Role of MIP-1beta and RANTES in HIV-1 infection of microglia: inhibition of infection and induction by IFNbeta

Interferon-β deficiency alters brain response to chronic HIV-1 envelope protein exposure in a transgenic model of NeuroHIV

Human immunodeficiency virus-1 (HIV-1) infects the central nervous system (CNS) and causes HIV-associated neurocognitive disorders (HAND) in about half of the population living with the virus despite combination anti-retroviral therapy (cART). HIV-1 activates the innate immune system, including the production of type 1 interferons (IFNs) α and β. Transgenic mice expressing HIV-1 envelope glycoprotein gp120 (HIVgp120tg) in the CNS develop memory impairment and share key neuropathological features and differential CNS gene expression with HIV patients, including the induction of IFN-stimulated genes (ISG). Here we show that knocking out IFNβ (IFNβKO) in HIVgp120tg and non-tg control mice impairs recognition and spatial memory, but does not affect anxiety-like behavior, locomotion, or vision. The neuropathology of HIVgp120tg mice is only moderately affected by the KO of IFNβ but in a sex-dependent fashion. Notably, in cerebral cortex of IFNβKO animals presynaptic terminals are reduced in males while neuronal dendrites are reduced in females. The IFNβKO results in the hippocampal CA1 region of both male and female HIVgp120tg mice in an ameliorated loss of neuronal presynaptic terminals but no protection of neuronal dendrites. Only female IFNβ-deficient HIVgp120tg mice display diminished microglial activation in cortex and hippocampus and increased astrocytosis in hippocampus compared to their IFNβ-expressing counterparts. RNA expression for some immune genes and ISGs is also affected in a sex-dependent way. The IFNβKO abrogates or diminishes the induction of MX1, DDX58, IRF7 and IRF9 in HIVgp120tg brains of both sexes. Expression analysis of neurotransmission related genes reveals an influence of IFNβ on multiple components with more pronounced changes in IFNβKO females. In contrast, the effects of IFNβKO on MAPK activities are independent of sex with pronounced reduction of active ERK1/2 but also of active p38 in the HIVgp120tg brain. In summary, our findings show that the absence of IFNβ impairs memory dependent behavior and modulates neuropathology in HIVgp120tg brains, indicating that its absence may facilitate development of HAND. Moreover, our data suggests that endogenous IFNβ plays a vital role in maintaining neuronal homeostasis and memory function.

Mechanisms underlying HIV-associated cognitive impairment and emerging therapies for its management

People living with HIV are affected by the chronic consequences of neurocognitive impairment (NCI) despite antiretroviral therapies that suppress viral replication, improve health and extend life. Furthermore, viral suppression does not eliminate the virus, and remaining infected cells may continue to produce viral proteins that trigger neurodegeneration. Comorbidities such as diabetes mellitus are likely to contribute substantially to CNS injury in people living with HIV, and some components of antiretroviral therapy exert undesirable side effects on the nervous system. No treatment for HIV-associated NCI has been approved by the European Medicines Agency or the US Food and Drug Administration. Historically, roadblocks to developing effective treatments have included a limited understanding of the pathophysiology of HIV-associated NCI and heterogeneity in its clinical manifestations. This heterogeneity might reflect multiple underlying causes that differ among individuals, rather than a single unifying neuropathogenesis. Despite these complexities, accelerating discoveries in HIV neuropathogenesis are yielding potentially druggable targets, including excessive immune activation, metabolic alterations culminating in mitochondrial dysfunction, dysregulation of metal ion homeostasis and lysosomal function, and microbiome alterations. In addition to drug treatments, we also highlight the importance of non-pharmacological interventions. By revisiting mechanisms implicated in NCI and potential interventions addressing these mechanisms, we hope to supply reasons for optimism in people living with HIV affected by NCI and their care providers.

Sustained induction of IP-10 by MRP8/14 via the IFNβ-IRF7 axis in macrophages exaggerates lung injury in endotoxemic mice

Background

As a damage-associated molecular pattern, the myeloid-related protein 8/14 (MRP8/14) heterodimer mediates various inflammatory diseases, such as sepsis. However, how MRP8/14 promotes lung injury by regulating the inflammatory response during endotoxemia remains largely unknown. This study aims at illuminating the pathological functions of MRP8/14 in endotoxemia.

Methods

An endotoxemic model was prepared with wild-type and myeloid cell-specific Mrp8 deletion (Mrp8ΔMC) mice for evaluating plasma cytokine levels. Lung injury was evaluated by hematoxylin and eosin (H&E) staining, injury scoring and wet-to-dry weight (W/D) ratio. The dynamic profile of interferon γ (IFNγ)-inducible protein 10 (IP-10) mRNA expression induced by macrophage MRP8/14 was determined by quantitative real-time polymerase chain reaction (qPCR). Immunoblotting was used to evaluate the increase in IP-10 level induced by activation of the JAK-STAT signaling pathway. Luciferase reporter assay was performed to detect the involvement of IRF7 in Ip-10 gene transcription. In vivo air pouch experiments were performed to determine the biological function of IP-10 induced by MRP8/14.

Results

Experiments with Mrp8ΔMC mice showed that MRP8/14 promoted the production of cytokines, including IP-10, in the bronchoalveolar lavage fluid (BALF) and lung injury in endotoxic mice. The result of qPCR showed sustained expression of Ip-10 mRNA in macrophages after treatment with MRP8/14 for 12 h. Neutralization experiments showed that the MRP8/14-induced Ip-10 expression in RAW264.7 cells was mediated by extracellular IFNβ. Western blotting with phosphorylation-specific antibodies showed that the JAK1/TYK2-STAT1 signaling pathway was activated in MRP8/14-treated RAW264.7 cells, leading to the upregulation of Ip-10 gene expression. IRF7 was further identified as a downstream regulator of the JAK-STAT pathway that mediated Ip-10 gene expression in macrophages treated with MRP8/14. In vivo air pouch experiments confirmed that the IFNβ-JAK1/TYK2-STAT1-IRF7 pathway was required for chemokine (C-X-C motif) receptor 3 (CXCR3)+ T lymphocyte migration, which promoted lung injury in the context of endotoxemia.

Conclusions

In summary, our study demonstrates that MRP8/14 induces sustained production of IP-10 via the IFNβ-JAK1/TYK2-STAT1-IRF7 pathway to attract CXCR3+ T lymphocytes into lung tissues and ultimately results in lung injury by an excessive inflammatory response in the context of endotoxemia.

Innate Immune Sensing of Viruses and Its Consequences for the Central Nervous System

Viral infections remain a global public health concern and cause a severe societal and economic burden. At the organismal level, the innate immune system is essential for the detection of viruses and constitutes the first line of defense. Viral components are sensed by host pattern recognition receptors (PRRs). PRRs can be further classified based on their localization into Toll-like receptors (TLRs), C-type lectin receptors (CLR), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), NOD-like receptors (NLRs) and cytosolic DNA sensors (CDS). TLR and RLR signaling results in production of type I interferons (IFNα and -β) and pro-inflammatory cytokines in a cell-specific manner, whereas NLR signaling leads to the production of interleukin-1 family proteins. On the other hand, CLRs are capable of sensing glycans present in viral pathogens, which can induce phagocytic, endocytic, antimicrobial, and pro- inflammatory responses. Peripheral immune sensing of viruses and the ensuing cytokine response can significantly affect the central nervous system (CNS). But viruses can also directly enter the CNS via a multitude of routes, such as the nasal epithelium, along nerve fibers connecting to the periphery and as cargo of infiltrating infected cells passing through the blood brain barrier, triggering innate immune sensing and cytokine responses directly in the CNS. Here, we review mechanisms of viral immune sensing and currently recognized consequences for the CNS of innate immune responses to viruses.

