IL17F and psoriasis: Moreover, IL-17A, IL-17C, and IL-17F protein levels are increased in psoriatic lesions in humans as well as in some mouse models of psoriasis, e.g., after TPA application in transgenic mice with skin-specific expression of vascular endothelial growth factor, and in the imiquimod (a toll-like receptor 7 and 8 ligand and potent immune stimulator) model [24, 25].