IFNβ induces apoptosis in mature but not immature DCs. CD11c⁺ DCs were treated with IFNβ (1000 IU/mL) or the cytokine cocktail containing TNF-α (20 ng/mL), IL-1β (10 ng/mL), IL-6 (10 ng/mL), and PGE2 (10⁻⁶ M) in the presence or absence of IFNβ (1000 IU/mL). DCs were collected at different time points (24, 48, and 72 hours) and analyzed for apoptosis through annexin V and PI staining (A) or subjected to TUNEL assay (at 48 and 72 hours; B). DCs were matured with the cytokine cocktail in the presence of different concentrations of IFNβ for 48 hours followed by apoptosis assays (C). Percentage viability represents the percentage of annexin V– and PI-negative cells (lower left quadrant). Data are representative of 3 independent experiments.