Demonstration of virus particles in Moloney murine sarcoma virus-induced periosteal bone in mice.

Balb/c mice were inoculated intramuscularly with Moloney murine sarcoma virus in one of the hind legs. This led to the rapid development of a regressive sarcoma and also to the proliferation and osteogenic differentiation of cells in the adjacent periosteum. Examination of the tissues by transmission electron microscopy revealed the presence of type A and C virus particles within the sarcoma cells as well as within the cells of the newly formed bone. Extracellular type C virus particles were formed by budding from the cell surface and by release from disintegrating cells. No virus particles were found in the bone or the surrounding soft tissues of the contralateral, noninfected leg. These observations suggest that viral infection of periosteal cells are at least partly responsible for the osteogenic response associated with the virus-induced sarcoma. Production of growth factors by the sarcoma cells could also contribute to this process.