Fig 1.

Virus-specific antibody responses in immunized mice. Purified PR8 virus was used as an antigen to analyze IgG and IgA antibody titers in the sera, nasal washes, and BAL fluids (top, middle, and bottom, respectively) of mice mock immunized with medium or immunized with the formalin-inactivated virus or with the PB2-KO virus. Sera (top panels) were obtained at different time points, i.e., prevaccination (bars A), before the second vaccination (bars B), before the third vaccination (bars C), and before challenge (bars D). Nasal washes and BAL fluids (middle and bottom panels, respectively) were obtained 1 day before challenge from mice given 1 vaccination (bars 1), 2 vaccinations (bars 2), or 3 vaccinations (bars 3). Values are expressed as the mean absorbance ± standard deviation (SD) (n = 3). Statistical significance between samples obtained from mice immunized with inactivated virus and PB2-KO virus is indicated.