The regulation of alpha chemokines during HIV-1 infection and leukocyte activation: relevance for HIV-1-associated dementia

Macrophages: Key Cellular Players in HIV Infection and Pathogenesis

Although cells of the myeloid lineages, including tissue macrophages and conventional dendritic cells, were rapidly recognized, in addition to CD4+ T lymphocytes, as target cells of HIV-1, their specific roles in the pathophysiology of infection were initially largely neglected. However, numerous studies performed over the past decade, both in vitro in cell culture systems and in vivo in monkey and humanized mouse animal models, led to growing evidence that macrophages play important direct and indirect roles as HIV-1 target cells and in pathogenesis. It has been recently proposed that macrophages are likely involved in all stages of HIV-1 pathogenesis, including virus transmission and dissemination, but above all, in viral persistence through the establishment, together with latently infected CD4+ T cells, of virus reservoirs in many host tissues, the major obstacle to virus eradication in people living with HIV. Infected macrophages are indeed found, very often as multinucleated giant cells expressing viral antigens, in almost all lymphoid and non-lymphoid tissues of HIV-1-infected patients, where they can probably persist for long period of time. In addition, macrophages also likely participate, directly as HIV-1 targets or indirectly as key regulators of innate immunity and inflammation, in the chronic inflammation and associated clinical disorders observed in people living with HIV, even in patients receiving effective antiretroviral therapy. The main objective of this review is therefore to summarize the recent findings, and also to revisit older data, regarding the critical functions of tissue macrophages in the pathophysiology of HIV-1 infection, both as major HIV-1-infected target cells likely found in almost all tissues, as well as regulators of innate immunity and inflammation during the different stages of HIV-1 pathogenesis.

HIV-1 Persistence and Chronic Induction of Innate Immune Responses in Macrophages

A hallmark of HIV-1 infection is chronic inflammation, which plays a significant role in disease pathogenesis. Acute HIV infection induces robust inflammatory responses, which are insufficient to prevent or eliminate virus in mucosal tissues. While establishment of viral set-point is coincident with downregulation of acute innate responses, systemic inflammatory responses persist during the course of chronic HIV infection. Since the introduction of combination antiviral therapy (cART), most HIV-1⁺ individuals can suppress viremia under detection levels for decades. However, chronic immune activation persists and has been postulated to cause HIV associated non-AIDS complications (HANA). Importantly, inflammatory cytokines and activation markers associated with macrophages are strongly and selectively correlated with the incidence of HIV-associated neurocognitive disorder (HAND), cardiovascular dysfunctions (CVD) and other HANA conditions. In this review, we discuss the roles of macrophages in facilitating viral persistence and contributing to generation of persistent inflammatory responses.

HIV and the Macrophage: From Cell Reservoirs to Drug Delivery to Viral Eradication

Macrophages serve as host cells, inflammatory disease drivers and drug runners for human immunodeficiency virus infection and treatments. Low-level viral persistence continues in these cells in the absence of macrophage death. However, the cellular microenvironment changes as a consequence of viral infection with aberrant production of pro-inflammatory factors and promotion of oxidative stress. These herald viral spread from macrophages to neighboring CD4⁺ T cells and end organ damage. Virus replicates in tissue reservoir sites that include the nervous, pulmonary, cardiovascular, gut, and renal organs. However, each of these events are held in check by antiretroviral therapy. A hidden and often overlooked resource of the macrophage rests in its high cytoplasmic nuclear ratios that allow the cell to sense its environment and rid it of the cellular waste products and microbial pathogens it encounters. These phagocytic and intracellular killing sensing mechanisms can also be used in service as macrophages serve as cellular carriage depots for antiretroviral nanoparticles and are able to deliver medicines to infectious disease sites with improved therapeutic outcomes. These undiscovered cellular functions can lead to reductions in persistent infection and may potentially facilitate the eradication of residual virus to eliminate disease.

