How does HIV cause AIDS? The homing theory

The mechanism by which HIV causes depletion of CD4(+) T cells in infected i ndividuals remains unknown. Numerous theories have been proposed, but none can fully explain all of the events observed to occur in patients. Recent s tudies have shown that HIV binding to resting CD4(+) T cells upregulates L- selectin, causing the cells to home from the blood into lymph nodes at an e nhanced rate. It is possible that the disappearance of CD4(+) T cells in th e blood is actually the result of them leaving the blood, which can help ex plain the loss of CD4(+) T cells in the blood occurring at a much faster ra te than in lymphoid tissues. Furthermore, secondary signals through homing receptors received during the homing process induce many of these cells int o apoptosis,These cells die in the lymph nodes without producing HIV partic les, which can explain the 'bystander effect' observed in the lymph nodes o f HIV infected individuals, If this scenario occurs in HIV+ patients, it mi ght explain many of the clinical observations.