Quantitation of AID message in B-CLL cells. Quantitative real-time PCR was performed on cDNA from purified B-CLL cells, and the relative expression units are plotted on a log scale. The open bars represent the B-CLL cases with less than 2% nucleotide difference from the corresponding germ line Ig V region gene, and the filled bars are B-CLL cases with 2% or more differences. The results of either single or nested AID-specific RT-PCR for the same samples are shown below the graph. The single PCR used the primers 63F and 1137R for 33 cycles. Nested PCR was performed on the single PCR products using the primers 68F and 676R for 15 cycles.