IL17A and psoriasis: However, the dominant immune response in psoriasis is T helper 17 (Th17), whose characteristic cytokines are interleukin 17A (IL-17A), interleukin 17F (IL-17F), interleukin 21 (IL-21), interleukin 22 (IL-22), interleukin 29 (IL-29), interleukin 8 (CXCL-8), and tumor necrosis factor α (TNF-α).