CD32a

CD32A, also known as Fc gamma receptor IIa (FcγRIIa), is a receptor for the Fc portion of IgG antibodies. It is encoded by the FCGR2A gene in humans and is a member of the Fc gamma receptor family that mediates immune complex recognition and cellular activation.

Structurally, CD32A is a type I transmembrane glycoprotein with two extracellular immunoglobulin-like domains. It associates with an ITAM-containing signaling adaptor, the Fc receptor gamma chain, to transmit activating signals that promote phagocytosis, oxidative burst, and cytokine production. Because it signals through the gamma chain, CD32A itself has a short cytoplasmic tail and relies on the adaptor for downstream signaling.

CD32A is primarily expressed on myeloid cells, including neutrophils, monocytes, macrophages, and dendritic cells, as well as on platelets. It binds IgG subclasses, with binding affinity affected by genetic polymorphisms. A common single-nucleotide polymorphism at residue 131 (histidine or arginine; H131/R131) influences binding to IgG2, with the H131 variant generally showing higher affinity for IgG2 and better opsonization of certain bacteria.

Functionally, CD32A mediates the phagocytosis of opsonized pathogens, participates in antigen presentation, and contributes to inflammatory responses. Clinically, it plays a role in platelet activation in conditions such as heparin-induced thrombocytopenia and can influence responses to antibody-based therapies that rely on Fc receptor engagement. Genetic variations in FCGR2A have been linked to susceptibility to certain infections and inflammatory diseases, though effects are context-dependent.