Effects of leukemogenic retroviruses on condylar cartilage in vitro: an ultrastructural study.

Mandibular condyles of late embryonic NMRI mice were used in an in vitro organ culture system to study the effect of bone tumor-derived murine leukemia viruses OS-5 MuLV and OA MuLV known to induce osteopetrosis and osteomas. Skeletal precursor cells present in the condylar tissue normally undergo rapid differentiation in vitro which results in new bone formation. The infection of condyles with either OS-5 MuLV or OA MuLV markedly interfered with the normal developmental pattern of the organ leading to the formation of an atypical, heavily mineralized tissue. Many spindlelike cells and pleomorphic cells were encountered, whereas fibroblastlike cells were found to penetrate an underlying collagen substratum. These observations indicate that bone tumor-inducing leukemogenic retroviruses directly affect cartilage and/or bone precursor cells resulting in pathologic developments in the skeleton.