Fig. 8.

MHV nsp15 mutant viruses confers protective immunity against WT virus infection. Ten-week-old naïve C57BL/6 mice or mice immunized with mutant virus 4 wk prior (from Fig. 7A) were intraperitoneally inoculated with 6.0 × 10⁴ pfu of WT virus. At 5 dpi, organs were harvested for (A) viral titration and (B) liver pathology. Red dashed line in A indicates limit of detection. Images of liver sections in B are representative of four mice per group. (Magnification, 40×.) Black arrowheads indicate the liver lesions caused by MHV infection. (C and D) Thirteen-week-old naïve mice and mice immunized seven weeks prior with N15m1 (from Fig. 7E) were challenged with 6.0 × 10³ pfu WT virus by intracranial inoculation. Viral pathogenicity was evaluated by (C) body weight loss and (D) percent survival. Mouse numbers (n) are indicated in parentheses. The P values of survival rate were calculated using a log-rank test. Data are a pool of two independent experiments. Error bars in A and C represent the mean ± SEM.