Table 1.
Characteristics of human and mouse Fc receptors
| Fc receptor | Function | ITAM, ITIM or ITAMi | Binding affinity for antibody isotypesa | Cell type-specific expression |
|---|---|---|---|---|
| Human | ||||
| FcμR | Endocytosis | None | IgM (+++) | B cells; subpopulations of T cells and NK cells |
| Fcα/μR | Endocytosis | None | IgM (+++), IgA (+++) | Subpopulations of B cells and DCs |
| FcαRI | Cell activation or inhibition | ITAM or ITAMi | IgA (++) | Neutrophils and eosinophils; subpopulations of monocytes/macrophages and DCs |
| FcεRI | Cell activation | ITAM | IgE (+++) | Basophils, mast cells and platelets; subpopulations of monocytes/macrophages, DCs and eosinophils |
| FcεRII | IgE regulation | None | IgE (++) | B cells, eosinophils and platelets; inducible expression on monocytes/macrophages and DCs |
| FcγRI | Cell activation | ITAM | IgG1 (+++), IgG3 (+++), IgG4 (+++) | Monocytes/macrophages; inducible expression on neutrophils and mast cells |
| FcγRIIA | Cell activation or inhibition | ITAM or ITAMi | IgG1 (++), IgG2 (++), IgG3 (++), IgG4 (++) | Monocytes/macrophages, neutrophils, DCs, basophils, mast cells, eosinophils and platelets |
| FcγRIIB | Cell inhibition | ITIM | IgG1 (+), IgG2 (+), IgG3 (++), IgG4 (++) | B cells, DCs and basophils; majority of monocytes/macrophages (except alveolar macrophages); subpopulations of neutrophils |
| FcγRIICb | Cell activation | ITAM | IgG1 (+), IgG2 (+), IgG3 (++), IgG4 (++) | NK cells |
| FcγRIIIA | Cell activation or inhibition | ITAM or ITAMi | IgG1 (++), IgG2 (+), IgG3 (+++), IgG4 (++) | NK cells and monocytes/macrophages; uncertain expression on neutrophils |
| FcγRIIIB | Cell activation or decoy receptor | None | IgG1 (++), IgG3 (++) | Neutrophils; subpopulations of basophils |
| Mouse | ||||
| FcμR | Endocytosis | None | IgM (+++) | B cells |
| Fcα/μR | Endocytosis | None | IgM (+++), IgA (+++) | B cells; subpopulations of DCs |
| FcεRI | Cell activation | ITAM | IgE (+++) | Basophils and mast cells; inducible expression on neutrophils and DCs |
| FcεRII | IgE regulation | None | IgE (+++) | B cells; subpopulations of DCs |
| FcγRI | Cell activation | ITAM | IgG2a (+++), IgG2b (++) | Neutrophils; subpopulations of monocytes/macrophages and DCs |
| FcγRIIB | Cell inhibition | ITIM | IgG1 (++), IgG2a (++), IgG2b (++), IgE (+) | B cells, monocytes/macrophages, neutrophils, DCs, basophils, mast cells and eosinophils |
| FcγRIII | Cell activation or inhibition | ITAM or ITAMi | IgG1 (++), IgG2a (++), IgG2b (++), IgE (+) | NK cells, monocytes/macrophages, neutrophils, DCs, basophils, mast cells and eosinophils |
| FcγRIV | Cell activation | ITAM | IgG2a (+++), IgG2b (+++), IgE (++) | Monocytes/macrophages, neutrophils and DCs |
DC, dendritic cell; Fc, crystallizable fragment; FcR, Fc receptor; ITAM, immunoreceptor tyrosine-based activation motif; ITAMi, inhibitory ITAM; ITIM, immunoreceptor tyrosine-based inhibitory motif; NK, natural killer. aMeasured in terms of the association constant (Ka): +++, >1 × 107 M−1; ++, 1 × 105–1 × 107 M−1; +, <1 × 105 M−1. bEncoded by a pseudogene that is only expressed in a fraction of the human population owing to allelic polymorphism.