Generation of B lymphocytes in long-term cultures of BMs of C/EBPβ+/+ and C/EBPβ−/− mice. BM cells of C/EBPβ+/+ mice and C/EBPβ−/− mice were cultured at 10⁶/mL in 10-cm tissue-culture dishes as detailed in Materials and Methods. At the indicated times, cultures were examined by flow cytometry for the number of B220⁺ cells. The data are expressed as the mean ± the standard deviations of five independent experiments.