HIV-1 Infection of T Lymphocytes and Macrophages Affects Their Migration via Nef

The human immunodeficiency virus (HIV-1) disseminates in the body and is found in several organs and tissues. Although HIV-1 mainly targets both CD4⁺ T lymphocytes and macrophages, it has contrasting effects between these cell populations. HIV-1 infection namely reduces the viability of CD4⁺ T cells, whereas infected macrophages are long-lived. In addition, the migration of T cells is reduced by the infection, whereas HIV-1 differentially modulates the migration modes of macrophages. In 2-dimensions (2D) assays, infected macrophages are less motile compared to the control counterparts. In 3D environments, macrophages use two migration modes that are dependent on the matrix architecture: amoeboid and mesenchymal migration. HIV-1-infected macrophages exhibit a reduced amoeboid migration but an enhanced mesenchymal migration, via the viral protein Nef. Indeed, the mesenchymal migration involves podosomes, and Nef stabilizes these cell structures through the activation of the tyrosine kinase Hck, which in turn phosphorylates the Wiskott–Aldrich syndrome protein (WASP). WASP is a key player in actin remodeling and cell migration. The reprogramed motility of infected macrophages observed in vitro correlates in vivo with enhanced macrophage infiltration in experimental tumors in Nef-transgenic mice compared to control mice. In conclusion, HIV infection of host target cells modifies their migration capacity; we infer that HIV-1 enhances virus spreading in confined environments by reducing T cells migration, and facilitates virus dissemination into different organs and tissues of the human body by enhancing macrophage mesenchymal migration.

HIV Associated Neurocognitive Disorders

Human immunodeficiency virus type 1 is associated with the development of neurocognitive disorders in many infected individuals, including a broad spectrum of motor impairments and cognitive deficits. Despite extensive research, the pathogenesis of HIV-associated neurocognitive disorders (HAND) is still not clear. This review provides a comprehensive view of HAND, including HIV neuroinvasion, HAND diagnosis and different level of disturbances, influence of highly-active antiretroviral therapy to HIV-associated dementia (HAD), possible pathogenesis of HAD, etc. Together, this review will give a thorough and clear understanding of HAND, especially HAD, which will be vital for future research, diagnosis and treatment.

HIV-1 Tat-mediated neurotoxicity in retinal cells

The current study was aimed at investigating the effect of HIV-1 protein Tat on the retinal neurosensory cell line R28. Exposure of Tat resulted in induction of pro-inflammatory mediators such as CXCL10 and TNF-α in addition to the activation marker GFAP in these cells. Conditioned media from Tat-treated R28 cells was able to induce monocyte migration, an effect that was blocked by CXCR3 antagonist. Complementary studies in the HIV-1 Tat-transgenic mice, showed a complete absence of the nuclear layer and the outer photoreceptor segments of the retina with a concomitant increase in glial activation. These findings lend support to the observation in post-HAART era of increased incidence of immune response-mediated retinal degeneration. These findings have direct relevance to diseases such as immune response uveitis and patients recovering from CMV retinitis.

Molecular mechanism(s) involved in the synergistic induction of CXCL10 by human immunodeficiency virus type 1 Tat and interferon-gamma in macrophages

Synergistic interactions between viral proteins and soluble host factors released from infected mononuclear phagocytes play a critical role in the pathogenesis of human immunodeficiency virus (HIV)-associated dementia (HAD). The chemokine CXCL10 has been found to be closely associated with the progression of HIV-1-related central nervous system (CNS) disease and its related neuropsychiatric impairment. In this report the authors demonstrate that the HIV-1 protein Tat can interact with the proinflammatory cytokine interferon (IFN)-gamma to dramatically induce the expression of CXCL10 in macrophages. Synergistic induction of CXCL10 by both Tat and IFN-gamma was susceptible to inhibition by the MEK1/2 inhibitor U0126 and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580. In addition, JAK/STAT pathway plays a major role in Tat/gamma-mediated CXCL10 induction in macrophages because pretreatment of stimulated macrophages with JAK inhibitor completely abrogated the synergistic induction of the chemokine. Functionality of the synergistically induced CXCL10 was further demonstrated by its chemotactic activity for peripheral blood lymphocytes. Taken together, these findings demonstrate that the cooperative interaction of Tat and IFN-gamma results in enhanced chemokine expression, which in turn can amplify the inflammatory responses within the CNS of HAD patients by recruiting more lymphocytes in the brain.

