Microglia and HIV/AIDS

1. Morner A, Thomas JA, Bjorling E, Munson PJ, Lucas SB, McKnight A (2003) Productive HIV-2 infection in the brain is restricted to macrophages/Microglia. AIDS 17:1451-1455
   Abstract: OBJECTIVES: HIV-2 can use a broader range of co-receptors than HIV-1 in vitro, and is less dependent on CD4 for infection. The aim of this study was to detect productive HIV-2 infection in the brain and investigate whether HIV-2 has an expanded tropism for brain cells in vivo, in comparison with HIV-1, which productively infects macrophages/Microglia. DESIGN: Brain samples taken at autopsy from eight patients who died from AIDS, six HIV-2 and two HIV-1/HIV-2 dually seropositive, with HIV encephalitis (HIVE), collected in Abidjan, Cote d'Ivoire in 1991, were examined for the presence and localization of productive HIV-2 infection. METHODS: Using immunohistochemistry, the presence of HIV-2 p26 in formalin-fixed, wax-embedded brain tissue sections was investigated. Double-staining with glial fibrillary acidic protein (GFAP),

2. Bell JE, Arango JC, Robertson R, Brettle RP, Leen C, Simmonds P (2002) HIV and drug misuse in the Edinburgh cohort. J.Acquir.Immune.Defic.Syndr. 31 Suppl 2:S35-S42
   Abstract: The Edinburgh cohort of intravenous drug users (IVDUs) became infected with HIV between 1983 and 1984. Before the era of effective therapy, many of these infected IVDUs displayed cognitive impairments on progressing to AIDS and were found to have HIV encephalitis (HIVE). Full autopsies were conducted on these patients, providing an opportunity to study the intersecting pathology of pure HIVE and drug use. High proviral load in the brain correlated well with the presence of giant cells and HIV p24 positivity. In presymptomatic HIV infection, IVDUs were found to have a lymphocytic infiltrate in the central nervous system (CNS). Apart from the expected Microglial activation in the presence of HIV infection of the CNS, drug use in its own right was found to be associated with Microglial activation. Examination of HIV-negative IVDUs revealed a number of neuropathologic features, including Microglial activation, which may underpin HIV-related pathology in the CNS. HIV isolated from different regions of the brain was exclusively of R5-tropic type throughout the course of infection. Detailed studies of p17 and V3 sequences suggest that viral sequestration occurs in the CNS before the onset of AIDS and that increasing diversity of HIV variants within the brain is associated with increasing severity of HIVE. Because brain isolates have proved to be different from those in lymphoid tissue (and blood), it is likely that selective neuroadaptive pressures operate before HIVE supervenes. Drug abuse may be synergistic in this process through activation of Microglia, breakdown of the blood-brain barrier, and direct neurotoxicity. Collections of clinically well-characterized HIV-infected tissues such as those in the Edinburgh Brain Bank are a vital resource to support ongoing studies of viral pathogenesis in the CNS and interactions with drug abuse

3. Clements JE, Babas T, Mankowski JL, Suryanarayana K, Piatak M, Jr., Tarwater PM, Lifson JD, Zink MC (2002) The central nervous system as a reservoir for simian immunodeficiency virus (SIV): steady-state levels of SIV DNA in brain from acute through asymptomatic infection. J.Infect.Dis. 186:905-913
   Abstract: Latent reservoirs of human immunodeficiency virus (HIV) present significant challenges for eradicating HIV from infected persons, particularly reservoirs in the brain established during acute infection. A simian immunodeficiency virus (SIV)/macaque model of HIV dementia was used to show that viral DNA levels in the brain remained at constant levels from acute through asymptomatic infection, despite significant down-regulation of viral RNA in the brain after the acute phase of infection. Viral replication in the brain coincided with activation of macrophages and Microglia in the central nervous system; down-regulation of viral replication coincided with increased infiltration of cytotoxic lymphocytes and reduced activation of macrophages and Microglia in the brain. Comparison of viral genotypes in the central nervous system and peripheral blood mononuclear cells suggests that recrudescence of viral replication in brain occurs by reactivation of latent viral DNA. Latent virus in the brain must be considered in therapeutic strategies to eliminate HIV from infected persons

4. Cosenza MA, Zhao ML, Si Q, Lee SC (2002) Human brain parenchymal Microglia express CD14 and CD45 and are productively infected by HIV-1 in HIV-1 encephalitis. Brain Pathol. 12:442-455
   Abstract: Microglia are endogenous brain macrophages that show distinct phenotypes such as expression of myeloid antigens, ramified morphology, and presence within the neural parenchyma. They play significant roles in a number of human CNS diseases including AIDS dementia. Together with monocyte-derived (perivascular) macrophages, Microglia represent a major target of HIV-1 infection. However, a recent report challenged this notion based on findings in SIV encephalitis. This study concluded that perivascular macrophages can be distinguished from parenchymal Microglial cells by their expression of CD14 and CD45, and that macrophages, but not Microglia, are productively infected in SIV and HIV encephalitis. To address whether parenchymal Microglia are productively infected in HIV encephalitis, we analyzed expression of CD14, CD45 and HIV-1 p24 in human brain. Microglia were identified based on their characteristic ramified morphology and location in the neural parenchyma. We found that parenchymal Microglia are CD14+ (activated), CD45+ (resting and activated), and constitute approximately two thirds of the p24+ cells in HIV encephalitis cases. These results demonstrate that Microglia are major targets of infection by HIV-1, and delineate possible differences between HIVE and SIVE. Because productively infected tissue macrophages serve as the major viral reservoir, these findings have important implications for AIDS

5. D'Aversa TG, Weidenheim KM, Berman JW (2002) CD40-CD40L interactions induce chemokine expression by human Microglia: implications for human immunodeficiency virus encephalitis and multiple sclerosis. Am.J.Pathol. 160:559-567
   Abstract: CD40 is a protein on Microglia that is up-regulated with interferon (IFN)-gamma and is engaged by CD40L, found on CD4+ T cells, B cells, and monocytes. These interactions may be important in central nervous system inflammatory diseases. Microglia have been shown to be a source of chemokines, whose expression plays a key role in central nervous system pathologies. We examined the expression of CD40 on Microglia in human immunodeficiency virus (HIV) encephalitic brain, and the effects of CD40-CD40L interactions on the expression of chemokines by cultured Microglia. We found significantly increased numbers of CD40-positive Microglia in HIV-infected brain tissue. Treatment of cultured Microglia with IFN-gamma and CD40L increased expression of several chemokines. IFN-gamma- and CD40L-induced MCP-1 protein was mediated by activation of the ERK1/2 MAPK pathway, and Western blot analysis demonstrated phosphorylation of ERK1/2 upon stimulation of Microglia. In contrast, IFN-gamma- and CD40L-induced IP-10 protein production was mediated by the p38 MAPK pathway. Our data suggest a mechanism whereby CD40L+ cells can induce Microglia to secrete chemokines, amplifying inflammatory processes seen in HIV encephalitis and multiple sclerosis, and implicate CD40-CD40L interactions as a target for interventional strategies

6. Garden GA (2002) Microglia in human immunodeficiency virus-associated neurodegeneration. Glia 40:240-251
   Abstract: Infection with the human immunodeficiency virus (HIV) is associated with a syndrome of cognitive and motor abnormalities that may develop in the absence of opportunistic infections. Neurons are not productively infected by HIV. Thus, one hypothesis to explain the pathophysiology of HIV-associated dementia (HAD) suggests that signals released from other infected cell types in the CNS secondarily lead to neuronal injury. Microglia are the predominant resident CNS cell type productively infected by HIV-1. Neurologic dysfunction in HAD appears to be a consequence of Microglial infection and activation. Several neurotoxic immunomodulatory factors are released from infected and activated Microglia, leading to altered neuronal function, synaptic and dendritic degeneration, and eventual neuronal apoptosis. This review summarizes findings from clinical/pathological studies, animal models, and in vitro models of HAD. Most of these studies support the hypothesis that altered Microglial physiology is the nidus for a cascade of events leading to neuronal dysfunction and death. Several molecular mediators of neuronal injury in HAD that emanate from Microglia have been identified, and strategies for altering the impact of these neurotoxins are discussed

7. Garden GA, Budd SL, Tsai E, Hanson L, Kaul M, D'Emilia DM, Friedlander RM, Yuan J, Masliah E, Lipton SA (2002) Caspase cascades in human immunodeficiency virus-associated neurodegeneration. J.Neurosci. 22:4015-4024
   Abstract: Many patients infected with human immunodeficiency virus-1 (HIV-1) develop a syndrome of neurologic deterioration known as HIV-associated dementia (HAD). Neurons are not productively infected by HIV-1; thus, the mechanism of HIV-induced neuronal injury remains incompletely understood. Several investigators have observed evidence of neuronal injury, including dendritic degeneration, and apoptosis in CNS tissue from patients with HAD. Caspase enzymes, proteases associated with the process of apoptosis, are synthesized as inactive proenzymes and are activated in a proteolytic cascade after exposure to apoptotic signals. Here we demonstrate that HAD is associated with active caspase-3-like immunoreactivity that is localized to the soma and dendrites of neurons in affected regions of the human brain. Additionally, the cascade of caspase activation was studied using an in vitro model of HIV-induced neuronal apoptosis. Increased caspase-3 proteolytic activity and mitochondrial release of cytochrome c were observed in cerebrocortical cultures exposed to the HIV coat protein gp120. Specific inhibitors of both the Fas/tumor necrosis factor-alpha/death receptor pathway and the mitochondrial caspase pathway prevented gp120-induced neuronal apoptosis. Caspase inhibition also prevented the dendrite degeneration observed in vivo in transgenic mice with CNS expression of HIV/gp120. These findings suggest that pharmacologic interventions aimed at the caspase enzyme pathways may be beneficial for the prevention or treatment of HAD

8. Gartner S, Liu Y (2002) Insights into the role of immune activation in HIV neuropathogenesis. J.Neurovirol. 8:69-75
   Abstract: How does HIV infection lead to the development of central nervous system disease? Central to this question is identification of the relative contributions of (1) the virus, (2) its host cells, and (3) secondary or downstream events to the pathological process. These are re-examined in this brief review. Also, a greater appreciation for the role of systemic events in neuroinflammation is emerging, with likely relevance to HIV-associated dementia. We propose here a model for HIV neuropathogenesis that highlights the role of systemic monocyte activation and subsequent neuroinvasion in initiating the disease

9. Grassi MP, Clerici F, Vago L, Perin C, Borella M, Nebuloni M, Moroni M, Mangoni A (2002) Clinical aspects of the AIDS dementia complex in relation to histopathological and immunohistochemical variables. Eur.Neurol. 47:141-147
   Abstract: To correlate cerebral histopathological and immunohistochemical changes in the neuroclinical features of the AIDS dementia complex (ADC), autopsy results of 28 ADC patients were related, in a retrospective analysis, to scores on a standardised neurological examination performed at neurologic onset. From a histopathological point of view, the cases were classified as follows: 9 cases of HIV leucoencephalopathy (HIVL; diffuse myelin damage and rare Microglial nodules), 7 cases of HIV encephalitis (HIVE; several Microglial nodules and no myelin damage) and 12 cases of mixed HIVL and HIVE (HIVL-E). The groups differed significantly with respect to symptoms and CD4 count at neurologic onset, survival and neurological impairment. Immunohistochemically, the interstitial component (p24-positive cells scattered singly within the white matter) was significantly more prevalent in HIVL, and the micronodular component (p24-positive cells confined within Microglial nodules) in HIVE. Neurological damage was worse in cases with a high prevalence of interstitial component or a low prevalence of micronodular component. HIVE, HIVL and HIVL-E are distinct clinical forms of ADC. Neurological impairment is related to white matter damage

