Atopic Dermatitis Mediates the Association Between an IL4RA Variant and Food Allergy in School-Aged Children

Genetic and Immunological Pathogenesis of Atopic Dermatitis

Type 2 immune-mediated diseases give a clear answer to the issue of nature (genetics) versus nurture (environment). Both genetics and environment play vital complementary roles in the development of atopic dermatitis (AD). As a key component of the atopic march, AD demonstrates the interactive nature of genetic and environmental contributions to atopy. From sequence variants in the epithelial barrier gene encoding FLG to the hygiene hypothesis, AD combines a broad array of contributions into a single syndrome. This review will focus on the genetic contribution to AD and where genetics facilitates the elicitation or enhancement of AD pathogenesis.

The IL-4Rα Q576R polymorphism is associated with increased severity of atopic dermatitis and exaggerates allergic skin inflammation in mice

BACKGROUND

Atopic dermatitis (AD) is characterized by TH2-dominated skin inflammation and systemic response to cutaneously encountered antigens. The TH2 cytokines IL-4 and IL-13 play a critical role in the pathogenesis of AD. The Q576->R576 polymorphism in the IL-4 receptor alpha (IL-4Rα) chain common to IL-4 and IL-13 receptors alters IL-4 signaling and is associated with asthma severity.

OBJECTIVE

We sought to investigate whether the IL-4Rα R576 polymorphism is associated with AD severity and exaggerates allergic skin inflammation in mice.

METHODS

Nighttime itching interfering with sleep, Rajka-Langeland, and Eczema Area and Severity Index scores were used to assess AD severity. Allergic skin inflammation following epicutaneous sensitization of mice 1 or 2 IL-4Rα R576 alleles (QR and RR) and IL-4Rα Q576 (QQ) controls was assessed by flow cytometric analysis of cells and quantitative RT-PCR analysis of cytokines in skin.

RESULTS

The frequency of nighttime itching in 190 asthmatic inner-city children with AD, as well as Rajka-Langeland and Eczema Area and Severity Index scores in 1116 White patients with AD enrolled in the Atopic Dermatitis Research Network, was higher in subjects with the IL-4Rα R576 polymorphism compared with those without, with statistical significance for the Rajka-Langeland score. Following epicutaneous sensitization of mice with ovalbumin or house dust mite, skin infiltration by CD4+ cells and eosinophils, cutaneous expression of Il4 and Il13, transepidermal water loss, antigen-specific IgE antibody levels, and IL-13 secretion by antigen-stimulated splenocytes were significantly higher in RR and QR mice compared with QQ controls. Bone marrow radiation chimeras demonstrated that both hematopoietic cells and stromal cells contribute to the mutants' exaggerated allergic skin inflammation.

CONCLUSIONS

The IL-4Rα R576 polymorphism predisposes to more severe AD and increases allergic skin inflammation in mice.

Endotypes of atopic dermatitis and food allergy

Atopic dermatitis (AD) and food allergy (FA) are strongly associated, with one-third of children with AD developing concomitant FA. Epithelial barrier dysfunction is important in both conditions. Genetic factors, such as filaggrin mutations and IL-4 receptor alpha chain polymorphisms, are linked to increased risk. In addition, several environmental exposures lead to reduced filaggrin and contribute to skin barrier dysfunction. Staphylococcus aureus colonization appears to contribute to AD and FA, as well as activating the type 2 immune response. Comprehensive multiomic studies using skin tape stripping have identified distinct atopic endotypes with unique characteristics of the stratum corneum lipids, proteins, S aureus abundance, and type 2 cytokine expression. Our new understanding of AD and FA presents an area of opportunity to move toward improved diagnosis and prevention of atopy.

Microbiome Therapeutics for Food Allergy

The prevalence of food allergies continues to rise, and with limited existing therapeutic options there is a growing need for new and innovative treatments. Food allergies are, in a large part, related to environmental influences on immune tolerance in early life, and represent a significant therapeutic challenge. An expanding body of evidence on molecular mechanisms in murine models and microbiome associations in humans have highlighted the critical role of gut dysbiosis in the pathogenesis of food allergies. As such, the gut microbiome is a rational target for novel strategies aimed at preventing and treating food allergies, and new methods of modifying the gastrointestinal microbiome to combat immune dysregulation represent promising avenues for translation to future clinical practice. In this review, we discuss the intersection between the gut microbiome and the development of food allergies, with particular focus on microbiome therapeutic strategies. These emerging microbiome approaches to food allergies are subject to continued investigation and include dietary interventions, pre- and probiotics, microbiota metabolism-based interventions, and targeted live biotherapeutics. This exciting frontier may reveal disease-modifying food allergy treatments, and deserves careful study through ongoing clinical trials.

Treatment options for moderate to severe atopic dermatitis

Background: The treatment of chronic refractory moderate-to-severe atopic dermatitis (AD) has traditionally relied on broad-spectrum systemic anti-inflammatory agents. With the introduction of biologics and Janus kinase inhibitors (Jakinib), the step management of moderate-to-severe AD is rapidly changing; however, guidelines have yet to provide formal recommendations for how to best incorporate these agents into the treatment plan. Objective: To summarize the updated evidence-based medical treatment for AD, including a proposed position for biologics and Jakinibs in the treatment algorithm. Methods: A literature search of several medical literature data bases for guidelines, position papers, systematic reviews, and clinical trials from 2012 to 2022 on the treatment of moderate-to-severe AD was conducted to prepare this narrative review. Results: Emollients and topical corticosteroids are the mainstay for treating acute flares and for maintaining chronic control. Second-line topical agents include calcineurin inhibitors, e.g., tacrolimus and pimecrolimus; crisaborole; and ruxolitinib. For acute flares, cyclosporine is preferred over systemic corticosteroids. For chronic treatment, phototherapy should be considered before systemic anti-inflammatory agents. Of the traditional anti-inflammatory agents, cyclosporine is the first-line choice, with methotrexate and azathioprine equal secondary choices. Although abrocitinib may have better efficacy then dupilumab based on indirect comparisons, abrocitinib requires closer monitoring for adverse events. Based on package labeling, Jakinibs, e.g., abrocitinib and upadacitinib, should be used only after failure with other systemic agents, including biologics (e.g., dupilumab and tralokinumab). Biologics and Jakinibs should be considered before the traditional systemic anti-inflammatory agents. Conclusion: Clinicians should consider a modified step management for AD as they await the development of national and international guideline recommendations for how best to position the biologics and Jakinibs into the AD treatment algorithm.