TABLE 1.
Protection against challenge with a lethal dose of PR8 in mice inoculated with HA-KO/GFP or HA-KO/PspA virusa
| Inoculum | Days postinfection | Organ | Mean virus titer ± SD (log10 PFU/g) |
|---|---|---|---|
| Medium | 3 | NT | 6.3 ± 0.4 |
| 3 | Lung | 7.9 ± 0.2 | |
| 6 | NT | NA | |
| 6 | Lung | NA | |
| HA-KO/GFP | 3 | NT | ND |
| 3 | Lung | ND | |
| 6 | NT | ND | |
| 6 | Lung | ND | |
| HA-KO/PspA | 3 | NT | ND |
| 3 | Lung | 2.9, 4.3 | |
| 6 | NT | ND | |
| 6 | Lung | ND |
a
Six mice from each group were intranasally infected with 100 MLD50 of PR8 (50 μl per mouse) 2 weeks after the final vaccination. Three mice per group were sacrificed on days 3 and 6 postinfection, and lungs and nasal turbinate were collected to determine virus titers. When virus was not recovered from all three mice, individual titers are given. Abbreviations: NT, nasal turbinate; NA, not applicable because the mice died; ND, not detected (detection limit, 10 PFU/lung or 5 PFU/NT).