In conclusion, our data suggest that IL-21 contributes to the pathogenesis of psoriasis by promoting CD4+ T cell proliferation, enhancing Th17 cell differentiation and function, downregulating the differentiation of Treg cells, and aggravating the imbalance of Th17 and Treg cells (Figure 6), and therefore IL-21 may be potential therapeutic targets in psoriasis. The gene discussed is CD4; the disease is psoriasis.