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Toll-like receptor
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<p>Toll-like receptors (TLRs) are a class of <a href="/facts/Protein/Jxmagu3E">proteins</a> that play a key role in the <a href="/facts/Innate_immune_system/lz4BpSQI">innate immune system</a>. They are <a href="/facts/Single-pass_membrane_protein/2fEb1WCB">single-spanning</a> <a href="/facts/Receptor_(biochemistry)/tjTAC76a">receptors</a> usually expressed on <a href="/facts/Sentinel_cell/hjBvVDqr">sentinel cells</a> such as <a href="/facts/Macrophage/z7hkQu3o">macrophages</a> and <a href="/facts/Dendritic_cell/19KBuKFK">dendritic cells</a>, that recognize structurally conserved molecules derived from <a href="/facts/Microorganism/pysJYcE2">microbes</a>. Once these microbes have reached physical barriers such as the skin or <a href="/facts/Intestinal_tract/nK2zwqBS">intestinal tract</a> <a href="/facts/Mucosa/oIw0vyel">mucosa</a>, they are recognized by TLRs, which activate <a href="/facts/Immune_cell/vsDunUK0">immune cell</a> responses. The TLRs include <a href="/facts/TLR1/5HpfNyr8">TLR1</a>, <a href="/facts/TLR2/bIakKlze">TLR2</a>, <a href="/facts/TLR3/fuMMcUcb">TLR3</a>, <a href="/facts/TLR4/0EUN8zKI">TLR4</a>, <a href="/facts/TLR5/SHAwTAwT">TLR5</a>, <a href="/facts/TLR6/PCRFz7Xl">TLR6</a>, <a href="/facts/TLR7/ATccMT3u">TLR7</a>, <a href="/facts/TLR8/bArkjd6c">TLR8</a>, <a href="/facts/TLR9/2uxbm5kB">TLR9</a>, <a href="/facts/TLR10/f6w2Kup4">TLR10</a>, <a href="/facts/TLR11/s8xhD6vK">TLR11</a>, TLR12, and TLR13. Humans lack genes for TLR11, TLR12 and TLR13 and mice lack a functional gene for TLR10. The receptors TLR1, TLR2, TLR4, TLR5, TLR6, and TLR10 are located on the <a href="/facts/Cell_membrane/vAXSD0DT">cell membrane</a>, whereas TLR3, TLR7, TLR8, and TLR9 are located in <a href="/facts/Intracellular_receptor/Up8SbQIX">intracellular</a> <a href="/facts/Vesicle_(biology_and_chemistry)/1KjHpjMM">vesicles</a> (because they are sensors of <a href="/facts/Nucleic_acid/2tTgcI0v">nucleic acids</a>). </p><p>TLRs received their name from their similarity to the protein coded by the <a href="https://wikidoc.org/index.php/Toll_(gene)">toll gene</a>. </p>