Synergy between ATP/ATPγS and IFN-γ on the functional expression of IDO. (A) DCs were either untreated or treated with ATP (300 μM) or ATPγS (100 μM) alone or in the presence of IFN-γ (10 or 100 U/mL) for 24 hours in complete medium. The same amounts of total protein were analyzed by Western blotting with an anti–human IDO rabbit polyclonal antibody. (B) After a similar treatment with ATP (300 μM) or ATPγS (100 μM), DCs were washed and incubated for 5 additional hours in red-phenol–free RPMI supplemented with 300 μM L-tryptophan. Kynurenine levels were determined in each supernatant by HPLC. Data (mean ± range) were obtained in an experiment performed in duplicate and representative of 3 independent experiments.