Activating Fc-gamma receptor (Activating FcγR)

Activating Fc-gamma receptors (FcγRs) are essential cell surface glycoproteins that bridge the humoral and cellular immune responses by binding the Fc portion of immunoglobulin G (IgG) antibodies (Nimmerjahn & Ravetch, 2008). This group includes FcγRI (CD64), FcγRIIa (CD32a), and FcγRIIIa (CD16a), which are expressed on various immune cells such as macrophages, natural killer (NK) cells, and neutrophils (Hogarth & Pietersz, 2012). Upon binding to IgG-antigen complexes, these receptors trigger intracellular signaling via immunoreceptor tyrosine-based activation motifs (ITAMs), leading to effector functions like phagocytosis, antibody-dependent cellular cytotoxicity (ADCC), and the release of pro-inflammatory cytokines (Bournazos & Ravetch, 2017). In oncology, many therapeutic monoclonal antibodies, such as Rituximab and Trastuzumab, rely on activating FcγRs to mediate the destruction of tumor cells (Wang et al., 2018). Conversely, the dysregulation or overactivation of these receptors is implicated in the pathogenesis of autoimmune diseases like systemic lupus erythematosus and rheumatoid arthritis (Smith & Clatworthy, 2010). Therapeutic strategies often involve engineering antibody Fc regions to enhance affinity for activating receptors or using small molecules to inhibit downstream signaling components like Spleen Tyrosine Kinase (SYK) (Cartron et al., 2002).

Other names

Fc gamma receptorFcγRCD16CD32CD64Activating Fc-gamma receptorsFCGRFc-gamma receptor IFc-gamma receptor IIaFc-gamma receptor IIIa

Binding of the IgG Fc region to activating FcγRs induces receptor clustering and phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) by Src-family kinases. This recruits Spleen Tyrosine Kinase (SYK), which activates downstream pathways including PLCγ and PI3K, resulting in calcium mobilization, cellular degranulation, and the transcriptional activation of pro-inflammatory genes.