Reciprocal Inhibition of Mouse Leukemia Virus Infection by Fv-1 Allele Cell Extracts

Soluble extracts of mouse cells with Fv-1nor Fv-1bgene alleles specifically and reciprocally inhibit infection of B- or N-tropic mouse leukemia viruses in permissive cell cultures. NB-tropic virus infection was not inhibited by either cell extract. Extracts from Fv-1-cells did not inhibit infection by the three virus host-range types, but N- or B-tropic virus infection of Fv-1-cells was inhibited by extracts of the nonpermissive cells, and Fv-1nbcell extracts inhibited both viruses. The maximum degree of inhibition was 50-80% as determined by immunofluorescent or plaque assays, with extracts containing up to 500 μ g/ml of nonpermissive cell protein. The inhibitor(s) is relatively unstable since activity is lost after 2 hr at 37 degrees or 30 min at 56 degrees. The inhibitor(s) was most effective if added 2 hr before or within 2 hr after infection, did not react with the virus directly, inhibit virus attachment, or inhibit the normal cell functions tested. These results indicate that nonpermissive mouse cells contain a product, possibly determined by the Fv-1 gene, which inhibits some early postpenetration event(s) in leukemia virus infection.