Table 2.
PAMP recognition and responses by PRRs.
| PRR | Main ligand | Ligand binding domain | Signalling domain | Signalling pathway | Main immune response | Main target pathogen | References |
|---|---|---|---|---|---|---|---|
| TLRs | |||||||
| TLR 1 | Triacylglyceride | LRR | TIR | MyD88 – NF-κB | Proinflammatory cytokines | Gram-positive bacteria & fungi | Kumar et al. (2011) |
| TLR 2 | Peptidoglycans & Zymosan | LRR | TIR | MyD88 – NF-κB | Proinflammatory cytokines | Gram-positive bacteria & fungi | Kumar et al. (2011) |
| TLR 3 | dsRNA | LRR | TIR | TRIF – IRF3/7 | Type-1 IFN | RNA viruses | Kumar et al. (2011) |
| TLR 4 | LPS | LRR | TIR | MyD88 – NFκB & TRIF – IRF3/7 | Proinflamm. cytokines & type-1 IFN | Gram-negative bacteria | Kumar et al. (2011) |
| TLR 5 | Flagellin | LRR | TIR | MyD88 – NF-κB | Proinflammatory cytokines | Flagellated bacteria | Kumar et al. (2011) |
| TLR 6 | Diacylglyceride | LRR | TIR | MyD88 – NF-κB | Proinflammatory cytokines | Gram-positive bacteria & fungi | Kumar et al. (2011) |
| TLR 7 | ssRNA | LRR | TIR | MyD88 – NF-κB & MyD88 – IRF7 | Type-1 IFN (& proinflamm. cytokines) | Endosomal bacteria and viruses | Kumar et al. (2011) |
| TLR 8 | ssRNA | LRR | TIR | MyD88 – NF-κB | Proinflammatory cytokines | RNA viruses | Kumar et al. (2011) |
| TLR 9 | Unmethylated CpG DNA | LRR | TIR | MyD88 – NF-κB & MyD88 – IRF7 | Type-1 IFN (& proinflamm. cytokines) | Endosomal bacteria and viruses | Kumar et al. (2011) |
| TLR 10 | (Listeria monocytogenes?) | LRR | TIR | MyD88 – NF-κB | Proinflammatory cytokines | (Listeria monocytogenes?) | Kumar et al. (2011) |
| NLRs | |||||||
| NLRA (CIITA) subfamily | |||||||
| CIITA | Unknown | LRR | AD | NF-κB, MAPK and IRFs | Regulates MHC-II antigen presentation | Unknown | Kobayashi and van den Elsen (2012) and Lupfer and Kanneganti (2013) |
| NLRB subfamily | |||||||
| NAIPs | Flaggelin, Rod proteins in T3SS | LRR | BIR | Inflammasome | Secretion of IL-1β and IL-18, pyroptosis | Bacteria | Lupfer and Kanneganti (2013) |
| NLRC subfamily | |||||||
| NOD1 | Peptidoglycans (DAP-type) | LRR | CARD | NF-κB, MAPK and IRFs | Proinflamm. cytokines & type-1 IFN | Gram-positive bacteria | Kumar et al. (2011) |
| NOD2 | Peptidoglycans (mDP) | LRR | CARD | NF-κB, MAPK and IRFs | Proinflamm. cytokines & type-1 IFN | Gram-positive bacteria | Kumar et al. (2011) |
| NLRC4 (IPAF) | Flaggelin, Rod proteins in T3SS | LRR | CARD | Inflammasome | Secretion of IL-1β and IL-18, pyroptosis | Bacteria | Kumar et al. (2011) |
| NLRC3 | Unknown | LRR | X | Inhibits NF-κB activation | TLR signaling attenuation | Unknown | Schneider et al. (2012) |
| NLRC5 | Unknown | LRR | X | NF-κB, MAPK and IRFs | Regulates MHC-I antigen presentation | Unknown | Kobayashi and van den Elsen (2012) |
| NLRX1 | Viral RNA | LRR | X | NF-κB, MAPK and IRFs | TLR signaling attenuation | RNA viruses | Hong et al. (2012) |
| NLRP (NALP) subfamily | |||||||
| NLRP1 (Nalp1) | (“Lethal factor” of Bacillus anthracis) | LRR + FIIND + CARD | PYD | Inflammasome | Secretion of IL-1β and IL-18, pyroptosis | (Bacillus anthracis, Toxoplasma gondii) | Ewald et al. (2014) |
| NLRP (Nalp)2-9,11-14 | Various but often unknown | LRR | PYD | Inflammasome &/or inhibition of inflammation | Secretion of IL-1β and IL-18, pyroptosis &/or TLR signaling attenuation | Various but often unknown | Lupfer and Kanneganti (2013) |
| NLRP10 (Nalp10) | Unknown | No LRR | PYD | Inflammasome and IL-1β independent | Inflammasome and IL-1β independent | (Candida albicans) --> fungi | Joly et al. (2012) |
| RLRs | |||||||
| RIG-1 | dsRNA in the cytoplasm | RNA helicase | CARD | NF-κB & IRF3/7 | Proinflamm. cytokines & type-1 IFN | RNA viruses | Szabo and Rajnavolgyi (2013) |
| MDA5 | dsRNA in the cytoplasm | RNA helicase | CARD | NF-κB & IRF3/8 | Proinflamm. cytokines & type-1 IFN | RNA viruses | Szabo and Rajnavolgyi (2013) |
| LGP2 | dsRNA in the cytoplasm | RNA helicase | No CARD | Influences RIG-1 & MDA5 activity | Uncertain, either activating or inhibiting RIG-1 & MDA5 | RNA viruses | Szabo and Rajnavolgyi (2013) |
| Selected CLRs | |||||||
| Dectin-1 | β-glucan | CRD | ITAM | Syk – Card9-complex and/ or inflammasome | Proinflammatory cytokines incl. IL-1β + TH1 & TH17 support | Fungi | Hardison and Brown (2012) and Lepenies et al. (2013) |
| Dectin-2 | Mannose-based structures | CRD | ITAM | Syk – Card9-complex and/ or inflammasome | Proinflammatory cytokines incl. IL-1β + TH1 & TH17 support | Fungi | Hardison and Brown (2012) and Lepenies et al. (2013) |
| Mincle | Mannose-based structures | CRD | ITAM | Syk – Card9-complex and/ or inflammasome | Proinflammatory cytokines incl. IL-1β + TH1 & TH17 support | Fungi | Hardison and Brown (2012) and Lepenies et al. (2013) |
| MR | Mannose-based structures | CRD | Unknown | Unknown | Cytokine production, T-cell costimulation and differentiation | Fungi | Hardison and Brown (2012) and Lepenies et al. (2013) |
| DC-SIGN | Mannose-based structures | CRD | Unknown | Raf-1 | Cytokine production, T-cell costimulation and differentiation | Fungi | Hardison and Brown (2012) and Lepenies et al. (2013) |
| DNA sensors | |||||||
| DAI | DNA | D3 region, Zα+Zβ | Unknown | NF-κB & IRF3/IRF7 | Proinflamm. cytokines & type-1 IFN | DNA viruses and intracellular bacteria | Wang et al. (2008) |
| AIM2 | DNA | HIN200 | PYD | Inflammasome | Secretion of IL-1β and IL-18, pyroptosis | DNA viruses and intracellular bacteria | Warren et al. (2010) |