Figure 8. NK cell-mediated cytotoxicity promoted by 91R mAb in human MOLT-4 leukemia cells. (A) Specific NK-dependent cytotoxicity mediated by 91R, 112509, negative control mAb or positive control M4 serum. NK cells were isolated from BALB/c spleens and cultured for 6–7 d in medium containing IL-2. CFSE-labeled MOLT-4 target cells were preincubated with 91R, 112509 or control mAb (20 μg/ml), or M4 pooled sera (1:1000) (30 min, 37 °C). NK cells and labeled target cells were then co-cultured at a 20:1 ratio (4 h, 37 °C). Specific lysis was determined by staining dead cells with 7-AAD and analyzing the number of 7-AAD⁺ green cells by flow cytometry. Each condition was analyzed in triplicate. Data show mean ± SEM (n = 5 independent experiments). (B) Dose-response curve for specific complement lysis using 91R and a control IgG2b mAb at indicated concentrations. Data show mean ± SEM for duplicates from one representative experiment of four. *** P < 0.001, ** P < 0.01, * P < 0.05.