Apoptosis induced by anti-CD20 mAb. mAbs were either added in free solution (A-B) or coated onto wells for 2 hours at 37°C, and unbound mAbs were removed (C) before Daudi, EHRB, or Raji cells were added to the wells. Numbers in quadrants represent the percentage of cells in each section of the quadrant. Bars represent mean apoptosis value ± SD from at least 3 separate experiments. Apoptosis was assessed 18 to 24 hours later by annexin V/PI staining (left-hand dot plots in A), annexin V staining (B-C), or DioC6 staining (right-hand plots in A).