Digestive System > Small Intestine

M Cells (Microfold Cells)

Microfold or M cells are epithelial cells embedded in the epithelium of mucosal tissues such as intestine, lung, and nasopharynx. Their name derives from the characteristic morphology of their apical or lumen-facing surface which has few if any microvilli.

The importance of M cells is that they are a critical player in the mucosal immune response and immune surveillance. The have have a unique ability to take up a variety of antigens - bacteria, viruses, parasites and proteins - from the lumen, transport them by transcytosis across the cell and deliver them to immune cells lying underneath, particularly dendritic cells. In other words, M cells are antigen-delivery cells for the immune system in places like the intestine and lung, the first step in eliciting a mucosal immune response. The capture of lumenal antigens occurs through electrostatic interactions and by binding to a number of adhesion molecules on the surface of the M cell.

M cells are most abundant in the epithelium overlying lymphoid follicles such as Peyer's patches in the intestine. There are additional types of M cells such as villous M cells interspersed among entercytes over villi in the small intestine.

The ability of M cells to deliver antigens to the mucosal immune system has led to the concept of exploiting the cells for delivery of vaccines targeting mucosal immune responses, which is an active area of research.

Paradoxically, although M cells are important in generating an effective mucosal immune response to protect against many pathogens, they also serve as an entry portal for a number of pathogens that can be present in the intestinal lumen. Examples include bacteria such as Brucella, Yersinia, and Salmonella species, viruses like reoviruses and poliovirus, and prions. In these cases, the pathogen is taken up and sometimes replicates in M cells, and is then transferred across the cell to induce a systemic infection.

References and Reviews

Small Intestine: Introduction and Index

Updated November 2018. Send comments to Richard.Bowen@colostate.edu