FIG 4.

Growth, virulence, and interference with STAT1 pathway. (A) Plaque assay on HFF monolayers examining growth of wild-type and NTPase knockout parasites. (B) Virulence of NTPase knockout strains in CD-1 mice infected intraperitoneally with 200 tachyzoites per mouse. Groups of five mice per strain were infected, and the survival was monitored. The experiment was repeated once, and the results of both experiments were plotted together. (C) A fluorescence assay performed to examine the interference of wild-type T. gondii with IRF1 protein expression as a readout for STAT1-activated transcription compared to NTPase knockout strains showed no NTPase-dependent effect. HFF monolayers were infected for 2 h and subsequently activated with 100 U of IFN-γ/ml for 5 h. Quantification of the IRF1 fluorescence of infected cells versus controls. Data points represent the mean red fluorescence in a ROI overlaying the host cell nucleus. IRF1, red; DAPI, blue; T. gondii-GFP, green. Scale bar, 10 μm. ***, P < 0.0001 (Kruskal-Wallis with Dunn's correction).