A bioluminescent reporter influenza A/H1N1 virus to track viral infections in vivo and ex vivo

Influenza A viruses (IAV) infect a wide range of mammals and birds, causing seasonal outbreaks and occasional pandemics, causing significant public health and economic loss. Studying IAV requires methods to detect viruses to facilitate the study of IAV in infected cells or animal models, recombinant IAVs expressing fluorescent proteins have been developed. However, fluorescent IAVs are often attenuated and are not sensitive enough to be detected by the in vivo imaging systems (IVIS). To address this challenge, we developed replication-competent recombinant IAVs expressing nanoluciferase (Nluc) from the non-structural (NS) segment of the pandemic influenza A/California/04/2009 H1N1 (pH1N1) strain, hereafter referred to as pH1N1-Nluc. The pH1N1-Nluc replicate efficiently in vitro, showing growth and plaque morphology comparable to the wild-type pH1N1 strain (pH1N1-WT). The pH1N1-Nluc has been also effectively neutralized by monoclonal antibodies and antivirals, with inhibition levels that are comparable to pH1N1-WT. Using IVIS, recombinant pH1N1-Nluc virus enabled the non-invasive, real-time tracking of viral infection in vivo and ex vivo following infection of C57BL/6J mice. In animal models including mice and ferrets, the pH1N1-Nluc resulted in morbidity, mortality, and viral replication patterns in animal organs to comparable levels to the wild-type virus. We assume that pH1N1-Nluc represent a valuable tool for studying IAV pathogenesis and host interactions and for evaluating antiviral drugs and vaccines/neutralizing antibodies both in cell culture and animal models.