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Vaccinia virus (VV) strain Western Reserve gene B8R encodes a 43 kDa glycoprotein that is secreted from infected cells early in infection as a homodimer. This protein has amino acid similarity with the extracellular domain of cellular IFN-γ receptor (IFN-γR) and binds and inhibits IFN-γ from a wide range of species. Here we demonstrate that the B8R protein also inhibits equine IFN-γ. The 5′ end of the B8R mRNA has been mapped by primer extension analysis and the contribution of IFN-γRs to VV virulence was studied by the construction of a deletion mutant lacking the B8R gene (vΔB8R) and a revertant virus (vB8R-R) in which the B8R gene was re-inserted into the deletion mutant. A recombinant virus that expressed a soluble form of the mouse IFN-γR was also constructed and studied. The virulence of these viruses was tested in rodent models of infection. In mice, the loss of the VV IFN-γR did not affect virulence compared with WT and revertant viruses, consistent with the low affinity of the VV IFN-γR for mouse IFN-γ. However, expression of the mouse soluble IFN-γR increased virus virulence slightly. In rabbit skin, loss of the VV IFN-γR produced lesions with histological differences compared with WT and revertant viruses. Lastly, the affinity constants of the VV IFN-γR for human and mouse IFN-γ were determined by surface plasmon resonance.

Original publication




Journal article


Journal of General Virology


Microbiology Society

Publication Date





1953 - 1964