HIV associated Dementia (HAD) is an important co-morbidity of HIV infection. Its less severe form appears to be resistant to highly active anti-retroviral therapy (HAART) and HIV infected macrophages (MDM) and microglia are key to its development. Because of their importance in this and other facets of HIV infection, the cycle in MDM has been studied extensively, and most investigators believe that macrophage infection can be long-lived and produce little cytopathology, making these cells ideal potential reservoirs for the virus in a treated individual, and that while most steps in the infectious process parallel those in lymphocytes, virus assembly and egress are different, and involve intracytoplasmic assembly and routing into multivesicular bodies (MVBs) in preference to budding at the plasma membrane. Subsequent release of virus is believed to take place via an exocytotic pathway involving direct fusion of plasma and MVB limiting membranes. Using a model microglia/macrophage infection that has been modified so that there is low production of virus, we have identified binding between gag and an annexin II (Anx2), a pleiotropic protein involved in exosomal formation and fusion. This protein is expressed to high levels in macrophages and microglia, particularly in the infected brain. In this proposal we will develop these preliminary results in three specific aims. In the first aim, we will determine the effects of reduction of Anx2 in MDM on HIV infection, and analyze the differences between the protein expressed in activated vs. non-activated MDM. In the second specific aim, we will map the binding sites between p55/p24 and Anx2 and introduce mutations into HIV proviruses, to determine the effects on viral infection. In the third specific aim we will study its surface expression and study Anx2 distribution in the HIV and SIV infected brain, and perform collocation experiments using fluorescence tagged molecules. These results will expand our understanding of lentiviral infection of macrophages, and potentially provide an additional target for therapeutic intervention in HIV and HAD.