Maturation efficiency of viral glycoproteins in the ER impacts the production of influenza A virus.

We have studied which steps are enhanced in the infectious cycle of influenza A virus in Madin-Darby canine kidney (MDCK) cells, a cell line investigated for use in the production of an influenza vaccine because of its ability to yield high levels of virus. We have confirmed that MDCK had the highest production levels of virions among several cell lines early in the infection. Influenza A virus showed similar levels of viral genomic RNA replication, mRNA transcription, and protein expression in A549 as in MDCK. Thus, we focused on the post-translational transport of viral glycoproteins from the endoplasmic reticulum (ER) to the plasma membrane. Comparative characterization revealed more efficient processing in the folding and maturation of hemagglutinin and neuraminidase in the ER in MDCK than in A549. Also, the subsequent transport of these glycoproteins to the plasma membrane occurred much earlier in MDCK. These results indicate that the folding and maturation efficiencies of viral glycoproteins in the ER impact the efficiency with which influenza A viral particles are produced.