Decreased BCR internalization in ZAP-70+ BJAB B cells. (A) Histograms show IgM staining with R-PE F(ab′)2 in parental and ZAP-70 transfected BJAB B cells. Open histograms show staining of cells that were acid treated to inactivate the fluorescence of cell surface R-PE and thus represent the signal of internalized BCR; shaded histograms correspond to untreated cells stained at 4°C and provide a measure of the starting amount of R-PE F(ab′)2 bound to surface IgM. (B) Percentage of BCR internalization at various time points in wild-type BJAB B cells and ZAP-70+ stable transfectant clones, calculated as described in “Patients, materials, and methods.” Values represent means from 3 independent experiments that were performed with 2 different ZAP-70 transfectant clones (clone A and clone D).
