Low affinity immunoglobulin gamma Fc receptor II-a (FcγRIIa) and Low affinity immunoglobulin gamma Fc receptor II-b (FcγRIIb) (FcγRIIa / FcγRIIb)

Fc gamma receptor IIa (FcγRIIa/CD32a) and Fc gamma receptor IIb (FcγRIIb/CD32b) are key members of the Fc gamma receptor family that bridge the adaptive and innate immune systems by binding the Fc portion of IgG antibodies [1, 2, 5]. FcγRIIa is an activating receptor containing an immunoreceptor tyrosine-based activation motif (ITAM) in its cytoplasmic tail, primarily expressed on myeloid cells and platelets where it triggers phagocytosis and pro-inflammatory responses [3, 5, 15]. In contrast, FcγRIIb is the only inhibitory Fc receptor, containing an immunoreceptor tyrosine-based inhibitory motif (ITIM), and is expressed on B cells and myeloid cells to provide essential negative feedback that maintains immune homeostasis [4, 6, 12]. The functional balance between these two receptors, often expressed as the activating-to-inhibitory (A/I) ratio, determines the threshold for immune cell activation and the efficacy of therapeutic antibodies [1, 13, 16]. Dysregulation or genetic polymorphisms in these receptors are strongly associated with autoimmune diseases like systemic lupus erythematosus and the progression of certain B-cell malignancies [6, 11, 15]. In drug development, these receptors are targeted through Fc-engineering of monoclonal antibodies to enhance effector functions like ADCC or through specific agonists/antagonists to modulate immune signaling in inflammatory conditions [2, 7, 16].

Other names

CD32CD32aCD32bFCGR2AFCGR2BFCG2IGFR2CDw32

Modulation of immune cell activation through the balance of ITAM-mediated activating and ITIM-mediated inhibitory signaling [1, 2]; enhancement of antibody-dependent effector functions via Fc-region engineering [13, 16]; and inhibition of B-cell activation via ITIM-mediated negative feedback [4, 7].