Endogenous murine leukemia viruses: frequency of radiation-activation and novel pathogenic effects of viral isolates.

Female C57BL/6 and BALB/c mice were injected i.p. with 0.06 microCi/kg or 0.5 microCi/kg of the short-lived alpha-emitting radionuclide 224radium at 3-day intervals. Infectious N-ecotropic XC+, and xenotropic C-type retroviruses were activated in several tissues in both strains. In C57BL/6 mice the activation of ecotropic and xenotropic virus was dose-dependent as observed 4 weeks after the start of irradiation. In BALB/c mice a few animals showed activation of ecotropic virus after four weeks of irradiation. The expression of xenotropic virus was similar in irradiated mice and controls. Viral antigen, indicative for viraemia, was not detected in irradiated or control animals. Antiviral antibodies were found in both control and irradiated mice but higher titers were found in the irradiated mice. Bone tissue-derived N-tropic XC+ virus isolates were found to be non-oncogenic in newborn mice of the parental strain. In contrast, the same virus isolates induced a novel pattern of disease, such as osteopetrosis and osteomas together with malignant lymphomas in NMRI mice. The data indicate that the pattern of endogenous murine leukemia virus activation by internal alpha-irradiation is dependent on the dose rate, and on the genetics of the mouse strain.