CD4 and infection: 1. Depletion of DN and DP thymocytes. DP1 and DP2 decreased significantly while the expression of Bcl2 in DP3 increased.2. Delayed maturation of SP led to the accumulation of CD24highCD3high SP cells.3. Blockage of the development of DN1.4. Apoptosis in thymic cortex in chicks, but no significant change in CD4+/CD8+ T cell ratio.5. Thymic atrophy but maintained T cell maturation and migration in attenuated strains (SL3261) infection. Increase in naive T cells in peripheral lymphatic organs.