The planned work seeks to answer a number of questions relating to the nature of the reservoir of HIV in the central nervous system (CNS) at different stages of disease progression, the dynamics and mechanism of HIV entry into the CNS, and the relationship between virus populations in the CNS with those infecting tissue macrophages in the periphery. Using archived autopsy tissues from pre-symptomatic, untreated individuals, the entry of HIV-1 and the relationship of virus populations established in the CNS to those in the peripheral lymphoid system before the onset of AIDS and development of HIV encephalitis (HIVE) will be investigated. A highly sensitive and quantitative polymerase chain reaction-based method will be used to screen autopsy tissue from several regions of the brain for HIV proviral sequences of the resident viral population in the CNS. Genetic and phenotypic(cellular tropism, coreceptor usage) comparisons between CNS- and lymphoid tissue-derived variants will indicate the degree of compartmentalization and independent evolution of HIV that has occurred at this early disease stage. The nature of the virus-adaptive processes that underlie HIV infection of the CNS, and their relation to macrophage tropism will investigated by phenotypic analysis of HIV variants infecting defined cell types(microglia, tissue macrophages and different subsets of lymphocytes) in vivo. Different cell types will be separated from autopsy brain, spleen, lung and colon samples for HIV-infected individuals by an immunomagnetic cell separation method using monoclonal antibodies to cell type-specific markers. The principal information sought from this investigation is the genetic and phenotypic relationship between HIV populations infecting microglia and tissue macrophages, and the role the latter may play in the trafficking of HIV-infected macrophages into the CNS in the development of HIVE. The planned work will produce considerable new information on the timing and dynamics of HIV entry into the brain, and on the importance of the CNS as a reservoir of HIV infection, and a potential source of reactivated virus in individuals on long term anti-retroviral therapy. [unreadable] [unreadable] [unreadable] [unreadable]