26 Chapter 2 Table 1. Pattern recognition receptors and their ligands in humans Pattern recognition receptor Ligand Origin of ligand Toll-like receptors (TLRs) TLR1 Triacyllipoprotein (forms heterodimer with TLR2), soluble factors Bacteria TLR2 Lipoprotein (forms heterodimer with TLR1 and TLR6) Bacteria, viruses, fungi, self TLR3 Double-stranded RNA Viruses TLR4 Lipopolysaccharide, envelop proteins (syncytial viruses), glycoinositol phospholipids, HSPs 60 and 70, S100a8 (ligand from dying cells) Bacteria, viruses, self TLR5 Flagellin Bacteria TLR6 Diacyllipoprotein (forms heterodimer with TLR2) Bacteria, viruses TLR7 Single stranded RNA, synthetic compounds (e.g. imidazoquinolines) Bacteria, viruses, self TLR8 Single stranded RNA, small purine analog compounds (imidazoquinolines) Viruses TLR9 CpG-DNA, insoluble crystal hemozoin (Plasmodium falciparum) Bacteria, viruses, parasites, self TLR10 Unknown NOD-like receptors (NLRs) NOD1 Peptidoglycan (iE-DAP) Bacteria NOD2 Peptidoglycan (MDP) Bacteria C-type lectins (CLRs) Dectin-1 β-Glucan Fungi Dectin-2 β-Glucan Fungi MINCLE SAP130 Fungi, self Retinoic-acid inducible gene (RIG)-I-like receptors (RLRs) RIG-I Short double-stranded RNA, 5’triphosphate dsRNA Viruses MDA5 Long double-stranded RNA Viruses LGP2 Double-stranded RNA Viruses DDX3 Viral RNA Viruses The innate immune system recognizes pathogens by four main classes of pattern recognition receptors. The table shows the main receptors, their main ligands and the origin of these ligands. Note that some receptors also recognize “self” antigens, primarily in the context of injury, wherein self-antigens function as alarmins to the host. Abbreviations: CpG-DNA: cytosine-phosphateguanosine-DNA, DDX3: DEAD/H Box 3, iE-DAP: g-D-glutamyl-meso-diaminopimelic acid, LGP2: Laboratory of genetics and physiology-2, MDA5: melanoma differentiation-associated gene 5, MDP: muramyl dipeptide, MINCLE: macrophage-inducible C-type lectin, SAP130: Sin3Aassociated protein of 130kDa. Table adapted from references 8, 10 and 59.
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