Low affinity immunoglobulin gamma Fc region receptor III (FcγRIII)

The low affinity immunoglobulin gamma Fc region receptor III (FcγRIII) is a cell surface receptor that binds the Fc region of IgG antibodies with low to intermediate affinity, primarily recognizing complexed or aggregated IgG. It exists in two main forms: transmembrane FcγRIIIa (on NK cells, macrophages, monocytes) associated with signaling adapters like the γ-chain for ADCC and cytokine production, and GPI-anchored FcγRIIIb (on neutrophils). It mediates immune effector functions including immune complex clearance, NK cell degranulation, and inflammation modulation. Structural studies show conserved hinge binding similar to other FcγRs but unique features in high-affinity variants; polymorphisms influence binding and disease susceptibility.

Other names

FcγRIIIa (transmembrane form, encoded by FCGR3A)FcγRIIIb (GPI-anchored form, encoded by FCGR3B)CD16a (for FcγRIIIa)CD16b (for FcγRIIIb)

Binding to IgG Fc region triggers ITAM-dependent signaling via associated γ-chain or CD247, leading to phosphorylation, PI3K activation, calcium influx, cytokine release, and cytotoxicity; low-affinity binding to monomeric or complexed IgG