Impaired B lymphopoiesis in Eμ-myc/bcl-2^−/− reconstituted mice. Analysis of total numbers of leukocytes and B lymphocyte populations in peripheral blood (A) and bone marrow (B) from lethally irradiated mice reconstituted 8 to 12 weeks earlier with wt, bcl-2^−/−, Eμ-myc, or Eμ-myc/bcl-2^−/− fetal liver–derived stem cells. (A) Blood leukocytes were counted in an automated blood analyzer and percentages of donor-derived sIg⁺ B cells determined by staining with fluorochrome-conjugated monoclonal antibodies to B220, IgM, IgD, and Ly5.2 followed by FACS analysis. (B) Leukocytes from bone marrow (2 femurs per mouse) were counted in a hemocytometer and donor derived pro-B (Ly5.2⁺ B220⁺ c-Kit⁺ sIg⁻), pre-B (Ly5.2⁺ B220⁺ c-Kit⁻ sIg⁻), and B cells (Ly5.2⁺ B220⁺ c-Kit⁻ sIg⁺) quantified by staining with surface marker–specific monoclonal antibodies followed by FACS analysis. Data represent means ± SEM from 4 to 6 mice of each genotype. Statistically significant differences: *P < .05; **P < .005.