Enriched B cells were cultured in a 96-well plate (2 × 105/well) for 4 days with an indicated MoAb (10 μg/mL). Cells were pulsed with 1 μCi of [3H]TdR for the last 6 hours. They were then harvested onto glass fiber filters and the incorporated radioactivity was determined on a Beta plate flat-bed liquid scintillation counter (Pharmacia-Wallac, Gaithersburg, MD). The results are presented as a mean ± SD of triplicate wells.