FIG. 3.
(A) Cross-protective antibody responses against PR8 HA in the mice immunized intranasally with A/PR8 (H1N1), A/Beijing (H1N1), A/Yamagata (H1N1), A/Guizhou (H3N2), B/Ibaraki, B/Yamagata, and B/Aichi vaccine with poly(I:C) as an adjuvant. Secondary immunization was performed 4 weeks after primary immunization without the adjuvant. The same groups of mice were infected with 1,000 PFU in 2 μl of PR8 influenza virus 2 weeks after the second immunization. The nasal wash fluid was collected 3 days after virus challenge. The virus titer was measured by plaque assay. Each column represents the mean ± SD. The serum collected at 2 weeks after the booster was analyzed for the presence of neutralizing antibodies against homologous or heterologous influenza virus. Inhibition of the virus was assessed by the additional reduction in infectivity beyond the background of naive mice. Samples were run in duplicate, and data are presented per group, where the ability to inhibit 50% of infection at the indicated dilution is shown. The dash indicates lack of reduction of infectivity. (B) The survival curve of the mice immunized with poly(I:C) and the various vaccines after the lethal A/PR8 (H1N1) challenge. Mice were immunized with 3 μg of A/PR8 (H1N1), A/Yamagata (H1N1), A/Guizhou (H3N2), and B/Ibaraki vaccine with 10 μg of poly(I:C) as an adjuvant. Secondary immunization was performed 4 weeks after primary immunization with the same amount of vaccine with the adjuvant. The survival rates of the mice until 10 days after the virus challenge are presented in a line graph.