INTERFERENCE WITH THE GROWTH OF VACCINIA VIRUS BY AN ATTENUATED MUTANT VIRUS

Abstract
A mutant of vaccinia virus, strain DIs, grew in primary cultures of chick embryo cells. Ultraviolet-irradiated DIs virus (UV-DIs) interfered with the growth of DIE strain, the parent virus, in chick embryo cell monolayers, when the cells were inoculated with UV-DIs at a relatively low multiplicity (in terms of the original infectivity) not less than 6 hours prior to DIE virus infection. Soluble interfering factor was isolated from the culture fluid and cells inoculated with UV-DIs, and it had characters of interferon. Titration method of interferon activity, mode of interferon production and the optimal conditions for the production of interferon were investigated. Comparison of DIs and DIE strains concerning interferon production and interferon sensitivity revealed that DIs virus was a more active interferon-producer, while it was less sensitive to interferon than DIE virus.