IFN-γ synthesis was crucial for the ability of DCs to activate CD8⁺ T cells. (A-B) IFN-γ regulated IL-12 and TNF-α synthesis in DCs. When mentioned, recombinant human IFN-γ (10 ng/mL) or blocking anti–IFN-γ antibody (10 μg/mL) were added to immature DCs 1 hour before LPS in the presence or absence of MPA for 2 days. Levels of IL-12p70 and TNF-α in supernatants were analyzed by ELISA. n = 3 (A) and n = 6 (B). (C) IFN-γ increased the ability of MPA-DCs to induce cytotoxic CD8⁺ T cells whereas anti–IFN-γ decreased this ability in mDCs. When mentioned, recombinant human IFN-γ (10 ng/mL) or blocking anti–IFN-γ antibody (10 μg/mL) were added to immature DCs 1 hour before LPS in the presence or absence of MPA for 2 days. After maturation, DCs were mixed with allogeneic purified CD8⁺ T cells for 24 hours and expression of CD107 was analyzed by FACS. One representative experiment of 3 is presented. (D-E) IFN-γ partially restored the ability of MPA-DCs to induce CD8⁺ T-cell proliferation whereas IL-12, TNF-α, and IL-2 had no effect. Immature DCs were incubated with rhIL-12 or rhTNF-α or rhIL-2 or rhIFN-γ and matured with LPS in the presence of MPA for 2 days. After maturation, DCs were mixed with allogeneic purified CD8⁺ T cells for 5 days. T-cell proliferation was assessed by CFSE dilution (D) or 3H-thymidine incorporation (E) during the last 18 hours of MLR (mean cpm ± SD of triplicate wells). Results are representative of 3 donors. *P < .05.