Effect of IL-9 on terminal differentiation of the HL-60 cell line.

(A) The time course of the IL-5R–α chain expression on the HL-60 cell line in the presence of IL-9. The HL-60 cell line was differentiated toward eosinophils as described in “Materials and methods” and examined for the presence of IL-5R–α by flow cytometry. We added 10 ng/mL IL-9 or the vehicle control (medium alone) to medium at day 6 (t0 = time 0). The surface expression of the IL-5R–α chain was investigated at 4, 6, 8, 18, and 24 hours following IL-9 stimulation (bold line) or control stimulation (broken line) using mAb anti–IL-5R–α. The IgG1 control isotype is also shown (thin line). (B) The increase in the mean ± SD of SMFI with 10 ng/mL IL-9 over control stimulation. The maximal effect of IL-9 was observed after 6 hours of stimulation. The results represent the mean ± SD of 2 independent experiments.