CD22-mediated apoptosis induction was CD22 blocking MoAb-specifc and equivalent to ligation of sIgM. Ramos B cells were incubated with media, the CD22 MoAb HB22.7 (20 μg/mL), the nonblocking CD22 MoAb HB22.27 (20 μg/mL), F(ab′)₂fragments of goat MoAb to BCR (20 μg/mL), or CD3 (10 μg/mL) for 24 and 48 hours. Apoptosis was assayed by trypan blue exclusion and confirmed via PI staining and BRDU incorporation as described in Fig 5. The results shown are an average of 4 replicate experiments, with the error bars representing the standard deviation.