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

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Abstract
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.

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