Table 1.
Membrane-bound innate receptors and their ligands
| Receptors and their ligands | Locations | Adaptors | |
|---|---|---|---|
| TLRs and ligands | |||
| TLR1 | Tri-acyl lipoprotein | Cell surface | MyD88/Mal |
| TLR2 | Gram-positive peptidoglycan and lipoteichoic acid; fungi zymosan; mycobacteria lipoarabinomannan; Trypanosoma cruzi glycoinositolphospholipids; Treponema maltophilum glycolipids; Neisseria porins; viral glycoproteins |
Cell surface | MyD88/Mal |
| TLR3 | Virus double-stranded RNA; poly I : poly C; poly I [150] | Endosomal | TRIF |
| TLR4 | Gram-negative LPS; MMTV envelope proteins; RSV fusion proteins; toxol | Cell surface | MyD88/Mal/Trif/Tram |
| TLR5 | Bacteria flagellin | Cell surface | MyD88 |
| TLR6 | Mycoplasma di-acyl lipopeptides | Cell surface | MyD88/Mal |
| TLR7 | Virus single-stranded RNA; small synthetic compounds—bropirimine, imidazoquinoline; loxoribine |
Endosomal | MyD88 |
| TLR8 | Virus single-stranded RNA; imidazoquinoline | Endosomal | MyD88 |
| TLR9 | Bacterial and viral unmethylated CpG DNA; malaria pigment haemozoin | Endosomal | MyD88 |
| TLR10 | Unknown (human only) | Cell surface | Unknown |
| TLR11 | Toxoplasma gondi profilin-like protein [151] | Cell surface | MyD88 |
| TLR12 | Unknown (mice only) | Unknown | Unknown |
| TLR13 | Unknown (mice only) | Unknown | Unknown |
| C-type lectin receptors | |||
| MR* | Ligands bearing mannose, fucose, or N-acetyl glucosamine | Cell surface | Cdc42, Rho [152] |
| DC-SIGN | ICAM2/3; HIVgp120; M. tuberculosis ManLAM | Cell surface | Unknown |
| Dectin-1 | Fungus β-glucans; zymosan | Cell surface | Src; Syk; Tec [153] |
| Scavenger receptors | |||
| CD36 | Apoptotic cells; collagen types I and IV; erythrocyte membrame protein 1; oxidized LDL; Plasmodium falciparum GPI [154]; platelet-agglutinating protein p37; thrombospondin |
Cell surface | Lyn; MEKK2 [155] |
| MARCO | LPS, LTA (lipoteichoic acid); acetylated LDL; uteroglobin-related protein 1 | Cell surface | Unknown |
| SRA* | Apoptotic cells; LPS; LTA; oxidized LDL; polyribonucleic acids | Cell surface | Unknown |
| Complement receptors | |||
| CR3, CR4 | iC3b; β-glucan; fibrinogen | Cell surface | Cytohesin-1 [156] |
| C5aR | C5a | Cell surface | Unknown |
| gC1qR | C1q | Cell surface | CD59 [157] |