Later, IL-17A was also identified as a crucial player in the innate-like immune response against extracellular bacterial and fungal infections, and as a key component in autoimmune diseases including psoriasis, multiple sclerosis, and ankylosing spondylitis (Acosta-Rodriguez et al. 2007; Ouyang et al. 2008; Korn et al. 2009; Zielinski et al. 2012). Here, IL17A is linked to autoimmune disease.