Role of the Gut Microbiota in Maintaining GI Health: Highlights on Inflammatory Bowel Disease

The human gut harbors trillions of microbes, with an area of at least 300 m² intestinal tissue in constant contact with this microbial ecological system (Artis, Nat Rev Immunol 8(6):411–420, 2008, Ley et al. Cell 124(4):837–848, 2006). The intestinal epithelium with a number of different cell types shapes the frontier between microbes and the host. Intestinal epithelial cells (IECs) as well as cells of the immune system guard the local interface of microbes and host and actively tolerate selected commensal microbiota while mounting an adequate inflammatory response toward pathogens in the context of infection or disease. Although there is no clear definition of a “normal” intestinal microbiota as such, it is apparent that perturbations of a certain homeostatic system may lead to a dysregulated interaction between microbes and the host intestinal mucosal immune system, resulting in aberrant or disproportionate inflammatory conditions. The following chapter gives a general introduction to the role of the microbiota in gut health, focuses on aberrations in microbe-host mutualism that are implicated in the etiopathology of inflammatory bowel diseases, and then briefly addresses the possibilities of dietary modulation of intestinal microbiota in the context of inflammatory bowel diseases.