Apoptosis and CD8-down-regulation in the thymus of chickens infected with Marek's disease virus

Summary Marek's disease virus (MDV)-infected chickens show thymic atrophy during the acute phase of infection. We examined whether the thymic atrophy by MDV-infection was mediated by apoptosis. Apoptosis-specific DNA ladderings were clearly observed in thymocytes one week after MDV-infection. Histological and flow cytometry studies revealed that immature CD4⁺CD8⁺ thymocytes underwent apototic cell death. In addition, the expression level of CD8 molecules on both CD4^–CD8⁺ and CD4⁺CD8⁺ thymocyte populations was down-regulated in the infected chickens. These thymic changes might be involved in the pathogenesis of Marek's disease.