Persistent infection of BHK21/WI-2 cells with rubella virus and characterization of rubella variants

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Abstract
Persistently infected cell lines of BHK21/WI-2 cells have been established by infection with the wild type rubella virus strain M-33. These cell lines, BHK-MP1 and BHK-MP2, showed immunity-like resistance to superinfection with M-33 virus at both 34° and 39.5° C. They also showed intrinsic interference with the replication of Newcastle Disease Virus at 34° C but not at 39.5° C. They released a small number of infectious virus particles which were temperature sensitive variants, being able to form plaques at 34° C, but not at 39.5° C on BHK21/WI-2 and on its derivative, BSR. When BHK-MP1 cells were cultured at 34° C in growth medium containing 10–20 µg/ml of 5-bromodeoxyuridine (BudR) there was a 5- to 10-fold increase in infectious virus in the medium as compared with the untreated controls. Mitomycin C (0.5 µg/ml) treatment for 7 hours likewise stimulated the release of virus from these cells. The enhancement of viral release by BudR was completely blocked by pretreatment with actinomycin D (5 µg/ml) for 3 hours prior to BudR treatment. Since the variant can be induced by these prophage inducers and inhibited by actinomycin D it is suggested that the viral genome is converted to a DNA provirus which is analogous to the lysogenic state of bacteriophage.