Pivotal Role of Dermal IL-17-producing γδ T Cells in Skin Inflammation

Summary Interleukin-23 (IL-23) and CD4 + T helper 17 (Th17) cells are thought to be critical in psoriasis pathogenesis. Here, we report that IL-23 predominantly stimulated dermal γδ T cells to produce IL-17 that led to disease progression. Dermal γδ T cells constitutively expressed the IL-23 receptor (IL-23R) and transcriptional factor RORγt. IL-17 production from dermal γδ T cells was independent of αβ T cells. The epidermal hyperplasia and inflammation induced by IL-23 were significantly decreased in T cell receptor δ-deficient ( Tcrd −/− ) and IL-17 receptor-deficient ( Il17ra −/− ) mice but occurred normally in Tcra −/− mice. Imiquimod-induced skin pathology was also significantly decreased in Tcrd −/− mice. Perhaps further promoting disease progression, IL-23 stimulated dermal γδ T cell expansion. In psoriasis patients, γδ T cells were greatly increased in affected skin and produced large amounts of IL-17. Thus, IL-23-responsive dermal γδ T cells are the major IL-17 producers in the skin and may represent a novel target for the treatment of psoriasis.