IFN-γ transgenic mice are virtually devoid of B-lineage cells in the bone marrow and spleen. Splenocytes or bone marrow cells from 2-month-old transgenic mice or normal littermate controls were labeled for immunofluorescence using PE-conjugated B220 (detects B-lineage cells) and FITC-conjugated goat antimouse IgM (detects immature and mature B cells) and analyzed by FCA. The values in the corner grids indicate the percentage of cells in each quadrant.