Microfold Cells

Where the M Cells present?

Microfold  Cells or M Cells are present in follicle-associated epithelium (FAE)

Follicle -associated epithelium is a specialized epithelium present over  Peyer’s  patch in small intestine and isolated lymphoid follicles.

M cells are seen in epithelial cells of the mucosa-associated lymphoid tissues.

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.

	Microfold cells (or M cells) are found
1	GALT - Gut-associated lymphoid tissue	Peyer's patches in the small intestine
2	MALT - Mucosa-associated lymphoid tissue	Other parts of the gastrointestinal tract.

What are the antigen-presenting cells?

	Antigen-presenting cells
1	B lymphocytes
2	Dendritic cells

What is function of the M Cells?

M cells helps to transport antigens from intestinal lumen to  immune system cells, and starts

an immune response or tolerance.

M cells function are phagocytosis and transcytosis. M cells are capable of taking up large particulate antigens from the lumen and transporting them intact into the subepithelial space.

	Function of the M Cells
1	Selective endocytosis of antigens from gut lumen
2	Transport of microbes and antigens to intraepithelial macrophages and lymphocytes
3	Macrophages and lymphocytes migrate to lymph nodes to start immune response

How the M Cells take up antigens from lumen and delivered to antigen-presenting cells?

	M Cells mechanism to take up antigens
1	Endocytosis
2	Phagocytosis
3	Transcytosis

Which pathogens exploit M Cells ?

	Mechanism of exploiting M Cells	Organisms
	To penetrate intestinal epithelium	Shigella flexneri
		Salmonella typhimurium
		Yersinia pseudotuberculosis
		Prions- bovine spongiform encephalitis (Mad-cow disease)
	Exploitation as a virulence factor	EPEC -Pathogenic Escherichia coli
	For Dissemination	Polio and Reovirus

How polio virus exploits M Cells for dissemination?

M cells express lectin-like molecules in the apical surface. These molecules  help to promote binding to poliovirus and helps in dissemination.

What is the mechanism where M cells involved with IgA response in payer patches?

Antigens that bind to the M cell and are transported to the underlying Peyer patches generally elicit a positive (IgA) response.

M cell helps to connect  Peyer patches and lymphoid follicles as conduit.

Once antigens enter the Peyer patch, TGF-β-secreting T cells promote B cell isotype switching to IgA.

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If Peyer patch B cells are absent then  M cells are also absent. [M cells have not seen in B cell–deficient animals, which lack Peyer patches]

Peyer  patches have T cell-dependent areas and B cell-dependent/germinal centers typical of lymph nodes, but only efferent lymphatics.