Pathogenesis of Marek's disease; effect of immunization with inactivated viral and tumor-associated antigens.

Inactivated Marek's disease virus-infected chicken kidney cells and inactivated MSB-1 lymphoblastoid Marek's disease tumor cells were used to immunize chickens as virus- and tumor-associated antigens, respectively. Immune and nonimmune birds were then challenged by exposure to live virulent Marek's disease virus. Both vaccines protected significant numbers of chickens (P less than 0.05) against subsequent tumor development, although viral antigen appeared superior to tumor antigen. After challenge, the early appearance of viral antigen, infected lymphocytes, and degenerative changes in lymphoid organs was inhibited only by the viral antigen vaccine, whereas the early appearance of cells bearing tumor antigen was prevented by both vaccines. These results support the hypothesis that effective immunity in Marek's disease could be directed against either virus replication and spread or events associated with transformation and proliferation of lymphoid cells.