Comparison of effects of IL-6 with those of IL-4 on mast cell development supported by SCF. Ten-week or 40-week cultured mast cells (2 × 10⁴) were incubated in culture wells containing 10 or 100 ng/mL of SCF, 50 ng/mL of IL-6, or 20 ng/mL of IL-4, alone or in combination. After 2 weeks, the number of viable cells was determined, and the cells were then processed for immunocytochemical staining with an antitryptase or antichymase MoAb. At the same time, histamine amounts in cell lysates were analyzed by the RIA. The results shown are from one representative experiment of three. Similar results were obtained in the other two experiments. Experiment groups using 10 ng/mL of SCF (□) experiment groups using 100 ng/mL of SCF (▩); tryptase⁺ chymase⁻cells (▩); tryptase⁺chymase⁺ cells (▪). Significantly different from SCF alone (*P < .0005, **P < .0001). Significantly different among the two- or three-factor combinations (†P < .0005, ††P < .0001).