IL17A and psoriasis: One review reported that the onset of psoriasis primarily involves the cytokines such as interferon (IFN)‐γ, tumor necrosis factor (TNF)‐α, and interleukin (IL)‐17, IL‐22, and IL‐23 and that an imbalance between effector T cells, such as Th‐17, and regulatory T cells plays a role in the etiology of psoriasis.7, 18