Table 1.

TLRs, their cellular location, ligand recognitions, and adaptor usage.

Type of TLR	Cellular location	Exogenous ligands (PAMP)	Endogenous ligands (DAMP)	Signal adaptor
TLR1 (in association with TLR2)	Cell surface	Bacteria: triacyl lipopeptides	Unknown	MyD88
TLR2 (in association with TLR1 or TLR6)	Cell surface	Bacteria: peptidoglycan, lipoproteins, lipoteichoic acid, lipoarabinomannan, glycophosphatidylinositol anchors, porin; fungi: zymosan	HSP60, HSP70, Gp96 biglycan, hyaluronic acid, hyaluronan, HMGB1, versican, monosodium urate crystal	MyD88/TIRAP
TLR6 (in association with TLR2)	Cell surface	Mycoplasma: macrophage-activating lipopeptide 2	Versican	MyD88
TLR3	Endosomal compartment	Viruses: dsRNA	mRNA	TRIF
TLR4	Cell surface	Bacteria: LPS Viruses: RSV fusion protein Fungi: mannan Protozoa: glycoinositolphospholipids	HSP22, HSP 60, HSP70, HSP72, Gp96, HMGB1, S100, oxidized phospholipids, heparin sulfate, fibrinogen, fibronectin, tenascin-C, b-defensin 2, versican, hyaluronic acid, hyaluronan	MyD88/TIRAP/ TRAM/TRIF
TLR5	Cell surface	Bacteria: flagellin	Unknown	MyD88
TLR7	Endosomal compartment	Viruses: ssRNA	ssRNA (immune complex)	MyD88
TLR8	Endosomal compartment	Viruses: ssRNA	ssRNA (immune complex)	MyD88
TLR9	Endosomal compartment	Bacteria: CpG DNA Viruses: CpG DNA Protozoa: CpG DNA, haemozoin	Chromatin IgG complex, HMGB	MyD88