Table 1.
Toll-like receptors and their principal ligands.
| TLRs | Localization | Ligands | |||
|---|---|---|---|---|---|
| Exogenous | Endogenous | Synthetic analogs | Fully synthetic molecules | ||
| TLR1 | Plasma membrane | Lipopeptides (Bacteria and Mycobacteria) Soluble factors (Neisseria meningitidis) | Triacyl lipopeptides | ||
| TLR2 | Plasma membrane | Lipoprotein/lipopeptides (Gram-positive bacteria, Mycoplasma, Mycobacteria, Spirochetes) Peptidoglycan (Gram-positive bacteria) Lipoteichoic acid (Gram-positive bacteria) Phenol-soluble modulin (Staphylococcus epidermidis) Heat-killed bacteria (Listeria monocytogenes) Porins (Neisseria) Atypical lipopolysaccharides (Leptospira interrogans, Porphyromonas gingivalis) Soluble factors (Neisseria meningitidis) Glycolipids (Treponema maltophilia) Outer membrane protein A (Klebsiella pneumonia) Glycoinositolphospholipids (Trypanosoma cruzi) Phospholipomannan (Candida albicans) Structural viral proteins (Herpes simplex virus, Cytomegalovirus) Hemagglutinin (Measles virus) Lipoarabinomannan (Mycobacteria) Zymosan (Saccharomyces) |
HSP60 HSP70 HSP96 HMGB1 Hyaluronic acid |
Diacyl and triacyl lipopeptides | |
| TLR3 | Endolysosome | Single-stranded viral RNA (ssRNA) and double-stranded RNA (dsRNA; Viruses) | mRNA | Poly(I:C) Poly(I:C12U) |
|
| TLR4 | Plasma membrane | Lipopolysaccharide (Gram-negative bacteria) HSP60 (Chlamydia pneumonia) Envelope proteins (Respiratory syncytial virus and mouse mammary tumor virus) Fusion protein (syncytial virus) Glycoinositolphospholipids (Trypanosoma cruzi) Taxol (Plant product) |
HSP22 HSP60 HSP70 HSP96 HMGB1β-defensin 2 Extra domain A of fibronectin Hyaluronic acid Heparan sulfate Fibrinogen Surfactant-protein A |
Lipid A mimetics (Monophosphoryl lipid A, aminoalkyl glucosamine 4-phosphate) |
E6020 E5531 E5564 |
| TLR5 | Plasma membrane | Flagellin (Gram-positive or Gram-negative bacteria) | Discontinuous 13- amino acid peptide CBLB502 | ||
| TLR6 | Plasma membrane | Diacyl lipopeptides (Mycoplasma) Lipoteichoic acid (Gram-positive bacteria) Phenol-soluble modulin (Staphylococcus epidermidis) Zymosan (Saccharomyces) Heat-liable soluble factor (Group B streptococcus) |
Diacyl lipopeptides | ||
| TLR7 | Endolysosome | Single-stranded RNA (Viruses) | Endogenous RNA | Oligonucleotides | Imidazoquinolines (Imiquimod, Resiquimod) Guanosine nucleotides (Loxoribine, Isatoribine) Bropirimine |
| TLR8 | Endolysosome | Single-stranded RNA (Viruses) | Endogenous RNA | Imidazoquinolines (Resiquimod) | |
| TLR9 | Endolysosome | Unmethylated CpG motifs (Bacteria and viruses) Hemozoin (Plasmodium) |
Endogenous DNA | CpG oligodeoxynucleotides (CPG 7909, CPG 10101, 1018 ISS) | |
| TLR10 | Extracellular | Unknown, may interact with TLR2 and TLR1 | |||
| TLR11 | Plasma membrane | Profiling-like molecule (Toxoplasma gondii) | |||