Dissecting key contributions of T_H2 and T_H17 cytokines to atopic dermatitis pathophysiology

Background: In atopic dermatitis (AD), epidermal disease hallmarks are driven by a complex cutaneous inflammatory milieu that varies between patients. How these variable inflammatory signals affect cellular and molecular epidermal AD phenotypes is difficult to study in vivo. Objective: We aimed to unravel which AD-associated cytokines drive specific epidermal disease hallmarks. Methods: We utilized primary and immortalized keratinocyte-derived human epidermal equivalents stimulated with T_H2, T_H17, and T_H22 cytokines. Results: Morphologic, functional, and transcriptomic analyses revealed that T_H2 cytokines IL-4 and IL-13 were the main inducers of a proinflammatory and hyperproliferative epidermis. The presence of IL-17A or IL-22 in the T_H2 milieu, and especially T_H2 + IL-22, most closely resembled AD hallmarks including spongiosis, more severe keratinocyte differentiation defects, and epidermal barrier dysfunction. Single-cell spatial transcriptomics showed expansion of keratinocytes expressing high levels of proliferation genes and downregulation of differentiation genes in the upper epidermal layers. The transcriptomic comparison to in vivo AD lesional skin indicated that the T_H2 + IL-22 AD model demonstrated greatest resemblance and identified AD disease marker genes altered by T_H2 + IL-22 such as downregulated ACER1 and AKR1C3. Gene expression levels were restored by combinatory exposure to the aryl hydrocarbon receptor ligand tapinarof and the Janus kinase inhibitor tofacitinib. This combined therapeutic approach also completely restored epidermal barrier function and improved morphologic disease hallmarks. Conclusion: Our results reveal the important role of IL-22 in the T_H2-driven acute AD pathophysiology and highlight the potential of combinatory medicine in targeted treatment of AD.