Lipocalin-2 mediates HIV-1 induced neuronal injury and behavioral deficits by overriding CCR5-dependent protection

People living with HIV (PLWH) continue to develop HIV-associated neurocognitive disorders despite combination anti-retroviral therapy. Lipocalin-2 (LCN2) is an acute phase protein that has been implicated in neurodegeneration and is upregulated in a transgenic mouse model of HIV-associated brain injury. Here we show that LCN2 is significantly upregulated in neocortex of a subset of HIV-infected individuals with brain pathology and correlates with viral load in CSF and pro-viral DNA in neocortex. However, the question if LCN2 contributes to HIV-associated neurotoxicity or is part of a protective host response required further investigation. We found that the knockout of LCN2 in transgenic mice expressing HIVgp120 in the brain (HIVgp120tg) abrogates behavioral impairment, ameliorates neuronal damage, and reduces microglial activation in association with an increase of the neuroprotective CCR5 ligand CCL4. In vitro experiments show that LCN2 neurotoxicity also depends on microglia and p38 MAPK activity. Genetic ablation of CCR5 in LCN2-deficient HIVgp120tg mice restores neuropathology, suggesting that LCN2 overrides neuroprotection mediated by CCR5 and its chemokine ligands. RNA expression of 168 genes involved in neurotransmission reveals that neuronal injury and protection are each associated with genotype- and sex-specific patterns affecting common neural gene networks. In conclusion, our study identifies LCN2 as a novel factor in HIV-associated brain injury involving CCR5, p38 MAPK and microglia. Furthermore, the mechanistic interaction between LCN2 and CCR5 may serve as a diagnostic and therapeutic target in HIV patients at risk of developing brain pathology and neurocognitive impairment.

A pivotal role for Interferon-α receptor-1 in neuronal injury induced by HIV-1

BACKGROUND

HIV-1 infection remains a major public health concern despite effective combination antiretroviral therapy (cART). The virus enters the central nervous system (CNS) early in infection and continues to cause HIV-associated neurocognitive disorders (HAND). The pathogenic mechanisms of HIV-associated brain injury remain incompletely understood. Since HIV-1 activates the type I interferon system, which signals via interferon-α receptor (IFNAR) 1 and 2, this study investigated the potential role of IFNAR1 in HIV-induced neurotoxicity.

METHODS

We cross-bred HIVgp120-transgenic (tg) and IFNAR1 knockout (IFNAR1KO) mice. At 11-14 months of age, we performed a behavioral assessment and subsequently analyzed neuropathological alterations using deconvolution and quantitative immunofluorescence microscopy, quantitative RT-PCR, and bioinformatics. Western blotting of brain lysates and an in vitro neurotoxicity assay were employed for analysis of cellular signaling pathways.

RESULTS

We show that IFNAR1KO results in partial, sex-dependent protection from neuronal injury and behavioral deficits in a transgenic model of HIV-induced brain injury. The IFNAR1KO rescues spatial memory and ameliorates loss of presynaptic terminals preferentially in female HIVgp120tg mice. Similarly, expression of genes involved in neurotransmission reveals sex-dependent effects of IFNAR1KO and HIVgp120. In contrast, IFNAR1-deficiency, independent of sex, limits damage to neuronal dendrites, microgliosis, and activation of p38 MAPK and restores ERK activity in the HIVgp120tg brain. In vitro, inhibition of p38 MAPK abrogates neurotoxicity caused similarly by blockade of ERK kinase and HIVgp120.

CONCLUSION

Our findings indicate that IFNAR1 plays a pivotal role in both sex-dependent and independent processes of neuronal injury and behavioral impairment triggered by HIV-1.

Potential pharmacological approaches for the treatment of HIV-1 associated neurocognitive disorders

HIV associated neurocognitive disorders (HAND) are the spectrum of cognitive impairments present in patients infected with human immunodeficiency virus type 1 (HIV-1). The number of patients affected with HAND ranges from 30 to 50% of HIV infected individuals and although the development of combinational antiretroviral therapy (cART) has improved longevity, HAND continues to pose a significant clinical problem as the current standard of care does not alleviate or prevent HAND symptoms. At present, the pathological mechanisms contributing to HAND remain unclear, but evidence suggests that it stems from neuronal injury due to chronic release of neurotoxins, chemokines, viral proteins, and proinflammatory cytokines secreted by HIV-1 activated microglia, macrophages and astrocytes in the central nervous system (CNS). Furthermore, the blood-brain barrier (BBB) not only serves as a route for HIV-1 entry into the brain but also prevents cART therapy from reaching HIV-1 brain reservoirs, and therefore could play an important role in HAND. The goal of this review is to discuss the current data on the epidemiology, pathology and research models of HAND as well as address the potential pharmacological treatment approaches that are being investigated.

Type I Interferons in NeuroHIV

Infection with Human Immunodeficiency Virus (HIV)-1 continues to cause HIV-associated neurocognitive disorders despite combined antiretroviral therapy. Interferons (IFNs) are important for any antiviral immune response, but the lasting production of IFNα causes exhaustive activation leading eventually to progression to AIDS. Expression of IFNα in the HIV-exposed central nervous system has been linked to cognitive impairment and inflammatory neuropathology. In contrast, IFNβ exerts anti-inflammatory effects, appears to control, at least temporarily, lentiviral infection in the brain and provides neuroprotection. The dichotomy of type I IFN effects on HIV-1 infection and the associated brain injury will be discussed in this review, because the underlying mechanisms require further investigation to allow harnessing these innate immune factors for therapeutic purposes.

Brain Cell Type Specific Gene Expression and Co-expression Network Architectures

Elucidating brain cell type specific gene expression patterns is critical towards a better understanding of how cell-cell communications may influence brain functions and dysfunctions. We set out to compare and contrast five human and murine cell type-specific transcriptome-wide RNA expression data sets that were generated within the past several years. We defined three measures of brain cell type-relative expression including specificity, enrichment, and absolute expression and identified corresponding consensus brain cell “signatures,” which were well conserved across data sets. We validated that the relative expression of top cell type markers are associated with proxies for cell type proportions in bulk RNA expression data from postmortem human brain samples. We further validated novel marker genes using an orthogonal ATAC-seq dataset. We performed multiscale coexpression network analysis of the single cell data sets and identified robust cell-specific gene modules. To facilitate the use of the cell type-specific genes for cell type proportion estimation and deconvolution from bulk brain gene expression data, we developed an R package, BRETIGEA. In summary, we identified a set of novel brain cell consensus signatures and robust networks from the integration of multiple datasets and therefore transcend limitations related to technical issues characteristic of each individual study.

Effects of Post-Treatment Hydrogen Gas Inhalation on Uveitis Induced by Endotoxin in Rats

Background

Molecular hydrogen (H₂) has been widely reported to have benefiicial effects in diverse animal models and human disease through reduction of oxidative stress and inflammation. The aim of this study was to investigate whether hydrogen gas could ameliorate endotoxin-induced uveitis (EIU) in rats.

