CD32B antigen modulation following antibody treatment in vitro and in vivo. (A) Daudi cells were cultured in the presence of ch2B6 (1 μg/mL) or hu2B6-3.5 (1 μg/mL) for 24 hours and analyzed for expression of CD32B or the presence of anti-CD32B antibodies, at the indicated time points. (B) Residual Daudi tumors, treated with 8 weekly doses of hu2B6-3.5 (25 μg/mouse), rituximab (25 μg/mouse), or PBS were allowed to grow in vivo for an additional week. Tumors were removed, dissociated, and incubated with the following antibodies (1-2 μg/mL): anti–CD32B-FITC (2B6, bold line), anti–CD20-FITC (L27, dotted line), or murine IgG1-FITC (solid area). The anti-CD32B (2B6) and anti-CD20 (L27) antibodies used do not cross-react with the corresponding mouse antigens.