Immunological effects of reticuloendotheliosis virus as potential contaminant of Marek's disease vaccines.
Certain properties of four strains of reticuloendotheliosis virus (REV), namely REV-F, REV-S, REV-C and chick syncytial virus (CSV) were studied in vivo and in vitro. In chicken embryo fibroblast (CEF) cultures these viruses caused a chronic infection which could be detected by indirect immunofluorescence (FA) tests. Precipitating antigens were present in infected cultured cells as well as in culture supernatants. Antibodies in sera of REV-inoculated chickens were demonstrated by FA tests and agar gel precipitin (AGP) tests. No antigenic differences between the four reference virus strains could be detected by either method. The immune response of chickens was shown to be a sensitive indicator of REV infection. AGP tests proved to be as suitable as FA tests provided that the serum samples were taken not later than 3 weeks after inoculation, since antibody titres decreased afterwards. Infectivity titres of the apathogenic REV-C strain proved to be the same in CEF cultures and in chickens assayed by this method. The immunogenicity of REV was unaffected by the presence of HVT. The humoral immune response to HVT, however, was drastically reduced if REV was present in the inoculum. These results suggest that even minor contaminations with REV can markedly reduce the efficacy of Marek's disease vaccines, and that such REV contaminations can effectively be controlled by tests using chickens.
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Bundesforschungsanstalt für Viruskrankheiten der Tiere, Tübingen, W. Germany.