IL17A and psoriasis: Involvement of IL17A in the pathogenesis of psoriasis has been thoroughly demonstrated [10], by directly activating IL17R of keratinocytes and triggering down-streamed signaling, IL17A induced expression of several pro-inflammatory cytokines and chemokines which recruit neutrophils and monocytes, and subsequently activate T-cells, finally causes hyperproliferation of keratinocyte and the generation of psoriasis [11].