Table 1.

TLRs—their microbial, endogenous ligands and cellular distribution

Receptor	Microbial ligand(s)	Endogenous ligands	Cellular expression
TLR1	Triacyl lipopeptides		B cells, monocytes, macrophages, and certain dendritic cells
TLR2	Peptodoglycan, zymosan, lipoteichoic acid, and glycolipids	HSP60, HSP70, hyaluronan, HMGB1	Monocytes and macrophages, mast cells and myeloid dendritic cells
TLR3	Double-stranded RNA, poly I:C	Messenger RNA (mRNA)	B cells, dendritic cells, and fibroblasts
TLR4	LPS	Fibrinogen, HSPs, surfactant protein A, b-defensin 2, hyaluronan, fibronectin extra domain A, heparin sulfate, HMGB-1	Monocytes and macrophages, mast cells, certain dendritic cells, B cells; intestinal epithelium and hepatocytes (low)
TLR5	Flagellin		Monocytes and macrophages, subset of dendritic cells; intestine
TLR6	Multiple diacyl lipopeptides on mycoplasma		B cells, mast cells, and macrophages
TLR7	Single-stranded RNA imidazoquinolines	RNA and protein complexes	Plasmacytoid dendritic cells, monocytes, and macrophages; B cells
TLR8	Single-stranded RNA imidazoquinolines and small synthetic compounds		Monocytes and macrophages; subset of dendritic cells; mast cells
TLR9	CpG oligodeoxynucleotide DNA		Monocytes, macrophages, and plasmacytoid dendritic cells
TLR10	Undefined		B cells, monocytes, and regulatory T cells
TLR11	Profilin		Kidney and urinary bladder epithelium
TLR12	Profilin		Macrophages, neurons, and dendritic cells
TLR13	Conserved bacterial 23S ribosomal RNA (rRNA) sequence		Monocytes, macrophages, and dendritic cells

Data based on Robson (2009).