The growth inhibitory effect of JunB on B lymphocytes extends to CD19⁺/CD43⁺ B-cell precursors. (A-B) Bone marrow cells of wild-type (n = 3) and Ubi-junB transgenic (n = 3) mice were analyzed by FACS to evaluate the numbers of B-cell precursors. Numbers in the right corners show the amount of B-cell precursors in the bone marrow. One representative experiment is shown (n = 6) (A). The remaining cells were cocultivated on IL-7-producer cells for 7 days to enrich for B-cell precursors. After 7 days, the bulk cultures, which now consisted of 80% CD19⁺/CD43⁺ cells, were subjected to [3H]thymidine incorporation assay after stimulation with 10 ng/mL IL-7 (B). Data represent means ± SDs from 6 individual wells. One representative experiment is shown (n = 2).