The maintenance of a homeostatic environment in intestinal the lumen which harbors pathogenic and non-pathogenic microbiota, is regulated by host cells-derived secretory molecules. Interaction between intestinal epithelial cells and immune cells is necessary for the maintenance of host-microbe symbiosis mediated by secretory molecules. Here, we describe how host cell-derived molecules shape the composition of intestinal microbiota based on the latest evidence.

In the gut, where tremendous numbers of bacteria exist, the epithelial barrier of intestinal epithelial cells regulates gut bacteria by either chemical barriers, such as bacteriocidal molecules in the small intestine, or physical barriers such as mucins in the large intestine. The control of gut bacteria by the epithelial barrier is required for the maintenance of gut homeostasis. That is why disruption of the balance between gut bacteria and the epithelial barrier, due to a change in microbial composition or dysfunction of the barrier system resulting from a genetic predisposition, leads to inflammatory bowel diseases elicited by excessive immune responses to gut bacteria.