2005). A dysregulation of Th17/Treg balance, with a decrease of Treg cells and an increase of Th17 cells in the colonic mucosa, is a typical manifestation of colonic inflammation in UC patients (Gong et al. 2016). It is proven that AhR expression is significant in intestinal Treg cells in steady state (Ye et al. 2017). However, the specific absence of the AHR gene in Treg cells leads to an obvious reduction of Treg cells in the intestine, which is linked to the fact that AhR can promote the intestinal homing of Treg cells (Ye et al. 2017). The gene discussed is AHR; the disease is inflammation.