Figure 2.

Regulation of short-chain fatty acids to host inflammation and immune. SCFAs can stimulate intestinal epithelial cells to release Muc2, which enhance the gut barrier function and heighten the response to pathogens and commensal bacteria. Moreover, SCFAs can reduce the recruitment of neutrophils under certain condition, with an increase in the levels of TGF-β, IL-10 and a decrease in the levels of IL-6, IL-1β, NO, and TNF-α to inhibit inflammation. Meanwhile, SCFAs promote T-cell production of IL-10 and Treg to prevent inflammatory responses. On the other hand, SCFAs act on DCs to limit the expression of T cell-activating molecules such as MHC II molecules and costimulatory molecules, leading to the generation of tolerogenic T cells rather than inflammatory T cells. The tolerogenic effect of SCFAs on DCs can lower inflammatory responses. However, the direct effect of SCFAs on T cells enhances the generation of Th1 and Th17 cells to boost immunity to fight pathogens, which means that activation of SCFAs for immune cells and epithelial cells may increase inflammatory responses, if not properly regulated.

Abbreviations: DCs, dendritic cells; FAs, short-chain fatty acids; GPCRs, G protein-coupled receptors; HDAC, histone acetylation; NO, nitrous oxide; TGF-β, transforming growth factor-β; TNF-α, tumor necrosis factor-α.