IL17A and psoriasis: Lots of studies had shown that Th1/Th17 cells played crucial roles in the pathogenesis of psoriasis.18, 19, 20 Psoriatic lesions can secrete many inflammatory cytokines such as IFN-γ, IL-6, IL-1 β, IL-8, IL-17, and TNF-α, which contribute to the development of psoriasis.21