IL17A and psoriasis: Psoriasis is a chronic, inflammatory, multisystemic disease which affects approximately 2–3% of the population globally, whose onset is triggered by genetic and environmental factors which activate both dendritic cells and keratinocytes, resulting in the production of proinflammatory cytokines such as tumor necrosis factor alpha, interleukin 17, interleukin 23, interleukin 22, and interleukin 1β.