Specific restriction of avian sarcoma viruses by a line of transformed lymphoid cells.

MSB-1 cells are a line of transformed chicken lymphoid cells derived from tumors induced by Marek's disease viruses and free of exogenous avian leukosis viruses (ALV). They can be infected by ALV of subgroups A and C including transformation-defective (td) deletion mutants of avian sarcoma viruses (ASV). In terms of virus titers in supernatant culture medium, proportion of virus-producing cells, and levels of viral RNA detected by hybridization with a cDNA probe, infection by td ASV of MSB-1 cells was indistinguishable from infection of chicken embryo fibroblasts. In contrast, wild type ASV was restricted in its growth on MSB-1 cells. Different clones of ASV varied in their restriction by all these parameters of viral growth by factors of 10^?1 to 10^?4 Studies of a severely restricted viral clone showed equal quantities of hybridizable viral DNA in Hirt supernatant fractions of both fibroblasts and MSB-1 cells at 10 hr after high multiplicity infection, and transfection assays indicated infectious viral DNA in both cell types. Viral DNA largely disappeared from Hirt supernatant fractions of MSB-1 cells by 48 hr after infection, and sarcoma virus-specific DNA was not detected in Hirt pellet fractions from MSB-1 cells at levels found in comparably infected fibroblasts. Infectious ASV DNA, while easily detected in fibroblasts, could not be detected on MSB-1 cells at 48 hr or later times after infection. Because replication of td ASV does not appear restricted in MSB-1 cells, the failure of ASV DNA to integrate normally in these cells seems to be related to the presence of src sequences in the viral genome.