HIV-1 activates proinflammatory and interferon-inducible genes in human brain microvascular endothelial cells: putative mechanisms of blood-brain barrier dysfunction

The mechanisms underlying blood-brain barrier (BBB) dysfunction seen in human immunodeficiency virus 1 (HIV-1) infection are poorly understood; however, they are believed to be caused by interactions of human brain microvascular endothelial cells (HBMEC) with virus-infected macrophages. Using a transwell system and Affymetrix arrays, we investigated HIV-1-induced genomic changes in HBMEC after coculture with HIV-1-infected or -uninfected monocyte-derived macrophages (MDM). Differentially expressed genes were determined by linear modeling and then were grouped by hierarchical clustering. Compared to HBMEC cocultured with noninfected MDM, 184 probe sets corresponding to 84 genes were differentially expressed in HBMEC cocultured with HIV-infected MDM. Genes activated in HIV-1 MDM-exposed HBMEC included proinflammatory cytokines and chemokines, tumor necrosis factor-alpha-induced proteins, interferon (IFN)-inducible genes, intercellular adhesion molecule-1, transcription factors of the nuclear factor-kappaB family, and signal transducer and activator of transcription 1. Analysis of molecular networks and canonical pathways associated with differentially expressed genes suggest that HIV-1 causes BBB impairment by mechanisms involving inflammation, cytokine, and IFN signaling in HBMEC.

Decreased CXCR3+ CD8 T cells in advanced human immunodeficiency virus infection suggest that a homing defect contributes to cytotoxic T-lymphocyte dysfunction

To exert their cytotoxic function, cytotoxic T-lymphocytes (CTL) must be recruited into infected lymphoid tissue where the majority of human immunodeficiency virus (HIV) replication occurs. Normally, effector T cells exit lymph nodes (LNs) and home to peripheral sites of infection. How HIV-specific CTL migrate into lymphoid tissue from which they are normally excluded is unknown. We investigated which chemokines and receptors mediate this reverse homing and whether impairment of this homing could contribute to CTL dysfunction as HIV infection progresses. Analysis of CTL chemokine receptor expression in the blood and LNs of untreated HIV-infected individuals with stable, chronic infection or advanced disease demonstrated that LNs were enriched for CXCR3(+) CD8 T cells in all subjects, suggesting a key role for this receptor in CTL homing to infected lymphoid tissue. Compared to subjects with chronic infection, however, subjects with advanced disease had fewer CXCR3(+) CD8 T cells in blood and LNs. CXCR3 expression on bulk and HIV-specific CD8 T cells correlated positively with CD4 count and negatively with viral load. In advanced infection, there was an accumulation of HIV-specific CD8 T cells at the effector memory stage; however, decreased numbers of CXCR3(+) CD8 T cells were seen across all maturation subsets. Plasma CXCL9 and CXCL10 were elevated in both infected groups in comparison to the levels in uninfected controls, whereas lower mRNA levels of CXCR3 ligands and CD8 in LNs were seen in advanced infection. These data suggest that both CXCR3(+) CD8 T cells and LN CXCR3 ligands decrease as HIV infection progresses, resulting in reduced homing of CTL into LNs and contributing to immune dysfunction.

Addition of GM-CSF to a peptide/KLH vaccine results in increased frequencies of CXCR3-expressing KLH-specific T cells

T-cell trafficking is determined by expression patterns of chemokine receptors. The chemokine receptor CXCR3 is expressed on a subpopulation of type 1 T cells and plays an important role for migration of T cells into inflamed and tumor tissues. Here, we studied the chemokine receptor expression on specific T cells generated against the neoantigen keyhole limpet hemocyanin (KLH) in patients who had been immunized in the context of a tumor peptide vaccination trial with or without the adjuvant granulocyte-macrophage colony-stimulating factor (GM-CSF). In patients immunized in the presence of GM-CSF the fraction of CXCR3(+) KLH-specific T cells was significantly higher than in patients immunized in the absence of GM-CSF (median 45 vs. 20%, P = 0.001). In contrast, the chemokine receptor CCR4, associated with migration to the skin was found in both cohorts on less than 10% of KLH-specific T cells. These results show that CXCR3 expression on vaccine-induced T cells can be modulated by modifying the local vaccine milieu.

