IL-5 in combination with SCF had no additional mitogenic activity. (A) Cell cycle distribution of TF-1 cells cultured in various combinations of cytokines. TF-1 cells were cultured in the indicated media as described in Fig 1 for 24 hours before BrdU-labeling and PI staining as described in Materials and Methods. Similar numbers of viable cells were analyzed for the percentages of cells in the G1, S, and G2/M phases and results are shown within the panel. The cytokines present in each culture medium are also indicated inside the panels. The x-axis represents the intensity of PI fluorescence and the y-axis represents the intensity of FITC-conjugated anti-BrdU antibody fluorescence. These plots are a set of representative results and the percentages of cells in various cell cycle stages are the averages from four independent determinations. (B) DNA synthesis rates of TF-1 cells cultured in various combinations of cytokines. TF-1 cells were cultured in the indicated media for 48 hours and ten thousand viable cells were subjected to [³H]thymidine incorporation assay to determine the DNA synthesis rate. The data shown are the averages of four independent triplicated experiments.