Then, to investigate the mechanism of TGF-β induction, we stimulated healthy keratinocytes (NHEK) in vitro with a number of cytokines characterizing the psoriasis microenvironment including IL-1β, IL-6, IL-17A, IL-19, IL-22, IL-23, IL-26, and IFN-γ. This evidence concerns the gene IL17A and psoriasis.