MICROGLIA, CYTOKINE AND HIV

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Central nervous system (CNS) dysfunction is a prominent feature in patients with AIDS. As many as 70% of AIDS patients show neurological dysfunctions during the course of the disease, and nervous system manifestations are leading clinical problems for many. There is significant evidence for direct infection of the CNS by HIV-1, and the presence of HlV-1 viral genome, viral antigens and viral particles within brain macrophages and microglia has been well documented. We have established and characterized human glial cell cultures for the study of HIV-1 infection and pathogenesis. We have determined that late second trimester human microglia can be productively infected by HIV-1 in vitro. In addition, both microglia and astrocytes produce cytokines and growth factors in an interdependent manner. In this application, we propose to examine the role of HIV-1 as a direct modulator of cytokine production in microglia, and the role of astrocytes as an intermediary cell linking microglia and injury of target cells such as neurons and oligodendroglia. The guiding objectives of this proposal are to determine the mechanisms by which HIV-1 mediates functional and structural pathology associated with AIDS> There are four specific aims: 1) to determine if HIV-1 induces the production of cytokines in cultured human fetal microglia; 2) to determine if HIV-1 induces the production of nitric oxide in cultured human fetal microglia and astrocytes; 3) to determine the effects of cytokines or nitric oxide produced by glia on neuronal survival and growth in culture; and 4) to determine the expression of cytokines and nitric oxide synthase in the CNS in vivo. The hypothesis to be tested is that in humans, astrocytes rather than microglia are the major source of the neurotoxin nitric oxide and that HIV-1 directly, or indirectly through soluble factors from HIV-infected microglia, may activate the astrocyte inducible nitric oxide synthase (iNOS) pathway. The ability of various laboratory strains and clinical isolates of HIV-1 to activate microglia-astrocyte cytokine cascades and high output nitric oxide generation will be examined. Nitric oxide and cytokines produced as a result of HIV-1 exposure of microglia will be tested for their autocrine and paracrine effects on astrocytes and microglia in vitro, since nitric oxide has been shown to be a profound modulator of cell growth and immune function. Finally, using human fetal neuronal cell cultures established from late second trimester abortuses, we propose to study the effects of these putative neurotoxins with respect to the mechanisms of cell death.