Material/Methods

Male Sprague-Dawley rats were divided into a normal group, a model group, a nitrogen-oxygen (N-O) group, and a hydrogen-oxygen (H-O) group. EIU was induced in rats of the latter 3 groups by injection of lipopolysaccharide (LPS). After that, rats in the N-O group inhaled a gas mixture of 67% N₂ and 33% O₂, while those in the H-O group inhaled a gas mixture of 67% H₂ and 33% O₂. All rats were graded according to the signs of uveitis after electroretinography (ERG) examination. Protein concentration in the aqueous humor (AqH) was measured. Furthermore, hematoxylin-eosin staining and immunostaining of anti-ionized calcium-binding adapter molecule 1 (Iba1) in the iris and ciliary body (ICB) were carried out.

Results

No statistically significant differences existed in the graded score of uveitis and the b-wave peak time in the Dark-adapted 3.0 ERG among the model, N-O, and H-O groups (P>0.05), while rats of the H-O group showed a lower concentration of AqH protein than that of the model or N-O group (P<0.05). The number of the infiltrating cells in the ICB of rats from the H-O group was not significantly different from that of the model or N-O group (P>0.05), while the activation of microglia cells in the H-O group was somewhat reduced (P<0.05).

Conclusions

Post-treatment hydrogen gas inhalation did not ameliorate the clinical signs, or reduce the infiltrating cells of EIU. However, it inhibited the elevation of protein in the AqH and reduced the microglia activation.

Transgenic mice expressing HIV-1 envelope protein gp120 in the brain as an animal model in neuroAIDS research

HIV-1 infection causes injury to the central nervous system (CNS) and is often associated with neurocognitive disorders. One model for brain damage seen in AIDS patients is the transgenic (tg) mouse expressing a soluble envelope protein gp120 of HIV-1 LAV in the brain in astrocytes under the control of the promoter of glial fibrillary acidic protein. These GFAP-gp120tg mice manifest several key neuropathological features observed in AIDS brains, such as decreased synaptic and dendritic density, increased numbers of activated microglia, and pronounced astrocytosis. Several recent studies show that brains of GFAP-gp120tg mice and neurocognitively impaired HIV patients share also a significant number of differentially regulated genes, activation of innate immunity and other cellular signaling pathways, disturbed neurogenesis, and learning deficits. These findings support the continued relevance of the GFAP-gp120tg mouse as a useful model to investigate neurodegenerative mechanisms and develop therapeutic strategies to mitigate the consequences associated with HIV infection of the CNS, neuroAIDS, and HAND.

IFNβ Protects Neurons from Damage in a Murine Model of HIV-1 Associated Brain Injury

Infection with human immunodeficiency virus-1 (HIV-1) causes brain injury. Type I interferons (IFNα/β) are critical mediators of any anti-viral immune response and IFNβ has been implicated in the temporary control of lentiviral infection in the brain. Here we show that transgenic mice expressing HIV-1 envelope glycoprotein 120 in their central nervous system (HIVgp120tg) mount a transient IFNβ response and provide evidence that IFNβ confers neuronal protection against HIVgp120 toxicity. In cerebrocortical cell cultures, neuroprotection by IFNβ against gp120 toxicity is dependent on IFNα receptor 1 (IFNAR1) and the β-chemokine CCL4, as IFNAR1 deficiency and neutralizing antibodies against CCL4, respectively, abolish the neuroprotective effects. We find in vivo that IFNβ mRNA is significantly increased in HIVgp120tg brains at 1.5, but not 3 or 6 months of age. However, a four-week intranasal IFNβ treatment of HIVgp120tg mice starting at 3.5 months of age increases expression of CCL4 and concomitantly protects neuronal dendrites and pre-synaptic terminals in cortex and hippocampus from gp120-induced damage. Moreover, in vivo and in vitro data suggests astrocytes are a major source of IFNβ-induced CCL4. Altogether, our results suggest exogenous IFNβ as a neuroprotective factor that has potential to ameliorate in vivo HIVgp120-induced brain injury.

Targeting TNF and TNF Receptor Pathway in HIV-1 Infection: from Immune Activation to Viral Reservoirs

Several cellular functions such as apoptosis, cellular proliferation, inflammation, and immune regulation involve the tumor necrosis factor-α (TNF)/TNF receptor (TNFR) pathway. Human immunodeficiency virus 1 (HIV-1) interacts with the TNF/TNFR pathway. The activation of the TNF/TNFR pathway impacts HIV-1 replication, and the TNF/TNFR pathway is the target of HIV-1 proteins. A hallmark of HIV-1 infection is immune activation and inflammation with increased levels of TNF in the plasma and the tissues. Therefore, the control of the TNF/TNFR pathway by new therapeutic approaches could participate in the control of immune activation and impact both viral replication and viral persistence. In this review, we will describe the intricate interplay between HIV-1 proteins and TNF/TNFR signaling and how TNF/TNFR activation modulates HIV-1 replication and discuss new therapeutic approaches, especially anti-TNF therapy, that could control this pathway and ultimately favor the clearance of infected cells to cure HIV-infected patients.

Modeling the Effects of Morphine on Simian Immunodeficiency Virus Dynamics

Complications of HIV-1 infection in individuals who utilize drugs of abuse is a significant problem, because these drugs have been associated with higher virus replication and accelerated disease progression as well as severe neuropathogenesis. To gain further insight it is important to quantify the effects of drugs of abuse on HIV-1 infection dynamics. Here, we develop a mathematical model that incorporates experimentally observed effects of morphine on inducing HIV-1 co-receptor expression. For comparison we also considered viral dynamic models with cytolytic or noncytolytic effector cell responses. Based on the small sample size Akaike information criterion, these models were inferior to the new model based on changes in co-receptor expression. The model with morphine affecting co-receptor expression agrees well with the experimental data from simian immunodeficiency virus infections in morphine-addicted macaques. Our results show that morphine promotes a target cell subpopulation switch from a lower level of susceptibility to a state that is about 2-orders of magnitude higher in susceptibility to SIV infection. As a result, the proportion of target cells with higher susceptibility remains extremely high in morphine conditioning. Such a morphine-induced population switch not only has adverse effects on the replication rate, but also results in a higher steady state viral load and larger CD4 count drops. Moreover, morphine conditioning may pose extra obstacles to controlling viral load during antiretroviral therapy, such as pre-exposure prophylaxis and post infection treatments. This study provides, for the first time, a viral dynamics model, viral dynamics parameters, and related analytical and simulation results for SIV dynamics under drugs of abuse.

Human astrocytes: secretome profiles of cytokines and chemokines

Astrocytes play a key role in maintenance of neuronal functions in the central nervous system by producing various cytokines, chemokines, and growth factors, which act as a molecular coordinator of neuron-glia communication. At the site of neuroinflammation, astrocyte-derived cytokines and chemokines play both neuroprotective and neurotoxic roles in brain lesions of human neurological diseases. At present, the comprehensive profile of human astrocyte-derived cytokines and chemokines during inflammation remains to be fully characterized. We investigated the cytokine secretome profile of highly purified human astrocytes by using a protein microarray. Non-stimulated human astrocytes in culture expressed eight cytokines, including G-CSF, GM-CSF, GROα (CXCL1), IL-6, IL-8 (CXCL8), MCP-1 (CCL2), MIF and Serpin E1. Following stimulation with IL-1β and TNF-α, activated astrocytes newly produced IL-1β, IL-1ra, TNF-α, IP-10 (CXCL10), MIP-1α (CCL3) and RANTES (CCL5), in addition to the induction of sICAM-1 and complement component 5. Database search indicated that most of cytokines and chemokines produced by non-stimulated and activated astrocytes are direct targets of the transcription factor NF-kB. These results indicated that cultured human astrocytes express a distinct set of NF-kB-target cytokines and chemokines in resting and activated conditions, suggesting that the NF-kB signaling pathway differentially regulates gene expression of cytokines and chemokines in human astrocytes under physiological and inflammatory conditions.