10. Hatori K, Nagai A, Heisel R, Ryu JK, Kim SU (2002) Fractalkine and fractalkine receptors in human neurons and glial cells. J.Neurosci.Res. 69:418-426
    Abstract: Fractalkine has been identified as a novel chemokine that exhibits cell adhesion and chemoattractive properties in the central nervous system (CNS), and the fractalkine receptors, CX3CR1, are also expressed in the CNS. In the present study, the expression of fractalkine and fractalkine receptors was investigated in enriched populations of human CNS neurons, astrocytes, and Microglia. In addition, the regulatory role played by protein kinase C (PKC) in fractalkine secretion in neurons was determined in A1 human hybrid neuronal cell line produced between a human cerebral neuron and a human neuroblastoma cell. Human neurons and astrocytes expressed fractalkine mRNA as determined by the revserse transcriptase-polymerase chain reaction (RT-PCR) analysis, while human Microglia preparation did not express the fractalkine message. Human neurons and Microglia expressed CX3CR1 mRNA, but astrocytes did not. These results suggest that fractalkine secreted by CNS neurons and astrocytes produce biological effects in neurons and Microglia. Although phorbol ester did not change the expression of fractalkine mRNA level in A1 hybrid neurons, it did upregulate fractalkine secretion over unstimulated controls. This upregulation of fractalkine production was suppressed by the treatment with Ro32-0432, a PKC inhibitor. These results indicate that intracellular signals transduced by PKC play an important role in the regulation of soluble fractalkine at the post-transcriptional level in human neurons. As for the biological function of fractalkine, extracellularly applied fractalkine increased the number of bromodeoxyuridine-labeled Microglia 3-fold over the untreated controls, indicating fractalkine induces proliferation of human Microglia. These observations suggest that fractalkine released by injured neurons could induce proliferation, activation and/or migration of Microglia at the injured brain sites

11. Hughes PM, Botham MS, Frentzel S, Mir A, Perry VH (2002) Expression of fractalkine (CX3CL1) and its receptor, CX3CR1, during acute and chronic inflammation in the rodent CNS. Glia 37:314-327
    Abstract: In this study, we investigate the expression of fractalkine (CX3CL1) and the fractalkine receptor (CX3CR1) in the naive rat and mouse central nervous system (CNS). We determine if the expression of this chemokine and its receptor are altered during chronic or acute inflammation in the CNS. In addition, we determine if CX3CL1, which has been reported to be chemoattractant to leukocytes in vitro, is capable of acting as a chemoattractant in the CNS in vivo. Immunohistochemistry was performed using primary antibodies recognizing soluble and membrane-bound CX3CL1 and the N-terminus of the CX3CR1. We found that neurons in the naive rodent brain are immunoreactive for CX3CL1 and CX3CR1, both showing a perinuclear staining pattern. Resident Microglia associated with the parenchyma and macrophages in the meninges and choroid plexus constituitively express CX3CR1. In a prion model of chronic neurodegeneration and inflammation, CX3CL1 immunoreactivity is upregulated in astrocytes and CX3CR1 expression is elevated on Microglia. In surviving neurons, expression of CX3CL1 appears unaltered relative to normal neurons. There is a decrease in neuronal CX3CR1 expression. Acute inflammatory responses in the CNS, induced by stereotaxic injections of lipopolysaccharide or kainic acid, results in activation of Microglia and astrocytes but no detectable changes in the glial expression of CX3CL1 or CX3CR1. The expression of CX3CL1 and CX3CR1 by glial cells during inflammation in the CNS may be influenced by the surrounding cytokine milieu, which has been shown to differ in acute and chronic neuroinflammation

12. Kandanearatchi A, Zuckerman M, Smith M, Vyakarnam A, Everall IP (2002) Granulocyte-macrophage colony-stimulating factor enhances viral load in human brain tissue: amelioration with stavudine. AIDS 16:413-420
    Abstract: BACKGROUND: Granulocyte-macrophage colony-stimulating factor (GM-CSF) is elevated in cerebrospinal fluid in HIV- associated dementia; in addition, therapeutic GM-CSF elevates plasma viral load. OBJECTIVE: To assess the effect of GM-CSF on viral replication and the potential ameliorative effect of antiretroviral therapy. DESIGN: A primary human brain aggregate system is used as a model of the in vivo situation. METHOD: Cultured aggregates were infected with the macrophage tropic strain HIV-1SF162 and then exposed to varying GM-CSF concentrations and 0.3 micromol/l stavudine. Viral replication was assessed by p24 expression in the supernatant and aggregates. Immunohistochemistry identified neurons, astrocytes, Microglia and oligodendrocytes. RESULTS: A GM-CSF concentration of 1 ng/ml resulted in a fivefold increase in Microglial cells, the main HIV cellular reservoir (P = 0.0001). Prior GM-CSF exposure before infection of the aggregates resulted in sixfold increase in p24 levels compared with non-GM-CSF-exposed infected aggregates. Infected aggregates with or without GM-CSF had significant neuronal loss of 50% and 45%, respectively, and astrocytosis. Addition of stavudine to the infected aggregates, even in the presence of GM-CSF, reduced p24 levels to zero and prevented neuronal loss and astrocytosis. CONCLUSIONS: This study demonstrates that GM-CSF enhances viral replication while addition of stavudine prevents this potentially detrimental process

13. Kanmogne GD, Kennedy RC, Grammas P (2002) Infection of baboon Microglia with SIV-HIV recombinant viruses: role of CD4 and chemokine receptors. AIDS Res.Hum.Retroviruses 18:557-565
    Abstract: Microglia constitute the primary cell type infected with HIV in the brain and play a major role in viral persistence in the CNS and in the development of AIDS dementia. Lack of a suitable animal model and limitations in the availability of human tissues hinder most HIV/AIDS studies investigating the neuropathogenesis of AIDS dementia. The aims of this study were to determine whether baboon Microglia can be productively infected with SIV-HIV (SHIV) recombinant viruses in vitro and whether they express HIV-1 receptors and coreceptors. Our results show the presence of mRNA for CD4, CCR5, and CXCR4 chemokine receptors on baboon Microglial cells. Microglia lacked mRNA for the CCR3 chemokine receptor. We also show productive infection of baboon Microglial cells by two SHIV isolates, SHIV-KU and SHIV-89.6P, and blockade of the infection with soluble CD4 protein, CCR5, and CXCR4 monoclonal antibodies. This study demonstrating the feasibility of infecting baboon Microglia with SHIV isolates is an important first step in using the baboon as an alternative nonhuman primate model to study HIV neuropathogenesis

14. Kolson DL (2002) Neuropathogenesis of central nervous system HIV-1 infection. Clin.Lab Med. 22:703-717
    Abstract: Neuronal damage and death are consistent pathologic findings in the brains of patients with ADC, and multiple cell model systems have demonstrated neurotoxicity through the effects of HIV-1 infection in macrophages and Microglia. Brain MRI studies (1H-MRS) indicate that reversible neuronal cell dysfunction occurs early during the course of HIV-1 infection, long before overt symptoms of ADC appear. Epidemiologic studies suggest that a high viral load in the CNS is a major risk factor for ADC and that HAART may significantly reduce, but not eliminate, the risk of developing ADC. Targeted adjunctive therapies administered early are likely necessary to maximize CNS protection against HIV, and rational approaches to such therapy are rapidly evolving through in vitro analysis of the mechanisms of HIV-associated neurotoxicity. Soluble factors released by infected cells may directly or indirectly damage neurons and induce apoptosis at the level of NMDA subtype of glutamate receptors, and NMDA receptor antagonists represent a major therapeutic option currently under intense clinical investigation. Likewise, drugs with antioxidant or free radical scavenging effects offer another rational approach to adjunctive therapy and are also under intense clinical scrutiny. Finally, agents that inhibit neuronal death-signaling pathways (e.g., p38 MAPK inhibitors) and that stimulate cell survival pathways (e.g., Akt/PKB) may represent the next investigational step in designing anti-ADC therapies

15. Li Y, Wang X, Tian S, Guo CJ, Douglas SD, Ho WZ (2002) Methadone enhances human immunodeficiency virus infection of human immune cells. J.Infect.Dis. 185:118-122
    Abstract: Opiate abuse has been postulated to be a cofactor in the immunopathogenesis of acquired immunodeficiency syndrome (AIDS). This study evaluated whether methadone, a drug widely prescribed for the treatment of drug abusers with opioid dependence, affects human immunodeficiency virus (HIV) infection of human immune cells. When added to human fetal Microglia and blood monocyte-derived macrophage cultures, methadone significantly enhanced HIV infection of these cells. This enhancement was associated with the up-regulation of expression of CCR5, a primary coreceptor for macrophage-tropic HIV entry into macrophages. Most importantly, the addition of methadone to the cultures of latently infected peripheral blood mononuclear cells from HIV-infected patients enhanced viral activation and replication. Although the in vivo relevance of these findings remains to be determined, the data underscore the necessity of further studies to define the role of opioids, including methadone, in the immunopathogenesis of HIV infection and AIDS

16. Mankowski JL, Queen SE, Tarwater PM, Fox KJ, Perry VH (2002) Accumulation of beta-amyloid precursor protein in axons correlates with CNS expression of SIV gp41. J.Neuropathol.Exp.Neurol. 61:85-90
    Abstract: Axonal damage represented by accumulation of beta-amyloid precursor protein (beta-APP) develops in numerous central nervous system (CNS) diseases including human immunodeficiency virus (HIV) infection. To study the underlying mechanisms of axonal damage associated with HIV CNS infection, the amount of axonal beta-APP immunostaining in the corpus callosum of 24 simian immunodeficiency virus (SIV)-infected macaques and 3 control macaques was measured by computerized image analysis. The amounts of beta-APP accumulation were then compared with time post-inoculation, extent and character of CNS inflammation, and viral load in the CNS measured by the amount of immunohistochemical staining for the viral transmembrane protein gp41. Significant increases over control values were present in 10 of 24 SIV-infected animals. SIV encephalitis was present in 9 of the 10 animals with elevated beta-APP Increases in beta-APP correlated most strongly with levels of SIV gp41 in the brain (p = 0.005), but significant associations with macrophage infiltration and Microglial activation (p = 0.04) and infiltration by cytotoxic lymphocytes (p = 0.05) also were identified. These data demonstrate that beta-APP accumulation in the white matter of SIV-infected macaques develops during SIV infection in close correlation with levels of viral replication and may serve as a sensitive marker of neuronal/axonal damage mediated by viral proteins

