Toll-like Receptor - Summary of Known Mammalian TLRs

Summary of Known Mammalian TLRs

Toll-like receptors bind and become activated by different ligands, which, in turn, are located on different types of organisms or structures. They also have different adapters to respond to activation and are located sometimes at the cell surface and sometimes to internal cell compartments. Furthermore, they are expressed by different types of leucocytes or other cell types:

Receptor Ligand(s) Ligand location Adapter(s) Location Cell types
TLR 1 multiple triacyl lipopeptides Bacteria MyD88/MAL cell surface
  • monocytes/macrophages
  • a subset of dendritic cells
  • B lymphocytes
TLR 2 multiple glycolipids Bacteria MyD88/MAL cell surface
  • monocytes/macrophages
  • Myeloid dendritic cells
  • Mast cells
multiple lipopeptides Bacteria
multiple lipoproteins Bacteria
lipoteichoic acid Gram-positive bacteria
HSP70 Host cells
zymosan (Beta-glucan) Fungi
Numerous others
TLR 3 double-stranded RNA, poly I:C viruses TRIF cell compartment
  • Dendritic cells
  • B lymphocytes
TLR 4 lipopolysaccharide Gram-negative bacteria MyD88/MAL/TRIF/TRAM cell surface
  • monocytes/macrophages
  • Myeloid dendritic cells
  • Mast cells
  • B lymphocytes
  • Intestinal epithelium
several heat shock proteins Bacteria and host cells
fibrinogen host cells
heparan sulfate fragments host cells
hyaluronic acid fragments host cells
nickel
Various opioid drugs
TLR 5 flagellin Bacteria MyD88 cell surface
  • monocyte/macrophages
  • a subset of dendritic cells
  • Intestinal epithelium
TLR 6 multiple diacyl lipopeptides Mycoplasma MyD88/MAL cell surface
  • monocytes/macrophages
  • Mast cells
  • B lymphocytes
TLR 7 imidazoquinoline small synthetic compounds MyD88 cell compartment
  • monocytes/macrophages
  • Plasmacytoid dendritic cells
  • B lymphocytes
loxoribine (a guanosine analogue)
bropirimine
single-stranded RNA RNA viruses
TLR 8 small synthetic compounds; single-stranded RNA MyD88 cell compartment
  • monocytes/macrophages
  • a subset of dendritic cells
  • Mast cells
TLR 9 unmethylated CpG Oligodeoxynucleotide DNA Bacteria, DNA viruses MyD88 cell compartment
  • monocytes/macrophages
  • Plasmacytoid dendritic cells
  • B lymphocytes
TLR 10 unknown unknown ?
TLR 11 Profilin Toxoplasma gondii MyD88 cell compartment
  • monocytes/macrophages
  • liver cells
  • kidney
  • urinary bladder epithelium
TLR 12 unknown unknown ?
  • Neurons
TLR 13 bacterial ribosomal RNA sequence “CGGAAAGACC” Virus, bacteria MyD88, TAK-1 cell compartment
  • monocytes/macrophages
  • conventional dendritic cells

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