Enhanced expression of fractalkine in HIV-1 associated dementia

The CX(3)C chemokine fractalkine was found to be up-regulated in the brain during inflammatory processes. In this study, we tried to assess the role of fractalkine in HIV-1-associated dementia. Fractalkine expression is up-regulated in the brains of AIDS patients with HAD. Fractalkine immunoreactivity was mainly detected in astrocytes. In addition, fractalkine expression was found to be up-regulated in cocultures of astrocytes and HIV-infected macrophages. This up-regulation was dependent on cell-cell contact. We propose that fractalkine produced during interactions between astrocytes and HIV-infected macrophages plays a role in HAD by regulating the trafficking of monocytic cells in the brain parenchyma.

Interactions between HIV-infected monocyte-derived macrophages and human brain microvascular endothelial cells result in increased expression of CC chemokines

The presence of perivascular monocytic infiltration is a major hallmark of HIV-1-associated dementia. Since CC chemokines are chemoattractant cytokines that are able to attract T cells and monocytes/macrophages to sites of inflammation, and since infiltrating monocytes/macrophages remain in close contact with the brain endothelium, we investigated whether interactions between HIV-1-infected macrophages and brain endothelium result in an altered chemokine production. We found an increased mRNA expression of monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein (MIP)-1 alpha and MIP-1 beta, and RANTES by macrophages after HIV-1 infection. Interactions between HIV-infected macrophages and brain microvascular endothelial cells resulted in an additional upregulation of chemokine mRNA expression, during cell-cell contact as well as in a trans-well system. Since IL-1 beta can function as a modulator of chemokine expression we investigated if interleukin-1 beta could be involved in the regulation of chemokine induction. Coculturing of HIV-infected macrophages and endothelial cells resulted in immune-activation as indicated by increased mRNA expression of IL-1 beta. Subsequently, addition of a neutralizing antibody against IL-1 beta resulted in altered chemokine expression by macrophages, but not by endothelial cells. Thus, IL-1 beta appears to play a major role in the regulation of chemokines during cellular interactions in HIV-associated dementia, but other factors may also be involved.

Induction of cyclooxygenase-2 expression during HIV-1-infected monocyte-derived macrophage and human brain microvascular endothelial cell interactions

Human immunodeficiency virus type-1 (HIV-1)-associated dementia (HAD) is a neurodegenerative disease characterized by HIV infection and replication in brain tissue. HIV-1-infected monocytes overexpress inflammatory molecules that facilitate their entry into the brain. Prostanoids are lipid mediators of inflammation that result from cyclooxygenase-2 (COX-2) activity. Because COX-2 is normally induced during inflammatory processes, the aim of this study was to investigate whether COX-2 expression is up-regulated during monocyte-brain endothelium interactions. In vitro cocultures of HIV-infected macrophages and brain endothelium showed an up-regulation of COX-2 expression by both cell types. This up-regulation occurs via an interleukin-1beta (IL1beta)-dependent mechanism in macrophages and via an IL-1beta-independent mechanism in endothelial cells. Thus, interactions between HIV-infected monocytes and brain endothelium result in COX-2 expression and, as such, might contribute to the neuropathogenesis of HIV infection.

Monocyte infiltration is highly associated with loss of the tight junction protein zonula occludens in HIV-1-associated dementia

In human immunodeficiency virus (HIV)-1-associated dementia (HAD), consequences of interactions between infiltrating monocytes and brain endothelial cells are not yet fully understood. This study investigated whether the blood-brain barrier is affected in brain tissue of patients suffering from HAD and whether it was possible to find a correlation with the presence or absence of monocytic cells, which have been suggested to play a major role in HAD. Immunohistochemical analysis for zonula occludens 1, a tight junction protein, and CD68, a macrophage marker, revealed that loss of tight junction immunoreactivity was highly correlated with monocyte infiltration and with HAD. This suggests that the presence of perivascular macrophages cells is associated with breakdown of the blood-brain barrier thereby facilitating infiltration of more monocytic cells hence enhancing disease progression.

DC-SIGN, a dendritic cell-specific HIV-1-binding protein that enhances trans-infection of T cells

Dendritic cells (DC) capture microorganisms that enter peripheral mucosal tissues and then migrate to secondary lymphoid organs, where they present these in antigenic form to resting T cells and thus initiate adaptive immune responses. Here, we describe the properties of a DC-specific C-type lectin, DC-SIGN, that is highly expressed on DC present in mucosal tissues and binds to the HIV-1 envelope glycoprotein gp120. DC-SIGN does not function as a receptor for viral entry into DC but instead promotes efficient infection in trans of cells that express CD4 and chemokine receptors. We propose that DC-SIGN efficiently captures HIV-1 in the periphery and facilitates its transport to secondary lymphoid organs rich in T cells, to enhance infection in trans of these target cells.

Overexpression of nerve growth factor and basic fibroblast growth factor in AIDS dementia complex

Although neurotrophic factors are currently considered as treatment for neurodegenerative diseases, little is still known about their presence in the central nervous system under pathological conditions. We investigated the expression of the neurotrophic molecules NGF, bFGF, BDNF and IGF-1 in brain tissue of patients suffering from AIDS dementia complex. In contrast to IGF-1 and BDNF, NGF and bFGF mRNA levels were significantly elevated. Strong NGF immunoreactivity was found in perivascular areas and was colocalized with infiltrating macrophages, whereas intense bFGF staining was found in cells with characteristic astrocytic morphology. These data suggest that the induction of NGF and bFGF alone appears to be insufficient as a compensatory mechanism to prevent ADC.