Distinct Roles of IL-4, IL-13, and IL-22 in Human Skin Barrier Dysfunction and Atopic Dermatitis.

BACKGROUND: Atopic dermatitis (AD) is a chronic type-2 inflammatory skin disease characterized by eczema and epithelial barrier dysfunction. Along with the type-2 cytokines IL-4 and IL-13, IL-22 contributes to AD pathogenesis. To date, most skin studies rely on reconstructed keratinocytes, which do not represent the real skin response. OBJECTIVE: Here, we report the distinct effects of IL-4, IL-13, and IL-22 on bio-stabilized human skin with intact barriers and immune cells. METHODS: Spatial transcriptomics on AD-lesions and non-lesional skin was performed. Ex vivo skin barrier integrity was evaluated using electrical impedance spectroscopy (EIS), RNA-sequencing, and untargeted proteomics, complemented by analyses of skin biopsies from dupilumab-treated AD patients. RESULTS: Spatial transcriptomics demonstrated that AD lesions showed reduced expression of key barrier genes, including CLDN1, FLG, and FLG2. IL-4, IL-13, and IL-22 disrupted the skin barrier in the ex vivo human skin. Combining type-2 cytokines and IL-22 alone downregulated genes critical for barrier function and keratinization. In addition, IL-4 and IL-13 downregulated antimicrobial peptides, while IL-22 upregulated them. Interestingly, IL-4 and IL-13 reduced IL-22Rα1, and IL-22 upregulated IL-4Rα, suggesting immune cross-regulation. Proteomic analysis confirmed that all three cytokines (IL-4, IL-13, and IL-22) reduced the expression of key skin barrier proteins, particularly filaggrin and claudin-1. Dupilumab treatment of AD patients for 3 months restored IL-4/IL-13-dysregulated genes, whereas it had limited effect on IL22-associated pathways. CONCLUSION: This comprehensive study provides insights into the distinct immune profiles following IL-4, IL-13, and IL-22 stimulation on human skin, highlighting their complex interplay in disrupting skin barrier function and modulating innate immune responses.