17. McCarthy M, He J, Auger D, Geffin R, Woodson C, Hutto C, Wood C, Scott G (2002) Cellular tropisms and co-receptor usage of HIV-1 isolates from vertically infected children with neurological abnormalities and rapid disease progression. J.Med.Virol. 67:1-8
    Abstract: The longitudinal evolution of HIV-1 phenotypes was studied in a cohort of six vertically infected children with early onset and rapid progression of clinical disease. Among 30 viral isolates obtained from peripheral blood, tropisms for both human blood-derived cells (macrophages, T-lymphocytes), and for human neural (brain-derived) cells (Microglia, astrocytes) were determined, as was chemokine co-receptor usage. All children harbored from birth macrophage-tropic isolates using the CCR5 co-receptor. Two children later developed T-cell tropic isolates with CXCR4 and CCR3 usage. While all six patients developed neurological abnormalities, only three produced neural cell tropic isolates, which used CCR5. However, early and persistent finding of both astrocyte- and Microglia-tropic isolates in one patient did associate with the most rapid progression to brain atrophy among the six patients. Viral phenotypic properties determined in cell culture did not specifically predict clinical features or course, and the development of AIDS did not coincide with, or depend on, the appearance T-tropic, syncytia-inducing viruses

18. Nath A (2002) Human immunodeficiency virus (HIV) proteins in neuropathogenesis of HIV dementia. J.Infect.Dis. 186 Suppl 2:S193-S198
    Abstract: Human immunodeficiency virus (HIV) infection of the nervous system is unique when compared with other viral encephalitides. Neuronal cell loss occurs in the absence of neuronal infection. Viral proteins, termed "virotoxins," are released from the infected glial cells that initiate a cascade of positive feedback loops by activating uninfected Microglial cells and astrocytes. These activated cells release a variety of toxic substances that result in neuronal dysfunction and cell loss. The virotoxins act by a hit and run phenomenon. Thus, a transient exposure to the proteins initiates the neurotoxic cascade. High concentrations of these proteins likely occur in tight extracellular spaces where they may cause direct neurotoxicity as well. The emerging concepts in viral protein-induced neurotoxicity are reviewed as are the neurotoxic potential of each protein. Future therapeutic strategies must target common mechanisms such as oxidative stress and dysregulation of intracellular calcium involved in virotoxin-mediated neurotoxicity

19. Rauer M, Pagenstecher A, Schulte-Monting J, Sauder C (2002) Upregulation of chemokine receptor gene expression in brains of Borna disease virus (BDV)-infected rats in the absence and presence of inflammation. J.Neurovirol. 8:168-179
    Abstract: Infection of adult rats with Borna disease virus (BDV) causes CD8 T cell-mediated meningoencephalitis. Previously, we described a complex pattern of chemokine gene expression in the central nervous system (CNS) of such rats. We now found that expression of chemokine receptor genes CXCR3, CCR5, CX(3)CR1, and CXCR4 was also upregulated, which is in agreement with the predominance in brains of adult infected rats of T cells and monocytes/macrophages that express these receptors. In contrast to these rats, neonatally infected rats (designated PTI-NB) develop a persistent CNS infection associated with neurodegenerative processes in the absence of inflammation. In brains of PTI-NB rats, sustained expression of chemokines also takes place. We therefore analyzed mRNA expression of selected chemokine receptor genes, as well as of the chemokine fractalkine in brains of PTI-NB rats. We observed a marked increase of CCR5 and CX(3)CR1 transcripts in brains of these rats. CX(3)CR1 expressing cells were predominantly Microglia, and upregulation of CX(3)CR1 was mainly due to an increase in the number of CX(3)CR1 expressing Microglia. Fractalkine gene expression was found to be reduced to similar extents in brains of adult and newborn infected rats. These findings might be of relevance with respect to the selective neuronal cell loss observed in brains of PTI-NB rats

20. Ryan LA, Cotter RL, Zink WE, Gendelman HE, Zheng J (2002) Macrophages, chemokines and neuronal injury in HIV-1-associated dementia. Cell Mol.Biol.(Noisy.-le-grand) 48:137-150
    Abstract: Human immunodeficiency virus type-one (HIV- 1)-associated dementia (HAD) is manifested as a spectrum of behavioral, motor and cognitive dysfunctions. The disorder commonly occurs during late stage HIV disease and remains an important complication despite highly active antiretroviral therapies. A metabolic encephalopathy, fueled by neurotoxic secretions from brain mononuclear phagocytes (MP) (macrophages and Microglia) underlies HIV- I neuropathogenesis. One pivotal question, however, is how brain MP evolve from neurotrophic to neurotoxic cells. The interplay between the virus, the macrophage and the neuron has just recently begun to be unraveled. Along with a multitude of other MP secretory products, chemokines effect neuronal function by engaging neuronal receptors then activating pathways that alter synaptic transmission, cell growth, injury and protection. Both neurons and glia secrete chemokines. Interestingly, HIV-1 and its gene products can mimic chemokine neuronal signaling by binding to neuronal chemokine receptors or by other non-specific mechanisms. The elucidation of mechanisms involved in chemokine-mediated neural compromise will likely provide unique insights into the pathogenesis and treatment, not only of HAD, but of a wide range of neurodegenerative disorders

21. Ryzhova EV, Crino P, Shawver L, Westmoreland SV, Lackner AA, Gonzalez-Scarano F (2002) Simian immunodeficiency virus encephalitis: analysis of envelope sequences from individual brain multinucleated giant cells and tissue samples. Virology 297:57-67
    Abstract: Simian immunodeficiency virus (SIV)-infected macaques develop an encephalitis (SIVE) that is pathologically virtually indistinguishable from that associated with HIV infection, with multinucleated giant cells (MNGCs) being the principal histopathological manifestation. To dissect SIV variants responsible for MNGC development, we examined the relationships between env sequences transcribed in individual MNGCs and those from genomic DNA of brain and spleen tissues. The brain-specific variant found in all brain clones was dominant among the clones from MNGCs, suggesting a role in the formation of giant cells. Furthermore, two additional minor groups of sequences were present in MNGCs. One group consisted of sequences closely related to those from spleen, indicating recent and probably multiple episodes of neuroinvasion. The second group represented clones similar or identical to the initial inoculum. The survival of arcHIVal sequences and their activation presumably by the fusion of productively and quiescently infected macrophages/Microglia identify the central nervous system as a possible anatomical reservoir for latent infection

22. Sharshar T, Gray F, Poron F, Raphael JC, Gajdos P, Annane D (2002) Multifocal necrotizing leukoencephalopathy in septic shock. Crit Care Med. 30:2371-2375
    Abstract: OBJECTIVE: Multifocal necrotizing leukoencephalopathy, characterized by multiple microscopic foci of necrosis involving the white matter of the pons, has been described mainly after chemotherapy or radiotherapy for brain cancer and in HIV infection. The role of circulating cytokines has been suggested but remains to be assessed. DESIGN: Prospective case series. SETTING: A 26-bed general medical intensive care unit at a university hospital. PATIENTS: Septic shock patients. MEASUREMENTS AND PATIENTS: In three patients who died from septic shock, careful postmortem examination of the brain was performed, including studies of neuronal apoptosis and cytokine expression. MAIN RESULTS: In one patient, typical lesions of multifocal necrotizing leukoencephalopathy were seen. As compared with control 1 and control 2 who did not have multifocal necrotizing leukoencephalopathy, marked lesions of the pons, including vacuolization, apoptosis, Microglial activation, and expression of tumor necrosis factor-alpha and interleukin-1beta, were observed in the case. Simultaneously, case 1 had markedly increased circulating levels for tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, interleukin-8, interleukin-10, soluble tumor necrosis factor receptor II, and for interleukin-1 receptor antagonist. CONCLUSION: Septic shock is a newly described cause of multifocal necrotizing leukoencephalopathy, probably mediated by an excessive systemic inflammatory response

23. Si Q, Kim MO, Zhao ML, Landau NR, Goldstein H, Lee S (2002) Vpr- and Nef-dependent induction of RANTES/CCL5 in Microglial cells. Virology 301:342-353
    Abstract: Microglia are pivotal in the pathogenesis of AIDS dementia, as they serve as the major target of HIV infection in the CNS. In addition, activation of Microglia correlates best with clinical dementia. Although the beta-chemokine RANTES/CCL5 is important in modulating HIV infection as well as cellular activation, no information is available regarding how its expression is regulated in Microglia by HIV-1. Here we report that RANTES/CCL5 expression is induced in Microglia by HIV-1, but that this requires infection by HIV-1. This conclusion was supported by (1) the delayed kinetics coinciding with viral replication; (2) the lack of effect of X4 viruses; (3) inhibition by the reverse transcriptase inhibitor AZT, and (4) the lack of effect of cytokine antagonists or antibodies. Interestingly, RANTES/CCL5 production was dependent on the viral accessory protein Vpr, in addition to Nef, demonstrating a novel role for Vpr in chemokine induction in primary macrophage-type cells. Furthermore, the specific p38 MAP kinase inhibitor SB203580 augmented chemokine expression in Microglia, indicating a negative role played by p38. These data suggest unique features of RANTES/CCL5 regulation by HIV-1 in human Microglial cells

24. Si Q, Cosenza M, Zhao ML, Goldstein H, Lee SC (2002) GM-CSF and M-CSF modulate beta-chemokine and HIV-1 expression in Microglia. Glia 39:174-183
    Abstract: Significant numbers of patients with acquired immunodeficiency syndrome (AIDS) develop CNS infection primarily in macrophages and Microglial cells. Therefore, the regulation of human immunodeficiency virus type 1 (HIV-1) infection and activation of the brain mononuclear phagocytes subsequent to infection are important areas of investigation. In the current report, we studied the role of granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage-CSF (M-CSF) in the expression of antiviral beta-chemokines and HIV-1 p24 in cultures of primary human fetal Microglia. We found that stimulation with GM-CSF or M-CSF induced macrophage inflammatory proteins (MIP-1alpha and MIP-1beta) and augmented RANTES expression, after HIV-1 infection of Microglia. This was not due to the effect of GM-CSF on viral expression because GM-CSF was neither necessary nor stimulatory for viral infection, nor did GM-CSF enhance the expression of env-pseudotyped reporter viruses. Blocking GM-CSF-induced Microglial proliferation by nocodazole had no effect on beta-chemokine or p24 expression. The functional significance of the GM-CSF-induced beta-chemokines was suggested by the finding that, in the presence of GM-CSF, exogenous beta-chemokines lost their anti-HIV-1 effects. We further show that although HIV-1-infected Microglia produced M-CSF, they failed to produce GM-CSF. In vivo, GM-CSF expression was localized to activated astrocytes and some inflammatory cells in HIV-1 encephalitis, suggesting paracrine activation of Microglia through GM-CSF. Our results demonstrate a complex interplay between CSFs, chemokines, and virus in Microglial cells and may have bearing on the interpretation of data derived in vivo and in vitro

