Fc gamma receptor IIIb (FcγRIIIb)

Fc gamma receptor IIIb (FcγRIIIb; CD16b) is a low-affinity IgG Fc region-binding cell surface receptor predominantly expressed on human neutrophils. Unlike other members of the Fc gamma receptor family, it is anchored to the plasma membrane via a glycosylphosphatidylinositol (GPI) linkage and lacks an intracellular signaling domain. This structural feature means that while it can bind monomeric or aggregated IgG and immune complexes in circulation, its ability to directly transduce activating signals is limited compared to related receptors such as FcγRIIa or FcγRIIIa. Instead, it often modulates neutrophil functions by cooperating with other receptors or accessory proteins. Functionally, aggregation of this receptor on neutrophils leads to actin polymerization, integrin activation, degranulation, calcium influx through TRPM2 channels via PKC and ROS pathways, NET formation, and enhanced cell adhesion—distinct from the phagocytosis typically mediated by other activating receptors like FcγRIIa. It plays a role in capturing immune complexes in peripheral blood and contributes to inflammatory responses but does not efficiently mediate antibody-dependent cellular cytotoxicity or phagocytosis itself. Genetically encoded by FCGR3B on chromosome 1q23.3 in humans,[4] polymorphisms in this gene are associated with susceptibility to certain autoimmune diseases and conditions involving abnormal neutrophil function.[1][2][5]

Other names

CD16bFCGR3BFCG3BIgG Fc receptor III-2Low affinity immunoglobulin gamma Fc region receptor III-B