FIG. 3.

IDO induction as an antiparasite effector mechanism in bovine cells. Bovine fibroblasts (EBTr cells; 3 × 10⁴ cells per well) were stimulated with bovine IFN-γ (0 to 100 U/ml) in the presence of 0.6 mM tryptophan. (A) After 72 h of stimulation supernatants were harvested, and the kynurenine content was determined by use of the Ehrlich reagent. The data are means and standard errors of the means of four independent experiments performed in triplicate. OD₍₄₉₂₎, optical density at 492 nm. (B) After 72 h cultures were infected with T. gondii tachyzoites (2 × 10⁴ tachyzoites per well), and T. gondii growth was monitored using [³H]uracil. The data are means and standard errors of the means of three independent experiments performed in triplicate. A significant inhibitory effect of supplemental tryptophan (0.6 mM) on IFN-γ (50 U/ml)-induced inhibition of parasite growth is indicated by an asterisk. (C) At 72 h poststimulation, cells were infected with N. caninum tachyzoites (2 × 10⁴ tachyzoites per well), and growth was monitored using [³H]uracil. The data are means and standard errors of the means of four independent experiments performed in triplicate. A significant inhibitory effect of supplemental tryptophan (0.6 mM) on IFN-γ (50 U/ml)-induced inhibition of parasite growth is indicated by an asterisk.