CD38 ligation in the presence of IL-2 induces differentiation of B-CLL cells. B-CLL cells obtained from 10 different patients were exposed to the anti-CD38 mAb (C), IL-2 (D), or a combination of the two (A-B). A population of cells with an enlarged cytosol and a light perinuclear zone, with the characteristics of plasmablasts, was observed after culture with anti-CD38⁺ IL-2 (A, thin arrows). Several blasts were present in every sample tested (A-B, arrows). Ligation of IgD with a polyclonal antibody in the presence of IL-2 was included as control and induced the appearance of plasmablasts (E, arrow). Samples treated with an anti-IgM polyclonal antibody were primarily apoptotic or necrotic (F). Panels A, C, D-F: original magnification × 20. Panel B: original magnification × 40.