Low affinity immunoglobulin gamma Fc receptor IIa (FcγRIIa) and Low affinity immunoglobulin gamma Fc receptor IIb (FcγRIIb) (FcγRIIa and FcγRIIb)

Fc gamma receptors (FcγRs) are a family of cell surface glycoproteins that bind the Fc portion of immunoglobulin G (IgG) antibodies, serving as a critical link between the adaptive and innate immune systems (NIH: 1.1.1, 1.3.2). Among these, FcγRIIa (CD32a) and FcγRIIb (CD32b) are low-affinity receptors with opposing functions: FcγRIIa contains an immunoreceptor tyrosine-based activation motif (ITAM) that triggers pro-inflammatory responses like phagocytosis and cytokine release, while FcγRIIb contains an immunoreceptor tyrosine-based inhibition motif (ITIM) that suppresses immune activation (NIH: 1.2.1, 1.4.3). The balance between these activating and inhibitory signals, often referred to as the A/I ratio, is essential for maintaining immune homeostasis (NIH: 1.1.4, 1.3.1). Dysregulation of this balance is implicated in various autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis, as well as in the efficacy of therapeutic monoclonal antibodies (NIH: 1.3.1, 1.4.1). Pharmacological strategies include using bispecific antibodies to co-engage FcγRIIb with activating receptors to dampen B-cell activity or engineering the Fc region of therapeutic antibodies to optimize their interaction with specific FcγRs for enhanced anti-tumor activity (NIH: 1.2.2, 1.4.4).

Other names

CD32CD32aCD32bFCGR2AFCGR2BFc-gamma RIIaFc-gamma RIIbFc gamma receptor IIAFc gamma receptor IIBLow affinity immunoglobulin gamma Fc region receptor II-aLow affinity immunoglobulin gamma Fc region receptor II-b

Drugs targeting these receptors modulate the balance between activating (FcγRIIa) and inhibitory (FcγRIIb) signals (NIH: 1.1.1). Activating receptors like FcγRIIa utilize immunoreceptor tyrosine-based activation motifs (ITAMs) to promote phagocytosis and pro-inflammatory cytokine release (NIH: 1.4.3). Conversely, the inhibitory FcγRIIb utilizes immunoreceptor tyrosine-based inhibition motifs (ITIMs) to recruit phosphatases like SHIP, which dampen B-cell receptor (BCR) and activating Fc receptor signaling (NIH: 1.2.1). Therapeutic strategies include direct blockade of CD32b to enhance mAb efficacy in cancer, or using bispecifics to co-engage CD32b and CD19 to suppress B-cell activity in autoimmune diseases (NIH: 1.2.2). Additionally, Fc-engineering of monoclonal antibodies is used to optimize their affinity for these receptors to enhance or reduce effector functions (NIH: 1.1.4).