Apoptosis of Ramos cells incubated with anti-CD20 MoAbs in the presence of FcγR-expressing accessory cells. Each well of a 24-well plate was coated with 5 × 10⁵ FcγR-expressing accessory cells at 37°C overnight. 10⁶ Ramos cells were added to each coated well with PBS, control anti-CD3 antibody (64.1), or anti-CD20 MoAbs. After 24 hours incubation at 37°C, cells were stained with PI and analyzed by flow cytometry. Anti-CD20 MoAbs (B1 and 1F5) plus GAM and anti-sIgM antibody were used as positive control in the absence of FcγR-expressing accessory cells. Data are representative of four concordant experiments.