Improved survival of FDCP1 cells following apoptotic prestimulation. (a) Colony formation in soft agar. One thousand FDCP1 cells were seeded into agar cultures as previously described . After incubation for 0, 1, 2 and 4 h, IL-3 was added at the indicated concentrations. Colonies were counted in duplicate after incubating for 7 days. Results were derived from two independent experiments. (b) Frequency of apoptotic cells. 1 × 106 cells were deprived of IL-3 for 1 and 2 h, respectively. After re-adding IL-3 for 4 h, cells were washed and incubated without IL-3. After 6, 9 and 12 h factor deprivation, the cells were stained with annexin and the frequency of apoptotic cells was estimated by flow cytometry. Results were derived from two independent experiments.