Abrogation of age-related resistance to chicken infectious anemia by embryonal bursectomy.

Embryonally bursectomized (Ebx) chickens developed signs and lesions typical of chicken infectious anemia (CIA) when infected with CIA-1 isolate of chicken infectious anemia virus (CIAV) at 21 or 38 days of age. In both cases, the chickens had low hematocrit values after the 14th day of inoculation, and the percentage of CD4+ and CD8+ cells in the thymus was markedly reduced at 21 days postinoculation. Even though intact chickens became infected, they never developed low hematocrit values. The data support the hypothesis that age-related resistance to CIA is antibody-mediated and is not due to disappearance of the CIAV target cell; the data also suggest that CD4+/CD8+ cells are the target for infection.