TNF and TNF receptor superfamily members in HIV infection: new cellular targets for therapy?

Tumor necrosis factor (TNF) and TNF receptors (TNFR) superfamily members are engaged in diverse cellular phenomena such as cellular proliferation, morphogenesis, apoptosis, inflammation, and immune regulation. Their role in regulating viral infections has been well documented. Viruses have evolved with numerous strategies to interfere with TNF-mediated signaling indicating the importance of TNF and TNFR superfamily in viral pathogenesis. Recent research reports suggest that TNF and TNFRs play an important role in the pathogenesis of HIV. TNFR signaling modulates HIV replication and HIV proteins interfere with TNF/TNFR pathways. Since immune activation and inflammation are the hallmark of HIV infection, the use of TNF inhibitors can have significant impact on HIV disease progression. In this review, we will describe how HIV infection is modulated by signaling mediated through members of TNF and TNFR superfamily and in turn how these latter could be targeted by HIV proteins. Finally, we will discuss the emerging therapeutics options based on modulation of TNF activity that could ultimately lead to the cure of HIV-infected patients.

Initial immunopathogenesis of multiple sclerosis: innate immune response

Multiple sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system. The hallmark to MS is the demyelinated plaque, which consists of a well-demarcated hypocellular area characterized by the loss of myelin, the formation of astrocytic scars, and the mononuclear cell infiltrates concentrated in perivascular spaces composed of T cells, B lymphocytes, plasma cells, and macrophages. Activation of resident cells initiates an inflammatory cascade, leading to tissue destruction, demyelination, and neurological deficit. The immunological phenomena that lead to the activation of autoreactive T cells to myelin sheath components are the result of multiple and complex interactions between environment and genetic background conferring individual susceptibility. Within the CNS, an increase of TLR expression during MS is observed, even in the absence of any apparent microbial involvement. In the present review, we focus on the role of the innate immune system, the first line of defense of the organism, as promoter and mediator of cross reactions that generate molecular mimicry triggering the inflammatory response through an adaptive cytotoxic response in MS.

Impact of highly active antiretroviral treatment on expression of HIV-1 coreceptors and ligand levels in peripheral blood from HIV-1 infected patients in China

OBJECTIVE

Coreceptors are important for HIV-1 entry into target cells and disease progression. The impact of HIV-1 and highly active antiretroviral treatment (HAART) on coreceptor expression has been little studied.

METHODS

Expression of C-C chemokine receptor (CCR) 5 and C-X-C chemokine receptor (CXCR) 4 on CD4+ and CD8 + T cells was compared in HIV-1-infected individuals who had/had not received HAART, and in healthy controls. Relationships between coreceptors and their chemokine ligands were studied.

RESULTS

This study included 23 controls and 88 HIV-1-infected individuals, 35 of whom were HAART naïve. Percentages of CCR5 and CXCR4+ CD8 + T cells were higher, and CXCR4+ CD4 + T cells were lower, in patients than in controls. Patients receiving HAART showed a higher percentage of CCR5 expression on CD4 + T cells compared with HAART-naïve patients. HIV-infected individuals had significantly increased levels of peripheral ligands for coreceptors, compared with controls; levels were significantly higher in those receiving HAART compared with the HAART-naïve.

CONCLUSIONS

HIV-1 infection increases coreceptor expression on T cells; HAART increases CCR5 expression further and decreases CXCR4 expression, reversing the switch from CCR5 to CXCR4, which was significant for CD4 + T.

Increased levels of circulating cytokines with HIV-related immunosuppression

Cytokines may contribute to the severity of CD4 cell depletion with human immunodeficiency virus (HIV) infection, but quantitative relationships are not well defined. Serum and plasma from 181 HIV-infected individuals were tested with Millipore 30-plex Luminex cytokine assays. Within-individual correlations among cytokines were summarized by two-dimensional hierarchical cluster analysis. Associations with age, sex, race, CD4 count, and HIV viral load were determined with linear regression models. Tests for statistical significance were corrected for multiple comparisons, using a false discovery rate of 0.1. African-Americans had significantly higher levels than whites of six cytokines (IL-2, IL-5, IL-7, IL-15, fractalkine, and IFN-γ), and lower levels of MCP-1. Females had higher fractalkine levels than males. Age was not associated with levels of any cytokine. Six cytokines, including the T-helper (Th) type 1 cytokine IL-15, the Th2 cytokines IL-1ra and IL-10, the chemokines fractalkine and MCP-1, and the growth factor G-CSF were each inversely associated with CD4 count; no cytokine was directly associated with CD4 count. Fractalkine was directly associated with HIV viral load, adjusted for CD4 count. Cytokines clustered by primary function (e.g., Th1, Th2, proinflammatory, chemokines, or growth factors) whereas individuals clustered according to cytokine levels (generally high, intermediate, or low) had significantly different CD4 counts [medians (interquartile range) of 60 (17-162), 131 (62-321), and 155 (44-467), respectively; p<0.0001]. CD4 deficiency is associated with generalized increases in cytokines of various functions. Racial differences in cytokine response to HIV infection could contribute to disparities in disease progression.

Interactive Effects of Morphine on HIV Infection: Role in HIV-Associated Neurocognitive Disorder

HIV epidemic continues to be a severe public health problem and concern within USA and across the globe with about 33 million people infected with HIV. The frequency of drug abuse among HIV infected patients is rapidly increasing and is another major issue since injection drug users are at a greater risk of developing HIV associated neurocognitive dysfunctions compared to non-drug users infected with HIV. Brain is a major target for many of the recreational drugs and HIV. Evidences suggest that opiate drug abuse is a risk factor in HIV infection, neural dysfunction and progression to AIDS. The information available on the role of morphine as a cofactor in the neuropathogenesis of HIV is scanty. This review summarizes the results that help in understanding the role of morphine use in HIV infection and neural dysfunction. Studies show that morphine enhances HIV-1 infection by suppressing IL-8, downregulating chemokines with reciprocal upregulation of HIV coreceptors. Morphine also activates MAPK signaling and downregulates cAMP response element-binding protein (CREB). Better understanding on the role of morphine in HIV infection and mechanisms through which morphine mediates its effects may help in devising novel therapeutic strategies against HIV-1 infection in opiate using HIV-infected population.

Activation of p38 MAPK is required in monocytic and neuronal cells for HIV glycoprotein 120-induced neurotoxicity

HIV-1 envelope protein gp120 has been implicated in neurotoxin production by monocytic cells (i.e., macrophages and microglia), as well as in the pathogenesis of HIV-1-associated neurocognitive disorders. We previously showed in cerebrocortical cell cultures from rodents containing microglia, astrocytes, and neurons that overall inhibition of p38 MAPK signaling abrogated the neurotoxic effect of HIV-1 gp120. However, the time course of p38 MAPK activation and the contribution of this kinase in the various cell types remained unknown. In this study, we found that active p38 MAPK is required in monocytic lineage cells (i.e., macrophages and microglia) and neuronal cells for HIV gp120-induced neurotoxicity to occur. In cerebrocortical cell cultures, HIV-1 gp120 stimulated a time-dependent overall increase in active p38 MAPK, and the activated kinase was primarily detected in microglia and neurons. Interestingly, increased activation of p38 MAPK and neuronal death in response to gp120 were prevented by prior depletion of microglia or the presence of CCR5 ligand CCL4 or p38 MAPK inhibitors. In human monocytic THP-1 cells and primary monocyte-derived macrophages, HIV gp120-stimulated production of neurotoxins was abrogated by prior introduction into the cells of a dominant-negative p38 MAPK mutant or p38 MAPK small interfering RNA. In addition, the neurotoxic effects of cell-free supernatants from gp120-stimulated monocytic THP-1 cells were prevented in microglia-depleted cerebrocortical cells pretreated with a pharmacological inhibitor of p38 MAPK. Thus, p38 MAPK signaling was critical, upon exposure to HIV gp120, for the neurotoxic phenotype of monocytic cells and subsequent toxin-initiated neuronal apoptosis.

