TRANSFORMATION BY RETICULOENDOTHELIOSIS VIRUS - DEVELOPMENT OF A FOCUS ASSAY AND ISOLATION OF A NONTRANSFORMING VIRUS

A focus assay for quantitating in vitro transformation by oncogenic reticuloendotheliosis virus (REV) has been developed in Japanese quail embryo fibroblast cultures. The titer of the transforming virus detected in the in vitro focus-forming assay correlates with the development of reticuloendotheliosis in chickens. The titration pattern of REV focus formation appears to follow two-hit kinetics. A nontransforming member has been identified in the REV stocks and is designated reticuloendotheliosis-associated virus (REV-A). The non-transforming virus, REV-A, is present in REV stocks in 100- to 1000-fold excess over the transforming member. REV-A causes an initial cytopathic effect in chick and quail embryo fibroblast cultures. The surviving cells continue to divide leading to the development of a persistently infected culture. The persistently infected cultures are morphologically indistinguishable from uninfected avian fibroblast cultures. REV-A interferes with superinfection by the oncogenic member. The addition of REV-A to oncogenic preparations of REV increases focus formation and changes the titration pattern from two-hit to one-hit kinetics indicating that REV is defective. © 1979.