CD40 stimulation causes apoptosis in Burkitt lymphoma.

Daudi cells were cultured in media in the presence or absence of srhCD40L or anti-CD40 antibody (SGN-14 clone, mouse IgG1). TUNEL (A,B) and annexin V–fluorescein isothiocyanate (FITC; C) stains were performed following incubation. Twenty-four hours after culture initiation, Daudi cells were analyzed for nuclear DNA damage by TUNEL and for phospholipid externalization to the cell surface by annexin and flow cytometry. The results are expressed as the number of cells (percent of total) that have either DNA strand breaks or that bind annexin V-FITC and are therefore undergoing apoptosis. Culture with 10 μg/mL srhCD40L (A) caused a 60% increase in DNA strand breaks compared to an untreated control (from 1.4% to 58%). Dark gray shade (A) is the untreated control group. Light gray shade (B) is the group treated with srhCD40L. Culture with 3 μg/mL srhCD40L (C) induced a 5-fold increase in the number of apoptotic Daudi cells over that observed in the media culture alone (from 11% to 53%).