Effects of IL-6 on SCF-dependent development and intracellular histamine levels of cultured mast cells. Ten-week cultured mast cells (1 × 10⁴) were plated in wells containing SCF or SCF+IL-6 for 2 weeks. After the numbers of viable cells were counted, the percentages of tryptase⁺cells and chymase⁺ cells were determined by immunocytochemical staining. At the same time, the intracellular histamine concentrations were measured by the RIA. Results shown are the mean ± SD of three experiments. SCF, 10 or 100 ng/mL; IL-6, 50 ng/mL. Tryptase⁺chymase⁻ cells (▩), tryptase⁺chymase⁺ cells (▪). Significantly different from SCF alone (*P < .05, #P< .001).