CLL cells in infiltrated LNs express AID protein. (A) Representative low-power (100× original magnification) and high-power (600× original magnification, inset) views of AID⁺ cells in an infiltrated CLL LN. Scattered AID⁺ cells (black arrows), which are larger than the majority of cells, are present and have the morphology of paraimmunoblasts (inset). (B) Representative high-power confocal photomicrograph of CLL LN (600× original magnification) showing cells expressing the CLL marker CD23 (red). Several cells are Ki-67⁺ (blue). An AID⁺Ki-67⁺ cell (green) is indicated by the white arrow. (C) Flow cytometry of dispersed LN cells. The percentage of AID⁺ cells was determined by comparison of samples with and without the use of a peptide that specifically blocks binding of the AID Ab. At least 1% CD5⁺CD19⁺ were AID⁺. (D) Graph showing the mean fluorescence intensity (MFI) of CXCR4, CD5, CD23, and CD11a in AID⁺ cells compared with the total CD5⁺CD19⁺ sorted population using the same gating as in panel C.