Short-chain fatty acids (SCFAs), the most abundant microbial metabolites in the intestine, activate cells via G-protein−coupled receptors (GPRs), such as GPR41 and GPR43. We studied regulation of the immune response by SCFAs and their receptors in the intestines of mice.

Inflammatory responses were induced in GPR41^−/−, GPR43^−/−, and C57BL6 (control) mice by administration of ethanol; 2, 4, 6-trinitrobenzene sulfonic-acid (TNBS); or infection with Citrobacter rodentium. We examined the effects of C rodentium infection on control mice fed SCFAs and/or given injections of antibodies that delay the immune response. We also studied the kinetics of cytokine and chemokine production, leukocyte recruitment, intestinal permeability, and T-cell responses. Primary colon epithelial cells were isolated from GPR41^−/−, GPR43^−/−, and control mice; signaling pathways regulated by SCFAs were identified using immunohistochemical, enzyme-linked immunosorbent assay, and flow cytometry analyses.

GPR41^−/− and GPR43^−/− mice had reduced inflammatory responses after administration of ethanol or TNBS compared with control mice, and had a slower immune response against C rodentium infection, clearing the bacteria more slowly. SCFAs activated intestinal epithelial cells to produce chemokines and cytokines in culture and mice after administration of ethanol, TNBS, or C rodentium. These processes required GPR41 and GPR43 and were required to recruit leukocytes and activate effector T cells in the intestine. GPR41 and GPR43 activated extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase signaling pathways in epithelial cells to induce production of chemokines and cytokines during immune responses.

SCFAs activate GPR41 and GPR43 on intestinal epithelial cells, leading to mitogen-activated protein kinase signaling and rapid production of chemokines and cytokines. These pathways mediate protective immunity and tissue inflammation in mice.