Effects of SCF and/or TPO on the later phase of mast cell growth. Twenty thousand 15-week-old cultured cells, a large number of which reacted with antitryptase MoAb, were incubated in culture wells containing 10 ng/mL of SCF and/or 10 ng/mL of TPO for 3 weeks. The numbers of viable cells were counted weekly. The values are expressed as a percentage of the cell number at the beginning of the culture. The results shown are from one representative experiment of three. Similar results were obtained in the other two experiments. (□), no growth factors, (○), SCF; (▪), TPO, (•), SCF + TPO.