25. Su ZZ, Kang DC, Chen Y, Pekarskaya O, Chao W, Volsky DJ, Fisher PB (2002) Identification and cloning of human astrocyte genes displaying elevated expression after infection with HIV-1 or exposure to HIV-1 envelope glycoprotein by rapid subtraction hybridization, RaSH. Oncogene 21:3592-3602
    Abstract: Neurodegeneration and dementia are common complications of AIDS caused by human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system. HIV-1 target cells in the brain include Microglia, infiltrating macrophages and astrocytes, but rarely neurons. Astrocytes play an important role in the maintenance of the synaptic micro-environment and in neuronal signal transmission. To investigate potential changes in cellular gene expression associated with HIV-1 infection of astrocytes, we employed an efficient and sensitive rapid subtraction hybridization approach, RaSH. Primary human astrocytes were isolated from abortus brain tissue and low-passage cells were infected with HIV-1. To identify genes that display both early and late expression modifications after HIV-1 infection and to avoid cloning genes displaying normal cell cycle fluctuations in astrocytes, RNAs were isolated and pooled from 6, 12, 24 h and 3 and 7 day uninfected and infected cells and used for RaSH. Temporal cDNA libraries were prepared from double-stranded cDNAs that were enzymatically digested into small fragments, ligated to adapters, PCR amplified, and hybridized by incubation of tester and driver PCR fragments. By subtracting temporal cDNAs derived from uninfected astrocytes from temporal cDNAs made from HIV-1 infected cells, genes displaying elevated expression in virus infected cells, termed astrocyte elevated genes (AEGs), were identified. Both known and novel AEGs, not reported in current DNA databases, are described that display early or late expression kinetics following HIV-1 infection or treatment with recombinant HIV-1 envelope glycoprotein (gp120). For selected AEGs, expression of their protein products was also tested by Western blotting and found to display elevated expression following HIV-1 infection. The comparable pattern of regulation of the AEGs following HIV-1 infection or gp120 treatment suggest that HIV-1 exposure of astrocytes, even in the absence of productive infection, can induce changes in cellular gene expression

26. Tarozzo G, Campanella M, Ghiani M, Bulfone A, Beltramo M (2002) Expression of fractalkine and its receptor, CX3CR1, in response to ischaemia-reperfusion brain injury in the rat. Eur.J.Neurosci. 15:1663-1668
    Abstract: Fractalkine is a neuronally expressed chemokine that acts through its G-protein-coupled receptor CX3CR1, localized on Microglial and immune cells. Fractalkine might be involved in neuroinflammatory processes secondary to neuronal damage, which normally occur in a time frame of days after ischaemia. We evaluated by in situ hybridization and immunohistochemistry the expression of fractalkine and CX3CR1 in the rat brain, after a transient occlusion of the middle cerebral artery. We found that at 12 h after ischaemia neuronal fractalkine expression was transiently increased in scattered necrotic neurons of the cortex and lost from the ischaemic striatum. At 24 and 48 h after ischaemia, fractalkine immunoreactivity was strongly increased in morphologically intact cortical neurons of the ischaemic penumbra where also the stress-inducible HSP-72 was strongly up-regulated. The intensity of fractalkine immunoreactivity of neurons in the penumbra returned to basal levels at 7 days after ischaemia. Fractalkine synthesis was also induced in endothelial cells of the infarcted area, at 48 h and 7 days after ischaemia. CX3CR1 expression was detected in the activated Microglial cells of the ischaemic tissue 24 and 48 h after ischaemia, and became strongly up-regulated in macrophages/phagocytic Microglia inside the infarcted tissue 7 days after ischaemia. These data suggest that fractalkine may participate in the activation and chemoattraction of Microglia into the infarcted tissue, and contribute to the control of leucocyte trafficking from blood vessels into the injured area

27. Vilhardt F, Plastre O, Sawada M, Suzuki K, Wiznerowicz M, Kiyokawa E, Trono D, Krause KH (2002) The HIV-1 Nef protein and phagocyte NADPH oxidase activation. J.Biol.Chem. 277:42136-42143
    Abstract: Nef, a multifunctional HIV protein, activates the Vav/Rac/p21-activated kinase (PAK) signaling pathway. Given the potential role of this pathway in the activation of the phagocyte NADPH oxidase, we have investigated the effect of the HIV-1 Nef protein on the phagocyte respiratory burst. Microglia (cell line and primary culture) were transduced with lentiviral expression vectors. Expression of Nef did not activate the NADPH oxidase by itself but led to a massive enhancement of the responses to a variety of stimuli (Ca(2+) ionophore, formyl peptide, endotoxin). These effects were not caused by up-regulation of phagocyte NADPH oxidase subunits. Nef mutants lacking motifs involved in the interaction with Vav and PAK failed to reproduce the effects of wild type Nef, suggesting a role for the Vav/Rac/PAK signaling pathway. The following results suggest a key role for Rac in the priming effect of Nef. (i) Inactivation of Rac by Clostridium difficile toxin B abolished the Nef effect. (ii) The fraction of activated Rac1 was increased in Nef-transduced cells, and (iii) the dominant positive Rac1(V12) mutant mimicked the effect of Nef. These results are to our knowledge the first analysis of the effect of Rac activation on the NADPH oxidase in intact phagocytes. Rac activation is not sufficient to stimulate the phagocyte NADPH oxidase; however, it markedly enhances the NADPH oxidase response to other stimuli

28. Weiss RA (2002) HIV receptors and cellular tropism. IUBMB.Life 53:201-205
    Abstract: Viruses use specific cell surface receptors to bind to and subsequently gain entry into their host cells. Some retroviruses such as HIV-1 and HIV-2 utilize one receptor for high-affinity binding (CD4), and a separate coreceptor to mediate fusion of the viral envelope with the cell membrane (CCR5 or CXCR4). The identification of these receptors explains the cellular tropism of HIV, and hence its pathogenesis leading to immune deficiency (T-helper cell depletion), the wasting syndrome (macrophage infection), and dementia (Microglia infection). HIV can infect cells by membrane fusion at the cell surface and by receptor-mediated endocytosis. Knowledge of the HIV receptors has led to practical developments such as inhibitory drugs, reasons for genetic resistance to infection, and should inform the judicious choice of candidate vaccines

29. Williams K, Schwartz A, Corey S, Orandle M, Kennedy W, Thompson B, Alvarez X, Brown C, Gartner S, Lackner A (2002) Proliferating cellular nuclear antigen expression as a marker of perivascular macrophages in simian immunodeficiency virus encephalitis. Am.J.Pathol. 161:575-585
    Abstract: Brain perivascular macrophages are a major target of simian immunodeficiency virus (SIV) infection in rhesus macaques and HIV infection in humans. Perivascular macrophages are distinct from parenchymal Microglia in their location, morphology, expression of myeloid markers, and turnover in the CNS. In contrast to parenchymal Microglia, perivascular macrophages are continuously repopulated by blood monocytes, which undergo maturation to macrophages on entering the central nervous system (CNS). We studied differences in monocyte/macrophages in vivo that might account for preferential infection of perivascular macrophages by SIV. In situ hybridization for SIV and proliferating cellular nuclear antigen (PCNA) immunohistochemistry demonstrated that SIV-infected and PCNA-positive cells were predominantly found in perivascular cuffs of viremic animals and in histopathological lesions that characterize SIV encephalitis (SIVE) in animals with AIDS. Multilabel techniques including double-label immunohistochemistry and combined in situ hybridization and immunofluorescence confocal microscopy revealed numerous infected perivascular macrophages that were PCNA-positive. Outside the CNS, SIV-infected, PCNA-expressing macrophage subpopulations were found in the small intestine and lung of animals with AIDS. While PCNA is used as a marker of cell proliferation it is also strongly expressed in non-dividing cells undergoing DNA synthesis and repair. Therefore, more specific markers for cell proliferation including Ki-67, topoisomerase IIalpha, and bromodeoxyuridine (BrdU) incorporation were used which indicated that PCNA-positive cells within SIVE lesions were not proliferating. These observations are consistent with perivascular macrophages as terminally differentiated, non-dividing cells and underscores biological differences that could potentially define mechanisms of preferential, productive infection of perivascular macrophages in the rhesus macaque model of neuroAIDS. These studies suggest that within CNS and non-CNS tissues there exist subpopulations of macrophages that are SIV-infected and express PCNA

30. Williams KC, Hickey WF (2002) Central nervous system damage, monocytes and macrophages, and neurological disorders in AIDS. Annu.Rev.Neurosci. 25:537-562
    Abstract: This review focuses on the role of the extended macrophage/monocyte family in the central nervous system during HIV or SIV infection. The accumulated data, buttressed by recent experimental results, suggest that these cells play a central, pathogenic role in retroviral-associated CNS disease. While the immune system is able to combat the underlying retroviral infection, the accumulation and widespread activation of macrophages, Microglia, and perivascular cells in the CNS are held in check. However, with the collapse of the immune system and the disappearance of the CD4(+) T cell population, productive infection reemerges, especially in CNS macrophages. These cells, as well as noninfected macrophages, are stimulated to high levels of activation. When members of this cell group become highly activated, they elaborate a wide spectrum of deleterious substances into the neural parenchyma. In the final phases of HIV or SIV infection, this chronic, widespread, and dramatic level of macrophage/monocyte/Microglial activation constitutes a self-sustaining state of macrophage dysregulation, which results in pathological alterations and the emergence of various neurological problems

31. Albright AV, Martin J, O'Connor M, Gonzalez-Scarano F (2001) Interactions between HIV-1 gp120, chemokines, and cultured adult Microglial cells. J.Neurovirol. 7:196-207
    Abstract: HIV dementia (HIVD), a disease that is apparently mediated by neurotoxins and viral proteins secreted by HIV infected Microglia, is characterized neuropathologically by an increased number of activated Microglia in the brains of affected individuals. Consequently, the rational design of potential therapeutic strategies should take into account the mechanisms that lead to Microglial activation and to their increased prominence in the adult brain. In this regard, one leading hypothesis proposes that Microglia are recruited to specific sites in the central nervous system (CNS) as a result of interactions between Microglial chemokine receptors and chemokines, or even the viral glycoprotein gp120, which binds chemokine receptors in the process of cellular entry. Adult Microglia express the functional chemokine receptors CCR5 and CXCR4 molecules that mediate chemotaxis in these and other cell types. We determined that purified adult Microglial cultures contain a heterogeneous population with respect to their ability to respond to the alpha- and beta-chemokines, SDF1alpha, and MIP-1beta. A mean of 14.6% of the Microglia assayed responded to both alpha- and beta-chemokines (CCR5(+)CXCR4(+) phenotype); 45.4% of Microglia were phenotyped as CCR5(+)CXCR4(-); 12.9% of the Microglia were CXCR4(+)CCR5(-); and 27.0% of Microglia did not respond to either chemokine. No increase in intracellular calcium levels was seen in the vast majority of Microglia exposed to the soluble HIV envelope protein, gp120, or to HIV envelope (gp120/gp41) expressed on MLV virus pseudotypes. However, exposure of Microglia to soluble fractalkine or to other chemokines resulted in an intracellular calcium flux. Our results raise the possibility of Microglial heterogeneity with respect to their response to chemokines, and indicate that any effects due to gp120 are likely to be considerably less robust than the response of Microglia to the natural ligands of their chemokine receptors, for example SDF1alpha and MIP-1beta

