Immunogenic properties of PR8 influenza virus after treatment with acid protease.

Brief exposure of PR8 influenza virus at pH 4.5 to extracts of Aspergillus niger abolished the red cell agglutinating and infectious capacities of the virus without significantly decreasing its antigenicity or immunogenicity. The results of gel electrophoresis indicated that the HA1 portion of the viral hemagglutinin had been degraded by treatment of virus with Aspergillus extract. The immunogenicity in mice of virus that had been exposed to A. niger extract appeared to be very broad, since vaccination of mice with such material gave protection against challenge with strains of influenza A virus representing all major serotypes as well as one type B influenza virus.