PR8-NS1(1–73)GFP virus is pathogenic in mice.

<p>(A) BALB/c mice (n = 6 per group) were inoculated with 1 x 10³, 1 x 10⁴ or 1 x 10⁵ PFU of PR8-NS1(1–73)GFP virus or 1 x 10³ PFU of wild type PR8 virus. Body weight (relative to initial body weight on day 0) and survival were monitored for 14 days. Error bars represent the standard deviation. The body weight of mice infected with 1 x 10³ or 1 x 10⁵ PFU of PR8-NS1(1–73)GFP virus was significantly different on day 3–7 or day 2–6, respectively, from mice infected with 1 x 10³ PFU of wild type PR8 virus (one-way ANOVA with a Tukey’s multiple comparison test, * <i>P</i> < 0.05, ** <i>P</i> < 0.01, *** <i>P</i> < 0.001). The survival curves of mice infected with 1 x 10³ or 1 x 10⁵ PFU of PR8-NS1(-173)GFP virus were significantly different from mice infected with 1 x 10³ PFU of wild type PR8 virus (log-rank test, * <i>P</i> < 0.05, ** <i>P</i> < 0.01) (B) BALB/c mice (n = 8 per group) were inoculated with 1 x 10³ or 1 x 10⁴ PFU of PR8-NS1(1–73)GFP virus or 1 x 10³ PFU of wild type PR8 virus. Body weight (relative to initial body weight on day 0) was monitored for 5 days. Data points represent averages and error bars represent the standard deviation. Body weight of mice infected with PR8-NS1(1–73)GFP virus was significantly different from those infected with wild type PR8 virus (two-way ANOVA with a Tukey’s multiple comparison test, *** <i>P</i> < 0.001). The virus titer in the lungs was assessed on day 2 and day 5 by TCID₅₀ analysis of the lung homogenates (50 μl sample). For the titers on day two in the wild type PR8 infected group, one value was excluded due to technical failure. Differences in viral titers on day 2 or day 5 were not statistically significant (<i>P</i> > 0.05, one-way ANOVA, with a Tukey’s multiple comparison test).