IL17A and inflammatory bowel disease: Among the Th cell subsets, Th1 (IFN-γ+) and Th17 (IL-17A+) are the pro-inflammatory ones that drive the development of IBD, while regulatory T cell (Treg, Foxp3+) is the one that suppresses the inflammation, thus it is necessary to make a more detailed observation for their infiltration in the colon.