Detection of VSV(MuLV) pseudotypes by an immunobiochemical technique

Abstract Vesicular stomatitis virus (murine leukemia virus) (VSV(MuLV)) pseudotypes containing a [ 3 H]uridine-labeled VSV RNA genome and MuLV envelope glycoproteins (gp70) were produced by phenotypic mixing of the two viruses. In order to better detect such pseudotypes, an immunobiochemical (IB) technique was developed. [ 3 H]Uridine-labeled virus progeny of the dual virus infection was immunoprecipitated by monospecific MuLV gp70 antibodies complexed with fixed Staphylococcus aureus . The immunoprecipitated 3 H-labeled genomic RNA was identified as that of VSV by its sedimentation coefficient, by the lack of polyadenylate, and by molecular hybridization with complementary VSV RNA. By the IB technique, approximately 11% of the progeny of the dual virus infection were found to be VSV(MuLV). By neutralization and other biological assays, however, only 0.1% of the progeny were found to be VSV(MuLV) pseudotypes. Apparently, the IB technique is capable of detecting VSV pseudotypes encapsidated with only a few molecules of MuLV gp70. The IB technique, therefore, offers a quantitative and molecular technique for the detection of VSV(MuLV) pseudotypes and can be modified to detect other viral pseudotypes when other assays are lacking. In spite of its sensitivity however, the IB technique did not detect the formation of MuLV (VSV) pseudovirions among the virus progeny of the dual virus infection. These results confirmed a similar observation made previously using immunoelectron microscopy.