Brefeldin A induces apoptosis in fludarabine-refractory B-CLL cells. (A-B) Primary CLL cells exhibited a more extensive ER network than normal B lymphocytes. TEM was used to reveal the relative abundance of ER membranes (arrows) in primary CLL cells (A) and normal B lymphocytes (B). Original magnification, × 7500. Images were visualized using a JEM 1010 transmission electron microscope with a built-in camera and accelerating voltage of 80 KV (JEOL USA, Peabody, MA). A numeric aperture of 2.0 was used. (C-E) Fludarabine-refractory CLL cells were sensitive to BFA-induced apoptosis. CLL cells from 30 patients were treated in vitro with the indicated concentrations of fludarabine nucleoside (F-ara-A) or BFA for 48 hours. Drug-induced apoptosis was measured by flow cytometric analysis of activated caspase-3. Representative results are shown in panel C. The bar graphs in panels D and E show the percentage of cells with activated caspase-3 for nonrefractory patients (n = 15) and fludarabine-refractory CLL patients (n = 15), respectively. ▪ represent cells treated with F-ara-A; ⦾ depict cells treated with BFA. Error bars indicate standard error of the mean (SEM).