IL17A and inflammatory bowel disease: IBD is characterized by loss of tolerance to intestinal commensal bacterial and self-antigens, due to dysregulated CD4 T cell differentiation, with enhanced differentiation of Th1 and Th17 cells, as demonstrated by elevated levels of IFNγ, IL-17, and IL-22 in the intestinal biopsies and serum of patients with IBD (Fujino et al., 2003; Maloy and Powrie, 2011).