[Epithelial barriers of the intestine. Significance and function in defense against infection]

The epithelial surface of the intestinal tract provides for an important barrier between the organism and its environment. However, it permits the passage into the tissues of limited amounts of macromolecules and/or particles, especially bacteria. These functions are age- and species-dependent, and they are closely related to nonspecific and specific immune reactions. Continuous and intimate contact between antigenic material from the gut lumen and immunocompetent cells takes place in gut-associated lymphoid tissues.