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SUMMARY Two clonal preparations designated E+ and E- hog cholera (hc) viruses, which differed in interactions with Newcastle disease (nd) viruses in swine testicle (st) cell cultures, were obtained during adaptation of hc virus to guinea pig kidney cells. The E+ virus exerted an enhancing effect on the cytopathic effect (cpe) of nd virus in st cells, whereas the E- virus inhibited multiplication of nd virus in st cells. After 4 passages at limiting dilution, E- virus retained its distinctive character against nd virus. A quantitative assay procedure was developed for E- virus, using its interfering action. Although attenuated and wild strains of viruses were antigenically similar, attenuated virus was more sensitive to specific antibody than was the wild viral strain.
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Shimizu et al. (1970) studied this question.
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