Commensal Bacteria and Th17 Cells

Abstract

The intestinal tract is a unique organ that is constitutively exposed to countless antigens, including dietary antigens and commensal microorganisms. A large number of immune cells are accumulated in the gut. It is known that T helper 17 (Th17) cells, a subset of CD4 positive T helper cells, are constitutively present in the intestinal lamina propria. This is because microorganisms such as segmented filamentous bacteria (SFB) induce the differentiation and proliferation of Th17 cells. Interestingly, Th17 cells induced by commensal bacteria contribute to protection against pathogenic bacteria and the construction of the epithelial barrier system, and they also play an important role in maintaining intestinal homeostasis. Therefore, Th17 cells in the gut have different phenotypes from Th17 cells that induce pathological inflammation in the systemic compartment. SFB-induced Th17 cells have been reported to promote disease aggravation in rheumatoid arthritis and multiple sclerosis mouse models. Since intestinal Th17 cells are critical to the induction and regulation of host diseases, Th17 cells may be an important target for the treatment of diseases. It is expected that clarifying the detailed mechanism of the differentiation and control of intestinal Th17 cells will lead to the development of novel therapeutic approaches for various diseases.