M cells are cells found in the follicle-associated epithelium of the Peyer's patch. They transport organisms and particles from the gut lumen to immune cells across the epithelial barrier, and thus are important in stimulating mucosal immunity.

Unlike their neighbouring cells, they have the unique ability to take up antigen

Antigen

An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

 from the lumen

Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...

 of the small intestine

Small intestine

The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...

 via endocytosis

Endocytosis

Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...

 or phagocytosis, and then deliver it via transcytosis

Transcytosis

Transcytosis is the process by which various macromolecules are transported across the interior of a cell. Vesicles are employed to intake the macromolecules on one side of the cell, draw them across the cell, and eject them on the other side. While transcytosis is most commonly observed in cells...

 to dendritic cells (an antigen presenting cell) and lymphocytes (namely T cells) located in a unique pocket-like structure on their basolateral side.

Structure and function

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. These cells are also far less abundant than enterocytes. M cells are readily accessible for antigens in the gut lumen to travel through to the Peyer's patch because they do not secrete mucus or digestive enzymes and the filamentous brush border glycocalyx

Glycocalyx

Glycocalyx is a general term referring to extracellular polymeric material produced by some bacteria, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide matrix excreted by epithelial cells forming a...

 (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

Shigella flexneri

Shigella flexneri is a species of Gram-negative bacteria in the genus Shigella that can cause diarrhea in humans. There are several different serogroups of Shigella; S. flexneri belongs to group B. S. flexneri infections can usually be treated with antibiotics although some strains have become...

, Salmonella typhimurium, and Yersinia pseudotuberculosis

Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is a Gram-negative bacterium that causes Pseudotuberculosis disease in animals; humans occasionally get infected zoonotically, most often through the food-borne route.-Pathogenesis:In animals, Y...

, as well as infectious prions in Bovine spongiform encephalitis (Mad-cow disease), as a way to penetrate the intestinal epithelium.
EPEC containing plasmids with genes for EAF(E coli Adherence Factor)will adhere to M cells.

They are also exploited by viruses such as Polio and Reovirus for dissemination.
CXCR4

CXCR4

C-X-C chemokine receptor type 4 also known as fusin or CD184 is a protein that in humans is encoded by the CXCR4 gene.- Function :...

 tropic but not CCR5

CCR5

C-C chemokine receptor type 5, also known as CCR5, is a protein that in humans is encoded by the CCR5 gene. CCR5 is a member of the beta chemokine receptors family of integral membrane proteins...

tropic HIV has been noted to be able to bind to M cells and get transported across the epithelium by them.

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.

External links

• Slide at ucsd.edu