The epithelial cell cytoskeleton and intracellular trafficking. II. Intestinal epithelial cell exosomes: perspectives on their structure and function.
Intestinal epithelial cells (IEC) are located at the strategic interface between the external environment and the most extensive lymphoid compartment in the body. Besides their central role in the absorption of nutrients, they also provide sample information to the immune system on soluble or particulate antigens present in the intestinal lumen. Like professional antigen-presenting cells, IEC have recently been shown to secrete 30- to 90-nm diameter vesicles named exosomes from their apical and basolateral surfaces. These vesicles carry molecules that are implicated in adhesion and antigen presentation, such as major histocompatibility complex (MHC) class I molecules, MHC class II molecules, CD63, CD26/dipeptidyl-peptidase IV, tetraspan proteins, and A33 antigen. IEC exosomes therefore, constitute a link by which IEC may influence antigen presentation in the mucosal or systemic immune system independent of direct cellular contact with effector cells.