Interactions of viruses and microparticles with apical plasma membranes of M cells: implications for human immunodeficiency virus transmission.

In the rectal mucosa, specialized M cells of the lymphoid follicle-associated epithelium conduct vesicular transport of antigens from the mucosal surface into organized mucosal lymphoid tissues, where immune responses are induced. Bacteria and viruses may exploit this mechanism to initiate mucosal or systemic infection. Viral pathogens, including reovirus, poliovirus, and possibly human immunodeficiency virus (HIV), can enter the intestinal or rectal mucosa by adhering to apical membranes of M cells, but the membrane components involved in these interactions are unknown. Glycoprotein coats on the apical surfaces of epithelial cells act as diffusion barriers that limit access of particles and microorganisms to membrane glycolipids and to certain oligosaccharide epitopes of enterocytes but allow selective adherence to M cells. The accessibility of membrane glycolipids of M cells, along with their active endocytic activity, could promote entry of HIV into the rectal mucosa.