Abstract
Whole inactivated vaccines (WIVs) possess greater immunogenicity than split or subunit vaccines, and recent studies have demonstrated that WIVs with preserved fusogenic activity are more protective than non-fusogenic WIVs. In this work, we describe the inactivation of human influenza virus X-31 by high hydrostatic pressure (HHP) and analyze the effects on the structure by spectroscopic measurements, light scattering, and electron microscopy. We also investigated the effects of HHP on the glycoprotein activity and fusogenic activity of the viral particles. The electron microscopy data showed pore formation on the viral envelope, but the general morphology was preserved, and small variations were seen in the particle structure. The activity of hemagglutinin (HA) during the process of binding and fusion was affected in a time-dependent manner, but neuraminidase (NA) activity was not affected. Infectious activity ceased after 3 hours of pressurization, and mice were protected from infection after being vaccinated. Our results revealed full viral inactivation with overall preservation of viral structure and maintenance of fusogenic activity, thereby conferring protection against infection. A strong response consisting of serum immunoglobulin IgG1, IgG2a, and serum and mucosal IgA was also detected after vaccination. Thus, our data strongly suggest that applying hydrostatic pressure may be an effective method for developing new vaccines against influenza A as well as other viruses.
Highlights
Seasonal influenza virus infections cause significant morbidity and mortality worldwide [1,2]
high hydrostatic pressure (HHP) completely eliminates viral infectivity Figure 1A shows the effect of pressure on influenza virus infectivity, as determined by the TCID50/ml assay in Madin-Darby Canine Kidney (MDCK) cells
Total RNA was extracted from cells, avoiding the RNA in the supernatant, and the viral RNA was amplified. This was done to avoid the amplification of inactivated virus that may have remained in the supernatant due to the serial passages
Summary
Seasonal influenza virus infections cause significant morbidity and mortality worldwide [1,2]. Pandemic influenza strikes periodically, infecting a large number of people and potentially causing many deaths [3]. Since 1977, the H1N1 and H3N2 viruses have co-circulated globally and are responsible for seasonal epidemics that have caused an average of 36,000 deaths annually in the U.S alone [4]. Whole virus vaccine formulations have been shown to be more immunogenic in a naive population and may be needed in a pandemic situation to elicit an adequate immune response [6]. Many studies have demonstrated that whole inactivated influenza viruses are more immunogenic than split or subunit vaccines [7,8,9]
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