HCAR2 and colonic neoplasm: Third, GPR109A on colonic macrophages and DCs can be activated by microbiota-derived niacin and butyric acid to induce the production of IL-10, which protects against colitis and colon cancer by inducing the differentiation of IL-10-producing T cells and Treg cells and increasing the amount of monocyte-derived anti-inflammatory effector molecules (74).