Differentiation of an epiperiosteal sheath in avian hyperostosis induced by myeloblastosis associated virus MAV-2 (0).

If myeloblastosis associated virus MAV-2(0) is injected in chick embryos, it causes a severe, irreversible and generalized hyperostosis which subsequently follows a chronic course. An epiperiosteal sheath forms at the site of the lesion, whose development follows that of the hyperostosis. The sheath contains not only cell infiltrates, blood vessels and myoblasts, but also highly specialized cells such as Pacinian corpuscles. The structural lesions are absolutely different from these described in human, mammal or avian spontaneous or induced osteopetrosis. Our initial description of the "hyperostosis" is confirmed by observation of this sheath surrounding the pathological bone: it is a monodermic, mesenchymal, pluritissular tumor. The role of the virus is discussed: it probably acts early, when mesenchymal stem cells differentiate.