As another important source of cytokines, adaptive immune cells have been the subject of academic interest since 1979. A variety of studies showed that several related cytokines, such as tumor necrosis factor-α (TNF-α), interferon γ (IFN-γ), interleukin 23 (IL-23), interleukin 17 (IL-17), and interleukin 22 (IL-22), were highly correlated with psoriasis. Here, IL17A is linked to psoriasis.