Generation of multinucleated osteoclast-like cells from canine bone marrow: Effects of canine distemper virus

Recent evidence has implicated canine distemper virus (CDV) as a possible aetiologic agent in Pagetʹs disease of bone and the canine bone disorder, metaphyseal osteopathy. We have therefore examined the effects of CDV on the formation of multinucleated osteoclast-like cells in cultures of canine bone marrow mononuclear cells. Marrow cells from a distemper-infected dog and from five uninfected dogs were cultured in the presence of 1α,25-(OH)2 vitamin D3 and the number of tartrate resistant acid phosphatase positive multi-nucleated cells (MNCs) was determined. The presence of calcitonin (CT) receptors was confirmed by autoradiography with 125I-labeled human CT. Cultures from the distemper-infected dog contained a higher level of MNCs than those from the normal dogs. The in vitro addition of CDV to the cultures from all the dogs produced a dose-dependent increase in the number of MNCs, and an increase in size of these cells in the cultures from the infected dog. Cells infected with CDV were hyperresponsive to 1α,25-(OH)2 vitamin D3. The presence of the virus in the relevant samples was confirmed using molecular techniques. In situ hybridization studies also revealed a significant increase in the level of infection following in vitro addition of the virus to the culture from the distemper-infected dog, suggesting that further infection had taken place. Resorption pits were formed on bone slices, although the number of pits was not significantly altered by viral infection. These results support the hypothesis that CDV might be involved in the skeletal abnormalities seen in Pagetʹs disease and metaphyseal osteopathy and suggest that canine marrow culture systems should prove useful to examine the disease processes further.