Inhibition of Rous sarcoma virus-induced transformation by preinfection with rhabdoviruses

In vivo preinfection of chicks with rabies virus (RV) or vesicular stomatitis virus (VSV) ts 1026 inhibits tumour formation after superinfection with Rous sarcoma virus (RSV). The degree of inhibition depends on the titre of the infecting viruses and the interval between rhabdovirus and RSV infection. In vitro, cells preinfected with VSV ts 1026 under non-permissive conditions and superinfected with RSV, are not transformed as judged by cell morphology, serum requirement for growth or the capacity to form colonies in soft agar, all these being the same as in uninfected cells. Doubly infected cells take up less deoxyglucose than cells infected with RSV only and more than cells infected with VSV only. RSV multiplication in inhibited in doubly infected cells: the supernatant fluid of these cells contains fewer focus-forming units and less reverse transcriptase activity than that of cells infected with RSV only. Doubly infected cells contain both VSV and RSV internal antigens 15 days after infection. The supernatant fluid of cells infected with VSV and maintained under non-permissive conditions inhibits transformation by RSV and multiplication of RSV, but not of VSV. Under non-permissive conditions, the rhabdoviruses undergo at least part of the infectious cycle, but no infectious virus is produced. RV antigen can be detected in the brain of parenterally infected chicks and VSV antigen in cells infected 15 days previously. We conclude that the inhibition of RSV multiplication and expression is probably due to one or more processes linked to the persistence of rhabdovirus components and that it cannot be attributed exclusively to interferon.