Establishment and characterization of a Madin-Darby canine kidney reporter cell line for influenza A virus assays.

Influenza virus diagnosis has traditionally relied on virus isolation in chicken embryo or cell cultures. Many laboratories have adopted rapid molecular methods for detection of influenza viruses and discontinued routine utilization of the relatively slow viral culture methods. We describe an influenza A virus reporter cell line that contributes to more efficient viral detection in cell culture. Madin-Darby canine kidney (MDCK) cells were engineered to constitutively produce an influenza virus genome-like luciferase reporter RNA driven by the canine RNA polymerase I promoter. Induction of a high level of luciferase activity was detected in the Luc9.1 cells upon infection with various strains of influenza A virus, including 2009 H1N1 pandemic and highly pathogenic H5N1 virus. In contrast, infection with influenza B virus or human adenovirus type 5 did not induce significant levels of reporter expression. The reporter Luc9.1 cells were evaluated in neutralizing antibody assays with convalescent H3N2 ferret serum, yielding a neutralization titer comparable to that obtained by the conventional microneutralization assay, suggesting that the use of the reporter cell line might simplify neutralization assays by facilitating the establishment of infectious virus endpoints. Luc9.1 cells were also used to determine the susceptibility of influenza A viruses to a model antiviral drug. The equivalence to conventional antiviral assay results indicated that the Luc9.1 cells could provide an alternative cell-based platform for high-throughput drug discovery screens. In summary, the MDCK-derived Luc9.1 reporter cell line is highly permissive for influenza A virus replication and provides a very specific and sensitive approach for simultaneous detection and isolation of influenza A viruses as well as functional evaluation of antibodies and antiviral molecules.