Receptors for Fc portion of IgG (Fcγ Rs) are members of the Ig superfamily, and are divided into three classes designated Fcγ RI (CD64), Fcγ RII (CD32), and Fcγ RIII (CD16). CD32 protein is a low affinity receptor for IgG that binds only IgG immune complexes and is expressed on a diverse range of cells such as monocytes, macrophages, neutrophils, eosinophils, platelets, and B cells. Human CD32 class is encoded by three closely related genes, and designated Fcγ RII A, B, and C which share 94-99% amino acid identity in their extracellular domains but differ substantially in their transmembrane and cytoplasmic domains. CD32 is involved in a number of immune responses including antibody-dependent cell-mediated cytotoxicity, clearance of immune complexes, release of inflammatory mediators, and regulation of antibody production.