Table 1.

The TLRs specific for ligands associated with the exterior surfaces of microbes

Receptor	Best defined ligand(s)	Key features
TLR1	Triacylated bacterial lipoproteins	Forms heterodimers with TLR2
TLR2	Di- and triacylated bacterial lipoproteins	Forms heterodimers with TLR1 or TLR6 (TLR10 in humans)
TLR3	Double-stranded RNA	Ectodomain must be cleaved to form an active receptor
TLR4	Bacterial lipopolysaccharide	Recognizes ligands indirectly via MD2
TLR5	Bacterial flagellin
TLR6	Diacylated bacterial lipoproteins	Forms heterodimers with TLR2
TLR7	Single-stranded RNA	Ectodomain must be cleaved to form an active receptor
TLR8	Single-stranded RNA	Ectodomain must be cleaved to form an active receptor
TLR9	Unmethylated CpG-containing DNA	Ectodomain must be cleaved to form an active receptor
TLR10	Unknown	Pseudogene in mice; present in humans; forms heterodimers with TLR2
TLR11	Toxoplasma profilin/bacterial flagellin	Forms heterodimers with TLR12
TLR12	Toxoplasma profilin	Forms heterodimers with TLR11
TLR13	Bacterial 23s ribosomal RNA
Dectin-1	Fungal β-glucan
Dectin-2	Fungal α-mannans	Forms heterodimers with Dectin-3
Dectin-3	Fungal α-mannans	Forms heterodimers with Dectin-2
RIG-I	Short dsRNA with 5′ triphosphate	Detects ligands in the cytosol
MDA5	Long dsRNA	Detects ligands in the cytosol
cGAS	DNA	Detects ligands in the cytosol