IL-17-producing helper T (Th17) cells in psoriasis pathogenesis have been intensely studied, suggesting a model in which IL-23 derived from dendritic cells and macrophages activates the cytokine secretion of Th17 cells and that Th17-derived IL-17 and IL-22 provoke neutrophil recruitment and epidermal keratinocyte proliferation in the skin (10, 11). This evidence concerns the gene IL17A and psoriasis.