Hemagglutinin Stalk-Reactive Antibodies Are Boosted following Sequential Infection with Seasonal and Pandemic H1N1 Influenza Virus in Mice

Previously, it has been shown that infection in humans with the pandemic swine influenza virus induces antibodies with specificity to the stalk domain of the viral hemagglutinin. Following the generation of these data, we sought to recapitulate these findings in the mouse model by sequential influenza virus infection. Mice that were inoculated with a seasonal influenza H1N1 virus followed by infection with a pandemic H1N1 strain produced higher antihemagglutinin stalk antibody titers than mice sequentially infected with drifted seasonal strains. In order to achieve antibody titers of comparable magnitude using sequential infection, mice had to be infected with 100- to 1,000-fold more of the drifted seasonal virus. The antistalk antibodies produced by these infections were influenza virus neutralizing, which illustrates the utility of the mouse model in which to study this interaction between virus and host.