Table 1.
Human Paired Receptors and Their Shared Ligands
| Paired receptors: coactivating inhibitory | Paired receptors mainly expressed on | Shared cellular ligands for paired receptors | Cellular ligands mainly expressed on | Ligand–receptor affinitya | Pathogen ligands for paired receptors | Refs |
|---|---|---|---|---|---|---|
| CD28 CTLA4 |
T cells | CD80 and CD86 | DCs, monocytes, B cells, neutrophils, T cells, mesenchymal stem cells, and activated NK cells | CD28: 4 μM (CD80), 20 μM (CD86) CTLA4: 0.4 μM (CD80), 4 μM (CD86) |
SEB (for CD28) | 6, 27, 48 |
| KIR2DL and KIR3DL KIR2DS and KIR3DS |
NK cells | Intact classical MHC class I molecules (particularly for KIR2DL and KIR3DL) HLA-F and MHC class I open conformers (particularly for KIR2DS and KIR3DS) |
All nucleated cells | KIR2DL and KIR3DL: weak (could not be determined in most cases) KIR2DS and KIR3DS: 10 μM |
CpG DNA (for KIR2DL2) | 49, 50, 51, 52, 53 |
| CD300c CD300a |
NK cells, mast cells, eosinophils, basophils and neutrophils | PE and PS | Apoptotic cells | ND | Enveloped viruses containing PE and PS, such as dengue, vaccinia, West Nile, Sindbis and Ebola viruses | 7, 9, 25, 32, 36, 37, 45, 54, 55, 56, 57, 58, 59 |
| CEACAM1-S, CEACAM3 CEACAM1-L |
T cells, NK cells, mast cell and eosinophils | CEACAM1 | Most abundant in glandular epithelia of the gastrointestinal tract, bile canaliculi of the liver and intercalated ducts of the salivary gland. Also, activated immune cells (mainly T cells), resting and activated mast cells and eosinophils | ND | Opa (Neisseria spp.) P5 (Haemophilus influenzae) UspA1 (Moraxella catarrhalis) Carbohydrates on Escherichia coli and Salmonella spp. HopQ (Helicobacter pylori) |
12, 34, 60 |
| DNAM1 TIGIT |
NK cells, T cells and mast cells (DNAM1 only) | PVR | Wide tissue distribution, notable expression in the alimentary canal and nervous system | DNAM1: 114 nM TIGIT: 3.15 nM |
Fap2 of Fusobacterium nucleatum (for TIGIT only) | 8, 20, 38, 43 |
| DNAM1 CD112R |
NK cells and T cells | Nectin2 | Wide cellular distribution, including eosinophils (part of the AEU) | DNAM1: 8.97 mM CD112R: 88.4 nM |
ND | [13] |
| Siglec-14 Siglec-5 |
Monocytes | Sialylated glycans HSP70 |
Almost all cell types | ND | Group B Streptococcus | [14] |
| NKG2C NKG2A |
NK cells | HLA-E | All nucleated cells | NKG2C: 30 μM NKG2A: 1 μM |
UL-40 Leader peptide of HCMV bound to HLA-E | [15] |
| CD200RLa-e CD200R |
Myeloid cells, and B and T cells | CD200 | Cells of the hematopoietic lineage, specifically those of the myeloid lineage such as macrophages, DCs, neutrophils, mast cells, eosinophils and basophils | ND | K14 of HHV8 U85 of HHV6 and HHV7 (for CD200R) 1 vOX-2 of myxoma virus M141R 2 vCD200 for rhesus rhadinovirus R15 |
16, 33, 61, 62, 63 |
| Siglec-16 Siglec-11 |
Human brain microglia | α2–8-linked sialic acids | Widely distributed in mammalian tissues | ND | Polysialic acids on Escherichia coli | [64] |
HHV, human herpesvirus; ND, not determined; PE, phosphatidylethanolamine; PS, phosphatidylserine; SEB, Staphylococcus aureus enterotoxin B.
a
There is sometimes great variability in reported affinities; measurements representative of the range of values are shown.