Once psoriasis has manifested, a series of cells, including plasmacytoid dendritic cells (DCs) and macrophages, are excessively activated to promote the secretion of cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-17 (IL-17), interleukin-22 (IL-22), and interleukin-23 (IL-23) 1, 7. The gene discussed is IL17A; the disease is psoriasis.