Psoriasis is T cell-driven, with the Th1 and Th17 cells playing a pivotal role by producing different cytokines including interleukin (IL)-6, IL-17, and IL-22, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α, resulting in increased proliferation of epidermal cells, neo-angiogenesis, and infiltration of white cells in the skin. The gene discussed is IL17A; the disease is psoriasis.