TABLE 1.
Virulence of PR8 viruses with mutations in NS1 in mice
| Virus strain | RNA binding | CPSF binding | LD50 (FFU)a in: |
|
|---|---|---|---|---|
| C57BL/6 mice | B6-Mx1+/+ mice | |||
| R/FM/G | + | + | 5 | 5 × 102 |
| R/SI/G | + | − | 5 | 3 × 103 |
| R/FM/R | + | − | 50 | >106 |
| R/SI/R | + | − | 50 | >106 |
| A/FM/G | − | + | 20 | 5 × 105 |
| A/SI/G | − | − | 50 | 5 × 105 |
| A/FM/R | − | − | 500 | >106 |
| A/SI/R | − | − | 500 | >106 |
a
LD50 values were determined by infecting groups (n = 4) of mice with various doses of the indicated viruses. Animals were killed if they were severely ill or if weight loss approached 30%.