IL17A and psoriasis: It is known that IL-23 is essential for the terminal differentiation of IL-17-producing T effector cells (Park et al., 2005; McGeachy et al., 2009), which were initially shown to be a chief pathogenic cell population in EAE and CIA (Duerr et al., 2006; Remmers et al., 2010), human psoriasis (Wilson et al., 2007; Lubberts, 2015) and LAD1 (Moutsopoulos et al., 2017).