FIG. 2. .

Induction of intracellular interleukin-15 (IL-15) in interferon-α (IFN-α)–treated B16α cells and RM-1α cells. Monolayers of B16α and RM-1α cells were grown in medium containing 3,000 units/mL of IFN-α for 2 days or for 15 days. Control monolayers of parental cells were given medium alone without IFN treatment. At 2 days after providing fresh medium with or without IFN-α, the cells were harvested. The supernatant fluids were decanted, spun to remove floating cells, concentrated 30-fold (final volume = 0.5 mL), and assayed for the presence of IL-15 by ELISA. The cells were harvested for sonication, and the sonicates were assayed for the presence of IL-15 by ELISA. Standard curves of IL-15 were run concomitantly with the samples. The ELISA had a sensitivity of 6.25 pg. The data are expressed as IL-15 in picograms per 10⁶ cells (mean ± SE) versus days of IFN treatment. ANOVA analysis for intracellular IL-15: day 2 B16 parental cells versus day 2 B16α cells: P = NS; day 2 RM-1 parental cells versus day 2 RM-1α cells: P = NS; day 16 B16 parental cells versus day 16 B16α cells: P < 0.0001; day 16 RM-1 parental cells versus day 16 RM-1α cells: P < 0.0001; day 2 B16α cells versus day 16 B16α cells: P < 0.0001; day 2 RM-1α cells versus day 16 RM-1α cells: P < 0.0001.