Effects of IL-3 on mast cell growth by CD34⁺ cord blood cells. (A) CD34⁺ cord blood cells (1 × 10³ to 1 × 10⁵) were cultured with 10 ng/mL of SCF and/or 100 U/mL of IL-3. The number of viable cells was counted at 4 weeks, and then the percentage of tryptase⁺ cells (▪) was determined by immunocytochemical staining. Values are expressed as the mean ± SD. (B) Expression of c-kit on the 4-week cultured cells was analyzed by flow cytometry. The percentage of c-kit⁺ cells in the cultured cells grown by SCF+IL-3 was 12.7%. (—) Labeled with PE-conjugated anti–c-kit MoAb. (···) Labeled with PE-conjugated mouse IgG.