Heterogeneity of the sensitivity of vesicular stomatitis virus to interferons

Twelve cloned viruses were randomly isolated from original (uncloned) vesicular stomatitis virus (VSV), and their sensitivities to mouse and human interferons were examined. When the interferon sensitivities of these various VSVs were compared by the plaque reduction method in L cells, virus 3 was found to be sevenfold more sensitive than virus 11, and the interferon sensitivity of the original (uncloned) virus was intermediate. The present study shows that uncloned VSV Indiana strain is a mixture of viruses that have different sensitivities to interferon. The slope of the dose-response curve of original (uncloned) virus to mouse interferon was less steep than those of cloned viruses. Virus 11, which was the least sensitive to mouse interferon, was relatively sensitive to human interferon. There was no correlation between the sensitivities of virus clones to mouse interferon and their sensitivities to human interferon. When the interferon sensitivities were tested by various assay methods (plaque reduction, yield reduction, and cytopathic effect inhibition), the ranking of the interferon sensitivities of different viruses was not changed. These results indicate that the relative sensitivity of a virus to interferon is determined by the host cells in which the tests are performed, but not by assay method used.