The glycoproteins, heamagglutinin (HA) and neuraminidase (NA) of influenza virus confer host protective immune responses during vaccination, which is the most effective approach for preventing influenza-associated morbidity and mortality. Since the functional balance between the HA and NA proteins may affect viral receptor binding and replication, a pandemic influenza A virus (H1N1 pdm09), strain A/Texas/05/2009, was optimized to elevate its HA antigen content by modifying the NA gene. In this study, we have constructed two 2:6 reassortant viruses between pdmH1N1 (A/Texas/05/2009) and A/Puerto Rico/8/34 (PR8), in which the NA gene of A/Texas/05/2009 was modified to contain part of the NA gene from PR8. One chimeric NA virus has the PR8 transmembrane (TM) region (HNtm 2:6) and the other contains both the PR8 NA TM and stem regions (HNst 2:6). Using quantitative reverse phase-HPLC (RP-HPLC) analysis, we observed that the HNst2:6 virus contains a higher HA1 content than HN2:6 wild type. In addition, this mutant virus displays a higher HA1 to nucleoprotein (NP) ratio, based on gel electrophoresis densitometry analysis. Furthermore, the neuraminidase activity of purified HNst 2:6 virus is approximately 30% lower than that of HN2:6 virus, which is suggestive of a lower incorporation of NA into the viral envelope. Therefore, we propose that the reduction of NA packaging in the virion may lead to a compensatory increase of HA. Such an improvement in HA yield is possibly beneficial to H1N1 pdm09 vaccine production.
Published by Elsevier Ltd.