Growth characteristics of wild-type and mutant G-CSFR in factor-dependent Ba/F3 cells. Cells maintained in IL-3-containing medium were washed extensively and transferred to 100 ng/mL G-CSF-containing medium. Viable cells were determined at the indicated times by MTT cell proliferation assay, confirmed by trypan blue cell counting (data not shown). To facilitate inspection, data are presented in 2 graphs and are represented as the mean ± standard deviation.