Regulation of human immunodeficiency virus type 1 infection, beta-chemokine production, and CCR5 expression in CD40L-stimulated macrophages: immune control of viral entry.

Mononuclear phagocytes (MP) and T lymphocytes play a pivotal role in the host immune response to human immunodeficiency virus type 1 (HIV-1) infection. Regulation of such immune responses can be mediated, in part, through the interaction of the T-lymphocyte-expressed molecule CD40 ligand (CD40L) with its receptor on MP, CD40. Upregulation of CD40L on CD4+ peripheral blood mononuclear cells during advanced HIV-1 disease has previously been reported. Based on this observation, we studied the influence of CD40L-CD40 interactions on MP effector function and viral regulation in vitro. We monitored productive viral infection, cytokine and beta-chemokine production, and beta-chemokine receptor expression in monocyte-derived macrophages (MDM) after treatment with soluble CD40L. Beginning 1 day after infection and continuing at 3-day intervals, treatment with CD40L inhibited productive HIV-1 infection in MDM in a dose-dependent manner. A concomitant and marked upregulation of beta-chemokines (macrophage inhibitory proteins 1alpha and 1beta and RANTES [regulated upon activation normal T-cell expressed and secreted]) and the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) was observed in HIV-1-infected and CD40L-treated MDM relative to either infected or activated MDM alone. The addition of antibodies to RANTES or TNF-alpha led to a partial reversal of the CD40L-mediated inhibition of HIV-1 infection. Surface expression of CD4 and the beta-chemokine receptor CCR5 was reduced on MDM in response to treatment with CD40L. In addition, treatment of CCR5- and CD4-transfected 293T cells with secretory products from CD40L-stimulated MDM prior to infection with a CCR5-tropic HIV-1 reporter virus led to inhibition of viral entry. In conclusion, we demonstrate that CD40L-mediated inhibition of viral entry coincides with a broad range of MDM immune effector responses and the down-modulation of CCR5 and CD4 expression.

HIV-1 infected and immune competent mononuclear phagocytes induce quantitative alterations in neuronal dendritic arbor: relevance for HIV-1-associated dementia.

Neuronal loss, alterations in dendritic arbor, and decreased synaptic density, in infected brain tissue, are neuropathological signatures of HIV-1-associated dementia (HAD). Brain mononuclear phagocyte (MP) (macrophage and microglia) secretory products can effect neuronal compromise, although the underlying mechanism(s) remain incompletely defined. To these ends, we quantitatively assessed the effects of virus-infected and/or immune activated MP secretory products on multiple aspects of neuronal morphology. Rat cortical and hippocampal neurons were exposed to secretory products from HIV-1-infected and lipopolysaccharide (LPS)-activated human monocyte-derived macrophage (MDM). Our assays for alterations in neuronal dendritic arbor and cell loss included the quantification of neurofilament (NF), neuron-specific enolase (NSE), and MAP-2 by ELISA and cellular morphology. MDM conditioned media (MCM) enhanced neuronal survival. HIV-1 infection or activation by LPS had modest neurotoxic effects. In contrast, the combination of HIV-1 infection and activation of MDM produced significant neurotoxicity. Such MDM products altered dendritic arbor, decreased synaptic density, and increased LDH release. Comparable neurotrophic/toxic responses were observed when neurons were exposed to MCM collected from 12 separate human donors. Similar responses were observed with MCM from human fetal microglia, further supporting the role of HIV-1-infected and immune-activated brain MP in the overall neurotoxic responses. This work provides quantitative measures of neuronal damage by which virus infected and activated MP can elicit neuronal injury in HAD.

HIV-1 infected immune competent mononuclear phagocytes influence the pathways to neuronal demise.