32. Allen NJ, Attwell D (2001) A chemokine-glutamate connection. Nat.Neurosci. 4:676-678

33. An SF, Osuntokun O, Groves M, Scaravilli F (2001) Expression of CCR-5/CXCR-4 in spinal cord of patients with AIDS. Acta Neuropathol.(Berl) 102:175-180
    Abstract: The discovery that chemokines and their receptors (in particular CXCR-4 and CCR-5) play a role in HIV infection challenges traditional views on the pathogenesis of HIV infection in man and identifies new potential targets for therapeutic intervention. Several groups as well as our pilot study have found that increased numbers of CCR-5 positive macrophage/Microglia correlate with disease severity in brains of patients with AIDS. Among HIV-related disorders, vacuolar myelopathy (VM) is the most common spinal cord disorder in patients with AIDS. The purpose of this study was to investigate the possible relationship between the expression of CCR-5/CXCR-4 and spinal cord pathology in patients with AIDS. Thirty-four spinal cords (forming two groups: without and with VM) of patients with AIDS and 6 HIV-1-negative controls were investigated by routine histological examination and immunohistochemistry. Elevated expression of CXCR-4 was found in most AIDS cases with/without neuropathological disorders (8/17 and 13/16, respectively). No CCR-5 expression was detected in HIV-1-negative controls. Among 34 cases with AIDS, expression of CCR-5 was detected in 1/16 HIV-1-positive normal spinal cords and 5/18 with VM. Despite the lack of statistical significance between the two groups (P=0.1019), our results suggest that CCR-5/CXCR-4 are present in spinal cord of patients with AIDS and that CCR-5 is more frequently found in association with VM

34. Antinori A, Giancola ML, Alba L, Soldani F, Grisetti S (2001) Cardiomyopathy and encephalopathy in AIDS. Ann.N.Y.Acad.Sci. 946:121-129
    Abstract: HIV encephalopathy has been in the past years the most typical CNS disorder in patients with AIDS. Histologic abnormalities consist in astrocytosis, myelin pallor, infiltration by infected macrophages, resident Microglia and multinucleated giant cells, generally in absence of direct infection of neurons. Mononuclear phagocytes in the brain are the main target of HIV-1 infection and the site of productive viral replication, and viral stimulation leads to the release of neurotoxic products causing neurologic damage. Subclinical cardiac abnormalities are common in HIV+ patients and several studies suggested a role for cytokines and other inflammatory products as mediators of cardiac abnormalities. The common pathway for neurologic and cardiac manifestations supports the relationship between neurologic disease and cardiac dysfunction in HIV infection. Clinical observations suggest that cardiomyopathy could be associated with encephalopathy in HIV+ patients and that it may affect survival. Antiretroviral therapy may reduce impact of neurologic and cardiac abnormalities by suppressing plasma HIV-1 viral load

35. Asensio VC, Maier J, Milner R, Boztug K, Kincaid C, Moulard M, Phillipson C, Lindsley K, Krucker T, Fox HS, Campbell IL (2001) Interferon-independent, human immunodeficiency virus type 1 gp120-mediated induction of CXCL10/IP-10 gene expression by astrocytes in vivo and in vitro. J.Virol. 75:7067-7077
    Abstract: The CXC chemokine gamma interferon (IFN-gamma)-inducible protein CXCL10/IP-10 is markedly elevated in cerebrospinal fluid and brain of individuals infected with human immunodeficiency virus type 1 (HIV-1) and is implicated in the pathogenesis of HIV-associated dementia (HAD). To explore the possible role of CXCL10/IP-10 in HAD, we examined the expression of this and other chemokines in the central nervous system (CNS) of transgenic mice with astrocyte-targeted expression of HIV gp120 under the control of the glial fibrillary acidic protein (GFAP) promoter, a murine model for HIV-1 encephalopathy. Compared with wild-type controls, CNS expression of the CC chemokine gene CCL2/MCP-1 and the CXC chemokine genes CXCL10/IP-10 and CXCL9/Mig was induced in the GFAP-HIV gp120 mice. CXCL10/IP-10 RNA expression was increased most and overlapped the expression of the transgene-encoded HIV gp120 gene. Astrocytes and to a lesser extent Microglia were identified as the major cellular sites for CXCL10/IP-10 gene expression. There was no detectable expression of any class of IFN or their responsive genes. In astrocyte cultures, soluble recombinant HIV gp120 protein was capable of directly inducing CXCL10/IP-10 gene expression a process that was independent of STAT1. These findings highlight a novel IFN- and STAT1-independent mechanism for the regulation of CXCL10/IP-10 expression and directly link expression of HIV gp120 to the induction of CXCL10/IP-10 that is found in HIV infection of the CNS. Finally, one function of IP-10 expression may be the recruitment of leukocytes to the CNS, since the brain of GFAP-HIV gp120 mice had increased numbers of CD3(+) T cells that were found in close proximity to sites of CXCL10/IP-10 RNA expression

36. Bezzi P, Domercq M, Brambilla L, Galli R, Schols D, De Clercq E, Vescovi A, Bagetta G, Kollias G, Meldolesi J, Volterra A (2001) CXCR4-activated astrocyte glutamate release via TNFalpha: amplification by Microglia triggers neurotoxicity. Nat.Neurosci. 4:702-710
    Abstract: Astrocytes actively participate in synaptic integration by releasing transmitter (glutamate) via a calcium-regulated, exocytosis-like process. Here we show that this process follows activation of the receptor CXCR4 by the chemokine stromal cell-derived factor 1 (SDF-1). An extraordinary feature of the ensuing signaling cascade is the rapid extracellular release of tumor necrosis factor-alpha (TNFalpha). Autocrine/paracrine TNFalpha-dependent signaling leading to prostaglandin (PG) formation not only controls glutamate release and astrocyte communication, but also causes their derangement when activated Microglia cooperate to dramatically enhance release of the cytokine in response to CXCR4 stimulation. We demonstrate that altered glial communication has direct neuropathological consequences and that agents interfering with CXCR4-dependent astrocyte-Microglia signaling prevent neuronal apoptosis induced by the HIV-1 coat glycoprotein, gp120IIIB. Our results identify a new pathway for glia-glia and glia-neuron communication that is relevant to both normal brain function and neurodegenerative diseases

37. Bruce-Keller AJ, Barger SW, Moss NI, Pham JT, Keller JN, Nath A (2001) Pro-inflammatory and pro-oxidant properties of the HIV protein Tat in a Microglial cell line: attenuation by 17 beta-estradiol. J.Neurochem. 78:1315-1324
    Abstract: Microglia are activated in humans following infection with human immunodeficiency virus (HIV), and brain inflammation is thought to be involved in neuronal injury and dysfunction during HIV infection. Numerous studies indicate a role for the HIV regulatory protein Tat in HIV-related inflammatory and neurodegenerative processes, although the specific effects of Tat on Microglial activation, and the signal transduction mechanisms thereof, have not been elucidated. In the present study, we document the effects of Tat on Microglial activation and characterize the signal transduction pathways responsible for Tat's pro-inflammatory effects. Application of Tat to N9 Microglial cells increased multiple parameters of Microglial activation, including superoxide production, phagocytosis, nitric oxide release and TNF alpha release. Tat also caused activation of both p42/p44 mitogen activated protein kinase (MAPK) and NF kappa B pathways. Inhibitor studies revealed that Tat-induced NF kappa B activation was responsible for increased nitrite release, while MAPK activation mediated superoxide release, TNF alpha release, and phagocytosis. Lastly, pre-treatment of Microglial cells with physiological concentrations of 17 beta-estradiol suppressed Tat-mediated Microglial activation by interfering with Tat-induced MAPK activation. Together, these data elucidate specific components of the Microglial response to Tat and suggest that Tat could contribute to the neuropathology associated with HIV infection through Microglial promulgation of oxidative stress

38. Cambien B, Pomeranz M, Schmid-Antomarchi H, Millet MA, Breittmayer V, Rossi B, Schmid-Alliana A (2001) Signal transduction pathways involved in soluble fractalkine-induced monocytic cell adhesion. Blood 97:2031-2037
    Abstract: Fractalkine displays features that distinguishes it from the other chemokines. In particular, besides its chemoattractant action it promotes, under physiologic flow, the rapid capture and the firm adhesion of a subset of leukocytes or intervenes in the neuron/Microglia interaction. This study verified that indeed the human monocytic MonoMac6 cell line adheres to fibronectin-coated filters in response to soluble fractalkine (s-FKN). s-FKN stimulates, with distinct time courses, extracellular signal-related kinases (ERK1 and ERK2) and stress-activated protein kinases (SAPK1/JNK1 and SAPK2/p38). Both p60 Src and p72 Syk were activated under s-FKN stimulation with a rapid kinetic profile compatible with a downstream regulation on the mitogen-activated protein kinase (MAPK) congeners. The use of specific tyrosine kinase inhibitors revealed that the ERK pathway is strictly controlled by Syk, whereas c-Src up-regulated the downstream SAPK2/p38. In contrast, the SAPK1/JNK1 pathway was not regulated by any of these nonreceptor tyrosine kinases. The s-FKN-mediated increased adherence of MonoMac6 cells was partially inhibited by SB202190, a broad SAPKs inhibitor, PD98059, an MEK inhibitor, LY294002, a phosphatidyl inositol 3-kinase inhibitor, and a pertussis toxin-sensitive G protein. These data highlight that the integration of a complex array of signal transduction pathways is necessary to complete the full s-FNK-dependent adherence of human monocytic cells to fibronectin. (Blood. 2001;97:2031-2037)

39. Corasaniti MT, Maccarrone M, Nistico R, Malorni W, Rotiroti D, Bagetta G (2001) Exploitation of the HIV-1 coat glycoprotein, gp120, in neurodegenerative studies in vivo. J.Neurochem. 79:1-8
    Abstract: Neuronal loss has often been described at post-mortem in the brain neocortex of patients suffering from AIDS. Neuroinvasive strains of HIV infect macrophages, Microglial cells and multinucleated giant cells, but not neurones. Processing of the virus by cells of the myelomonocytic lineage yields viral products that, in conjunction with potentially neurotoxic molecules generated by the host, might initiate a complex network of events which lead neurones to death. In particular, the HIV-1 coat glycoprotein, gp120, has been proposed as a likely aetiologic agent of the described neuronal loss because it causes death of neurones in culture. More recently, it has been shown that brain neocortical cell death is caused in rat by intracerebroventricular injection of a recombinant gp120 coat protein, and that this occurs via apoptosis. The latter observation broadens our knowledge in the pathophysiology of the reported neuronal cell loss and opens a new lane of experimental research for the development of novel therapeutic strategies to limit damage to the brain of patients suffering from HIV-associated dementia

