Characterization of monocytes during different stages of differentiation that facilitate transmigration across the blood brain barrier and HIV infection: Implications for neuroAIDS

Abstract

Cognitive impairment is prevalent in human immunodeficiency virus 1(HIV) infected people. Accumulation of monocytes (Mo)/macrophages (Mac) within the CNS is the best indicator of severe neurocognitive dysfunction, rather than viral load, suggesting that the transmigration of both uninfected and infected Mo across the blood brain barrier (BBB) is important in HIV neuropathogenesis. Although Mo are infected in vivo, freshly isolated cells are resistant to infection, suggesting a Mo subpopulation is infected by HIV. Monocytes in the circulation are heterogeneous and there is a lack of markers that identifies circulating Mo subpopulations. Thus, it has been difficult to identify Mo subsets that cross the BBB and/or become infected by HIV. The goal of this thesis project was to identify markers of human Mo as they differentiate into Mac, to characterize the cells that transmigrate across the BBB and enter the CNS parenchyma, and to identify the Mo subpopulation that can be infected by HIV. We established optimal non-adherent culture conditions for CD14+ Mo and demonstrated by flow cytometry that the phenotype of these cells changed with time in culture. The percentage of cells expressing CD14 decreased or remained the same, while the percentage of CD11b+ and Mac387+ cells remains unchanged. The percentage of CD163+ cells decreased while the percentage of CD16+ and CD166+ cells increased. CD44v6 expression changed depending upon the expression of CD14. In transmigration experiments, using our in vitro model of the BBB, we found that CD14+ cells preferentially transmigrate across the BBB and express CD16, CD11b, Mac387 and likely CD166, CD163 and CD44v6. cDNA microarray analyses of maturing Mo/Mac yielded differentially regulated genes whose products interact with HIV proteins, function within the CNS, and distinguish between monocytes and macrophages. Genes that characterize the transmigrating Mo subpopulation were also identified. Freshly isolated Mo, as well as T cells, were shown to use the paracellular route of transmigration across the BBB as demonstrated by confocal microscopy. In contrast, HIV infected cells cross transcellularly. These studies contribute to our understanding of the role of Mo/Mac in the pathogenesis of NeuroAIDS and may suggest therapeutic interventional targets.