Current opinion on the pathogenesis of psoriasis emphasizes the role of cytokine signaling to drive an inflammatory cycle, in which infiltrating dendritic cells and autoreactive T lymphocytes, mainly represented by IL-17-producing T cells, T-helper-1 (Th1), and Th22 cells, release IL-17, IFN-γ, IL-22, and TNF-α. This evidence concerns the gene IL17A and psoriasis.