FIG 2.

MIIG mice are highly sensitive to LVS respiratory tularemia. MIIG mice contain macrophages which do not respond to IFN-γ stimulation. (A and B) MIIG and WT C57BL/6 mice (8 mice/group) were infected i.n. with 1 LD₅₀ (A) or 0.5 LD₅₀ (B) of F. tularensis LVS. Survival was monitored for 21 days. P values were determined by the log-rank test. *, P < 0.05; ***, P < 0.001. (C to E) MIIG and WT C57BL/6 mice (3 mice/group) were infected i.n. with 1 LD₅₀ of F. tularensis LVS. Lungs (C), livers (D), and spleens (E) were harvested at 4 days postinfection, and bacterial burdens were assessed. *, P < 0.05 by two-tailed t test. (F) MIIG and WT C57BL/6 mice (6 to 8 mice/group) were treated i.n. with IL-12 or PBS 1 day prior to i.n. infection with 1 LD₁₀₀ of F. tularensis LVS. Survival was monitored for 21 days. P values were determined by the log-rank test. ***, P < 0.001; NS, not significant. (G) C57BL/6 and WT mice (3 or 4 mice/group) were treated with IL-12 or PBS prior to infection as described above. At 1 day postinfection, lungs were harvested for analysis of IFN-γ-positive (IFN-γ⁺) NK cells by flow cytometry. No significant differences were detected between WT and MIIG mice.