Transfection of COS-7 cells with the novel cDNA confers reactivity to MoAbs V.1A7, V.5C7, and V.7C7. (A) COS-7 cells were transfected with the plasmid clones DW-5C7.3, DW-7C7.17, and DW-1A7.27 by the DEAE-dextran method. After 48 hours, the cells were detached and incubated with saturating levels of the respective MoAbs (thick line) or the control MoAb MRC OX86 (thin line), followed by a second incubation with fluorescein-conjugated goat antirat Ig antibody. Antibody binding was measured by flow cytometry. (B) Mock-transfected COS-7 cells (lane 1) or COS-7 cells transfected with the cDNA clone DW-7C7.17 (lane 2) were surface biotinylated and subjected to immunoprecipitation with MoAb V.5C7. Specifically bound proteins were analyzed and detected as described for Fig 1A. Molecular mass markers (in kilodaltons) are indicated on the left.