Table 2.
Overview of FcγRs and their functional effects (Modified from Bournazos et al. and Bruhns et al.).
| IgG receptor | FcγRI | FcγRIIa | FcγRIIb | FcγRIIc | FcγRIIIa | FcγRIIIb |
|---|---|---|---|---|---|---|
| Affinity for IgG (Ka) | High (109-1010/M) |
Low (<107/M) |
Low (<107/M) |
Low (<107/M) |
Low (<107/M) |
Low (<107/M) |
| Specificity for IgG subclass | IgG1 = IgG3 >>> IgG4 | IgG1 >>> IgG3 > IgG2 > IgG4 | IgG3 = IgG4 > IgG1 > IgG2 (only I232 for polymorphism) |
IgG3 = IgG4 > IgG1 > IgG2 (only Q13 for polymorphism) |
IgG3 >>> IgG1 = IgG4 > IgG2 | IgG3 > IgG1 |
| Cellular expression | Monocytes, macrophages, subset of dendritic cells and PMN (IFN-γ or G-CSF-induced) | PMN, monocytes, macrophages, platelets and subset of endothelial cells | Monocytes, macrophages, dendritic cells, basophil and B cells | Monocytes, macrophages, NK cells | Monocytes, macrophages, NK cells and gamma-delta T-cells | Neutrophils and basophils |
| Relevant SNP | c. -131C>G; c.845-23_845-17delTCTTTG; D324N |
R131H | I232T | Q57X | V158F | HNA-1a |
| Signalling activities | Activation | Activation | Inhibition | Activation | Activation | Activation |
| Functional effect | Regulation of IgG levels, phagocytosis and ADCC | Induces phagocytosis and mediator release | Regulation of B cells and phagocytosis | Mechanism unknown | Phagocytosis and ADCC | Phagocytosis |
| Functional effect of polymorphism | -131G: higher promoter activity; c.845-23_845-17delTCTTTG: lower CD64 expression; N324: higher degranulation and more pro-inflammatory cytokine production |
H131: higher affinity for IgG2 | T232: decreased inhibitory activity | Truncated non-functional protein | V158: higher affinity for IgG1 and IgG3, bind IgG4 | NA1: higher degranulation and more phagocytosis |
IFN-γ, interferon-γ; G-CSF, granulocyte colony-stimulating factor; NK cells, NK cells; PMN, polymorphonuclear leucocytes; SNP, single nucleotide polymorphism.