IL17A and psoriasis: However, psoriasis is caused by a plethora of activated immune cells and their respective cytokines, including tumor necrotizing factor alpha (TNF-α), interleukin (IL)-17, IL-22, IL-23, and the granulocyte-macrophage colony-stimulating factor (GM-CSF), which will present elevated levels during the pathophysiological course of the disease [1].