Proliferation synergism of SCF with IL-5 in TF-1 cells. Rapid growing TF-1 cells were washed and cultured separately in cytokine-free medium (□), SCF (50 ng/mL, ▪), GM-CSF (2 ng/mL, ○), GM-CSF+SCF (•), IL-5 (5 ng/mL, ▵), or IL-5 + SCF (▴)-containing medium. The viable cell numbers were determined daily by trypan blue staining and are shown as the percentage of the initial viable cell number. Each number represents the average from four independent duplicated experiments. The standard deviations are indicated as error bars.