Table 1.

Exogenous and endogenous TLR ligands.

TLRs	Major cell types	Exogenous ligands	Endogenous ligands
TLR1	Myeloid cells T, B and NK cells, microglia, astrocytes	Bacterial triacyl-lipopeptide
TLR2	Myeloid cells, T cells, microglia, astrocytes, oligodendrocytes, neurons	Lipoproteins/lipopeptides, lipoteichoic acid, lipoarabinomannan, peptidoglycan, glycoinositolphospholipids, glycolipids, porins, zymosan, atypical lipopolysaccharide	Heat-shock proteins 60 and 70, Gp96, Saturated fatty acids
TLR3	Epithelial cells, dendritic cells, microglia, astrocytes, oligodendrocytes, neurons	Double-stranded RNA	mRNA
TLR4	Myeloid cells, microglia, astrocytes, neurons	Lipopolysaccharide, paclitaxel, respiratory syncytial virus fusion protein, mouse mammary tumor virus envelope proteins	Heat-shock proteins 60 and 70, Gp96, Type III repeat extra domain A of fibronectin, oligosaccharides of hyaluronic acid, polysaccharide fragments of heparin sulfate, fibrinogen, high mobility group box 1, surfactant protein-A, β-defensin 2
TLR5	Myeloid cells, epithelial cells, microglia, astrocytes	Flagellin
TLR6	Myeloid cells, dendritic cells, microglia, astrocytes	Phenol-soluble modulin, diacyl lipopeptides, lipoteichoic acid, zymosan
TLR7	B cells, dendritic cells, microglia, astrocytes	Imidazoquinoline, loxoribine, bropirimine, Single-stranded RNA
TLR8	Myeloid cells, microglia, astrocytes, neurons	Single-stranded RNA
TLR9	Epithelial and B cells, dendritic cells, microglia, astrocyte, neuron	Unmethylated CpG DNA	Chromatin-IgG complexes
TLR10	B cells, dendritic cells	Unknown, may interact with TLR2
TLR11	Myeloid cells, uroepithelial cells	Uropathogenic E. coli

(Marsh et al., 2009b[13];Takeda and Akira, 2004[18]; Cristofaro and Opal, 2006[67]; Guo and Schluesener, 2007[68]; Tsan and Gao, 2004[69];)