For instance, OMVs can reprogram the TME toward a pro-TH1 pattern (CXCL10, IFN-g; Kim et al., 2017), while metabolites, such as butyrate and niacin, can mediate the Gpr109a-dependent induction of IL-18 in the colonic epithelium, suppressing colitis and colon cancer. Here, HCAR2 is linked to colitis.