CD62L expression among developing B cells in the BM and spleen. (A) BM and spleen cells were stained with FL-anti-CD62L, PE-anti-CD23, PE-Cy5.5-anti-B220, APC-anti-AA4, and APC-Cy7-anti-IgM before collection of 200 000 events on an LSR2 flow cytometer. AA4⁺ B220⁺ sIgM^high BM and splenic B cells were further gated as follows using the criteria illustrated in Figure 1A: CD23⁻, black line, CD23⁺, red line. Background staining with an isotype-matched control antibody for all BM and splenic AA4⁺ B220⁺ sIgM^high cells is shown with the filled gray histograms. Data are representative of 3 separate experiments. (B) cDNA prepared from the indicated sorted cell populations was subjected to semiquantitative RT-PCR as described in “Materials and methods.” Specific BM populations were AA4⁺ B220⁺ sIgM^high CD23⁻ and AA4⁺ B220⁺ sIgM^high CD23⁺ as shown in Figure 1.