IL17A,also named as IL-17,is a proinflammatory cytokine. IL-17,synthesized only by memory T cells and natural killer cells,has pleiotropic effects,mainly in the recruitment and activation of neutrophils. This cytokine regulates the activities of NF-kappaB and mitogen-activated protein kinases. This cytokine can stimulate the expression of IL6 and cyclooxygenase-2 (PTGS2/COX-2),as well as enhance the production of nitric oxide (NO). High levels of this cytokine are associated with several chronic inflammatory diseases including rheumatoid arthritis,psoriasis and multiple sclerosis. The IL-17 receptor is a type I transmembrane protein,that is widely expressed on epithelial cells,fibroblasts,B and T cells,and monocytic cells. In psoriatic skin lesions,both Th17 cells and their downstream effector molecules,e.g. IL-17 and IL-22,are highly increased.