Loss of hematopoietic cells in the bone marrow of IL-2^−/− mice. (A) Antibodies reactive with surface antigens that distinguish various stages of B-cell development were used to identify pro- (S7⁺), pre- (BP1⁺), and mature (IgM⁺) B cells in the bone marrow of 6-week old IL-2^−/− mice. (B) FITC-Gr–1 and PE-Ter–119 were used to distinguish cells of the myeloid and erythroid lineage, respectively. Stained cells were run on a flow cytometer and analyzed using CellQuest software. The level of staining obtained with isotype-matched control antibodies was used to establish quadrant settings for the dot plots and determine the frequency of cells stained with B cell, erythroid and myeloid cell-specific antibodies (numbers shown in each quadrant of dot plots in A and in histograms in B). The results shown are representative of 10 groups of mice.