Microfold cell

Microfold cells (or M cells) are found in the gut-associated lymphoid tissue (GALT) of the Peyer's patches in the small intestine, and in the mucosa-associated lymphoid tissue (MALT) of other parts of the gastrointestinal tract. These cells are known to initiate mucosal immunity responses on the apical membrane of the M cells and allow for transport of microbes and particles across the epithelial cell layer from the gut lumen to the lamina propria where interactions with immune cells can take place.^[1]

Unlike their neighbor cells, M cells have the unique ability to take up antigen from the lumen of the small intestine via endocytosis, phagocytosis, or transcytosis. Antigens are delivered to antigen-presenting cells, such as dendritic cells, and B lymphocytes. M cells express the protease cathepsin E, similar to other antigen-presenting cells. This process takes place in a unique pocket-like structure on their basolateral side. Antigens are recognized via expression of cell surface receptors such as glycoprotein-2 (GP2) that detect and specifically bind to bacteria. Cellular prion protein (PrP) is another example of a cell surface receptor on M cells.^[2]

M cells lack microvilli but, like other epithelial cells, they are characterized by strong cell junctions. This provides a physical barrier that constitutes an important line of defense between the gut contents and the immune system of the host. Despite the epithelial barrier, some antigens are able to infiltrate the M cell barrier and infect the nearby epithelial cells or enter the gut.^[3]