Furthermore, inhibition of HIF1α and AhR using HIF1α inhibitor YC-1 and AhR inhibitor CH-223191 suppressed butyrate-induced IL-22 production (Fig. 9f), indicating that butyrate promotes IL-22 production in human CD4+ T cells, including IBD patients, through regulation of HIF1α and AhR. Here, CD4 is linked to inflammatory bowel disease.