Immune privilege and HIV-1 persistence in the CNS

Human immunodeficiency virus-1 (HIV-1) neuroinvasion occurs early (during period of initial viremia), leading to infection of a limited amount of susceptible cells with low CD4 expression. Protective cellular and humoral immunity eliminate and suppress viral replication relatively quickly due to peripheral immune responses and the low level of initial central nervous system (CNS) infection. Upregulation of the brain protective mechanisms against lymphocyte entry and survival (related to immune privilege) helps reduce viral load in the brain. The local immune compartment dictates local viral evolution as well as selection of cytotoxic lymphocytes and immunoglobulin G specificity. Such status can be sustained until peripheral immune anti-viral responses fail. Activation of microglia and astrocytes, due to local or peripheral triggers, increases chemokine production, enhances traffic of infected cells into the CNS, upregulates viral replication in resident brain macrophages, and significantly augments the spread of viral species. The combination of these factors leads to the development of HIV-1 encephalitis-associated neurocognitive decline and patient death. Understanding the immune-privileged state created by virus, the brain microenvironment, and the ability to enhance anti-viral immunity offer new therapeutic strategies for treatment of HIV-1 CNS infection.

Inhibition of indoleamine 2,3-dioxygenase (IDO) enhances elimination of virus-infected macrophages in an animal model of HIV-1 encephalitis

Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the kynurenine pathway of tryptophan metabolism. IDO activity is linked with immunosuppression by its ability to inhibit lymphocyte proliferation, and with neurotoxicity through the generation of quinolinic acid and other toxins. IDO is induced in macrophages by HIV-1 infection, and it is up regulated in macrophages in human brain tissue with HIV-1 encephalitis (HIVE). Using a model of HIVE, we investigated whether IDO inhibitor 1-methyl-d-tryptophan (1-MT) could affect the generation of cytotoxic T lymphocytes (CTLs) and clearance of virus-infected macrophages from the brain. Severe combined immunodeficient mice were reconstituted with human peripheral blood lymphocytes, and encephalitis was induced by intracranial injection of autologous HIV-1-infected monocyte-derived macrophages (MDMs). Animals treated with 1-MT demonstrated increased numbers of human CD3+, CD8+, CD8+/interferon-gamma+ T cells, and HIV-1(gag/pol)-specific CTLs in peripheral blood compared with controls. At week 2 after MDM injection in the basal ganglia, mice treated with 1-MT showed a 2-fold increase in CD8+ T lymphocytes in the areas of the brain containing HIV-1-infected MDMs compared with untreated controls. By week 3, 1-MT-treated mice showed 89% reduction in HIV-infected MDMs in brain as compared with controls. Thus, manipulation of immunosuppressive IDO activity in HIVE may enhance the generation of HIV-1-specific CTLs, leading to elimination of HIV-1-infected macrophages in brain.

Roles for CXC chemokine ligands 10 and 11 in recruiting CD4+ T cells to HIV-1-infected monocyte-derived macrophages, dendritic cells, and lymph nodes

We investigated roles for chemoattractants in dissemination of HIV-1 by examining the induction of T cell-active chemokines in HIV-1-infected human monocyte-derived macrophages and dendritic cells. Of the 12 chemokines analyzed, mRNAs for two, CXCL10 and CXCL11, ligands for the chemokine receptor CXCR3, were up-regulated in both cell types upon infection by HIV-1. Induction of these chemokine genes in infected cultures was dependent on both viral entry and reverse transcriptase activity, but not on the HIV-1 envelope glycoprotein. Conditioned medium from infected cells was chemotactic for freshly isolated human CD4+ T cells, and chemotaxis was abolished by pretreatment with an Ab against CXCR3. A lymph node from an HIV-1-infected individual expressed CXCL10 and CXCL11 mRNAs in the paracortex, including venules, as detected by in situ hybridization, whereas neither mRNA was detected after highly active antiretroviral therapy. Because CCR5 on CD4+ T cells is found predominantly on cells that also express CXCR3, these data implicate CXCL10 and CXCL11 in the recruitment of susceptible T cells to HIV-1-infected lymph nodes, macrophages, and dendritic cells. This recruitment might enhance the sequestration of T cells in infected lymphoid organs and the spread of infection between cells, contributing to the immunopathology of AIDS.

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.

