Retroviral particles in radionuclide-induced murine osteosarcomas: mouse strain-related differences.

Twenty-six osteosarcomas from strain NMRI mice and twenty-six osteosarcomas from (C3H x 101)F1 hybrid mice were investigated by electron microscopy for the presence of retroviral particles. The bone tumors had been induced by the incorporation of the short-lived bone-seeking radionuclides 224Ra, 223Ra, or 227Th. All of the 26 osteosarcomas from NMRI mice contained retrovirus-like intracisternal type A particles in varying quantities. No type C retrovirus particles could be detected. In contrast, most of the 26 osteosarcomas from (C3H x 101)F1 mice contained budding, immature, and mature type C virus particles predominantly in large quantities. Intracisternal type A particles were also present in all tumors from these mice, but were found only occasionally after extensive search. The mouse strain-related differences in the presence of intracisternal type A particles and type C virus particles in the bone tumors do not provide evidence of an etiological relation of these particles to radionuclide-induced osteosarcomagenesis. Some of the mature type C virus particles observed in osteosarcoma tissue from the hybrid mice were atypical in structure and size. Such pleomorphic particles are probably associated with the spontaneous osteomagenesis which occurs in untreated old (C3H x 101)F1 mice.