Mechanism of binding of anti-Id to rituximab bound to CD20 on the surface of lymphoma cells. (A) Raji cells were preincubated in normal media (NT, open bar), 33% plasma (solid bar), or 50 μg/mL anti-FcγRII mAb AT10 (gray bar) prior to incubation with rituximab IgG or F(ab′)2, followed by washing and incubation with FITC-labeled mAb MB2A4 as in Figure 1C. (B) FITC-labeled rituximab was added to Raji cells in the presence of varying concentrations of either MB2A4 (▪) or SAB1.3 (♦). Bound FITC-mAb was detected as before. (C) Raji cells were coated with rituximab (solid lines) or 7D8 (dashed lines) at 10 μg/mL for 15 minutes at RT and washed, and then MB2A4-FITC or SAB1.3-FITC was added to the cells for 5 or 15 minutes at 4°C (♦), 20°C (▪), or 37°C (▴) before washing and detection of FITC-mAb binding. (D) Schematic of MB2A4 binding to rituximab bound to the surface of CD20+ cells.
