IL17A and ulcerative colitis: On the other hand, the inflammatory condition, both in the naïve and the developed models, elicited a clear Th17 response, with increased mRNA levels of the markers il17a/f1, il17a/f3, and il22, and decreased levels of the Treg markers foxp3 and il10. Studies in mice and humans indicate that Th17 cells play a major role in the pathogenesis of Crohn's disease and ulcerative colitis (49–51).