IL17A and psoriasis: The IFN-γ, IL-17A and IL-22 are key pathogenic cytokines in psoriasis and one of the main mediators of cytokine signaling is STAT1 (Wolk et al., 2006; Nograles et al., 2008; Antunes et al., 2011; Shi et al., 2011; Hald et al., 2013).