Editing Peyer's patch (section)

== Function ==
Because the [[Lumen (anatomy)|lumen]] of the [[gastrointestinal tract]] is exposed to the external environment, much of it is populated with potentially [[pathogen]]ic [[microorganism]]s. Peyer's patches thus establish their importance in the immune surveillance of the intestinal lumen and in facilitating production of the immune response within the [[mucosa]].

Pathogenic microorganisms and other [[antigen]]s entering the intestinal tract encounter [[macrophages]], [[dendritic cell]]s, [[B-cells|B-lymphocytes]], and [[T-lymphocytes]] found in Peyer's patches and other sites of [[gut-associated lymphoid tissue]] (GALT). Peyer's patches thus act for the gastrointestinal system much as the [[tonsil]]s act for the [[respiratory system]], trapping foreign particles, surveilling them, and destroying them. Peyer's patches have adaptive immune capabilities through inducing selective apoptosis of B cells due [[CD122]]-targeted [[Interleukin 2|interleukin-2]] (IL-2) signaling. Additionally, the B cell population can be restored. <ref>{{Cite journal |last1=Singh |first1=Ayushi |last2=Dhume |first2=Kunal |last3=Tejero |first3=Joanne D. |last4=Strutt |first4=Tara M. |last5=McKinstry |first5=K. Kai |date=2020-07-29 |title=CD122-targetted IL-2 signals cause acute and selective apoptosis of B cells in Peyer's Patches |journal=Scientific Reports |language=en |volume=10 |issue=1 |pages=12668 |doi=10.1038/s41598-020-69632-5 |issn=2045-2322 |pmc=7391758 |pmid=32728053|bibcode=2020NatSR..1012668S }}</ref>

Peyer's patches are covered by a special follicle-associated epithelium that contains specialized cells called microfold cells ([[Microfold cell|M cells]]) which sample antigen directly from the lumen and deliver it to [[antigen-presenting cells]] (located in a unique pocket-like structure on their [[Epithelial polarity#Basolateral membranes|basolateral side]]). Dendritic cells and macrophages can also directly sample the lumen by extending dendrites through transcellular M cell-specific pores.<ref>{{cite journal | vauthors = Lelouard H, Fallet M, de Bovis B, Méresse S, Gorvel JP | title = Peyer's patch dendritic cells sample antigens by extending dendrites through M cell-specific transcellular pores | journal = Gastroenterology | volume = 142 | issue = 3 | pages = 592–601.e3 | date = March 2012 | pmid = 22155637 | doi = 10.1053/j.gastro.2011.11.039 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Bonnardel J, Da Silva C, Henri S, Tamoutounour S, Chasson L, Montañana-Sanchis F, Gorvel JP, Lelouard H | title = Innate and adaptive immune functions of peyer's patch monocyte-derived cells | journal = Cell Reports | volume = 11 | issue = 5 | pages = 770–84 | date = May 2015 | pmid = 25921539 | doi = 10.1016/j.celrep.2015.03.067 | doi-access = free | url = https://amu.hal.science/hal-01212685/file/1-s2.0-S2211124715003587-main.pdf }}</ref> At the same time the paracellular pathway of follicle-associated epithelium is closed tightly to prevent penetration of antigens and continuous contact with immune cells.<ref>{{cite journal | vauthors = Diener M | title = Roadblock for antigens--take a detour via M cells | journal = Acta Physiologica | volume = 216 | issue = 1 | pages = 13–4 | date = January 2016 | pmid = 26335934 | doi = 10.1111/apha.12595 | doi-access = free }}</ref> [[T cells]], [[B-cell]]s and memory cells are stimulated upon encountering [[antigen]] in Peyer's patches. These cells then pass to the [[mesenteric lymph nodes]] where the immune response is amplified. Activated lymphocytes pass into the blood stream via the [[thoracic duct]] and travel to the gut where they carry out their final effector functions. The maturation of B-lymphocytes takes place in the Peyer's patch.