FIG. 8.

Effect of SNP-produced nitric oxide on IDO activity and C. trachomatis L2 growth in HeLa cells. HeLa cells were untreated or pretreated with IFN-γ for 24 h, then infected with C. trachomatis L2, and then cultured in complete medium (Table 1) supplemented with IFN-γ (20 U/ml) and/or sodium nitroprusside (0.5 mM). Following incubation for 48 h, medium nitrite levels were determined using Griess reagent, intracellular tryptophan pools were measured by HPLC, chlamydiae growth was assessed by titrating recoverable IFU, and IDO protein was detected by Western blotting. Growth data are presented as IFU (log₁₀) and represent the means ± standard errors of triplicate determinations. *, P < 0.0001 compared to the untreated control culture. See the legend to Fig. 1 and Materials and Methods for details. Medium nitrite levels were determined after 48 h of incubation using the Griess reagent. Data are presented as μM nitrite (A) or pmol tryptophan/10⁷ cells (B and C) and represent the means of two independent experiments with ranges shown. Intracellular tryptophan pools were measured by HPLC.