Activating Fc gamma receptors (Activating FcγRs)

Activating Fc gamma receptors (FcγRs) are a subset of the Fc receptor family that specifically bind the Fc portion of immunoglobulin G (IgG) antibodies to initiate stimulatory immune signals (Nimmerjahn & Ravetch, 2008). This group includes the high-affinity receptor FcγRI (CD64) and the low-affinity receptors FcγRIIa (CD32a), FcγRIIc (CD32c), FcγRIIIa (CD16a), and FcγRIIIb (CD16b) (Hogarth & Pietersz, 2012). These receptors are expressed on various leucocytes, including macrophages, natural killer (NK) cells, and neutrophils, where they signal through immunoreceptor tyrosine-based activation motifs (ITAMs) (Bournazos & Ravetch, 2017). Upon ligation by immune complexes or antibody-coated targets, they trigger critical effector functions such as antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and the release of pro-inflammatory cytokines (UniProt P08637). In oncology, the efficacy of many therapeutic monoclonal antibodies, such as Rituximab and Trastuzumab, depends on their ability to engage activating FcγRs to eliminate tumor cells (Wang et al., 2015). Conversely, dysregulation of these receptors is implicated in the pathogenesis of autoimmune and inflammatory diseases, where they can drive inappropriate tissue destruction (Smith & Clatworthy, 2010).

Other names

Activating Fc-gamma receptorsFc gamma receptor I (CD64)Fc gamma receptor IIa (CD32a)Fc gamma receptor IIc (CD32c)Fc gamma receptor IIIa (CD16a)Fc gamma receptor IIIb (CD16b)Low affinity immunoglobulin gamma Fc region receptorHigh affinity immunoglobulin gamma Fc region receptor

Therapeutic monoclonal antibodies engage activating FcγRs via their Fc domain to bridge target cells (e.g., tumor cells) with effector cells (e.g., NK cells, macrophages), inducing ADCC or ADCP (Bournazos & Ravetch, 2017). Some engineered antibodies, like Margetuximab, are designed with enhanced affinity for FcγRIIIa to boost these responses (Nordstrom et al., 2011). In autoimmune therapy, intravenous immunoglobulin (IVIG) or specific Fc-blockers may be used to saturate or inhibit these receptors to reduce inflammation (Samuelsson et al., 2001).