IDO and TTS expression and up-regulation in human PBMCs are dependent on IFN-γ. IDO (A) and TTS (B) mRNA expression in human PBMCs after 12 hours of culture under different conditions: (1) untreated control; (2) rhIFN-γ; (3) CTLA-4-Fc; (4) CTLA-4-Fc plus anti–IFN-γ mAb; and (5) anti–IFN-γ mAb. *P values less than .05 and **P values less than .005 are based on 4 independent experiments. Mean values plus standard errors are shown.