Bench-to-bedside review: Platelets and active immune functions - new clues for immunopathology?

Table 1 Proposed exogenous and endogenous ligands for principal Toll-like receptors

Receptor	Synthetic ligands	Natural ligands	Ligand origin
TLR1-2	Pam3CSK4	Triacyl lipopeptides	Bacteria and mycobacteria
TLR2		Lipoprotein/lipopeptide	Various pathogens
		Peptidoglycan	Gram-positive bacteria
		Lipoteichoic acid	Gram-positive bacteria
		Lipoarabinomannan	Mycobacteria
		Phenol-soluble modulin	Staphylococcus epidermidis
		Glycoinositol phospholipids	Trypanosoma cruzi
		Glycolipids	Treponema maltophilia
		Porins	Neisseria
		Atypical lipopolysaccharide	Leptospira interrogans
		Atypical lipopolysaccharide	Porphyromonas gingivalis
		Zymosan	Fungi
		HSP 70	Host
		Necrotic or dying cells	Host
		Versican	Host
		Antiphospholipid antibodies	Host
		Amyloids	Host
TLR2-6	FSL1, MALP2, Pam2CSK4	Diacyl lipopeptides	Mycoplasma
TLR2-4		HMGB1	Host
		Biglycan	Host
TLR4		Lipopolysaccharide	Gram-negative bacteria
		Taxol	Plants
		Fusion protein	Respiratory syncytial virus
		Envelope protein	Mouse mammary-tumor virus
		?	Chlamydia pneumoniae
		HSP 60	Host
		HSP 70	Host
		Type III repeat extra domain A of fibronectin	Host
		Oligosaccharides of hyaluronic acid	Host
		Polysaccharide fragments of heparan sulfate	Host
		Fibrinogen	Host
		Necrotic or dying cells	Host
		MRP-8/14	Host
		F-EDA	Host
		Hyaluronan	Host
		Tenascin-C	Host
		mmLDL	Host
		OxPAPC	Host
		OxLDL	Host
		AGE-LDL	Host
		Surfactant protein A	Host
		b-Defensin	Host
TLR6		Diacyl lipopeptides	Mycoplasma
		Lipoteichoic acid	Gram-positive bacteria
		Zymosan	Fungi
TLR9	CpG-A, CpG-B, CpG-C ODNs	CpG DNA	Bacteria

AGE-LDL, advanced glycation end-product of low-density-lipoprotein; F-EDA, extra domain A of fibronectin; HSP, heat-shock protein; mmLDL, minimally modified low density lipoprotein; MRP, myeloid-related protein; OxLDL, oxidized low-density lipoprotein; OxPAPC, oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycerol-2-phosphatidylcholine; ?, unknown.

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