IL-23, secreted by DCs or KCs, facilitates Th17 differentiation which produces proinflammatory cytokines including IL-17A, IL-17F, IL-6, IL-21, and IL-22, resulting in the infiltration of Th17 and high levels of Th17-mediated proinflammatory cytokines in skin lesions and peripheral blood of psoriasis patients [2, 36, 37]. This evidence concerns the gene IL21 and psoriasis.