What is Toll-like receptor?
[[Image:TLR3 structure.png|thumb|right|300px|The curved [[leucine-rich repeat]] region of Toll-like receptors, represented here by TLR3]] '''Toll-like receptors''' ('''TLRs''') are [[protein]]s which act in the [[innate immune system]] and the [[digestive system]]. They are [[Cell membrane|membrane]]-spanning, that is, they reach from the outside of the [[cell]] to the inside. TLRs recognize [[molecules]] which come from [[microbe]]s. Once microbes get through physical barriers such as the [[skin]] or [[intestinal tract]] [[mucosa]], they are recognized by TLRs. The TLRs set up an [[immune cell]] response. TLR signalling leads to the induction or suppression of genes that orchestrate the inflammatory response. In all, thousands of genes are activated by TLR signalling, and the TLRs are one of the most important means of [[Gene expression|gene modulation]]. Toll-like receptors have also been shown to be an important link between innate and [[Adaptive immune system|adaptive immunity]] through their presence in [[dendritic cell]]s. == Extended family == Most [[mammal]]ian [[species]] have between ten and fifteen types of Toll-like receptors. Thirteen TLRs (TLR1 to TLR13) have been identified in humans and [[mice]], and similar ones have been found in other mammalian species.<ref>{{cite journal |author=Du X, Poltorak A, Wei Y, Beutler B |title=Three novel mammalian toll-like receptors: gene structure, expression, and evolution |journal=Eur. Cytokine Netw. |volume=11 |issue=3 |pages=362–71 |year=2000 |pmid=11022119 |doi= |url=http://www.john-libbey-eurotext.fr/medline.md?issn=1148-5493&vol=11&iss=3&page=362}}</ref><ref>{{cite journal |author=Chuang TH, Ulevitch RJ |title=Cloning and characterization of a sub-family of human toll-like receptors: hTLR7, hTLR8 and hTLR9 |journal=Eur. Cytokine Netw. |volume=11 |issue=3 |pages=372–8 |year=2000 |pmid=11022120 |doi= |url=http://www.john-libbey-eurotext.fr/medline.md?issn=1148-5493&vol=11&iss=3&page=372}}</ref><ref>{{cite journal |author=Tabeta K, Georgel P, Janssen E