Taking inflammatory bowel disease up a Notch.

The epithelium of the gastrointestinal tract, which represents the largest surface area of the body, is constantly exposed to the contents of its surrounding environment. The intestinal epithelium forms barriers that are essential in maintaining equilibrium within the human body. This barrier supports nutrient and water transport while preventing microbial invasion. Intestinal epithelial cells (IECs) sit at the interface between an antigen-rich lumen and a lymphocyte-rich lamina propria (LP). IECs have the capability to discriminate between "peaceful" and "harmful" antigens. The epithelium is constantly sampling luminal contents and making molecular adjustments accordingly. These molecular changes influence the actions of innate and adaptive immune cells. The crosstalk that occurs between the epithelium and the immune compartments serves to maintain intestinal homeostasis. A better understanding of the nature of the interactions between normal LP lymphocytes (LPLs) and IECs will ultimately provide insights into the defects occurring in inflammatory bowel disease patients.