Fig. 7.

Engagement of CD22 with epratuzumab directly stimulates the phosphorylation of Tyr²⁹² on CD32B. Tonsil-derived B cells (a) and Daudi (b) cells were stimulated with 10 μg/mL of either epratuzumab IgG or epratuzumab F(ab’)₂ for the time periods indicated. Untreated cells were used as a control to assess the level of basal phosphorylation. Cells were also treated with 10 μg/mL human IgG1 isotype as a negative control. Following cell lysis, CD32B was immunoprecipitated using an anti-CD32B antibody as described in “Materials and Methods” section. Rabbit IgG whole molecule was used as a negative control antibody for immunoprecipations. The samples were immunoblotted and probed using an anti-CD32B (phospho Tyr²⁹²) antibody to assess the relative phosphorylation changes. To ensure equal protein loading an anti-CD22 blot was also carried out. The figure shown is a representative image from three independent experiments