Inhibition of vesicular stomatitis virus-defective interfering particle synthesis by shope fibroma virus

Undiluted passage of vesicular stomatitis virus (VSV) in a line of African green monkey kidney cells results in a cyclic synthesis of standard infectious VSV. This pattern of virus yield is due to the cyclic production of defective interfering (DI) particles [ Perrault, J., and Holland, J. J. (1972). Virology 50, 148–158 ; Palma, B. L., and Huang, A. S. (1974). J. Infect. Dis. 129, 403–410 ; Holland, J. J., Villareal, L. P., and Briendl, M. (1976). J. Virol. 17, 805–813 ]. When such cells were infected with Shope fibroma virus (ShFV) prior to serial undiluted passage of VSV, the normal cyclic yield of VSV was altered. Using two criteria for the determination of DI particles, i.e., the interference assay and the detection of physical particles by gradient technique, it was shown that ShFV exerted its effect by inhibiting the synthesis of VSV-DI particles. It is suggested that ShFV affects both the induction and the amplification of DI particles in this system. Experiments also indicate that the ShFV-mediated inhibition of VSV-DI particle synthesis is probably not due to poxvirus-induced inhibition of cellular macromolecular biosynthesis.