The decline in the CD4% and CD4/CD8 ratios have been compared in lymph nodes and blood from SIVMNE/E11S infected rhesus macaques. The results indicate that loss from the LN CD4+ cell pool does not occur until CD4/CD8 ratios of less than 0.5 is reached in blood. These changes also correlate with the ability to isolate virus from the blood and the transition of CD45RAhi to highly activated CD45RAlo CD8+ cells both of which may play a role in eliminating CD4+ cells. In end-stage disease, CD8+ cells also decline in LN and mitogen responsiveness no longer exists in any nodes. Interestingly at this stage, the circulating CD8% increases significantly and represents the only source of functional T cells remaining in the body.