Effect of IL-9 on IL-5R–α expression by human CD34⁺

progenitor cells. Human umbilical cord blood CD34⁺ progenitor cells were cultured with 1 ng/mL IL-9 alone or 1 ng/mL each of IL-3 and IL-5. Initial plating density was 1 × 10⁵ cells per mL. (A) Flow cytometric analysis of IL-5R–α expression by CD34⁺ cells at day 0 and after culture in 1 ng/mL IL-9 for 7 days. One representative experiment of 5 is shown. (B) RT-PCR products showing amplification of mRNA for both soluble (SOL) and transmembrane (TM) IL-5R–α in cord blood cells grown in IL-3 and IL-5 or IL-9 alone for 3, 7, or 14 days. There was no IL-5R–α mRNA detected in freshly isolated CD34⁺ cells at day zero. Data is shown for 1 of 3 independent experiments.