| Abstract
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Cattle and swine which have been vaccinated against foot-and-mouth disease (FMD) can be distinguished from convalescent animals by radioimmunoprecipitation and SDS-PAGE analysis of the virus-induced proteins reacting with the respective sera. BHK cells infected with FMD virus (serotype A{24}) were labelled with S-methionine and the virus-induced proteins reacted with sera from (a) vaccinated and subsequently challenged animals, (b) convalescent animals, (c) animals vaccinated or infected with viruses belonging to all serotypes of FMDV, or (d) animals infected with encephalomyocarditis (EMC), or porcine or bovine enteroviruses. Of the FMDV non-structural proteins 2C, 3ABC, 3C, 3CD, and 3D were precipitated by convalescent sera, but only 3D was precipitated by serum from vaccinated animals. Proteins L, 2C and 3C were precipitated only after challenge with a heterotypic virus (serotype O Tunisia), indicating that virus replication of the challenge virus had taken place. No precipitation was detected with sera from EMC or enterovirus infected animals. The results indicate that protein 2C, and to a lesser extent the polypeptide 3ABC, could be used to differentiate potential carrier convalescent animals from vaccinated livestock. This differential precipitation of 2C was explained by methods of vaccine manufacture. Virus was grown in BHK cell monolayers until cytopathic effect was complete, after which cell debris was separated from the supernatant containing the viral antigens that confer protective immunity (capsid proteins, and VP1 in particular). It was found that 2C was not destroyed by the action of binary ethylenimine, the inactivant used for vaccine production. Furthermore, it was identified that 2C was associated with the cell debris fraction of viral harvests, normally removed during vaccine production. Potential epitopes of protein 3D of FMD virus were identified by synthetic decapeptide mapping of the entire protein and probing with convalescent bovine sera. However, when eight selected peptides were used in an ELISA for screening large numbers of sera, none was recognized by convalescent antibody. Antibodies raised in guinea pigs against the eight peptides failed to immunoprecipitate native 3D.
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