Both seasonal and novel avian influenza viruses like H7N9 can result in severe infections requiring hospitalisation. Anti-influenza antibodies with Fc-mediated effector functions such as antibody-dependent cellular cytotoxicity (ADCC) are of growing interest in control of influenza but have not previously been studied during severe human infections.
We studied serial antibody responses in subjects hospitalised with both severe H7N9 (n = 18) and seasonal (n = 16) influenza infections. We studied HAI, neutralizing and ADCC antibodies to diverse influenza virus strains.
We found that the peak generation of Fc functional HA antibodies preceded that of neutralizing antibodies for both severe H7N9 and seasonal (n = 16) influenza infections. Subjects who succumbed to complications of H7N9 infection showed reduced HA-specific Fc receptor binding antibodies (both in magnitude and breadth) immediately prior to death compared to those who survived.
Our data suggest broadly binding HA antibodies with Fc mediated functions may be a useful component of protective immunity to severe influenza infection.