IL17A and psoriasis: Interleukin 17A, IL-22, and IL-19 are elevated in both active skin lesions and blood in psoriasis and have been associated with disease activity.18,23,24 Ustekinumab inhibits secretion of IL-17A and other cytokines in vitro,25 but ex vivo studies from clinical trial specimens have been limited by assay detection limits for low abundant serum proteins.