Inhibitory effect of c-fos on cell proliferation by primitive hematopoietic stem cells. Lin⁻Sca-1⁺ BM cells from Mx–c-fos or control littermates were cultured with SCF+IL-3+IL-6, SCF+IL-6, or IL-3. IFN-/β (200 U/mL) was added to the culture on day 0 and day 4. On day 7 of culture, the number of viable cells was counted by Trypan blue dye exclusion. Results represent mean and SD of four dishes. The data presented are representative of three independent experiments. Purified recombinant SCF was used in this experiment.