CD4 and viral infectious disease: To evaluate if the higher levels of thymocyte activation and proliferation found in HIV-infected individuals may result in higher susceptibility to viral infection and exhaustion of regenerative capacity, we investigated if in HIV-infected individuals the fraction of activated/proliferating thymocytes correlate with (i) the lower fraction of CD4+SP and the lower CD4+SP/CD8+SP ratio in the thymus, (ii) increased fraction of thymocytes expressing CCR5, and (iii) CD4+ T-cell count in blood.