Autocrine produced BLyS protects B-CLL cells from apoptosis.

B-CLL cells from 5 patients (nos. 1-5) were cultured in phenol red-free RPMI supplemented with 0.5% BSA and 1 μg/mL BCMA-Fc or 10 μg/mL human Ig-Fc at 37°C for 18 hours. Caspase-3 activity was determined using the fluorescent caspase-3–specific substrate Ac-DEVD-AMC as described in “Materials and methods.” Apoptosis, as measured by caspase-3 activity, is detected by cleavage of Ac-DEVD-AMC and subsequent fluorescence. The caspase-3–specific inhibitor was included in all conditions to demonstrate specificity.