40. Corasaniti MT, Piccirilli S, Paoletti A, Nistico R, Stringaro A, Malorni W, Finazzi-Agro A, Bagetta G (2001) Evidence that the HIV-1 coat protein gp120 causes neuronal apoptosis in the neocortex of rat via a mechanism involving CXCR4 chemokine receptor. Neurosci.Lett. 312:67-70
    Abstract: The HIV-1 coat protein, gp120 (100 ng given intracerebroventricularly (i.c.v.) daily for seven consecutive days) causes DNA fragmentation in the brain neocortex of rat. In neocortical cells bearing ultrastructural features typical of apoptosis, electron microscopy revealed specific immunopositivity for neurofilament cytoskeletal proteins, suggesting the neuronal nature of dying cells. Neuronal apoptosis by gp120 implicates CXCR4 chemokine receptors; in fact, in rats receiving a single daily, non-neurotoxic, dose of SDF-1alpha (0.25 pmoles given i.c.v. for 7 days before gp120), the natural ligand of CXCR4 receptor, apoptosis was significantly hindered. The mechanism of SDF-1alpha protection involves inhibition of gp120-enhanced expression of IL-1beta, a cytokine implicated in the mechanisms of apoptosis induced by the viral protein in the neocortex of rat

41. Cross AK, Woodroofe MN (2001) Immunoregulation of Microglial functional properties. Microsc.Res.Tech. 54:10-17
    Abstract: Microglia are the resident tissue macrophages of the central nervous system (CNS) parenchyma and are key players in the initiation of an inflammatory response. Microglia rapidly transform from a resting to an activated morphology in response to a variety of disease states. However, they can also be the target of infections, as in the case of HIV. Many of the effector properties of Microglia can be attributed to the array of substances they secrete in response to stimuli such as bacterial lipopolysaccharide, cytokines, and chemokines. The products of activated Microglia include: cytokines (pro- and anti-inflammatory), chemokines, nitric oxide, superoxide radicals, and proteases. Furthermore, Microglia have the ability to present antigen to T cells, migrate in response to chemotactic stimuli, and phagocytose cell debris. This report focuses on the immunomodulatory functions of Microglia, with particular attention to chemokines, and highlights their pivotal role in the CNS

42. Dugas N, Lacroix C, Kilchherr E, Delfraissy JF, Tardieu M (2001) Role of CD23 in astrocytes inflammatory reaction during HIV-1 related encephalitis. Cytokine 15:96-107
    Abstract: Soluble factors released by intra-cerebral activated cells are implicated in neuronal alterations during central nervous system inflammatory diseases. In this study, the role of the CD23 pathway in astrocyte activation and its participation in human immunodeficiency virus-1 (HIV-1)-induced neuropathology were evaluated. In human primary astrocytes, CD23 protein membrane expression was dose-dependently upregulated by gp120. It was also upregulated by gamma-interferon (gamma-IFN) and modulated by interleukin-1-beta (IL-1beta) whereas Microglial cells in these stimulation conditions did not express CD23. Cell surface stimulation of CD23 expressed by astrocytes induced production of nitric oxide (NO) and IL-1beta which was inhibited by a specific inducible NO-synthase (iNOS) inhibitor (aminoguanidine), indicating the implication of this receptor in the astrocyte inflammatory reaction. On brain tissues from five out of five patients with HIV-1-related encephalitis, CD23 was expressed by astrocytes and by some Microglial cells, whereas it was not detectable on brain tissue from five of five HIV-1-infected patients without central nervous system (CNS) disease or from two of two control subjects. In addition, CD23 antigen was co-localized with iNOS and nitrotyrosine on brain tissue from patients with HIV1-related encephalitis, suggesting that CD23 participates in iNOS activation of astrocytes in vivo. In conclusion, CD23 ligation is an alternative pathway in the induction of inflammatory product synthesis by astrocytes and participates in CNS inflammation

43. Fischer-Smith T, Croul S, Sverstiuk AE, Capini C, L'Heureux D, Regulier EG, Richardson MW, Amini S, Morgello S, Khalili K, Rappaport J (2001) CNS invasion by CD14+/CD16+ peripheral blood-derived monocytes in HIV dementia: perivascular accumulation and reservoir of HIV infection. J.Neurovirol. 7:528-541
    Abstract: Increases in circulating CD14+/CD16+ monocytes have been associated with HIV dementia; trafficking of these cells into the CNS has been proposed to play an important role in the pathogenesis of HIV-induced neurological disorders. This model suggests that events outside the CNS leading to monocyte activation initiate the process leading to HIV dementia. To investigate the role of this activated monocyte subset in the pathogenesis of HIV dementia, we examined brain specimens from patients with HIV encephalopathy (HIVE), HIV without encephalopathy, and seronegative controls. An accumulation of perivascular macrophages was observed in HIVE. The majority of these cells identified in Microglial nodules and in the perivascular infiltrate were CD14+/CD16+. P24 antigen colocalized with both CD14 and CD16 suggesting that the CD14+/CD16+ macrophage is a major reservoir of HIV-1 infection in CNS. Using CD45/LCA staining, the perivascular macrophage was distinguished from resident Microglia. In addition to perivascular and nodular localizations, CD16 also stained ramified cells throughout the white matter. These cells were more ramified and abundant than cells positive for CD14 in white matter. Double staining for p24 and CD16 suggests that these cells were often infected with HIV-1. The prominent distribution of CD14+ cells in HIVE prompted our analysis of soluble CD14 levels in cerebrospinal fluid. Higher levels of soluble CD14 (sCD14) were observed in patients with moderate-to-severe HIV dementia, suggesting the utility of sCD14 as a surrogate marker. CD14+/CD16+ monocytes may play a role in other neurological disorders and sCD14 may be useful for evaluating these conditions

44. Giralt M, Carrasco J, Penkowa M, Morcillo MA, Santamaria J, Campbell IL, Hidalgo J (2001) Astrocyte-targeted expression of interleukin-3 and interferon-alpha causes region-specific changes in metallothionein expression in the brain. Exp.Neurol. 168:334-346
    Abstract: Transgenic mice expressing IL-3 and IFN-alpha under the regulatory control of the GFAP gene promoter (GFAP-IL3 and GFAP-IFNalpha mice) exhibit a cytokine-specific, late-onset chronic-progressive neurological disorder which resemble many of the features of human diseases such as multiple sclerosis, Aicardi-Goutieres syndrome, and some viral encephalopathies including HIV leukoencephalopathy. In this report we show that the metallothionein-I+II (MT-I+II) isoforms were upregulated in the brain of both GFAP-IL3 and GFAP-IFNalpha mice in accordance with the site and amount of expression of the cytokines. In the GFAP-IL3 mice, in situ hybridization analysis for MT-I RNA and radioimmunoassay results for MT-I+II protein revealed that a significant upregulation was observed in the cerebellum and medulla plus pons at the two ages studied, 1-3 and 6-10 months. Increased MT-I RNA levels occurred in the Purkinje and granular layers of the cerebellum, as well as in its white matter tracts. In contrast to the cerebellum and brain stem, MT-I+II were downregulated by IL-3 in the hippocampus and the remaining brain in the older mice. In situ hybridization for MT-III RNA revealed a modest increase in the cerebellum, which was confirmed by immunohistochemistry. MT-III immunoreactivity was present in cells that were mainly round or amoeboid monocytes/macrophages and in astrocytes. MT-I+II induction was more generalized in the GFAP-IFNalpha (GIFN12 and GIFN39 lines) mice, with significant increases in the cerebellum, thalamus, hippocampus, and cortex. In the high expressor line GIFN39, MT-III RNA levels were significantly increased in the cerebellum (Purkinje, granular, and molecular layers), thalamus, and hippocampus (CA2/CA3 and especially lacunosum molecular layers). Reactive astrocytes, activated rod-like Microglia, and macrophages, but not the perivenular infiltrating cells, were identified as the cellular sources of the MT-I+II and MT-III proteins. The pattern of expression of the different MT isoforms in these transgenic mice differed substantially, demonstrating unique effects associated with the expression of each cytokine. The results indicate that the MT expression in the CNS is significantly affected by the cytokine-induced inflammatory response and support a major role of these proteins during CNS injury

45. Gorry PR, Bristol G, Zack JA, Ritola K, Swanstrom R, Birch CJ, Bell JE, Bannert N, Crawford K, Wang H, Schols D, De Clercq E, Kunstman K, Wolinsky SM, Gabuzda D (2001) Macrophage tropism of human immunodeficiency virus type 1 isolates from brain and lymphoid tissues predicts neurotropism independent of coreceptor specificity. J.Virol. 75:10073-10089
    Abstract: The viral determinants that underlie human immunodeficiency virus type 1 (HIV-1) neurotropism are unknown, due in part to limited studies on viruses isolated from brain. Previous studies suggest that brain-derived viruses are macrophage tropic (M-tropic) and principally use CCR5 for virus entry. To better understand HIV-1 neurotropism, we isolated primary viruses from autopsy brain, cerebral spinal fluid, blood, spleen, and lymph node samples from AIDS patients with dementia and HIV-1 encephalitis. Isolates were characterized to determine coreceptor usage and replication capacity in peripheral blood mononuclear cells (PBMC), monocyte-derived macrophages (MDM), and Microglia. Env V1/V2 and V3 heteroduplex tracking assay and sequence analyses were performed to characterize distinct variants in viral quasispecies. Viruses isolated from brain, which consisted of variants that were distinct from those in lymphoid tissues, used CCR5 (R5), CXCR4 (X4), or both coreceptors (R5X4). Minor usage of CCR2b, CCR3, CCR8, and Apj was also observed. Primary brain and lymphoid isolates that replicated to high levels in MDM showed a similar capacity to replicate in Microglia. Six of 11 R5 isolates that replicated efficiently in PBMC could not replicate in MDM or Microglia due to a block in virus entry. CD4 overexpression in Microglia transduced with retroviral vectors had no effect on the restricted replication of these virus strains. Furthermore, infection of transfected cells expressing different amounts of CD4 or CCR5 with M-tropic and non-M-tropic R5 isolates revealed a similar dependence on CD4 and CCR5 levels for entry, suggesting that the entry block was not due to low levels of either receptor. Studies using TAK-779 and AMD3100 showed that two highly M-tropic isolates entered Microglia primarily via CXCR4. These results suggest that HIV-1 tropism for macrophages and Microglia is restricted at the entry level by a mechanism independent of coreceptor specificity. These findings provide evidence that M-tropism rather than CCR5 usage predicts HIV-1 neurotropism

46. Gray F, Adle-Biassette H, Chretien F, Lorin dlG, Force G, Keohane C (2001) Neuropathology and neurodegeneration in human immunodeficiency virus infection. Pathogenesis of HIV-induced lesions of the brain, correlations with HIV-associated disorders and modifications according to treatments. Clin.Neuropathol. 20:146-155
    Abstract: A variety of HIV-induced lesions of the central nervous system (CNS) have been described, including HIV encephalitis, HIV leukoencephalopathy, axonal damage, and diffuse poliodystrophy with neuronal loss of variable severity resulting, at least partly, from an apoptotic process. However, no correlation could be established between these changes and HIV dementia (HIVD). From our study of HIV infected patients, it appeared that neuronal apoptosis is probably not related to a single cause. Microglial and glial activation, directly or indirectly related to HIV infection, plays a major role in neuronal apoptosis possibly through the mediation of oxidative stress. In our patients with full-blown AIDS, this mechanism predominated in the basal ganglia and correlated well with HIVD. Axonal damage, either secondary to Microglial activation, or to systemic factors also contributes to neuronal apoptosis. Although massive neuronal loss may be responsible for HIVD in occasional cases, we conclude that neuronal apoptosis is a late event and does not represent the main pathological substrate of HIVD. The dementia more likely reflects a specific neuronal dysfunction resulting from the combined effects of several mechanisms, some of which may be reversible. Introduction of highly active antiretroviral therapy dramatically improved patient survival, however, its impact on the incidence and course of HIVD remains debatable. In our series, the incidence of HIVE has dramatically decreased since the introduction of multitherapies, but a number of cases remain whose cognitive disorders persist, despite HAART. The poor CNS penetration of many antiretroviral agents is a possible explanation, but irreversible "burnt out" HIV-induced CNS changes may also be responsible

