Effects of FIΔ cytoplasmic truncations on factor-independent growth and viability. (A) Proliferation of FDB1 cells infected with cytoplasmic truncations of the FIΔ activated mutant. Growth without factor (diamonds) is shown compared with growth with the control cytokine IL-3 (squares). Results representative of at least 3 independent experiments are shown. Error bars represent the SD of triplicate samples. (B) Viability of cells without factor at day 5 after factor withdrawal. Cell viability was determined by trypan blue exclusion, and the combined results of at least 3 independent experiments are shown. Error bars represent the SD.