Plasmacytoid dendritic cells in multiple sclerosis: chemokine and chemokine receptor modulation by interferon-beta

Plasmacytoid dendritic cells (pDCs) are present in peripheral blood, leptomeninges and demyelinating lesions in patients with multiple sclerosis (MS). The ability of pDCs to produce chemokines and express the chemokine receptor CCR7 in MS is not known. We studied pDCs in MS patients and healthy subjects. The ability of pDCs to up-regulate CCR7 was significantly increased in untreated MS patients as compared to healthy subjects. IFN-beta treatment significantly inhibited TLR9 agonist-specific secretion of chemokines, which are ligands for CCR5-positive Th1 cells (CCL3, CCL4, and CCL5), and impaired TLR9 agonist-induced up-regulation of CCR7 and IFN-alpha in MS patients. This finding represents a new immunomodulatory effect of IFN-beta in patients with multiple sclerosis.

HIV-1 associated dementia: update on pathological mechanisms and therapeutic approaches

PURPOSE OF REVIEW

Infection with HIV-1 can induce dementia despite successful administration of life-prolonging highly active antiretroviral therapy. This review will discuss recent progress toward a better understanding of the pathogenesis and an improved design of therapies for HIV-associated neurocognitive disorders.

RECENT FINDINGS

Highly active antiretroviral therapy prolongs the lives of HIV patients, but the incidence of HIV-associated dementia as an AIDS-defining illness has increased and the brain is now recognized as a viral sanctuary that requires additional therapeutic effort. The neuropathology of HIV infection also has changed due to improved therapy, and while more similarities with other neurodegenerative diseases are being reported, predictive biomarkers remain elusive. However, improvements of in-vivo imaging technology and progress in uncovering the molecular mechanisms of HIV disease keep providing new insights. As such it appears that a prolonged activation of the immune system by HIV eventually leads to AIDS, and several lines of evidence indicate that simultaneously neurotoxic processes and impairment of neurogenesis both contribute to the development of HIV-associated neurocognitive disorders.

SUMMARY

The improved understanding of the interaction between HIV and its human host provides hope that adjunctive therapies to antiretroviral treatment can be developed for HIV-associated neurocognitive disorders.

CCL5/RANTES gene deletion attenuates opioid-induced increases in glial CCL2/MCP-1 immunoreactivity and activation in HIV-1 Tat-exposed mice

To assess the role of CC-chemokine ligand 5 (CCL5)/RANTES in opiate drug abuse and human immunodeficiency virus type 1 (HIV-1) comorbidity, the effects of systemic morphine and intrastriatal HIV-1 Tat on macrophage/microglial and astroglial activation were assessed in wild-type and CCL5 knockout mice. Mice were injected intrastriatally with vehicle or Tat and assessed after 7 days. Morphine was administered to some Tat-injected mice via time-release implant (5 mg/day, s.c. for 5 days) starting at 2 days post injection. Glial activation was significantly reduced in CCL5(-/-) compared to wild-type mice at 7 days following combined Tat and morphine exposure. Moreover, the percentage of 3-nitrotyrosine immunopositive macrophages/microglia was markedly reduced in CCL5(-/-) mice injected with Tat +/- morphine compared to wild-type counterparts, suggesting that CCL5 contributes to nitrosative stress in HIV-1 encephalitis. In CCL5(-/-) mice, the reductions in Tat +/- morphine-induced gliosis coincided with significant declines in the proportion of CCL2/MCP-1-immunoreactive astrocytes and macrophages/microglia compared to wild-type counterparts. In knockout mice, neither Tat alone nor in combination with morphine increased the proportion of CCL2-immunoreactive astrocytes above percentages seen in vehicle-injected controls. Macrophages/microglia differed showing modest, albeit significant, increases in the proportion of CCL2-positive cells with combined Tat and morphine exposure, suggesting that CCL5 preferentially affects CCL2 expression by astroglia. Thus, CCL5 mediates glial activation caused by Tat and morphine, thereby aggravating HIV-1 neuropathogenesis in opiate abusers and non-abusers. CCL5 is implicated as mediating the cytokine-driven amplification of CCL2 production by astrocytes and resultant macrophage/microglial recruitment and activation.

Human immunodeficiency virus infection inhibits granulocyte-macrophage colony-stimulating factor-induced microglial proliferation

It is well known that infection by the human immunodeficiency virus (HIV) dysregulates cell physiology, but little information is available on the consequences of HIV infection in primary macrophages and microglia. The authors examined the relationship between cell proliferation and HIV infection in primary cultures of microglia and in human central nervous system (CNS). In cultures infected with HIV (ADA and BaL), granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated cell proliferation was reduced in productively infected (p24+) cells as compared to p24- cells. The reduction was observed with both Ki67 and BrdU labeling, suggesting a G1/S block. The reduction was insignificant when microglia were infected with a Vpr- mutant virus. In human CNS, proliferating (Ki67+) cells were rare but were increased in the HIV+ and HIV encephalitis (HIVE) groups compared to the HIV- group. A positive correlation between GM-CSF immunoreactivity and Ki67 counts, implicating GM-CSF as a growth factor in human CNS was found. The relationship between total macrophage (CD68+) proliferation and infected macrophage (p24+) proliferation was assessed in HIVE by double labeling. Whereas 1.2% of total CD68+ cells were Ki67+, only 0.5% of HIV p24+ cells were Ki67+ (P < .05). Furthermore, staining for CD45RB (as opposed to CD68) facilitated the identification of Ki67+ microglia, indicating that CD68 could underestimate proliferating microglia. The authors conclude that although there is increased expression of GM-CSF and increased cell proliferation in the CNS of HIV-seropositive individuals, cell proliferation in the productively infected population is actually suppressed. These data suggest that there might be a viral gain in the suppressed host cell proliferation.

Human mesenchymal stem cells constitutively express chemokines and chemokine receptors that can be upregulated by cytokines, IFN-beta, and Copaxone

The factors associated with the migration of marrow-derived mesenchymal stem cells (MSCs) when transplanted into the diseased central nervous system (CNS) are unclear. Chemokines are key mediators of selective cell migration in neurodegenerative diseases and related inflammatory processes. We hypothesized that chemokines are likely to be the chief determinants of MSC migration. We, therefore, systematically assessed the expression and modulating factors for chemokines and chemokine receptors in human MSCs (HuMSCs). The present study demonstrates that unstimulated HuMSCs express a broad range of mRNAs encoding cytokines, chemokines, and their receptors. Using chemotaxis assays, we also assessed the functionality of the receptor expression in HuMSC and we show that CXCL12/stromal cell-derived factor-lalpha (SDF-lalpha), CX3CL1/fractalkine, and CXCL10/interferon-gamma (IFN-gamma)-inducible protein (IP-10) lead to significant HuMSC migration. Moreover, we provide evidence that tumor necrosis factor-alpha (TNF-alpha) and IFN-gamma act as major regulators of the expression of chemokines and their receptors in HuMSCs. Correspondingly, we demonstrate for the first time that current multiple sclerosis (MS) therapies, namely, IFN-beta and Copaxone, influence the expression of chemokines and their receptors in HuMSCs at both mRNA and protein levels. Administration of cytokines, including IFN-beta and Copaxone, may be important in stem cell transplantation therapies and perhaps important in the efficacy of existing MS therapies.

