In healthy homeostatic conditions, the levels of IL-17A in human sera are undetectable, however, the levels are markedly increased in inflammatory bowel disease, psoriasis, systemic lupus erythematosus (SLE), multiple sclerosis (MS), and rheumatoid arthritis (RA; Wang et al., 2012; Jiang et al., 2014; Babaloo et al., 2015; Mease, 2015; Talaat et al., 2015). Here, IL17A is linked to psoriasis.