MoAb90 induces apoptosis of CD40-activated B cells. Resting or 5-day CD40-activated B cells were cultured in the presence of 5 μg/mL control IgG1, MoAb90, W6/32, TP25-99, and 1 μg/mL anti-Fas MoAb CH11. (A) Cells were collected after 2 hours of treatment with the different MoAbs, and incorporation of dUTP-FITC was measured by TUNEL assay as described in Materials and Methods. Each histogram represents 10⁴cells and percentage of apoptotic cells are indicated above to the histogram profiles. (B) Kinetics of MoAb90-induced B-cell apoptosis are as follows: 5 μg/mL of control IgG1, W6/32, TP25.99, and MoAb90 were added to the cultures, and the percentage of DNA fragmented cells was measured by TUNEL assay after the indicated time. In parallel, the percentage of cell viability was measured by trypan blue dye exclusion after treatment with MoAb90 at 5 μg/mL for indicated time. Results represent average of duplicate determinations. This figure is representative of three independent experiments. (C) Cells were collected after 12 hours of treatment with the different MoAbs and DNA from 2 × 10⁶ cells was run on 2% agarose gel and stained with ethidium bromide.