Effect of IFN-gamma receptor gene deletion on vaccinia virus virulence

Two vaccinia virus (VV) strains, WR and Praha, were selected for a study un dertaken to determine whether the virus-encoded interferon-gamma receptor ( IFN-gammaR) plays any role in virus virulence. Both of the viruses expresse d the B8R gene coding for IFN-gammaR in infected cell cultures. The nucleot ide sequence of the Praha virus B8R gene was determined, and, when compared with the published sequence of the WR virus, it only displayed one silent nucleotide substitution. Mutants of the WR and Praha viruses with deleted B 8R gene were constructed. In rabbits, skin lesions produced by the WR B8R-d eleted mutants were smaller and tended to disappear earlier than those caus ed by wild-type WR virus. Similar results were obtained with both independe ntly prepared WR B8R-deleted mutants. These data strongly suggested that th e product of B8R gene did play a role in virus virulence. A similar compari son of the wild-type Praha virus and its mutant could not be done because o f the very low virulence of the parental virus for rabbits.