Pathogenesis of virus-induced osteopetrosis in the chicken.

Infection of chicken embryos with a nondefective avian leukosis virus MAV-2(0) induced bone hyperplasia and profound suppression of bursal and thymic lymphoid cell development within 2- to 3 weeks after hatching. A time-course study of infectivity during embryonal life showed a gradual loss of susceptibility between the 10th day of incubation and hatching. This finding suggests that an embryonal stem cell either before or early after seeding into the bone and primary lymphoid organs is a virus-susceptible target cell. Histologic observations of the bursa indicated only mild damage during the 1st week and severely impaired proliferation of follicular lymphoid cells during subsequent weeks of development. Thus, viral infection conferred a cytostatic rather than a cytolytic effect upon the lymphoid target cell. Infection of stem cells, which are progenitors of lymphoid cells as well as of bone osteoclasts, is compatible with the manifestations of the disease. A model of cellular disorders of the bone and lymphoid tissues is proposed. Adoptive transfer of lymphoid cells from adult MAV-2(0)-immunized chickens into histocompatible virus-infected juvenile recipients abrogated the manifestation of osteopetrosis. Passive injection of antiserum containing virus-neutralizing antibodies was also effective. Anti-gp85 viral surface glycoprotein-binding antibodies in sera from adoptively protected chickens receiving immune cells were exclusively of cell donor IgG allotype.