CD5⁺B220^low B CLL cells from TCL1-Tg mice have a high cell turnover. (A) In vivo cell proliferation of different cell populations of WT (top panel) or TCL1-Tg (bottom panels) mice was studied by injecting 10 mg/mL BrdU intraperitoneally into the mice strains indicated after analysis of splenic cells by flow 12 hours later using the antibodies indicated (n = 6 mice each strain). We gated on CD5⁺B220⁻ T cells (P1), CD5⁻B220⁺ B cells (P2), or CD5⁺B220^low B cells (P3), as indicated in the far left panels. We determined the proliferation rates for each of these subpopulations by evaluating for the proportion of cells that incorporated BrdU (rectangles), as indicated in the panels to the right. Each of these panels depicts the BrdU fluorescence of gated cells in P1, P2, or P3, respectively. (B) Statistical analysis of the results obtained in panel A. (C) CD5⁺B220^low B CLL cells from TCL1-Tg were also tested for levels for Ki-67 using intracellular flow cytometry and those results were compared with B220⁺ splenic B cells from WT mice (n = 3 mice each strain). (D-E) Frozen splenic sections of mouse strains indicated were costained for CD5-FITC and TUNEL-TMR-Red. Data shown were average of TUNEL-positive cells/field from splenic sections (n = 6 mice). Magnification of the objective lense: 40×/1.3 Oil DIC. Camera: Zeiss AxioCam HR. Software: AxioVs40AC v4.5.0.0.