Figure 3.

Impact of the gut microbiota on IL-17 and Th17 immune responses. The intestinal microbiota-derived signals to immune cells are classified into the following three parts: bacterial components, bacteria-derived metabolites and intestinal barrier function. Beneficial bacteria suppressed the expression of proinflammatory cytokine IL-6 and IL-17 and promoted the expression of major tight junction proteins. On the contrary, colonization of pathogenic commensal bacteria induces generation of Th17 and downregulates Tregs immune responses. Beneficial bacteria produce short-chain fatty acids, which participate in the generation of Tregs and IL-10 by suppressing proinflammatory cytokines. IL-17 injuries intestinal epithelium, releases inflammatory cytokines and cause intestinal microcirculation disturbance. IL-17 also induces impaired intestinal barrier function, including edema of the intestinal wall and destruction of the mucosal epithelial barrier.