M cell

M cells (or microfold cells) are cells found in the follicle-associated epithelium of the Peyer's patch that have the unique ability to sample antigen from the lumen of the small intestine and deliver it via transcytosis to antigen presenting cells and lymphocytes located in a unique pocket-like structure on their basolateral side.

Structure
M cells differ from normal enterocytes in that they lack microvilli on their apical surface, but instead possess broader microfolds that give the cell its name.

The filamentous brush border glycocalyx, an extracellular polysaccharide layer found throughout the intestine attached to enterocytes, is much thinner or absent on M cells.

Pathology
M cells are exploited by several pathogens, including Shigella flexneri, Salmonella typhimurium, and Yersinia pseudotuberculosis, as a way to penetrate the intestinal epithelium.

Development
Factors promoting the differentiation of M cells have yet to be elucidated, but they are thought to develop in response to signals from immune cells found in the developing Peyer's patch.