The membranous epithelial (M) cell and the mucosal immune system.

Membranous epithelial (M) cells are specialized epithelial cells overlying the subepithelial lymphoid follicles in the gastrointestinal and respiratory tracts. Antigens, including some viruses and bacteria, penetrate the mucosal barrier via the M cell, which endocytoses and transports antigens and microorganisms into the Peyer's patch or bronchial-associated lymphoid tissue. Here antigens may initiate an immune response and/or disseminate and induce disease. This review discusses the structure and function of the M cell, its role in macromolecular uptake, and its interaction with the immune system.