The effect of IFN-α/β and IFN-γ on the growth of sorted early (Fr B) pro–B cells from 3- to 5-week-old Eμ-ret (Tg+) and transgene-negative (Tg−) mice. A total of 2 to 4 × 104 Fr B cells were cultured in IL-7 (100 U/mL) for 4 days along with the indicated amount of the IFN. A total of 2 × 105 cells from the Eμ-ret–derived pro–B-cell lines, 2-19 and 02/1, were cultured for 3 days with (2-19) or without (02/1) IL-7. The proliferation percentages were calculated relative to the amount of proliferation (sum of live and dead cells) observed in the absence of the IFN (set at 100%). Mean percentages are given for two different sorts (Fr B cells) or two separate experiments (cell lines), and standard deviations are indicated by the error bars. Cell number was measured either by flow cytometry (Fr B cells) or by light microscopy (cell lines). The ratio of live to dead cells in the Fr B cell cultures from both the Eμ-ret and transgene-negative mice, as measured by propidium iodide staining, were similar for each IFN concentration.