Anti-CD45RO suppresses human immunodeficiency virus type 1 replication in microglia: role of Hck tyrosine kinase and implications for AIDS dementia

Macrophages and microglia are productively infected by HIV-1 and play a pivotal role in the pathogenesis of AIDS dementia. Although macrophages and microglia express CD45, a transmembrane protein tyrosine phosphatase, whether modulation of its activity affects human immunodeficiency virus type 1 (HIV-1) replication is unknown. Here, we report that of the five human CD45 isoforms, microglia express CD45RB and CD45RO (RB > RO) and treatment of microglia with a CD45 agonist antibody alphaCD45RO (UCHL-1) inhibits HIV-1 replication. alphaCD45RO prevented HIV-1 negative factor (Nef)-induced autophosphorylation of hematopoietic cell kinase (Hck), a myeloid lineage-specific Src kinase. Recombinant CD45 protein also inhibited HIV-1-induced Hck phosphorylation in microglia. Antennapedia-mediated delivery of Hck Src homology domain 3 (SH3), a domain that binds to the Nef PxxP motif with high affinity, reduced HIV-1-induced Hck phosphorylation and HIV-1 production in microglia. HIV-1-induced LTR transactivation was observed in U38 cells stably overexpressing wild-type Hck but not kinase-inactive Hck. In microglia, alphaCD45RO reduced activation of transcription factors (NF-kappaB and CCAAT enhancer binding protein) necessary for LTR transactivation in macrophages. These results establish that in myeloid lineage cells, Nef interacts with the Hck SH3 domain, resulting in autophosphorylation of Hck and an increase in HIV-1 transcription. alphaCD45RO-mediated inhibition of HIV-1 replication in microglia identifies the CD45 protein tyrosine phosphatase as a potential therapeutic target for HIV-1 infection/AIDS dementia.

Interferon-β Is a Potent Inducer of Interferon Regulatory Factor-1/2-Dependent IP-10/CXCL10 Expression in Primary Human Endothelial Cells

Most virus-infected cells release interferon-beta (IFN-beta) as a powerful inducer of antiviral defense. Endothelial cells tightly regulate local immune cell recruitment by expression of adhesion molecules and chemokines. Here, we studied the transcriptional regulation of IFN-beta-induced chemokine expression in primary human endothelial cells. IFN-beta moderately increased monocyte chemoattractant protein-1/CCL2 and potently raised IFN-gamma-inducible protein-10/CXCL10 mRNA steady-state levels and protein release, while no effect was detected on various other chemokines. As shown by transient transfections, induction of CXCL10 expression depends on an IFN-stimulated response element (ISRE) within the CXCL10 promoter. A double point mutation of the putative IFN regulatory factor (IRF)-1/2 binding site within this ISRE motif abolished IFN-beta-induced promoter activity. In electrophoretic mobility shift assays, this ISRE motif showed a basal IRF-2 and an IFN-beta-inducible IRF-1 and augmented IRF-2 binding. Furthermore, stimulation with IFN-beta induced a rapid nuclear translocation of signal transducer and activator of transcription 1 (STAT1) and STAT2 and their transient binding to a gamma-activated site within the CCL2 promoter. The kinetics of transient STAT1 binding to this gamma-activated site element correlated with the amount of Y701-phosphorylated nuclear STAT1, while S727-phosphorylated nuclear STAT1 remained stable over 24 h after stimulation. Therefore, IFN-beta potently induces endothelial chemokine expression at the transcriptional level.

Human brain parenchymal microglia express CD14 and CD45 and are productively infected by HIV-1 in HIV-1 encephalitis

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.

Using gene delivery to protect HIV-susceptible CNS cells: inhibiting HIV replication in microglia

Antiretroviral chemotherapy penetrates the CNS poorly. CNS HIV, thus sheltered, may injure the brain and complicate control of systemic HIV infection. Microglial cells play a major role in HIV persistence in the CNS but are rarely targeted for gene delivery. Because recombinant SV40 vectors (rSV40s) transduce other phagocytic cells efficiently, we tested rSV40 delivery of anti-HIV genetic therapy to microglial cells. Microglia prepared as enriched cultures from human fetal brain, were transduced with marker vectors, SV(RFP) and SV(Nef/FLAG), respectively, carrying DsRed and HIV-1 Nef bearing a FLAG epitope. By immunostaining and FACS, 95% of unselected cells expressed the transgenes, without detectable toxicity. Microglia were transduced with SV(AT), carrying human alpha1-antitrypsin (alpha1AT), which blocks Env and Gag processing. SV(AT)-treated microglia strongly resisted challenge with HIV-1BaL, even when microglia were transduced with SV(AT) following HIV challenge. Thus, rSV40s effectively transduce microglia and protect them from HIV.

Molecular and cellular mechanisms of neuronal cell death in HIV dementia

The deaths of neurons, astrocytes and endothelial cells have been described in patients with HIV (human immunodeficiency virus) dementia. HIV-1 does not infect neurons; instead, neurotoxic substances shed by infected glia and macrophages can induce a form of programmed cell death called apoptosis in neurons. These neurotoxins include the HIV-1 proteins Tat and gp120, as well as pro-inflammatory cytokines, chemokines, excitotoxins and proteases. In this article we review the evidence for apoptosis of various cell types within the brain of HIV-infected patients, and describe in vitro and in vivo experimental studies that have elucidated the mechanisms by which HIV causes apoptosis of brain cells.

Astrocytes and microglia differentially regulate trafficking of lymphocyte subsets across brain endothelial cells

Feline brain endothelial cells (BECs), astrocytes, and microglia were combined in different configurations in a cell culture insert system to assess the effect of different cell types on the trafficking of peripheral blood mononuclear cell (PBMC) subsets in response to feline immunodeficiency virus (FIV). The addition of astrocytes to BECs significantly increased the adherence of PBMCs. This increase in adherence was suppressed by microglia, whereas microglia alone had no effect on PBMC adherence. FIV exposure of the glial cells did not alter PBMC adherence as compared to same configurations with untreated cells. All PBMC subsets showed some level of trafficking across the endothelial cell layer. The level of trafficking of monocytes and B cells was significantly increased if astrocytes were present. The presence of microglia with the astrocytes reduced transmigration across all PBMC subsets. FIV exposure of astrocytes significantly increased the percentage of CD8 T cell transmigration from 24% to 64% of the total CD4 and CD8 numbers. The presence of microglia significantly reversed the preferential trafficking of CD8 cells in the presence of astrocytes. The results suggested that interaction between the triad of endothelial cells, astrocytes, and microglia played an important, but varying, role in the trafficking of different PBMC subsets. In general, astrocytes had a positive effect on trafficking of PBMCs, while microglia had a suppressive effect. Effects of FIV on trafficking were largely restricted to increases seen in CD8 T cells and monocytes.

