Quantitative expression analysis of prdm-1 gene before and after CD40L+IL-4 stimulation of CLL B cells. Peripheral B cells from 7 patients with CLL constitutively expressing AID (A) and 7 patients with CLL without constitutive AID expression (B) were stimulated and cDNA extraction was performed. Transcript expression of prdm-1 mRNA was evaluated by QRT-PCR. Amplifications were normalized to GAPDH mRNA and the gene copy number was calculated by dilution of plasmids calibration curve containing the amplified product of the prdm-1 gene. Results were expressed as the ratio of mean gene copy number divided by the mean GAPDH copy number. The 2-tailed Student t test was performed on the arithmetic mean of each experimental point. A 2-tailed P < .05 was considered significant (ns, not significant). All analyses were done using GraphPad Prism, version 3.0 (GraphPad Software, San Diego, CA).