Dendritic-cell maturation induces IDO expression. Extracted data from Affymetrix gene array studies (U133A chips) is shown for the 4 experiments. Immature dendritic cells were differentiated from monocyte precursors using GM-CSF and IL-4. These cells were then exposed to TNFα and PGE₂ for 36 hours to generate mature dendritic cells. The raw signal intensity reflects the relative expression of IDO (solid line) and GAPDH (dotted line). Each line indicates an independent donor.