AID mRNA expression relates to recent cell division. (A) CD5+CD19+ cells were sorted into recently divided (CD5+CD19+CD23BrCD11a+CXCRDim), intermediate (CD5+CD19+CD23ModCD11a+/−CXCR4Mod), and resting (CD5+CD19+ CD23DimCD11a−CXCR4Br) fractions before analysis of mRNA transcripts for AID. (B) Representative agarose gel of mRNA for AID and β-actin in sorted fractions. Both full-length and a spliced AID transcripts can be seen. (C) In this example, CLL patient-specific μ transcripts were found in all 3 cell fractions by RT-PCR, but switched γ transcripts were only detected in the proliferative fraction. DNA sequencing confirmed that the γ and μ transcripts were of patient origin.