Roles of intestinal epithelial cells in the maintenance of gut homeostasis

The intestine is a unique organ inhabited by a tremendous number of microorganisms. Intestinal epithelial cells greatly contribute to the maintenance of the symbiotic relationship between gut microbiota and the host by constructing mucosal barriers, secreting various immunological mediators and delivering bacterial antigens. Mucosal barriers, including physical barriers and chemical barriers, spatially segregate gut microbiota and the host immune system to avoid unnecessary immune responses to gut microbes, leading to the intestinal inflammation. In addition, various immunological mediators, including cytokines and chemokines, secreted from intestinal epithelial cells stimulated by gut microbiota modulate host immune responses, maintaining a well-balanced relationship between gut microbes and the host immune system. Therefore, impairment of the innate immune functions of intestinal epithelial cells is associated with intestinal inflammation. A review by researchers in Japan highlights how gut epithelial cells moderate interactions between foreign microbes and the immune system. Epithelial cells line the surface of the gut, separating the body’s immune system from the gut microbes that enter the body with food. Drawing on numerous recent studies, Ryu Okamura and Kiyoshi Takeda at Osaka University identify two main roles that epithelial cells perform to maintain a healthy balance in the gut. Firstly, the cells segregate gut microbes from the immune system by constructing physical and chemical barriers. Secondly, they mediate interactions by passing information between the microbes and the immune system, triggering immune responses where necessary. Understanding the role of these cells is important given increasing evidence that defects in their functions are strongly related to inflammatory bowel problems such as ulecerative colitis.