Effect of Formaldehyde Inactivation on Poliovirus

Inactivated polio vaccines, which have been used in many countries for more than 50 years, are produced by treating live poliovi-rus (PV) with formaldehyde. However, the molecular mechanisms underlying virus inactivation are not well understood. Infec-tion by PV is initiated by virus binding to specific cell receptors, which results in viral particles undergoing sequential conforma-tional changes that generate altered structural forms (135S and 80S particles) and leads to virus cell entry. We have analyzed the ability of inactivated PV to bind to the human poliovirus receptor (hPVR) using various techniques such as ultracentrifugation, fluorescence-activated cell sorting flow cytometry and real-time reverse transcription-PCR (RT-PCR). The results showed that although retaining the ability to bind to hPVR, inactivated PV bound less efficiently in comparison to live PV.We also found that inactivated PV showed resistance to structural conversion in vitro, as judged by measuring changes in antigenicity, the abil-ity to bind to hPVR, and viral RNA release at high temperature. Furthermore, viral RNA from inactivated PV was shown to be modified, since cDNA yields obtained by RT-PCR amplification were severely reduced and no infectious virus was recovered af-ter RNA transfection into susceptible cells. IMPORTANCE This study represents a novel insight into the molecular mechanisms responsible for poliovirus inactivation. We show that inac-tivation with formaldehyde has an effect on early steps of viral replication as it reduces the ability of PV to bind to hPVR, de