Antibody-dependent cellular cytotoxicity is associated with control of pandemic H1N1 influenza virus infection of macaques.

Emerging influenza viruses pose a serious risk to global human health. Recent studies in ferrets, macaques, and humans suggest that seasonal H1N1 (sH1N1) infection provides some cross-protection against 2009 pandemic influenza viruses (H1N1pdm), but the correlates of cross-protection are poorly understood. Here we show that seasonal infection of influenza-naïve Indian rhesus macaques (Macaca mulatta) with A/Kawasaki/173/2001 (sH1N1) virus induces antibodies capable of binding the hemagglutinin (HA) of both the homologous seasonal virus and the antigenically divergent A/California/04/2009 (H1N1pdm) strain in the absence of detectable H1N1pdm-specific neutralizing antibodies. These influenza virus-specific antibodies activated macaque NK cells to express both CD107a and gamma interferon (IFN-γ) in the presence of HA proteins from either sH1N1 or H1N1pdm viruses. Although influenza virus-specific antibody-dependent cellular cytotoxicity (ADCC)-mediated NK cell activation diminished in titer over time following sH1N1 infection, these cells expanded rapidly within 7 days following H1N1pdm exposure. Furthermore, we found that influenza virus-specific ADCC was present in bronchoalveolar lavage fluid and was able to activate lung NK cells. We concluded that infection with a seasonal influenza virus can induce antibodies that mediate ADCC capable of recognizing divergent influenza virus strains. Cross-reactive ADCC may provide a mechanism for reducing the severity of divergent influenza virus infections.