Hemagglutinin-pseudotyped green fluorescent protein-expressing influenza viruses for the detection of influenza virus neutralizing antibodies

Influenza virus is a highly contagious virus that causes yearly epidemics and occasional pandemics of great consequence. Influenza virus neutralizing antibodies (NAbs) are promising prophylactic and therapeutic reagents. Detection of NAbs in serum samples is critical to evaluate the prevalence and spread of new virus strains. Here we describe the development of a simple, sensitive, specific, and safe screening assay for the rapid detection of NAbs against highly pathogenic influenza viruses under biosafety level 2 (BSL-2) conditions. This assay is based on the use of influenza viruses in which the hemagglutinin (HA) gene is replaced by a gene expressing green fluorescent protein (GFP). These GFP-expressing influenza viruses replicate to high titers in HA-expressing cell lines, but in non-HA-expressing cells, their replication is restricted to a single cycle.