Coevolution between the Human Microbiota and the Epithelial Immune System.

The composition and spatial distribution of our gut microbiota is tightly controlled by the host to prevent bacterial invasion and systemic infection. The gastrointestinal epithelium is predominantly made up of a cellular monolayer equipped with a number of sophisticated autonomous defense mechanisms, which are strikingly efficient in maintaining homeostasis between the luminal microbes and the host. This short review highlights aspects of this finetuned interplay. We also address how deficiencies in mucosal defense can promote disease. First, genetic defects of sensors or effectors of epithelial defense can result in the disruption of the mucosal barrier and lead to chronic inflammatory conditions. Second, chronic colonizers of the gastrointestinal tract can actively manipulate mucosal defense to escape immune surveillance. As shown for Helicobacter pylori in the stomach, sustained manipulation of the epithelium through specialized virulence determinants can increase the risk for genetic lesions and malignant transformation.