CD32 (also designated Fcgamma RII) is a low affinity receptor for the Fc fragment of aggregated IgG. CD32 is responsible for the clearance of immunocomplexes by macrophages and also plays an important role in the regulation of , production by B cells. IgG can noncooperatively bind either one or two highly glycosylated CD32 molecules, and this binding delivers a negative signal for B cells. CD32 exists as several isoforms that are produced by alternative splicing of three distinct genes, A, B and C. These isoforms are designated Fcgamma RIIA, Fcgamma RIIB1, Fcgamma RIIB3 and Fcgamma RIIC. All isoforms are present on monocytes, placental trophoblasts and endothelial cells. In addition, the Fcgamma RIIB forms are present on B lymphocytes, and the Fcgamma RIIA and Fcgamma RIIC forms are found on neutrophils.