Endogenous type-C viral expression during lymphoma development in irradiated NFS mice.

The expression of the type-C retrovirus and the virus-related components in NFS mice were examined during preleukemic and leukemic phases after fractionated whole-body X irradiation. The NFS mice were highly susceptible to induction of thymoma by fractionated X irradiation. The leukemic tissues were negative for infectious type-C virus, as detected by both the XC-plaque test and mink S+ L- focus-inducing assays, but contained a substantially higher level of viral-specific RNA-dependent DNA polymerase activity and a major core protein p30 than the corresponding tissues from unirradiated age-control mice. In the preleukemic phase, the amount of p30-related antigen increased transiently in spleen. The leukemic cell lines established from radiation-induced lymphomas produced particulate entities with a buoyant density of about 1.15 g/ml. These virus-like particles lacked in vitro infectivity to mouse cells and mink lung cells and leukemogenicity in syngeneic mice. The p30-related antigens of these particles were immunologically similar to that of xenotropic virus derived from NZB mouse.