IL17A and psoriasis: The pathogenesis of psoriasis is accompanied by the infiltration and overactivation of effector T cells, such as Th1, Th2, and Th17 cells, in psoriasis lesions, which leads to an impaired balance between Treg and effector T cells and an upregulation of proinflammatory cytokines.25 Th17 cells are a subset of T-lymphocytes expressing IL-17 that induce keratinocyte proliferation and other characteristics of psoriasis.