Vesicular stomatitis virus phenotypically mixed with retroviruses: an efficient detection method

Two methods of assaying vesicular stomatitis virus (VSV) particles phenotypically mixed with retrovirus-coded antigens were compared. Each of them detected phenotypically mixed particles with different minimum proportion of surface glycoprotein molecules of the donor virus, and consequently also profoundly different proportions of VSV virions containing retrovirus antigens. Only a low proportion (10(-4) of VSV virions grown in XMuLV-infected rabbit SIRC cells behaved as pseudotypes, resistant to anti-VSV serum and neutralized by anti-XMuLV serum. VSV produced in mouse L cells did not contain significant titre of pseudotype particles in the neutralization test. However, when immunoprecipitation was used with corresponding antibody and Staphylococcus aureus cells, almost 100% of the VSV virions produced in L cells and in XMuLV-preinfected SIRC cells were found to contain MuLV-related antigen molecules.