Table 1.
PRRs in the pulmonary epithelium
| Receptor | Canonical Activating Ligands | Upregulated by | Compartment | Adaptor protein | |
|---|---|---|---|---|---|
| Toll-like Receptors | TLR2/1 | Triacylated lypopeptides (e.g., Pam3CSK4) | P.M. | MyD88 | |
| TLR2/6 | Diacylated lipopeptides (e.g., Pam2CSK4) | Diacylated lipopeptides, ODNs, NTHi | P.M. | MyD88 | |
| TLR3 | dsDNA, poly (I:C) | Poly (I:C) | Endosome | TRIF | |
| TLR4 | LPS, LBP | P.M. | MyD88, TRIF | ||
| TLR5 | Flagellin | P.M. | MyD88 | ||
| TLR7 | ssRNA | Endosome | MyD88 | ||
| TLR8 | ssRNA | Endosome | MyD88 | ||
| TLR9 | CpG ODN | Diacylated lipopeptides, ODNs, NTHI | Endosome | MyD88 | |
| TLR11 | Profilin, flagellin | P.M. | MyD88 | ||
|
| |||||
| NOD-Like Receptors | NOD1 | D-glutamyl-meso-diaminopimelic acid | Cytosol | RIP2, ATGL16 | |
| NOD2 | MDP | Cytosol | RIP2, ATGL16 | ||
| NLRP1 | B. anthracis lethal toxin, MDP, ribonucleoside triphosphate | TLR stimulation | Cytosol | ASC inflammasome | |
| NLRP3 | K. pneumonie, S. pneumonie, S. aureus, C. pneumonie, M. tuberculosis, influenza, rhinovirus, RSV, A. fumigatus, ROS, mitochondrial dysfunction, K efflux, Ca mobilization, ATP, uric acid, hyaluronan, silica, asbestos | Host GI microbiota, TLR stimulation | Cytosol | ASC inflammasome | |
| NLRP4 | Unknown | Unknown | Cytosol | Beclin-1 | |
| NAIP | T3SS needle protein (Cpr1), flagellin | Cytosol | NLRP4 inflammasome | ||
| NAIP2 | P. aeruginosa, T3SS (Prg1) | Cytosol | NLRP4 inflammasome | ||
| NAIP5 | Flagellin | Cytosol | NLRC4 inflammasome | ||
| NLRC4 | L. pneumophila, K. pneumonia, flagellum proteins, T3SS | Cytosol | ASC inflammasome | ||
| NLRC5 | Viruses | Cytosol | ASC inflammasome | ||
| NLRX1 | RNA | Mitochondria | MAVS | ||
|
| |||||
| RLRs | RIG-I | 5’PPP-ssRNA, Paramyxoviruses, influenza, Japanese encephalitis virus, reoviruses, flaviviruses | Type 1 IFN | Cytosol | MAVS |
| MDA5 | Poly (I:C), picoraviruses, flaviviruses, reoviruses | Type I IFN | Cytosol | MAVS | |
|
| |||||
| Nucleotide | cGAS | DNA | Cytosol | STING-IRF3 | |
| STING | Cyclic di-nucleotides | E.R. | STING-IRF3 | ||
| IFI16 | DNA | Cytosol | STING | ||
| AIM2 | DNA | Cytosol | AIM2 inflammasome | ||
TLR, toll-like receptor; P.M., plasma membrane; E.M., endoplasmic reticulum; LPS, lipopolysaccharide; LBP, lipopolysaccaride-binding protein; ODN, oligodeoxynucleotide; NTHi, non-typeable Haemophilus influenza; MDP, muramyl dipeptide; RSV, respiratory syncitial virus; ROS, reactive oxygen species; ATP, adenosine triphosphate; GI, gastrointestinal; TTSS, type three secretion system; RLRs, Rig-I-like receptors; Poly I:C: poly-inosine:poly-cytosine