47. Herzberg U, Sagen J (2001) Peripheral nerve exposure to HIV viral envelope protein gp120 induces neuropathic pain and spinal gliosis. J.Neuroimmunol. 116:29-39
    Abstract: Painful sensory neuropathy is a common and debilitating consequence of human immunodeficiency virus (HIV). The underlying causes of neuropathic pain are most likely not due to direct infection of the nervous system by active virus. The goal of this study was to determine whether epineural exposure to the HIV-1 envelope protein gp120 could lead to chronic painful peripheral neuropathy. Two doses of gp120 or BSA control were transiently delivered epineurally via oxidized cellulose wrapped around the rat sciatic nerve. Animals were assessed for neuropathic pain behaviors at several intervals from 1-30 days following nerve surgery. Allodynia and hyperalgesia were observed within 1-3 days following gp120 and sustained throughout the testing period. The gp120-exposed sciatic nerve exhibited early but transient pathology, notably axonal swelling and increased tumor necrosis factor alpha (TNF-alpha) within the nerve trunk. In contrast, intense astrocytic and Microglial activation was observed in the spinal cord, and this gliosis persisted for at least 30 days following epineural gp120, in parallel with neuropathic pain behaviors. These findings demonstrate that limited peripheral nerve exposure to HIV protein can induce persistent painful sensory neuropathy that may be sustained and magnified by long-term spinal neuropathology

48. Heyes MP, Ellis RJ, Ryan L, Childers ME, Grant I, Wolfson T, Archibald S, Jernigan TL (2001) Elevated cerebrospinal fluid quinolinic acid levels are associated with region-specific cerebral volume loss in HIV infection. Brain 124:1033-1042
    Abstract: Neuronal injury, dendritic loss and brain atrophy are frequent complications of infection with human immunodeficiency virus (HIV) type 1. Activated brain macrophages and Microglia can release quinolinic acid, a neurotoxin and NMDA (N-methyl-D-aspartate) receptor agonist, which we hypothesize contributes to neuronal injury and cerebral volume loss. In the present cross-sectional study of 94 HIV-1-infected patients, elevated CSF quinolinic acid concentrations correlated with worsening brain atrophy, quantified by MRI, in regions vulnerable to excitotoxic injury (the striatum and limbic cortex) but not in regions relatively resistant to excitotoxicity (the non-limbic cortex, thalamus and white matter). Increased CSF quinolinic acid concentrations also correlated with higher CSF HIV-1 RNA levels. In support of the specificity of these associations, blood levels of quinolinic acid were unrelated to striatal and limbic volumes, and CSF levels of beta(2)-microglobulin, a non-specific and non-excitotoxic marker of immune activation, were unrelated to regional brain volume loss. These results are consistent with the hypothesis that quinolinic acid accumulation in brain tissue contributes to atrophy in vulnerable brain regions in HIV infection and that virus replication is a significant driver of local quinolinic acid biosynthesis

49. Kaul M, Garden GA, Lipton SA (2001) Pathways to neuronal injury and apoptosis in HIV-associated dementia. Nature 410:988-994
    Abstract: Human immunodeficiency virus-1 (HIV-1) can induce dementia with alarming occurrence worldwide. The mechanism remains poorly understood, but discovery in brain of HIV-1-binding sites (chemokine receptors) provides new insights. HIV-1 infects macrophages and Microglia, but not neurons, although neurons are injured and die by apoptosis. The predominant pathway to neuronal injury is indirect through release of macrophage, Microglial and astrocyte toxins, although direct injury by viral proteins might also contribute. These toxins overstimulate neurons, resulting in the formation of free radicals and excitotoxicity, similar to other neurodegenerative diseases. Recent advances in understanding the signalling pathways mediating these events offer hope for therapeutic intervention

50. Langford D, Masliah E (2001) Crosstalk between components of the blood brain barrier and cells of the CNS in Microglial activation in AIDS. Brain Pathol. 11:306-312
    Abstract: During the progression of AIDS, a majority of patients develop cognitive disorders such as HIV encephalitis (HIVE) and AIDS dementia complex (ADC), which correlate closely with macrophage infiltration into the brain and Microglial activation. Microglial activation occurs in response to infection, inflammation and neurological disorders including HIVE, Alzheimer's disease, Parkinson's disease and multiple sclerosis. Microglia can be activated by immunoreactive cells independent of, but enhanced by HIV infection, from at least two routes. Activation may occur from signals originating from activated monocytes and lymphocytes in the blood stream, which initiate a cascade of stimuli that ultimately reach Microglia in the brain or from activated macrophages/Microglia/astrocytes within the brain. Effects of Microglial activation stemming from both systemic and CNS HIV infection act together to commence signaling feedback, leading to HIVE and increased neurodegeneration. Most recent data indicate that in AIDS patients, Microglial activation in the brain with subsequent release of excitotoxins, cytokines and chemokines leads to neurodegeneration and cognitive impairment. Since the presence of HIV in the brain results from migration of infected monocytes and lymphocytes across the vascular boundary, the development of novel therapies aimed at protecting the integrity of the blood brain barrier (BBB) upon systemic HIV infection is critical for controlling CNS infection

51. Levin MC, Rosenblum MK, Fox CH, Jacobson S (2001) Localization of retrovirus in the central nervous system of a patient co-infected with HTLV-1 and HIV with HAM/TSP and HIV-associated dementia. J.Neurovirol. 7:61-65
    Abstract: Persons co-infected with HTLV-1 and HIV are at increased risk for neurologic disease. These patients may develop HAM/TSP and/or HIV-associated dementia. In this study, we localized cells infected with retrovirus in the central nervous system (CNS) of a patient with both HAM/TSP and HIV-associated dementia. HTLV-1 was localized to astrocytes and HIV to macrophage/Microglia. There was no co-infection of a single cell phenotype in this patient. These data suggest that mechanisms other than co-infection of the same CNS cell may play a role in the development of neurologic disease in patients dual infected with HTLV-1 and HIV

52. Martin J, LaBranche CC, Gonzalez-Scarano F (2001) Differential CD4/CCR5 utilization, gp120 conformation, and neutralization sensitivity between envelopes from a Microglia-adapted human immunodeficiency virus type 1 and its parental isolate. J.Virol. 75:3568-3580
    Abstract: Human immunodeficiency virus type 1 (HIV-1) infects and induces syncytium formation in Microglial cells from the central nervous system (CNS). A primary isolate (HIV-1(BORI)) was sequentially passaged in cultured Microglia, and the isolate recovered (HIV-1(BORI-15)) showed high levels of fusion and replicated more efficiently in Microglia (J. M. Strizki, A. V. Albright, H. Sheng, M. O'Connor, L. Perrin, and F. Gonzalez-Scarano, J. Virol. 70:7654-7662, 1996). The parent and adapted viruses used CCR5 as coreceptor. Recombinant viruses demonstrated that the syncytium-inducing phenotype was associated with four amino acid differences in the V1/V2 region of the viral gp120 (J. T. C. Shieh, J. Martin, G. Baltuch, M. H. Malim, and F. Gonzalez-Scarano, J. Virol. 74:693-701, 2000). We produced luciferase-reporter, env-pseudotyped viruses using plasmids containing env sequences from HIV-1(BORI), HIV-1(BORI-15), and the V1/V2 region of HIV-1(BORI-15) in the context of HIV-1(BORI) env (named rBORI, rB15, and rV1V2, respectively). The pseudotypes were used to infect cells expressing various amounts of CD4 and CCR5 on the surface. In contrast to the parent recombinant, the rB15 and rV1V2 pseudotypes retained their infectability in cells expressing low levels of CD4 independent of the levels of CCR5, and they infected cells expressing CD4 with a chimeric coreceptor containing the third extracellular loop of CCR2b in the context of CCR5 or a CCR5 Delta4 amino-terminal deletion mutant. The VH-rB15 and VH-rV1V2 recombinant viruses were more sensitive to neutralization by a panel of HIV-positive sera than was VH-rBORI. Interestingly, the CD4-induced 17b epitope on gp120 was more accessible in the rB15 and rV1V2 pseudotypes than in rBORI, even before CD4 binding, and concomitantly, the rB15 and rV1V2 pseudotypes were more sensitive to neutralization with the human 17b monoclonal antibody. Adaptation to growth in Microglia--cells that have reduced expression of CD4 in comparison with other cell types--appears to be associated with changes in gp120 that modify its ability to utilize CD4 and CCR5. Changes in the availability of the 17b epitope indicate that these affect conformation. These results imply that the process of adaptation to certain tissue types such as the CNS directly affects the interaction of HIV-1 envelope glycoproteins with cell surface components and with humoral immune responses

53. Milligan ED, O'Connor KA, Nguyen KT, Armstrong CB, Twining C, Gaykema RP, Holguin A, Martin D, Maier SF, Watkins LR (2001) Intrathecal HIV-1 envelope glycoprotein gp120 induces enhanced pain states mediated by spinal cord proinflammatory cytokines. J.Neurosci. 21:2808-2819
    Abstract: Perispinal (intrathecal) injection of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein gp120 creates exaggerated pain states. Decreases in response thresholds to both heat stimuli (thermal hyperalgesia) and light tactile stimuli (mechanical allodynia) are rapidly induced after gp120 administration. gp120 is the portion of HIV-1 that binds to and activates Microglia and astrocytes. These glial cells have been proposed to be key mediators of gp120-induced hyperalgesia and allodynia because these pain changes are blocked by drugs thought to affect glial function preferentially. The aim of the present series of studies was to determine whether gp120-induced pain changes involve proinflammatory cytokines [interleukin-1beta (IL-1) and tumor necrosis factor-alpha (TNF-alpha)], substances released from activated glia. IL-1 and TNF antagonists each prevented gp120-induced pain changes. Intrathecal gp120 produced time-dependent, site-specific increases in TNF and IL-1 protein release into lumbosacral CSF; parallel cytokine increases in lumbar dorsal spinal cord were also observed. Intrathecal administration of fluorocitrate (a glial metabolic inhibitor), TNF antagonist, and IL-1 antagonist each blocked gp120-induced increases in spinal IL-1 protein. These results support the concept that activated glia in dorsal spinal cord can create exaggerated pain states via the release of proinflammatory cytokines

