IL-9 induces expression of M-Ras. IL-9–responsive cell lines were cultured for 10 days in medium containing saturating concentrations of the indicated cytokines: 100 U/mL IL-2, 200 U/mL IL-4, or 200 U/mL IL-9 for T-helper–cell clones (TS2, ST2K9, and TS3), and 200 U/mL of IL-3 or 200 U/mL of IL-9 for mast cell lines (L138 and MC9). After electrophoresis of 10 μg of total RNA and transfer on nitrocellulose, filters were hybridized with a 32P-labeled mouse M-Ras cDNA probe. Hybridization with a β-actin probe confirmed that comparable amounts of RNA had been loaded in each lane.