The virion of mengovirus contains anti-interferon activity.

Many viruses are resistant to the antiviral state induced by interferon (IFN) in certain cell lines because they produce factors having anti-IFN activity (AIA). We show here that is+, a mengovirus strain resistant to low concentrations of IFN, also produces an AIA, but that an IFN-sensitive mutant (is-1) does not. This activity was detected when is+ rescued is-1 from the antiviral state induced in mouse L cells by mouse IFN. The mengovirus AIA was found in cell lysates prepared from cells infected with is+, and in the virions of purified, inactivated is+ but not in lysates prepared from is-1-infected cells or in the is-1 virion. Also the pentameric subunits that make up the viral capsid contained AIA, whereas the individual monomeric subunits that constitute the pentamers did not. We also describe an assay system for detecting and quantitating the mengovirus AIA.