BCAP and CD19 regulate mature B-cell generation in vivo through their YXXM motifs. Lineage marker–negative bone marrow progenitor cells were cultured and infected with retrovirus vectors carrying BCAP, CD19, and their mutants. Mock transfectant was also prepared using retrovirus vector without cDNA. Infected cells were injected to irradiated C57BL/6 mice. Splenocytes were prepared from the mice after 2 months of injection and stained with anti-IgM and -IgD mAb followed by flow cytometric analysis. Top panels represent expression of GFP in splenocytes. Lines in fluorescence-activated cell sorting (FACS) profiles represent gates settled for discriminating donor-derived cells that are successfully infected retrovirus vectors. Bottom panels represent profiles for IgM and IgD expression on GFP-positive gated cells. The percentage of cells in each quadrant is indicated in panels. Averages of absolute numbers of IgMloIgD+ mature B cells per spleens (± SD) in 3 mice are as follows: 3.0 × 105 ± 0.8 × 105 (BCAP wt→B6), 0.56 × 105 ± 0.19 × 105 (BCAP 4YF →B6), 6.2 × 105 ± 2.6 × 105 (CD19 wt →B6), and 0.33 × 105 ± 0.10 × 105 (CD19 2YF→B6).
