CD16 is a 50-65 kDa cell surface molecule that exists in two forms - a transmembranous form expressed by natural killer (NK) cells, and some T cells and a phosphatidylinositol linked form expressed by granulocytes. CD16 is a low affinity receptor for IgG (FcR III), and is an important receptor mediating ADCC (antibody dependent cell mediated cytotoxicity) by NK cells. IN comparison, CD32 is a 40 kD glycoprotein that acts as a low affinity receptor for IgG (also known as Fc gamma RII), and mediates several functions including endocytosis, activation of secretion, cytotoxicity and immunomodulation. CD32 is expressed by B cells, monocytes, granulocytes and platelets. Further, CD32 is involved in the phagocytosis of immune complexes, the regulation of antibody production by B-cells, and variations of the CD32 gene may increase vulnerability to systemic lupus erythematosus (SLE). Several transcript variants encoding different isoforms of CD32 have been found.