Activation of ▵Raf-1:ER in combination with IL-4 stimulates DNA synthesis and the long-term growth of Ba/F3 cells. (A) Ba/F3 or ▵Raf-1:ER cells were washed free of IL-3 and plated at 250 cells/well in a Terasaki microtitre plate in medium alone or IL-4, with increasing concentrations of 4HT. After 40 hours, the cells were pulsed with [³H]-thymidine for an additional 8 hours, harvested, and counted in a scintillation counter. (B) ▵Raf-1:ER or (C) ▵Raf-1:ER K70W cells were washed free of IL-3 and incubated in IL-3, IL-4, 100 nmol/L 4HT, IL-4 plus 100 nmol/L 4HT or without factor (MA) at a density of 1 × 10⁵ cells/mL. Cells were counted in triplicate at the indicated times and diluted as appropriate to maintain a consistent density. The results are representative of several independent experiments, with two independent clones. Error bars represent the SEM of triplicate samples.