BrdU labeling of BM and peripheral B-cell pools. (A) Flow cytometric analysis showing gating strategy for assessing BrdU incorporation. (B) The 8-week-old C57BL/6 mice (3 mice per time point) were inoculated intraperitoneally with BrdU every 12 hours for the indicated time points. Mice were killed and BM and splenocytes were stained as shown in panel A, then stained intracellularly for BrdU incorporation as described in “Materials and methods.” Populations are as follows: AA4⁺ B220⁺ sIgM^low CD23⁻ BM cells, ♦ with dotted pink line; AA4⁺ B220⁺ sIgM^high CD23⁻ BM cells, ○ with solid purple line; AA4⁺ B220⁺ sIgM^high CD23⁺ BM cells, ▵ with solid red line; AA4⁻B220⁺ sIgM^low CD23⁺ BM cells, ▪ with solid green line; AA4⁺ B220⁺ sIgM^high CD23⁻ splenocytes (splenic T1), • with light blue solid line; AA4⁺ B220⁺ sIgM^high CD23⁺ splenocytes (splenic T2), ▴ with dotted dark blue line. Data are representative of 2 separate experiments.