Table 1.
Summary of some pattern recognition receptors and their functions in innate immunity.
| Ligand (adaptors in parentheses) | PRRs | Ligand (origin in parentheses) | Localization | Function in neutrophil | Signals | Response | Ref |
|---|---|---|---|---|---|---|---|
|
TLRs
(TRAM, Trif, Mal, MyD88) |
TLR1 | Triacyl lipopeptides (bacterial lipoprotein) Di-/triacyl lipopeptides |
Cell surface | Migration, Inhibit apoptosis, NET formation, Respiratory burst, Degranulation, Phagocytosis | IRFs NF-κB MAPKs |
Pro–IL-1, pro–IL-18 Antiviral proteins Chemokines Cytokines |
(85, 86) |
| TLR2 | Multiple lipoproteins, Lipoteichoic acid, Zymosan (fungi) |
Cell surface | Formation of heterophilic dimers with TLR1 and TLR6, Respiratory burst, Neutrophil migration, Degranulation, apoptotic regulator, Phagocytosis | (87, 88) | |||
| TLR4 | LPS (Gram-negative bacteria) | Cell surface | Recognition of LPS together with myeloid differentiation factor 2, Respiratory burst, NET formation, Neutrophil migration, Phagocytosis, Inhibit apoptosis, Degranulation | (89–91) | |||
| TLR5 | Flagellin (flagellated bacteria) | Cell surface | Activation of lung epithelial cells to induce inflammatory cytokine, NET formation, Inhibit apoptosis, Phagocytosis, Degranulation | (92, 93) | |||
| TLR6 | Triacyl lipopeptides (bacterial lipoprotein) |
Cell surface | Formation of heterophilic dimers with TLR2, Respiratory burst, Inhibition of apoptosis, Phagocytosis, NET formation, Degranulation, | (94) | |||
| TLR8 | ssRNA (viruses); small antiviral compounds | Endosome | Recognition of synthetic compound imidazoquinoline, Neutrophil migration, NET formation, Respiratory burst, Degranulation, Inhibition of apoptosis, Phagocytosis | (90, 91) | |||
| TLR9 | Unmethylated CpG DNA |
Endosome | Degranulation, Phagocytosis, Respiratory burst, Inhibit apoptosis, NET formation, Migration, Proinflammatory cytokines | (95, 96) | |||
| TLR10 | Unknown | No neutrophil function described | (94, 97) | ||||
| NLRs (MyD88) | NLRC4 (IPAF) | Bacterial flagellin and other components of the bacterial secretion apparatus | Cytoplasm | Trigger the secretion of IL-1β from neutrophils. | NF-κB Caspase-1 |
IL-1, IL-18 | (98, 99) |
| NOD1 | Peptidoglycan (Gram-negative bacteria) |
Cytoplasm | Recognition of intracellular bacterial cell products, Phagocytosis, Bacterial killing, neutrophil migration | (100, 101) | |||
| NOD2 | Peptidoglycan (Gram-positive bacteria) |
Cytoplasm | Recognition of intracellular bacterial cell products, Phagocytosis, neutrophil migration, Bacterial killing, Degranulation | (100, 102) | |||
| NOD5/NLRX1 | dsRNA (viruses) | In response to TLR2 ligands, NLRX1 induces the production of neutrophil ROS. | (103) | ||||
| NLRP1 | Muramyl dipeptide moiety of PGN (bacterial cell wall); Anthrax lethal toxin (Bacillus anthracis) |
No neutrophil function described | (98, 104) | ||||
| NLRP3 | PAMPs, virulence factor, DAMPs | Endosome | Response to multiple stimuli via forming a NALP3 inflammasome and secreting IL-1β, caspase-1 activation | (98, 100) | |||
| NLRP6 | Unknown | It negatively regulates TLR-induced canonical NF-kB and MAPK pathways in murine | (105, 106) | ||||
| NLRP12 | It mediates the secretion of IL-1β induced by inflammasomes in neutrophils. | (107) |