The 3G8 monoclonal antibody reacts with the 50-65kD transmembrane form of human CD16 (FCGR3A). CD16 is the low affinity IgG receptor III and is expressed on NK cells and macrophages. CD16 participates in signal transduction and mediates antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells. The second form of CD16 (FCGR3B) is a glycosyl-phosphatidylinositol (GPI) linked molecule expressed exclusively on neutrophils.