Sites of HIV Reservoir in the Brain: HIV in compartmentalized in the subcortical white matter and the midline structures of the brain. This includes the frontal and temporal lobe, the basal ganglia and the brain stem. The posterior parts of the brain are relatively spared. Within these regions HIV infects the macrophages/microglia and astrocytes most commonly located in the perivascular regions where they constitute the blood brain barrier. A previously under appreciated site of viral infection in the brain is the subarachnoid space where the meningeal macrophages form a rich plexus of cells surrounding the meningeal blood vessels. Viral sequencing suggests that the meninges harbor both brain and peripheral blood derived viruses, suggesting that this may be a route for viral transmission from brain to blood. Alternatively, the virus can spread along the meningeal macrophages to the brain parenchyma