Neuroregulatory events follow adaptive immune-mediated elimination of HIV-1-infected macrophages: studies in a murine model of viral encephalitis

HIV-1-specific cellular immunity serves to eliminate infected cells and disease. However, how this process specifically affects the CNS is poorly understood. To mirror the regulatory events that occur in human brain after HIV-1 infection, a murine model of viral encephalitis was used to study relationships, over time, among lymphocyte-mediated infected cell elimination, innate immune responses, and neuropathology. Nonobese diabetic SCID mice were reconstituted with human PBL and a focal encephalitis induced by intracranial injection of autologous HIV-1-infected, monocyte-derived macrophages (MDM). On days 7, 14, and 21 after MDM injection into the basal ganglia, the numbers of human lymphocytes and mouse monocytes, virus-infected MDM, glial (astrocyte and microglial) responses, cytokines, inducible NO (iNOS), neurotrophic factors, and neuronal Ags were determined in brain by immunohistochemistry, real-time PCR, and Western blot assays. Microglia activation, astrocytosis, proinflammatory cytokines, and iNOS expression accompanied the loss of neuronal Ags. This followed entry of human lymphocytes and mouse monocytes into the brain on days 7 and 14. Elimination of virus-infected human MDM, expression of IL-10, neurotropins, and a down-regulation of iNOS coincided with brain tissue restoration. Our results demonstrate that the degree of tissue damage and repair parallels the presence of infected macrophages and effectors of innate and adaptive immunity. This murine model of HIV-1 encephalitis can be useful in elucidating the role played by innate and adaptive immunity in disease progression and resolution.

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.

Mononuclear phagocyte immunity and the neuropathogenesis of HIV-1 infection

Human immunodeficiency virus type 1 (HIV-1)-associated dementia is a neuroinflammatory brain disorder that is fueled by viral infection and immune activation of brain mononuclear phagocytes (MP; macrophages and microglia). MP serve as a reservoir for persistent viral infection, a vehicle for viral dissemination throughout the brain, and a major source of neurotoxic products that when produced in abundance, affect neuronal function. Such neurotoxic substances secreted by MP lead to clinical neurological impairment (cognitive, behavior, and motor abnormalities), which occurs usually years after the initial viral infection. How HIV-1 evades the immune function characteristic for MP as a first line of defense, including phagocytosis and intracellular killing, is not well understood despite more than two decades of study. In this report, we review the complex role(s) played by MP in the neuropathogenesis of HIV-1 infection. The clinical manifestations, pathology and pathogenesis, and treatment options are discussed in relationship to innate and adaptive immunity. Particular emphasis is given to the diversity of MP functions and how it may affect the disease process and manifestations. New insights into disease mechanisms are provided by advances in enhanced magnetic resonance imaging and proteomics to identify cell movement and genetic profiles of disease. New therapeutic strategies are discussed based on current knowledge of HIV-1-associated dementia pathogenesis.

Neuroprotective strategies for HIV-1 associated dementia

The human immunodeficiency virus-1 (HIV-1) commonly affects cognitive, behavioral and motor functions during the disease course. The neuropathogenesis of viral infection revolves around neurotoxins produced from infected and immune-activated mononuclear phagocytes (MP; perivascular macrophages and microglia). Direct infection of neurons occurs rarely, if at all. Neurologic disease arises in part as a consequence of MP metabolic dysfunction. Although the advent of highly active antiretroviral therapy (HAART) has attenuated the incidence and severity of neurologic disease, it, nonetheless, remains a common and disabling problem for those living with HIV-1 infection. Adjunctive therapies are currently designed to ameliorate clinical outcomes and are included in the therapeutic armamentarium. Anti-inflammatory drugs that inhibit cytokines, chemokines and interferons linked to neurodegenerative processes can significantly ameliorate neuronal function. HIV-1 neurotoxins have the unique ability to up-regulate glycogen synthase kinase-3beta (GSK-3beta) activity that in turn elicits neuronal apoptosis. GSK-3beta inhibitors are neuroprotective in animal models of Neuro AIDS. They are also currently in Phase 1 clinical trials designed for safety and tolerability in patients with HIV-1 infection. Neurotrophins are only beginning to be realized for their therapeutic potential in HIV-1 associated neurologic disease. This review article provides a broad overview of neuroprotective strategies for HIV-1 infection and details how such strategies act and may be implemented for treatment of human disease.

