Figure 3
Polymerase activities and viral pathogenicity of different mouse-adapted variants. The polymerase activities of different mouse-adapted viruses were determined by using the minigenome assay in 293T cells at 33 °C (A) and 37 °C (B). The data presented are the mean ± SD of three independent experiments. P values were calculated by using Student’s t test, *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Six-week-old female BALB/c mice (n = 5/group) were inoculated intranasally with 50 µL containing 2 × 106 PFU of rJS/875 WT or the mouse-adapted viruses, and the PBS-infected group was used as the mock inoculation. C Body weight changes and D survival rate were monitored as the percentage of the weight on the day of inoculation (day 0). The MLD50 values of rJS/875 and MA#12 were also determined by inoculating groups of five 6-week-old female BALB/c mice with tenfold serial dilutions of different viruses in a 50 µL volume (2 × 105–2 × 107 PFU of rJS/875 or 2 × 103–2 × 106 PFU of MA#12). The body weight changes (E, G) and survival rate (F, H) of mice given these two viruses were assessed by measuring weight changes over a 14-day period and are depicted as a percentage of the animal’s weight on the day of inoculation (day 0). Mice that lost more than 25% of their original body weight were euthanized.