For example, propionate acts on CD11c+ dendritic cells (DCs), endowing them with regulatory functions that promote the conversion of naive CD4+ T cells into pTregs.16 Activation of GPR109A on colonic macrophages and DCs by butyrate further induces anti-inflammatory responses, increasing Treg and interleukin (IL) −10-producing CD4+ T cell frequencies in the colon, thereby reducing colitis.17 The gene discussed is CD4; the disease is colitis.