PGE₂ triggers the transcription of IDO mRNA. (A-B) IDO mRNA expression in DCs stimulated with TNFα, PGE₂, or a combination of both stimuli was monitored by qRT-PCR. The PCR amplification curves from a representative experiment, performed in duplicate, are displayed (A). The same data are reported as a ratio of IDO/GAPDH, again normalized to expression in iDCs (set to a value of 1.0). (B) The inset represents the level of IDO mRNA as a function of the dose of PGE₂. (C) DCs exposed to the conditions described above were monitored for their IDO activity. Kynurenine production was measured using a colorimetric assay; known concentrations were used for the establishment of a standard curve (Supplemental Figure S2B). Values are the mean of triplicate wells, and error bars indicate standard deviation. Data in Figure 3 are representative of 4 experiments.