FCGR3A

FCGR3A Full Name

Fc fragment of IgG, low affinity IIIa, receptor (CD16a)

FCGR3A Introduction

FCGR3A, commonly referred to as Fc gamma receptor IIIa (FcγRIIIa) or CD16a, is a surface-expressed receptor encoded by the FCGR3A gene that anchors into the plasma membrane of several innate immune effector cells. Its designation as "low-affinity" reflects how it preferentially engages IgG antibodies arranged in immune complexes or bound to target cells, rather than free monomeric IgG in circulation; this ensures activation only in the presence of antigen-coated targets. Structurally belonging to the immunoglobulin superfamily, FcγRIIIa is distinguished from its close homolog FcγRIIIb (CD16b) by possessing a transmembrane domain and an intracellular signaling motif that associates with ITAM-bearing adaptor chains, enabling it to transduce activation signals into the cell. Its expression is most prominent on natural killer (NK) cells, macrophages and subsets of monocytes, where it bridges humoral and cellular immunity by recognizing the Fc portion of IgG bound to pathogens or diseased cells.

Figure 1.Illustrative representation of ADCC of NK cells in the uterus with a CD16a receptor.(Sources: Habets DHJ, et al.; 2023)

Functionally, FCGR3A sits at the heart of antibody-dependent effector mechanisms that are central to both host defense and immunotherapy. When FcγRIIIa binds to clustered IgG on the surface of opsonized targets, it triggers a cascade of intracellular events that culminate in antibody-dependent cell-mediated cytotoxicity (ADCC), phagocytosis and release of inflammatory mediators; in NK cells, this engagement recruits kinases and adaptor proteins that promote degranulation and cytokine secretion. Beyond ADCC, FCGR3A collaborates with other pattern recognition and cytokine receptors to modulate immune cell activation thresholds and can undergo regulated ectodomain shedding that fine-tunes surface availability during immune responses. Because its activity hinges on the interplay between IgG glycoforms, receptor polymorphisms such as the V158F variant, and the cellular context, FCGR3A also serves as a modulatory node influencing the potency of therapeutic antibodies designed to harness effector functions.

Clinically, aberrations in FCGR3A expression or signaling are implicated in both protective and pathological processes. In oncology, high FCGR3A activity can enhance the efficacy of antibody-based therapies by improving immune clearance of tumor cells, and its engagement is actively exploited in the design of bispecific antibodies and NK cell engagers to amplify antitumor ADCC. Conversely, in autoimmune and inflammatory diseases, FcγRIIIa-mediated phagocytosis of antibody-coated host cells can contribute to tissue damage, as illustrated in immune thrombocytopenia where macrophage FcγRIIIa drives platelet destruction; experimental blockade of this receptor can ameliorate disease features, although careful modulation is required to avoid unintended inflammation. Moreover, functional variants of FCGR3A affect individual responses to infections and antibody therapies, making it a valuable biomarker in personalized medicine. To support research into these diverse roles, a suite of FcγRIIIa-specific reagents — including monoclonal antibodies for flow cytometry and IHC, recombinant receptor proteins, and activity assays — are used to probe its mechanisms and therapeutic relevance.

Alternate Names for FCGR3A

Fcγ RIII, Fc gamma RIII

• 1. Habets DHJ, et al.; Analysis of FCGR3A-p.176Val variants in women with recurrent pregnancy loss and the association with CD16a expression and anti-HLA antibody status. Sci Rep. 2023, 13(1):5232.