Secretory products from HIV-1-infected immune-competent mononuclear phagocytes (MP) damage neuronal dendritic arbor (Zheng et al., 2001). The mechanism behind neuronal injury and whether it is species and/or viral strain dependent is not fully understood. To these ends, we investigated whether HIV-1-infected and lipopolysaccharide (LPS)-activated MDM elicit neuronal injury in primary human neurons. Neuronal damage was compared to that seen in rat neurons. Utilizing a spectrum of HIV-1 strains to infect human monocyte-derived macrophages (MDM), productive viral replication proved necessary, but not sufficient, for neuronal injury. Neuronal demise was induced by virion-free HIV-1-infected and immune-activated MDM culture supernatants. Maximal alterations in glutamate mediated neuronal signaling, resulted from exposure to secretory products from HIV-1-infected and immune-activated MDM. Apoptosis was the predominant mechanism of cell death induced by HIV-1-infected and LPS-treated MDM. Importantly, neuronal injury and increases in calcium influx mediated by HIV-1-infected and immune-activated MDM culture supernatants was partially blocked by the N-methyl D-aspartate (NMDA) receptor antagonist, MK 801. These data support a primary role for immune-activation in MP neurotoxic activities. The upregulation of NMDA receptor sensitive soluble factors and neuronal apoptosis by HIV-1-infected and immune-activated MDM provide unique insights into links between soluble factors, produced as a consequence of MP immunity, and neuronal demise in HAD.

Lymphotropic virions affect chemokine receptor-mediated neural signaling and apoptosis: implications for human immunodeficiency virus type 1-associated dementia.

Chemokine receptors pivotal for human immunodeficiency virus type 1 (HIV-1) infection in lymphocytes and macrophages (CCR3, CCR5, and CXCR4) are expressed on neural cells (microglia, astrocytes, and/or neurons). It is these cells which are damaged during progressive HIV-1 infection of the central nervous system. We theorize that viral coreceptors could effect neural cell damage during HIV-1-associated dementia (HAD) without simultaneously affecting viral replication. To these ends, we studied the ability of diverse viral strains to affect intracellular signaling and apoptosis of neurons, astrocytes, and monocyte-derived macrophages. Inhibition of cyclic AMP, activation of inositol 1,4,5-trisphosphate, and apoptosis were induced by diverse HIV-1 strains, principally in neurons. Virions from T-cell-tropic (T-tropic) strains (MN, IIIB, and Lai) produced the most significant alterations in signaling of neurons and astrocytes. The HIV-1 envelope glycoprotein, gp120, induced markedly less neural damage than purified virions. Macrophage-tropic (M-tropic) strains (ADA, JR-FL, Bal, MS-CSF, and DJV) produced the least neural damage, while 89.6, a dual-tropic HIV-1 strain, elicited intermediate neural cell damage. All T-tropic strain-mediated neuronal impairments were blocked by the CXCR4 antibody, 12G5. In contrast, the M-tropic strains were only partially blocked by 12G5. CXCR4-mediated neuronal apoptosis was confirmed in pure populations of rat cerebellar granule neurons and was blocked by HA1004, an inhibitor of calcium/calmodulin-dependent protein kinase II, protein kinase A, and protein kinase C. Taken together, these results suggest that progeny HIV-1 virions can influence neuronal signal transduction and apoptosis. This process occurs, in part, through CXCR4 and is independent of CD4 binding. T-tropic viruses that traffic in and out of the brain during progressive HIV-1 disease may play an important role in HAD neuropathogenesis.

Insights into the neurodegenerative process of Alzheimer's disease: a role for mononuclear phagocyte-associated inflammation and neurotoxicity.

Since the first description of Alzheimer's disease (AD) in 1907, significant progress was made into understanding disease pathophysiology. The enormous effort in AD research has translated into the discovery of genetic linkages for disease, into elucidating the structure and function of the etiologic beta-amyloid protein, and into unraveling the seemingly complex neuroimmunological cascade that affects neuronal dysfunction. Although effective therapies do not currently exist, many are being developed. We propose that the neuropathogenesis of AD, in measure, revolves around the immunological activation of glial cells, which in turn leads to alterations in inflammatory neurotoxin production, and ultimately to neuronal injury and death. Elucidating the mechanisms involved in such glial cell immune activation should provide valuable insights into understanding the disease process and in providing effective therapeutics to prevent and/or retard the devastating neurodegeneration that afflicts so many of our elderly.