Immunoprecipitation of allele-specific FcγRIIIb recombinant isoforms from biotin surface-labeled CHO stable transfectants expressing SH (lane 1), NA2 (lane 2), and NA1 (lane 3) granulocyte antigens. After solubilization CHO lysates were immunoprecipitated with MoAb 3G8 specific for FcγRIIIb. Immunoprecipitates were separated on 7.5% SDS-PAGE under nonreducing conditions and were transferred by immunoblotting. Biotin-labeled proteins were visualized using streptavidin and chemiluminescence substrate system. Note the different electrophorectic migrations of the various FcγRIIIb isoforms.