Figure 1.

DBA/2J and C57BL/6J mice mounted influenza-specific IgG titers after immunization with live PR8M virus. Female DBA/2J and C57BL/6J mice were immunized by i.m. injection of 2 × 10³ FFU PR8M virus in 20 μl PBS. Injections were repeated after 14 days. Sera were taken before immunization (pre-imm) and 14 days after the booster immunization (after boost) by bleeding via the retro-orbital sinus. Mice were subsequently infected intra-nasally with 2 × 10³ FFU PR8M virus. Sera from surviving DBA/2J and C57BL/6J mice were collected by heart puncture 14 days after infection (p.i.). In addition, sera from non-immunized but infected C57BL/6J mice were collected by heart puncture 14 days after infection with 2 × 10³ FFU PR8M (naïve, p.i.). All sera were diluted 1:1000 and an ELISA for the presence of influenza-specific antibodies was performed. Absorbance at 405nm is shown. Responses in DBA/2J mice are indicated in green, responses in C57BL/6J mice in blue, respectively. Data represent mean values +/- SEM. The significance of differences between groups was tested using the Mann-Whitney-U-test, ***: p value < 0.0001.