IL-12 regulates in vivo homing of immature B cells. (A-D) Lymphocytes from control and IL15^−/− mice from lymph node (A) or spleen (B) were triple stained with anti-B220, anti-CD23, and anti-CD21 (panel Ai and graph in panel C) or anti-AA4.1 and anti-B220 (panel Aii, and graph in panel D). Dot plots show the expression of the various markers on B220⁺ cells. The results presented are representative of 3 separate experiments. (E) Mice were fed with drinking water containing 1 mg/mL BrdU for 3 days. Cells were collected and stained with FITC-labeled anti-BrdU, anti-B220, and anti-AA4.1 as described in “BrdU labeling of cells,” and were analyzed by FACS. The results show the percentage of BrdU⁺ cells in the AA4.1⁺B220⁺ population. (F) Splenocytes from control and IL-15^−/− mice were triple stained with anti-B220, anti-AA4.1, and anti-Annexin. Histograms show the expression of Annexin on B220⁺ AA4.1⁺cells. The results presented are representative of 3 separate experiments. Error bars represent SD.