Preexisting human antibodies neutralize recently emerged H7N9 influenza strains

NIAID CEIRS | Research Publication Commentary

Dunand, CJ et al. Preexisting human antibodies neutralize recently emerged H7N9 influenza strains. J Clin Invest. 2015 Feb 17.

Novel influenza strains emerge naturally from selective pressure and genetic reassortment, a process in which different virus strains will infect the same animal and exchange genetic material (RNA segments). Genetic reassortment is one mechanism that allows influenza to evade a host’s immune system. When an individual’s immune system comes in contact with an influenza virus or vaccine, it will develop antibodies that will then help to recognize and neutralize that strain in the future. However, a strain that has undergone genetic reassortment may no longer be recognized by the host’s immune system, allowing a productive infection to occur.

A novel influenza A virus (H7N9) that was able to infect humans arose in China in 2013. Since the novel strain’s hemagglutinin antigen (HA), belongs to the same HA group as a previously circulating H3N2 virus, Dunand et al. hypothesized that some antibodies developed from vaccination against or infection with H3N2 may be cross-reactive with some novel virus strains. The authors identified three antibodies from individuals vaccinated against the H3N2 virus that were capable of binding the H7N9 strain and protected mice challenged with a lethal dose of H7N9, indicating that the cross-reactivity of human antibodies to H3N2 and H7N9 viruses is protective. These antibodies were found to bind the broadly conserved stalk section of the virus and were also found to bind to H7 strains from both North America and Eurasia. These results suggest that the antibodies could have cross-reactivity with emerging H7 strains.

Given the evidence of cross-protection afforded by these H3N2 influenza antibodies against novel H7 influenza subtypes, Dunand et al. highlights the importance of annual influenza vaccination because there might be some protection against emerging novel strains as well as against circulating strains. Further, they advocate future studies of these cross-reactive antibodies and their potential use as therapeutic agents against novel influenza viruses.