Editing Immune system (section)

===Immune sensing===
Cells in the innate immune system use [[pattern recognition receptor]]s to recognize molecular structures that are produced by pathogens.<ref name="Kumar_2011">{{cite journal | vauthors = Kumar H, Kawai T, Akira S | title = Pathogen recognition by the innate immune system | journal = International Reviews of Immunology | volume = 30 | issue = 1 | pages = 16–34 | date = February 2011 | pmid = 21235323 | doi = 10.3109/08830185.2010.529976 | s2cid = 42000671 }}</ref> They are [[protein]]s expressed, mainly, by cells of the [[innate immune system]], such as dendritic cells, macrophages, monocytes, neutrophils, and epithelial cells,{{sfn|Alberts|Johnson|Lewis|Raff|2002|loc= Chapter: [https://www.ncbi.nlm.nih.gov/books/NBK26846/ "Innate Immunity"] }}<ref>{{cite journal | vauthors = Schroder K, Tschopp J | s2cid = 16916572 | title = The inflammasomes | journal = Cell | volume = 140 | issue = 6 | pages = 821–32 | date = March 2010 | pmid = 20303873 | doi = 10.1016/j.cell.2010.01.040 | doi-access = free }}</ref> to identify two classes of molecules: [[pathogen-associated molecular patterns]] (PAMPs), which are associated with microbial [[pathogens]], and [[damage-associated molecular patterns]] (DAMPs), which are associated with components of host's cells that are released during cell damage or cell death.{{sfn | Sompayrac | 2019 | p=20}}

Recognition of extracellular or endosomal PAMPs is mediated by [[transmembrane protein]]s known as [[toll-like receptor]]s (TLRs).<ref name="pmid16551253">{{cite journal | vauthors = Beutler B, Jiang Z, Georgel P, Crozat K, Croker B, Rutschmann S, Du X, Hoebe K | s2cid = 20991617 | title = Genetic analysis of host resistance: Toll-like receptor signaling and immunity at large | journal = Annual Review of Immunology | volume = 24 | pages = 353–89 | year = 2006 | pmid = 16551253 | doi = 10.1146/annurev.immunol.24.021605.090552 }}</ref> TLRs share a typical structural motif, the [[Leucine-rich repeat|leucine rich repeats (LRRs)]], which give them a curved shape.<ref>{{cite journal | vauthors = Botos I, Segal DM, Davies DR | title = The structural biology of Toll-like receptors | journal = Structure | volume = 19 | issue = 4 | pages = 447–59 | date = April 2011 | pmid = 21481769 | pmc = 3075535 | doi = 10.1016/j.str.2011.02.004 }}</ref> Toll-like receptors were first discovered in ''[[Drosophila melanogaster|Drosophila]]'' and trigger the synthesis and secretion of [[cytokine]]s and activation of other host defense programs that are necessary for both innate or adaptive immune responses. Ten toll-like receptors have been described in humans.<ref>{{cite journal |vauthors=Vijay K |title=Toll-like receptors in immunity and inflammatory diseases: Past, present, and future |journal=Int Immunopharmacol |volume=59 |pages=391–412 |date=June 2018 |pmid=29730580 |pmc=7106078 |doi=10.1016/j.intimp.2018.03.002 }}</ref>

Cells in the innate immune system have pattern recognition receptors, which detect infection or cell damage, inside. Three major classes of these "cytosolic" receptors are [[NOD-like receptor|NOD–like receptors]], [[RIG-I-like receptor|RIG (retinoic acid-inducible gene)-like receptors]], and cytosolic DNA sensors.<ref>{{cite journal | vauthors = Thompson MR, Kaminski JJ, Kurt-Jones EA, Fitzgerald KA | title = Pattern recognition receptors and the innate immune response to viral infection | journal = Viruses | volume = 3 | issue = 6 | pages = 920–40 | date = June 2011 | pmid = 21994762 | pmc = 3186011 | doi = 10.3390/v3060920 | doi-access = free }}</ref>