Activating Fc gamma receptor (Activating FcγR)

Activating Fc gamma receptors (FcγRs) are a group of cell surface glycoproteins that serve as critical links between the humoral and cellular branches of the immune system by binding the Fc region of immunoglobulin G (IgG) antibodies. This group primarily consists of FcγRI (CD64), FcγRIIa (CD32a), and FcγRIIIa (CD16a), which are distinguished by their association with immunoreceptor tyrosine-based activation motifs (ITAMs) that trigger stimulatory signaling upon receptor aggregation (Nimmerjahn & Ravetch, 2008). These receptors are widely expressed on innate immune cells, including natural killer (NK) cells, macrophages, and neutrophils, where they mediate essential functions such as antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and the release of pro-inflammatory cytokines (Wang et al., 2022). In clinical oncology, the therapeutic efficacy of many monoclonal antibodies, such as rituximab and trastuzumab, relies on their ability to engage these activating receptors to eliminate target cells (Hogarth & Pietersz, 2012). Conversely, the inappropriate activation of these receptors by immune complexes is a hallmark of various autoimmune and inflammatory disorders, such as systemic lupus erythematosus. Modern drug development often focuses on Fc-engineering to enhance the affinity of therapeutic antibodies for activating FcγRs, particularly the V158 variant of FcγRIIIa, to improve clinical outcomes in cancer patients (Bournazos & Ravetch, 2017).

Other names

CD64CD32aCD16aFCGR1AFCGR2AFCGR3AITAM-bearing Fc gamma receptorsStimulatory Fc gamma receptors

Engagement of the receptor by the Fc region of IgG antibodies leads to receptor clustering and phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) by Src-family kinases, which recruits Syk-family kinases to initiate downstream signaling pathways that induce phagocytosis, ADCC, and pro-inflammatory cytokine release (Nimmerjahn & Ravetch, 2008; Hogarth & Pietersz, 2012).