IL21 and psoriasis: In general, proinflammatory cytokines and factors stimulating proliferation in psoriasis are produced mainly by T cells (IL-17, IL-21, IL-22, IFN-γ), DCs (TNF-α, IL-6, IL-20, IL-23, NO), and KCs (antimicrobial peptides (AMPs), IL-20, chemokines).