Activation of CD160 prevents mitochondrial dysfunction via an increase in the ratio of Bcl-2/Bax. (A) Expression of Bcl-2, Bcl-XL, Mcl-1, and Bax proteins in CLL cells was detected by Western blot after treatment with 10 μg/mL anti-CD160 mAb (BY55) for 2 and 4 hours. (B) Mitochondrial cytochrome c levels were detected by anti–cytochrome c–conjugated PE mAb (6H2) and measured with a FACSCanto. Data show the average percentage of mitochondrial cytochrome c ± SEM from 8 patients, *P < .001. (C) CLL cells were treated with or without 10 μg/mL CL1-R2 for 18 hours and then incubated with 20nM TMRM for 30 minutes at 37°C. Cells were analyzed with a FACSCanto for loss of mitochondrial membrane potential (ΔΨm^LOW) and were gated as P5. Numbers indicated in each graph are the percentage of ΔΨm^LOW cells. The figure shows 1 representative experiment from 7 patients. (D) Activation of caspase-3 and caspase-9 was tested after treatment with 10 μg/mL CL1-R2 for 18 hours, with data normalized to the basal caspase-3, -8, and -9 level (0 hour, expressed as 100%). Data represent the average percentage of 8 patients ± SEM; caspase-3: *P < .001; caspase-9: *P = .01; caspase-8: *P = .026.