Interleukin-17 is a Th17 cytokine associated with inflammation, autoimmunity, and defence against some bacteria; it has been implicated in many chronic autoimmune diseases including psoriasis, Crohn's disease, autoimmune uveitis, SLE, ankylosing spondylitis, asthma, multiple sclerosis, and systemic sclerosis [26]. This evidence concerns the gene IL17A and Crohn disease.