Epithelial cell antigen presentation

For decades intestinal epithelial cells were thought of as passive barriers to luminal contents, cells involved in nutrient absorption and electrolyte secretion. Studies during the past 10 to 15 years have changed that concep t as our understanding of mucosal immunity has evolved and as we have come to understand that the regulation of this system is unique in terms of cell ular interactions and factors produced. The intestinal epithelial cell has moved to the forefront of these studies where it has been shown to be an ac tive participant in mucosal immunoregulation and inflammation. Results of t he earliest studies suggested that epithelial cells might be involved in im mune regulation because they expressed a series of cell surface molecules t hat correlate with classical antigen presentation (class I and II MHC molec ules). Later on, the expression of nonclassical class I molecules was ident ified on these cells as well, raising the possibility of novel forms of int eractions with unique cell populations. This was followed by the observatio n that epithelial cells secrete cytokines and chemokines, which not only re gulate mucosal immune responses but also regulate inflammatory responses. B y such processes, the IEC has been proposed as being a bridge between innat e and adaptive immunity. The recent description of Toll-like receptors on I ECs adds further support to this concept. Clearly there is growing apprecia tion of the multifaceted role that the IEC plays in the gut. The work on IE Cs in the past year has helped to refine this role. (C) 2000 Lippincott Wil liams & Wilkins, Inc.