T-cells are crucial in maintanence of intestinal homeostasis, however, it is still unclear how microbiota metabolites regulate T-effector cells. Here we show gut microbiota-derived short-chain fatty acids (SCFAs) promote microbiota antigen-specific Th1 cell IL-10 production, mediated by G-protein coupled receptors 43 (GPR43). Microbiota antigen-specific Gpr43−/− CBir1 transgenic (Tg) Th1 cells, specific for microbiota antigen CBir1 flagellin, induce more severe colitis compared with wide type (WT) CBir1 Tg Th1 cells in Rag−/− recipient mice. Treatment with SCFAs limits colitis induction by promoting IL-10 production, and administration of anti-IL-10R antibody promotes colitis development. Mechanistically, SCFAs activate Th1 cell STAT3 and mTOR, and consequently upregulate transcription factor B lymphocyte-induced maturation protein 1 (Blimp-1), which mediates SCFA-induction of IL-10. SCFA-treated Blimp1−/− Th1 cells produce less IL-10 and induce more severe colitis compared to SCFA-treated WT Th1 cells. Our studies, thus, provide insight into how microbiota metabolites regulate Th1 cell functions to maintain intestinal homeostasis.

The antimicrobial peptides (AMP) produced by intestinal epithelial cells (IEC) play crucial roles in the regulation of intestinal homeostasis by controlling microbiota. Gut microbiota has been shown to promote IEC expression of RegIIIγ and certain defensins. However, the mechanisms involved are still not completely understood. In this report, we found that IEC expression of RegIIIγ and β-defensins 1, 3, and 4 was lower in G protein-coupled receptor (GPR)43−/−mice compared to that of wild-type (WT) mice. Oral feeding with short chain fatty acids (SCFA) promoted IEC production of RegIIIγ and defensins in mice. Furthermore, SCFA induced RegIIIγ and β-defensins in intestinal epithelial enteroids generated from WT but not GPR43−/−mice. Mechanistically, SCFA activated mTOR and STAT3 in IEC, and knockdown of mTOR and STAT3 impaired SCFA induction of AMP production. Our studies thus demonstrated that microbiota metabolites SCFA promoted IEC RegIIIγ and β-defensins in a GPR43-dependent manner. The data thereby provides a novel pathway by which microbiota regulates IEC expression of AMP and intestinal homeostasis.

CD177 neutrophils represent functionally activated population and play a protective role in IBD through increased bactericidal activity and IL-22 production. Targeting CD177 neutrophils may be beneficial for treatment of IBD.

It has been shown recently that neutrophils are able to produce IL-22 and IL-17, which differentially regulate the pathogenesis of inflammatory bowel disease (IBD). However, it is still largely unknown how the neutrophil production of IL-22 and IL-17 is regulated, and their role in the pathogenesis of IBD. In this study, we found that IL-23 promoted neutrophil production of IL-17 and IL-22. IL-23 stimulated the neutrophil expression of IL-23 receptor as well as rorc and ahr. RORγt and AhR differentially regulated IL-23 induction of neutrophil IL-17 and IL-22. Additionally, IL-23 induced the activation of mTOR in neutrophils. Blockade of mTOR pathway inhibited IL-23-induced expression of rorc and ahr as well as IL-17 and IL-22 production. By utilizing a microbiota antigen specific T-cell mediated colitis model, we demonstrated that depletion of neutrophils, as well as blockade of IL-22, resulted in a significant increase in the severity of colitis, thereby indicating a protective role of neutrophils and IL-22 in chronic colitis. Collectively, our data revealed that neutrophils negatively regulate microbiota antigen specific T cell induction of colitis, and IL-23 induces neutrophil production of IL-22 and IL-17 through induction of rorc and ahr, which is mediated by mTOR pathway.

Intestinal IgA, which is regulated by gut microbiota, plays a crucial role in maintenance of intestinal homeostasis and in protecting the intestines from inflammation. However, the means by which microbiota promotes intestinal IgA responses remain unclear. Emerging evidence suggests that the host can sense gut bacterial metabolites in addition to pathogen-associated molecular patterns and that recognition of these small molecules influences host immune response in the intestines and beyond. We reported here that microbiota metabolite short-chain fatty acid acetate promoted intestinal IgA responses, which was mediated by "metabolite-sensing" GPR43. GPR43 −/− mice demonstrated lower levels of intestinal IgA and IgA + gut bacteria compared to those in WT mice. Feeding WT but not GPR43 −/− mice acetate but not butyrate promoted intestinal IgA response independent of T cells. Acetate promoted B cell IgA class switching and IgA production in vitro in the presence of WT but not GPR43 −/− dendritic cells (DC). Mechanistically, acetate induced DC expression of Aldh1a2, which converts Vitamin A into its metabolite retinoic acid (RA). Moreover, blockade of RA signaling inhibited the acetate induction Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use