54. Mitchell W (2001) Neurological and developmental effects of HIV and AIDS in children and adolescents. Ment.Retard.Dev.Disabil.Res.Rev. 7:211-216
    Abstract: HIV-related encephalopathy is an important problem in vertically infected children with HIV. Infected infants may manifest early, catastrophic encephalopathy, with loss of brain growth, motor abnormalities, and cognitive dysfunction. Even without evidence of AIDS, infected infants score lower than serorevertors on developmental measures, particularly language acquisition. Children with perinatal or later transfusion-related infection generally are roughly comparable developmentally to their peers until late in their course. Symptoms similar to adult AIDS dementia complex are occasionally seen in adolescents with advanced AIDS, including dementia, bradykinesia, and spasticity. Opportunistic CNS infections such as toxoplasmosis and progressive multifocal leukoencephalopathy are less common in children and adolescents than in adults. Increasing evidence suggests that aggressive antiretroviral treatment may halt or even reverse encephalopathy. Neuroimaging changes may precede or follow clinical manifestations, and include early lenticulostriate vessel echogenicity on cranial ultrasound, calcifying microangiopathy on CT scan, and/or white matter lesions and central atrophy on MRI. Differential diagnosis of neurological dysfunction in an HIV-infected infant includes the effects of maternal substance abuse, other CNS congenital infections, and other causes of early static encephalopathy. Initial entry of HIV into the nervous system occurs very early in infection. The risk of clinical HIV encephalopathy increases with very early age of infection and with high viral loads. Virus is found in Microglia and brain derived macrophages, not neurons. The neuronal effect of HIV is probably indirect, with various cytokines implicated. Apoptosis is the presumed mechanism of damage to neurons by HIV

55. Mrak RE, Griffinbc WS (2001) The role of activated astrocytes and of the neurotrophic cytokine S100B in the pathogenesis of Alzheimer's disease. Neurobiol.Aging 22:915-922
    Abstract: Activated astrocytes, overexpressing the neurotrophic signaling molecule S100beta, are invariant components of the Abeta plaques of Alzheimer's disease. Even early, nonfibrillar amyloid deposits in Alzheimer's disease contain such astrocytes, and the numbers and degree of activation of these wax and wane with the subsequent neuritic pathology of plaque evolution. Astrocytic overexpression of S100B in the neuritic plaques of Alzheimer's disease correlates with the degree of neuritic pathology in Abeta plaques in this disease, suggesting a pathogenic role for S100B's neurotrophic properties in the evolution of these lesions. Astrocytic overexpression of S100B, in turn, is promoted by high levels of interleukin-1 (IL-1), originating from activated Microglia that are also constant components of Abeta plaques in Alzheimer's disease. Similar patterns of astrocyte activation, S100B overexpression, Microglial activation, and IL-1 overexpression are seen in conditions that confer risk for Alzheimer's disease (aging, head trauma, Down's syndrome), in conditions that predispose to accelerated appearance of Alzheimer-like neuropathologic changes (chronic epilepsy, HIV infection), and in animal models of Alzheimer's disease. These cells and molecules are an important components of a cytokine cycle of molecular and cellular cascades that may drive disease progression in Alzheimer's disease

56. Nebuloni M, Pellegrinelli A, Ferri A, Bonetto S, Boldorini R, Vago L, Grassi MP, Costanzi G (2001) Beta amyloid precursor protein and patterns of HIV p24 immunohistochemistry in different brain areas of AIDS patients. AIDS 15:571-575
    Abstract: OBJECTIVES: To evaluate the correlation between immunohistochemical positive patterns (globular and filamentous structures) of beta-amyloid precursor protein (beta-APP), used as a marker of axonal damage, and the different distribution of HIV p24 antigens, in three different brain areas of AIDS patients. METHODS: Eighteen AIDS patients with HIV-related brain lesions were included in the study. Forty-nine sections from basal ganglia, frontal cortex and hippocampus were selected. After microwave oven pre-treatment, the sections were incubated with anti-HIV p24 and anti-beta-APP monoclonal antibodies; the reactions were developed with peroxidase/3,3'diaminobenzidine. The positivity was graded by semi-quantitative scores. Double immunohistochemical staining was used to evaluate the co-localization of the antigens. RESULTS: HIV p24 immunohistochemistry was positive in 44 of 49 sections (89%), with a prevalence of interstitial positive cells and positive Microglial nodules in 27 and 13 sections respectively. beta-APP-positive structures were demonstrated in 23 of 44 sections (52%) with HIV-related lesions, and were absent from the five sections without viral expression. Globular and filamentous lesions were observed in 21 of 23 sections and 10 of 23 lesions respectively. Moreover, a high grade of globular type lesion was related to an elevated presence of diffuse interstitial HIV p24-positive cells in basal ganglia; double immunohistochemical reactions demonstrated the co-localization of beta-APP globules and HIV p24 antigens. CONCLUSIONS: The data obtained confirm the coexpression of beta-APP and viral antigens in particular areas of the brain with HIV-related lesions; there is a strict correlation between beta-APP globules (indicating chronic cerebral damage) and the interstitial pattern of HIV p24 immunohistochemistry

57. Orenstein JM (2001) The macrophage in HIV infection. Immunobiology 204:598-602
    Abstract: Macrophages play a key role in several critical aspects of HIV disease. They appear to be the first cells infected by HIV and perhaps the very source of HIV production when CD4+ cells are markedly depleted in the patient. Macrophages and Microglial cells are the cells infected by HIV in the CNS. In tonsils and adenoids of HIV-infected patients, macrophages fuse into multinucleated giant cells that produce copious amounts of virus. Finally, opportunistic pathogens can cause an upregulation of HIV production by macrophages, often in the multinucleated form

58. Patrizio M, Colucci M, Levi G (2001) Human immunodeficiency virus type 1 Tat protein decreases cyclic AMP synthesis in rat Microglia cultures. J.Neurochem. 77:399-407
    Abstract: We have studied the modulation of cyclic AMP (cAMP) accumulation by the human immunodeficiency virus type 1 (HIV 1) protein Tat in Microglia and astrocyte cultures obtained from neonatal rat brain. Pretreatment of Microglia with recombinant Tat resulted in a dose- and time-dependent decrease of cAMP accumulation induced by subsequent exposure to isoproterenol (1 microM). The inhibitory action of 100 ng/mL Tat approached 50% after 4 h of preincubation and reached a maximum of 70% after 24 h. The Tat-induced time- and dose-dependent decrease of cAMP accumulation was observed also when Microglial cultures were stimulated with the adenylyl cyclase activator forskolin (100 microM). In both cases, Tat inhibitory action was 70% reverted by a specific monoclonal anti-Tat antibody, but was not prevented either by the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xantine (100 microM) or by a 16-h pretreatment of Microglial cultures with the Gi protein inhibitor pertussis toxin (10 ng/mL). All these results suggested that the viral protein acts at a step of the cAMP transduction pathway other than receptors, G proteins and phosphodiesterases. The target of Tat appeared to be adenylyl cyclase, whose activity was markedly reduced (up to 60%) in membranes prepared from Tat-treated Microglial cells, both in basal conditions and after stimulation with isoproterenol and forskolin. The inability of the competitive inhibitor of nitric oxide synthase N(G)-monometyl- L-arginine (20 and 200 microM) to revert Tat action on forskolin-induced cAMP accumulation, and of two potent nitric oxide donors, PAPA and DETA (0.1-2 m M), to alter forskolin-induced cAMP accumulation, excluded an involvement of nitric oxide in Tat-induced adenylyl cyclase inhibition. On the contrary, two inhibitors of nuclear factor kappaB activation, N-tosyl-( L)-phenylalanine chloromethyl ketone (10 microM) and SN50 (25 microM), markedly prevented the reduction of forskolin-evoked cAMP accumulation by Tat, suggesting a possible role for this nuclear transcriptional factor in the regulation of adenylyl cyclase by Tat in Microglia. This assumption was strengthened by the ability of lipopolysaccharide (100 ng/mL, 4 h) to mimic the inhibitory effect of the viral protein. Conversely, astrocyte cAMP accumulation was unaffected by the viral protein, as tested at various concentrations and time points. Finally, Tat inhibition of Microglial adenylyl cyclase was not due to non-specific cytotoxicity. As cAMP has been reported to exert a neuroprotective role in several in vivo and in vitro models of brain pathologies, and Microglia is believed to mediate Tat-induced neurotoxicity, these results suggest that the ability of Tat to inhibit cAMP synthesis in Microglia may contribute to neuronal degeneration and cell death associated with HIV infection

59. Peterson KE, Robertson SJ, Portis JL, Chesebro B (2001) Differences in cytokine and chemokine responses during neurological disease induced by polytropic murine retroviruses Map to separate regions of the viral envelope gene. J.Virol. 75:2848-2856
    Abstract: Infection of the central nervous system (CNS) by several viruses can lead to upregulation of proinflammatory cytokines and chemokines. In immunocompetent adults, these molecules induce prominent inflammatory infiltrates. However, with immunosuppressive retroviruses, such as human immunodeficiency virus (HIV), little CNS inflammation is observed yet proinflammatory cytokines and chemokines are still upregulated in some patients and may mediate pathogenesis. The present study examined expression of cytokines and chemokines in brain tissue of neonatal mice infected with virulent (Fr98) and avirulent (Fr54) polytropic murine retroviruses. While both viruses infect Microglia and endothelia primarily in the white matter areas of the CNS, only Fr98 induces clinical CNS disease. The pathology consists of gliosis with minimal morphological changes and no inflammation, similar to HIV. In the present experiments, mice infected with Fr98 had increased cerebellar mRNA levels of proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha), TNF-beta, and interleukin-1 alpha and chemokines macrophage inflammatory protein-1 alpha (MIP-1 alpha), MIP-1 beta, monocyte chemoattractant protein 1 (MCP-1), gamma-interferon-inducible protein 10 (IP-10), and RANTES compared to mice infected with Fr54 or mock-infected controls. The increased expression of these genes occurred prior to the development of clinical symptoms, suggesting that these cytokines and chemokines might be involved in induction of neuropathogenesis. Two separate regions of the Fr98 envelope gene are associated with neurovirulence. CNS disease associated with the N-terminal portion of the Fr98 env gene was preceded by upregulation of cytokines and chemokines. In contrast, disease associated with the central region of the Fr98 env gene showed no upregulation of cytokines or chemokines and thus did not require increased expression of these genes for disease induction

60. Petito CK, Roberts B, Cantando JD, Rabinstein A, Duncan R (2001) Hippocampal injury and alterations in neuronal chemokine co-receptor expression in patients with AIDS. J.Neuropathol.Exp.Neurol. 60:377-385
    Abstract: Hippocampal neurons express high levels of HIV chemokine co-receptors, activation of which causes injury or death in vitro. To determine if their in vivo expression correlates with injury, we evaluated neuronal CXCR4 and CCR5 immunoreactivity and reactive gliosis in autopsy hippocampus of 10 control cases, 11 AIDS cases without HIV encephalitis (HIVnE) or opportunistic infections/lymphomas (OI/L), and 11 AIDS cases with HIV encephalitis (HIVE). All groups had higher CXCR4 and CCR5 expression in CA3 and CA4 neurons than CA1 neurons (p < 0.05). HIVE cases had increased neuronal CXCR4 and decreased neu