However, since the discovery that IL-17A-producing CD4 T cells (Th17) are crucially involved in the pathogenesis of some mouse autoimmune diseases [8], [9], [10], and because psoriasis is often considered an autoimmune or autoinflammatory disorder, many investigators switched their attention to Th17 cells as possible main instigators of psoriasis. This evidence concerns the gene IL17A and psoriasis.