Table 1.
Exogenous and endogenous ligands of Toll-like receptors (TLR) and main gastrointestinal cancers implicated in TLRs.
| TLRs | Exogenous Ligands | Endogenous Ligands | Cancer | Citation |
|---|---|---|---|---|
| TLR1 | Triacyl lipopeptide, LPS, Peptidoglycan | HSP, HMGB1, and Proteoglycans | ||
| TLR 2 | LPS, Peptidoglycan | HSP, HMGB1, Proteoglycans | GC, CRC | [23,24] |
| TLR 3 | Double-stranded RNA | mRNA and tRNA | EAC, ESCC | [25,26] |
| TLR 4 | LPS | Fibronectin, Polysaccharide fragments of heparan sulfate, HSP, Surfactant protein A in the lung epithelium 1, Neutrophil elastase, HMGB1, Biglycan | EAC, ESCC, GC, CRC | [27,28,29,30] |
| TLR 5 | Flagellin | GC, CRC | [31,32] | |
| TLR 6 | Diacyl lipopeptide, Zymosan | CRC | [33] | |
| TLR 7 | Single-stranded RNA | Single-stranded RNA complex | EAC, ESCC, CRC | [25,34,35] |
| TLR 8 | Single-stranded RNA, imidazoquinolines, guanosine analogs | Single-stranded RNA complex | EAC, CRC | [25,35] |
| TLR 9 | Unmethylated CpG DNA | Chromatin–IgG complex | ESCC, GC, CRC | [34,36,37] |
| TLR 10 | HIV-1 proteins | |||
| TLR 11 | Uropathogenic Escherichia coli |
LPS, lipopolysaccharide; HSP, heat shock proteins; HMGB1, high-mobility group protein 1; GC, gastric cancer; EAC, esophageal adenocarcinoma; ESCC, esophageal squamous cell carcinoma; CRC, colorectal cancer.