Subcutaneous interferon-beta injections in patients with multiple sclerosis initiate inflammatory skin reactions by local chemokine induction

Subcutaneous Interferon-beta (IFN-beta) injections for the treatment of multiple sclerosis (MS) frequently cause inflammatory injection site reactions. To study the role of chemokines we obtained skin biopsies from 7 MS patients 24 h after injection. At the IFN-beta but not at the contralateral placebo injection sites, we observed strong IP-10/CXCL10 and moderate MCP-1/CCL2 expression associated with extensive perivascular, highly CXCR3-positive T cell and macrophage infiltrates. Primary human skin cells displayed a comparable pattern of chemokine induction after stimulation with IFN-beta in vitro. IFN-beta may therefore trigger inflammatory skin reactions through local chemokine induction followed by rapid immune cell extravasation.

Neuroinflammatory responses from microglia recovered from HIV-1-infected and seronegative subjects

Microglial and macrophage infection and immune activation underlie the pathogenesis of HIV-1-associated dementia (HAD). To assess microglial function in HAD, we isolated cells from brain tissues recovered from an HIV-1-infected patient within 4 h of death. Brain tissue from seronegative patients served as controls. Regional neuropathology was correlated to microglial function. HIV-1-patient microglia formed multinucleated giant cells and produced progeny virions. These microglia secreted reduced basal and LPS-stimulated TNF-alpha levels compared to controls. Monocytes from seronegative donors paralleled these diminished immune responses following repeated LPS-activation. These results demonstrate changes in innate microglial function following viral infection or chronic immune activation.

HIV-infection of the central nervous system: the tightrope walk of innate immunity

Infection of the central nervous system (CNS) by HIV is a frequent and sometimes very early event in the course of HIV pathogenesis. Possible consequences are diverse symptoms of neurological dysfunction, but also the establishment of a lifelong latent viral reservoir in the brain. Whereas in the periphery innate and adaptive immunity are equal partners, the blood-brain barrier (BBB) with its restricted access of peripheral immune effectors shifts this balance in favour of the local innate immunity. Four main elements of cerebral innate immunity are discussed in the present article, including two cell types with immunological functions and two soluble immune systems: (1) the stimulation of microglial cells as the predominant brain-resident immune cell and the main local reservoir for the virus; (2) the reaction of astrocytes in response to viral infection; (3) the activation of the local complement system as important soluble immune cascade; and (4) the role of chemokines and cytokines which help to conduct and cross-link the interplay between the different immune elements. These components of the cerebral innate immunity do not act separately from each other but form a functional immunity network. A dual role of these components with both harmful and protective effects further enhances the complexity of the mutual interactions.

Macrophage chemoattractant protein-1 levels in cerebrospinal fluid correlate with containment of JC virus and prognosis of acquired immunodeficiency syndrome–associated progressive multifocal leukoencephalopathy

In the highly active antiretroviral therapy (HAART) era, the role of the inflammatory response in acquired immunodeficiency syndrome (AIDS)-related progressive multifocal leukoencephalopathy (PML) remains controversial. In this study, JC virus DNA load and levels of cytokines were determined in cerebrospinal fluid (CSF) from 32 human immunodeficiency virus (HIV)-1-infected patients with confirmed PML who underwent HAART; cytokines were also measured in 12 HIV-positive controls. Predictors of survival were analyzed by Cox's models. Macrophage chemoattractant protein (MCP)-1 levels were significantly higher in PML patients than in controls (mean +/- SD, 2.45 +/- 0.64 versus 1.32 +/- 0.64 log(10) pg/ml, P<.0001). In PML patients, the higher concentration of MCP-1 correlated with lower JC viral load (r=-.405, P=.036). Higher concentrations of MCP-1 in CSF were associated with longer survival on HAART after adjusting for CD4 counts (for each log(10) pg/ml higher, hazard ratio for death 0.28, 95% confidence interval 0.08--1.00). Predictors of shorter survival were lower baseline CD4 counts, higher JCV DNA concentrations, lower Karnofsky, and no prior HAART exposure. These results showed that higher CSF levels of MCP-1, an inflammatory cytokine, were correlated with better prognosis in HAART-treated patients with PML.

Interferon-beta induces transient systemic IP-10/CXCL10 chemokine release in patients with multiple sclerosis

Reduction of chemokine expression induced by human recombinant Interferon (IFN)-beta is thought to be a therapeutic mechanism of its action in the treatment of multiple sclerosis (MS). In vitro, IFN-beta can induce chemokine expression. Here we show that a single injection of IFN-beta induced a transient strong increase of IP-10/CXCL10 and a weak elevation of MCP-1/CCL2 plasma levels in MS patients on continuing treatment with IFN-beta. IP-10/CXCL10 bursts, which were not observed in glatiramer acetate (GA)-treated patients, correlated with occurrence of flu-like symptoms. Systemic IP-10/CXCL10 release induced by IFN-beta may influence its therapeutic effect--either negatively or positively.

Role of microglia in central nervous system infections

The nature of microglia fascinated many prominent researchers in the 19th and early 20th centuries, and in a classic treatise in 1932, Pio del Rio-Hortega formulated a number of concepts regarding the function of these resident macrophages of the brain parenchyma that remain relevant to this day. However, a renaissance of interest in microglia occurred toward the end of the 20th century, fueled by the recognition of their role in neuropathogenesis of infectious agents, such as human immunodeficiency virus type 1, and by what appears to be their participation in other neurodegenerative and neuroinflammatory disorders. During the same period, insights into the physiological and pathological properties of microglia were gained from in vivo and in vitro studies of neurotropic viruses, bacteria, fungi, parasites, and prions, which are reviewed in this article. New concepts that have emerged from these studies include the importance of cytokines and chemokines produced by activated microglia in neurodegenerative and neuroprotective processes and the elegant but astonishingly complex interactions between microglia, astrocytes, lymphocytes, and neurons that underlie these processes. It is proposed that an enhanced understanding of microglia will yield improved therapies of central nervous system infections, since such therapies are, by and large, sorely needed.

15-Deoxy-Δ12,14-Prostaglandin J2 Inhibits IFN-Inducible Protein 10/CXC Chemokine Ligand 10 Expression in Human Microglia: Mechanisms and Implications

Regulation of cytokine and chemokine expression in microglia may have implications for CNS inflammatory disorders. In this study we examined the role of the cyclopentenone PG 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) in microglial inflammatory activation in primary cultures of human fetal microglia. 15d-PGJ(2) potently inhibited the expression of microglial cytokines (IL-1, TNF-alpha, and IL-6). We found that 15d-PGJ(2) had differential effects on the expression of two alpha-chemokines; whereas the Glu-Lys-Arg (ELR)(-) chemokine IFN-inducible protein-10/CXCL10 was inhibited, the ELR(+) chemokine IL-8/CXCL8 was not inhibited. These findings were shown in primary human microglia and the human monocytic cells line THP-1 cells, using diverse cell stimuli such as bacterial endotoxin, proinflammatory cytokines (IL-1 and TNF-alpha), IFN-beta, and HIV-1. Furthermore, IL-8/CXCL8 expression was induced by 15d-PGJ(2) alone or in combination with TNF-alpha or HIV-1. Combined results from EMSA, Western blot analysis, and immunocytochemistry showed that 15d-PGJ(2) inhibited NF-kappaB, Stat1, and p38 MAPK activation in microglia. Adenoviral transduction of super-repressor IkappaBalpha, dominant negative MKK6, and dominant negative Ras demonstrated that NF-kappaB and p38 MAPK were involved in LPS-induced IFN-inducible protein 10/CXCL10 production. Interestingly, although LPS-induced IL-8/CXCL8 was dependent on NF-kappaB, the baseline or 15d-PGJ(2)-mediated IL-8/CXCL8 production was NF-kappaB independent. Our results demonstrate that 15d-PGJ(2) has opposing effects on the expression of two alpha-chemokines. These data may have implications for CNS inflammatory diseases.

