OIT in two ways (OIT before sensitization or OIT during the sensitization phase) and evaluated the preventive effect of both methods. OIT before sensitization significantly ameliorated mast cell degranulation in sensitized skin, but there was no decrease in rectal temperatures or in mast cell degranulation in the jejunum. However, OIT administered during the sensitization phase significantly ameliorated the decrease in rectal temperature and mast cell degranulation in the skin and jejunum. OIT before sensitization increased the regulatory T cells in mesenteric lymph node (MLN), but not in the spleen, and it reduced antigen-specific IgG, but not IgE, production compared with the non-OIT control. However, OIT during sensitization caused a greater increase in regulatory T cells in both the MLN and spleen and reduced antigen-specific IgE and IgG generation compared with the non-OIT control group. Thus, OIT during the sensitization phase was effective for the prevention of epicutaneous-sensitized food allergy.

Recent developments in understanding the mechanisms of food allergy

PURPOSE OF REVIEW

The prevalence of food allergy is rising globally. This review will discuss recent discoveries regarding the immunologic mechanisms that drive the initial sensitization and allergic response to food antigens, which may inform prevention and treatment strategies.

RECENT FINDINGS

Tolerance to food antigens is antigen-specific and promoted by oral exposure early in life and maternal transfer of immune complexes via breast milk. IgG can inhibit both the initiation and effector phases of allergic responses to food antigens in mice, and high levels of food-specific IgG4 are associated with acquisition of tolerance in humans. Disruption of the skin barrier provides a route for food sensitization through the actions of mast cells, type 2 innate lymphoid cells, and IL-33 signaling. Regulatory T cells (Tregs) promote acquisition of oral tolerance, although defects in circulating allergen-specific Tregs are not evident in children with established food allergy. Certain microbes can offer protection against the development of IgE and food allergic responses, while dysbiosis increases susceptibility to food allergy.

SUMMARY

Tolerance to food antigens is antigen-specific and is promoted by oral exposure early in life, maternal transfer of immune complexes, food-specific IgG, Tregs, an intact skin barrier, and a healthy microbiome.

Organization of the Skin Immune System and Compartmentalized Immune Responses in Infectious Diseases

The skin is an organ harboring several types of immune cells that participate in innate and adaptive immune responses. The immune system of the skin comprises both skin cells and professional immune cells that together constitute what is designated skin-associated lymphoid tissue (SALT). In this review, I extensively discuss the organization of SALT and the mechanisms involved in its responses to infectious diseases of the skin and mucosa. The nature of these SALT responses, and the cellular mediators involved, often determines the clinical course of such infections. I list and describe the components of innate immunity, such as the roles of the keratinocyte barrier and of inflammatory and natural killer cells. I also examine the mechanisms involved in adaptive immune responses, with emphasis on new cytokine profiles, and the role of cell death phenomena in host-pathogen interactions and control of the immune responses to infectious agents. Finally, I highlight the importance of studying SALT in order to better understand host-pathogen relationships involving the skin and detail future directions in the immunological investigation of this organ, especially in light of recent findings regarding the skin immune system.