IL-4 is not a growth factor in Ba/F3 cells. Ba/F3 cells were labeled with the fluorescent dye PKH26. Immediately after labeling, incorporation of the dye was analyzed by flow cytometry (time 0). Cells were cultured in complete media supplemented with (A) IL-3 or (B) IL-4 and aliquots of cells were analyzed by flow cytometry at 24, 48, and 72 hours to determine the amount of dye dilution.