Differential regulation of innate and adaptive immune responses in viral encephalitis

Viral encephalitis is a global health concern. The ability of a virus to modulate the immune response can have a pivotal effect on the course of disease and the fate of the infected host. In this study, we sought to understand the immunological basis for the fatal encephalitis following infection with the murine coronavirus, mouse hepatitis virus (MHV)-JHM, in contrast with the more attenuated MHV-A59. Distinct glial cell cytokine and chemokine response patterns were observed within 3 days after infection, became progressively more polarized during the course of infection and with the infiltration of leukocytes. In the brain, MHV-JHM infection induced strong accumulation of IFNbeta mRNA relative to IFNgamma mRNA. This trend was reversed in MHV-A59 infection and was accompanied by increased CD8 T cell infiltration into brain compared to MHV-JHM infection. Increased apoptosis appeared to contribute to the diminished presence of CD8 T cells in MHV-JHM-infected brain with the consequence of a lower potential for IFNgamma production and antiviral activity. MHV-JHM infection also induced sustained mRNA accumulation of the innate immune response products interleukin (IL)-6 and IL-1. Furthermore, high levels of macrophage-inflammatory protein (MIP)-1alpha, MIP-1beta, and MIP-2 mRNA were observed at the onset of MHV-JHM infection and correlated with a marked elevation in the number of macrophages in the brain on day 7 compared to MHV-A59 infection. These observations indicate that differences in the severity of viral encephalitis may reflect the differential ability of viruses to stimulate innate immune responses within the CNS and subsequently the character of infiltrating leukocyte populations.

Molecular characterization of a putative antiretroviral transcriptional factor, OTK18

Elucidation of the factors involved in host defense against human immunodeficiency viral infection remains pivotal if viral control may be achieved. Toward these ends, we investigated the function of a putative antiretroviral factor, OTK18, isolated by differential display of mRNA from HIV type 1-infected primary human monocyte-derived macrophages. Molecular and immunohistochemical analyses showed that the OTK18 nucleotide sequence contains 13 adjacent C(2)H(2)-type zinc finger motifs, a Krüppel-associated box, and is localized to both cytosol and nucleus. Mutational analyses revealed that both the Krüppel-associated box and zinc finger regions of OTK18 are responsible for the transcriptional suppressive activities of this gene. OTK18 was copiously expressed in macrophages following HIV type I infection and diminished progeny virion production. A mechanism for this antiretroviral activity was by suppression of HIV type 1 Tat-induced viral long terminal repeat promoter activity. Our findings suggest that one possible function of OTK18 is as a HIV type 1-inducible transcriptional suppressor.

TNF-alpha microinjection upregulates chemokines and chemokine receptors in the central nervous system without inducing leukocyte infiltration

Chemokines (chemoattractant cytokines) are key players in the initiation of inflammatory cell accumulation in the central nervous system (CNS). Mechanisms leading to upregulation of chemokines in CNS pathologic conditions remain largely unknown. Numerous in vitro studies showed that inflammatory cytokines stimulate cultured CNS cells to produce chemokines. The main goal of this study was to analyze if an individual proinflammatory cytokine is sufficient to upregulate the chemokine system in the adult CNS in vivo. We analyzed CC chemokine ligand and receptor expression in brains from two different strains of mice (SJL and BALB) after stereotaxic, intracerebral injection of tumor necrosis factor-alpha (TNF-alpha). In both strains, we detected similarly increased expression of chemokines RANTES/CCL5, macrophage inflammatory protein-1alpha (MIP-1alpha)/CCL3, MIP-1beta/CCL4, and MIP-2, as well as chemokine receptors CCR1, CCR2, and CCR5. Interestingly, we did not observe parenchymal leukocyte infiltrates after local TNF-alpha delivery. This observation shows that upregulation of chemokines by TNF-alpha is not sufficient to cause accumulation of leukocytes in the CNS parenchyma in both strains of mice.

Chemokine-induced cell death in CCR5-expressing neuroblastoma cells

CCR5 is expressed in neurons but its function in this cellular context is hitherto poorly understood. We have generated CCR5-expressing SH-SY5Y neuroblastoma cells. CCR5 ligands induced cell death in these cells, but not in control neuroblastoma cells or in CCR5-expressing fibroblasts. CCR5-dependent killing of neuroblastoma cells occurred through apoptosis, since it was accompanied by caspase-3 activation and could be prevented by a caspase-3 inhibitor. Finally, cell killing by activated microglia was more rapid and extensive in CCR5-expressing neuroblastoma cells than in control cells. In summary, CCR5 may act as a death receptor in cells of neuronal lineage and therefore be involved in inflammatory neurodegeneration.

The influence of cytokines, chemokines and their receptors on HIV-1 replication in monocytes and macrophages

Monocytes, macrophages and dendritic cells play an important role in the initial infection and contribute to its pathogenesis throughout the course of infection. Myeloid cells express CD4 and chemokine receptors known for HIV-1 fusion and entry. The beta-chemokine receptor, CCR5, is the major co-receptor in conjunction with CD4 for macrophage (M)-tropic or (R5) isolates of HIV-1, whereas the alpha-chemokine receptor, CXCR4, facilitates entry of T-tropic or (X4) HIV-1 strains. Cells of myeloid lineage may be infected predominantly with R5- strains, although infection with dual-tropic isolates of HIV-1 (exhibiting the capacity to use CCR-5 and/or CXCR-4 for entry) or some strains of X4- isolates has also been reported. The expression of chemokine receptors, HIV-1 infection and replication is under continuous regulation by a complex cytokine network produced by a variety of cells. The effects of cytokines/chemokines on HIV-1 replication in cells of myeloid lineage can be inhibitory (IFN-alpha, IFN-beta, IFN-gamma, GM-CSF, IL-10, IL-13 and IL-16 and beta-chemokines), stimulatory (M-CSF, TNF-alpha, TNF-beta, IL-1, IL-6) or bifunction al, that is both inhibitory and stimulatory (IL-4). This review focuses on the overall expression of chemokine receptors on cells of myeloid lineage and considers the mechanisms of entry of R5-, X4- and dual-tropic strains of HIV-1 into these cells. The effects of cytokines/chemokines on viral entry and productive HIV-1 infection are also reviewed.

Fractalkine (CX3CL1) and brain inflammation: Implications for HIV-1-associated dementia

Leukocyte migration and activation play an important role in immune surveillance and the pathogenesis of a variety of neurodegenerative disorders, including human immunodeficiency virus (HIV)-1-associated dementia (HAD). A novel chemokine named fractalkine (FKN, CX3CL1), which exists in both membrane-anchored and soluble isoforms, has been proposed to participate in the generation and progression of inflammatory brain disorders. Upon binding to the CX3C receptor one (CX3CR1), FKN induces adhesion, chemoattraction, and activation of leukocytes, including brain macrophages and microglia (MP). Constitutively expressed in the central nervous system (CNS), mainly by neurons, FKN is up-regulated and released in response to proinflammatory stimuli. Importantly, FKN is up-regulated in the brain tissue and cerebrospinal fluid (CSF) of HAD patients. Together, these observations suggest that FKN and its receptor have a unique role in regulating the neuroinflammatory events underlying disease. This review will examine how FKN contributes to the recruitment and activation of CX3CR1-expressing MP, which are critical events in the neuropathogenesis of HAD.

Vpr- and Nef-dependent induction of RANTES/CCL5 in microglial cells

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.

GM-CSF and M-CSF modulate beta-chemokine and HIV-1 expression in microglia

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.