FCGR3B

FCGR3B is a human gene that encodes the Fc gamma receptor IIIb, also known as CD16b. It is a low-affinity receptor for the Fc portion of immunoglobulin G (IgG) and is primarily expressed on neutrophils. The receptor is attached to the cell surface by a glycosylphosphatidylinositol (GPI) anchor and lacks a cytoplasmic signaling region, distinguishing it from other Fc gamma receptors.

Functionally, FCGR3B participates in the recognition of IgG-opsonized particles and contributes to the clearance of immune complexes and pathogen opsonization by neutrophils. Because it is GPI-anchored and lacks intrinsic signaling capacity, receptor engagement often works in concert with other activating receptors to promote phagocytosis and neutrophil responses.

Genetically, FCGR3B is part of the Fc gamma receptor gene cluster on chromosome 1q23.3 and exhibits variations in copy number (copy number variation) and allelic polymorphisms. The NA1 and NA2 alleles are common functional variants that influence IgG binding and receptor activity. Copy number variation can lead to differences in surface expression levels of Fc gamma receptor IIIb on neutrophils.

Clinical relevance is most often discussed in the context of autoimmune and inflammatory diseases. Several studies have reported associations between FCGR3B copy number variation and disease susceptibility, particularly low copy number with increased risk for systemic lupus erythematosus and related immune complex–mediated conditions. Associations have also been explored in other diseases with variable and sometimes conflicting results, highlighting the need for further research to clarify FCGR3B’s role in disease.