The IFN-γ–triggered proinflammatory cytokine production and IDO induction in human DCs represent distinct cellular programs. (A) The amount of proinflammatory cytokine release at the end of the activation period was examined in cell culture supernatants of differently activated DCs (left panels). In the same culture supernatants, the concentrations of tryptophan (TRP; ▩) and kynurenine (KYN; ■) were examined (right). The bars indicate the median of 4 experiments. The numbers given in brackets indicate the range. (B) DCs were activated with LPS/IFN-γ for 48 hours to induce IDO competence. Proinflammatory cytokine release was examined in cell culture supernatants after removal of the activating agents and reculture of the activated DCs in fresh medium for a 48-hour period. The values of cytokine release on reculture are expressed as the percentage of the maximum release (= 100%) during the activation period (top). In the same culture supernatants, the concentrations of tryptophan and kynurenine were analyzed (bottom). Results of 1 experiment, representative of 2 experiments, are shown. (C) DCs were activated with LPS/IFN-γ for 48 hours in conditions of external manipulation of tryptophan metabolism, as indicated (TRP met indicates tryptophan metabolites). Proinflammatory cytokine release (left panels) and the concentrations of TRP and KYN (right) were examined. Results of 1 experiment, representative of 2 experiments, are shown.