Fig. 9.

Vaccination with chimeric A/B viruses protects C57BL/6 PKR^−/− mice from lethal infection with the parental influenza B/Ya88 virus. Eight-week-old female C57BL/6 PKR^−/− mice (n = 10) were immunized with 10-fold serial dilutions of rIBV-NS110-VN04HA, from 1 × 10⁵ PFU to 1 × 10² PFU, and PBS was used as a negative control. At 21 days postvaccination, serum samples were collected (n = 3). (A) B/Ya88 virus-specific antibodies were detected by ELISA as described in Materials and Methods. CD8⁺ T cells were isolated from splenocytes (n = 3). (B) Splenocytes from naïve mice were infected with rWT B/Ya88 viruses and used as antigen-presenting cells in an ELISpot assay with CD8⁺ T cells from vaccinated mice. The experiment was performed in triplicate, and the average number of spots per well ± standard deviations is graphed. In each group, the other four immunized mice per group were infected with 1 × 10⁶ PFU of rWT B virus for pathology study (n = 4). (C) After viral challenge, C57BL/6 PKR^−/− mice were monitored for body weight changes and survival for a total of 14 days postchallenge. *, P < 0.05; **, P < 0.01; and ***, P < 0.001 versus PBS control.