Combination of SCF and TPO stimulates mast cell production by CD34⁺ BM cells in serum-deprived liquid culture. (A) CD34⁺ BM cells (1 × 10⁴) were plated per well containing serum-deprived liquid culture medium supplemented with 10 ng/mL of SCF and/or 10 ng/mL of TPO. Half of the cell-free supernatant was replaced with fresh medium containing the growth factor(s) every 5 to 7 days. The numbers of viable cells were serially counted. This experiment was performed three times. Values are expressed as the mean ± SD of three experiments. (□), no growth factors; (○), SCF; (▪), TPO; (•), SCF + TPO. (B) Time course of the relative frequency of tryptase-positive cells and peroxidase-positive cells grown by SCF + TPO. The cultured cells grown by SCF + TPO were stained with a MoAb against tryptase or with POX. (▪), tryptase-positive cells; (▩), POX-positive cells; (□), others.