MAPPING AND COMPARISON OF THE INTERACTION SITES ON THE FC REGION OF IGG RESPONSIBLE FOR TRIGGERING ANTIBODY DEPENDENT CELLULAR CYTOTOXICITY (ADCC) THROUGH DIFFERENT TYPES OF HUMAN FC-GAMMA RECEPTOR

In the present study 3-iodo-4-hydroxy-5-nitrophenacetyl (NIP)-specific antibodies were compared for induction of antibody dependent lysis of NIP-derivatised red blood cells effected by pre-stimulated U937 or HL-60 cells and by K cells. The chimaeric antibodies have heavy chains corresponding to human IgG subclasses 1-4, and include site-directed mutants of IgG3 as well as the aglycosylated form of IgG3; a mouse IgG2b antibody and a site-directed mutant IgG2b were also examined. rIFN stimulated U937 or HL-60 cells express increased levels of Fc-gamma-R1 compared to unstimulated cells; PMA stimulated HL-60 and U937 cells express an increased level of Fc-gamma-R11 compared to unstimulated cells; K cells express Fc-gamma-R111. Using these effector cell populations and the target cells mentioned above, we have compared anti-NIP antibodies with different heavy chain constant domains for their ability to induce ADCC through human Fc-gamma-R1, Fc-gamma-R11 and Fc-gamma-R111. The results suggest that all three human Fc-gamma-receptors appear to recognise a binding site on IgG within the lower hinge (residues 234-237) and trigger ADCC via this site, but that each receptor sees this common site in a different way. The possibility that other amino acid residues also participate in the binding/triggering site(s) cannot be excluded.