IL17A and psoriasis: Produced by various immune cells such as Th17, neutrophils, and mast cells, IL-17 is a key cytokine responsible for keratinocyte proliferation and production of other cytokines and antimicrobial peptides in psoriasis (Veldhoen et al., 2006; Lin et al., 2011; Keijsers et al., 2014; Dyring-Andersen et al., 2017).