IL-23 from Langerhans Cells Is Required for the Development of Imiquimod-Induced Psoriasis-Like Dermatitis by Induction of IL-17A-Producing γδ T Cells

Psoriasis is a common chronic inflammatory skin disease that involves dysregulated interplay between immune cells and keratinocytes. Recently, it has been reported that IL-23 induces CCR6(+) gamma delta T cells, which have the pivotal role in psoriasis-like skin inflammation in mice of producing IL-17A and IL-22. Langerhans cells (LCs) are a subset of dendritic cells that reside in the epidermis and regulate immune responses. The role of LCs has been extensively investigated in contact hypersensitivity, but their role in psoriasis remains to be clarified. In this study, we focused on Th17-related factors and assessed the role of LCs and gamma delta T cells in the development of psoriasis using a mouse psoriasis model triggered by topical application of imiquimod (IMQ). LC depletion by means of diphtheria toxin (DT) in Langerin DT receptor-knocked-in mice suppressed hyperkeratosis, parakeratosis, and ear swelling in the IMQ-treated regions. In addition, LC-depleted mice showed decreased levels of Th17-related cytokines in IMQ-treated skin lesions. Moreover, the IMQ-treated skin of LC-depleted mice showed a decreased number of IL-17A-producing CCR6(+) gamma delta T cells. These results suggest that LCs are required for the development of psoriasis-like lesions induced by IMQ in mice.