Microarray analysis of cytokine and chemokine genes in the brains of macaques with SHIV-encephalitis

Human immunodeficiency virus (HIV)-encephalitis results from a cascade of viral-host interactions that lead to cytokine and chemokine imbalance, which then leads to neuropathologic manifestations of the disease. These include macrophage/microglia activation, astrocytosis and neuronal dysfunction or death. As the molecular mechanisms of this process are poorly understood, we used Atlas human cytokine or cytokine receptor microarray analysis to highlight gene expression profiles that accompanied encephalitis in Simian human immunodeficiency virus (SHIV) 89.6P-infected macaques. Of the 277 genes screened, marked upregulation of monocyte chemoattractant protein-1, interferon-inducible peptide IP-10 and interleukin-4 were observed specifically in the encephalitic brains. These genes are collectively known to promote macrophage infiltration and activation and virus replication. In contrast, genes regulating neurotrophic functions, such as brain-derived neurotrophic factor were downregulated. We also found that some of the apoptosis genes were up- or down-regulated. These data provide a comprehensive spectrum of gene expression that underscores the two major clinical manifestations of this unique syndrome: enhanced virus replication in brain macrophages and dystrophic changes in neurons.

CXCL10 production from cytomegalovirus-stimulated microglia is regulated by both human and viral interleukin-10

Glial cells orchestrate immunocyte recruitment to focal areas of viral infection within the brain and synchronize immune cell functions through a regulated network of cytokines and chemokines. Since recruitment of T lymphocytes plays a critical role in resolving cytomegalovirus (CMV) infection, we investigated the production of a T-cell chemoattractant, CXCL10 (gamma interferon-inducible protein 10) in response to viral infection of human glial cells. Infection with CMV was found to elicit the production of CXCL10 from primary microglial cells but not from astrocytes. This CXCL10 expression was not dependent on secondary protein synthesis but did require the phosphorylation of p38 mitogen-activated protein (MAP) kinase. In addition, migration of activated lymphocytes toward supernatants from CMV-stimulated microglial cells was partially suppressed by anti-CXCL10 antibodies. Since regulation of central nervous system inflammation is essential to allow viral clearance without immunopathology, microglial cells were then treated with anti-inflammatory cytokines. CMV-induced CXCL10 production from microglial cells was suppressed following treatment with interleukin-10 (IL-10) and IL-4 but not following treatment with transforming growth factor beta. The IL-10-mediated inhibition of CXCL10 production was associated with decreased CMV-induced NF-kappa B activation but not decreased p38 MAP kinase phosphorylation. Finally, CMV infection of fully permissive astrocytes resulted in mRNA expression for the viral homologue to human IL-10 (i.e., cmvIL-10 [UL111a]) in its spliced form and conditioned medium from CMV-infected astrocytes inhibited virus-induced CXCL10 production from microglial cells through the IL-10 receptor. These findings present yet another mechanism through which CMV may subvert host immune responses.

Expression of chemokines and their receptors in human and simian astrocytes: evidence for a central role of TNF alpha and IFN gamma in CXCR4 and CCR5 modulation

Chemokines are key mediators of the selective migration of leukocytes that occurs in neurodegenerative diseases and related inflammatory processes. Astrocytes, the most abundant cell type in the CNS, have an active role in brain inflammation. To ascertain the role of astrocytes during neuropathological processes, we have investigated in two models of primary cells (human fetal and simian adult astrocytes) the repertoire of chemokines and their receptors expressed in response to inflammatory stimuli. We demonstrated that, in the absence of any stimulation, human fetal and simian adult astrocytes express mRNA for receptors APJ, BOB/GPR15, Bonzo/CXCR6, CCR2, CCR3, CCR5, CCR8, ChemR23, CXCR3/GPR9, CXCR4, GPR1, and V28/CX3CR1. Moreover, TNFalpha and IL-1beta significantly increase BOB/GPR15, CCR2, and V28/CX3CR1 mRNA levels in both models. Furthermore, TNFalpha and IFNgamma act synergistically to induce expression of the major coreceptors for HIV infection, CXCR4 and CCR5, at both the mRNA and protein levels in human and simian astrocytes, whereas CCR3 expression was not affected by cytokine treatment. Finally, TNFalpha/IFNgamma was the most significant cytokine combination in leading to a pronounced upregulation in a comparable, time-dependent manner of the production of chemokines IP-10/CXCL10, RANTES/CCL5, MIG/CXCL9, MCP-1/CCL2, and IL-8/CXCL8. In summary, these data suggest that astrocytes serve as an important source of chemokines under the dependence of a complex cytokine regulation, and TNFalpha and IFNgamma are important modulators of chemokines and chemokine receptor expression in human as well as simian astrocytes. Finally, with the conditions we used, there was no difference between species or age of tissue.

The C-X-C chemokine IP-10 stimulates HIV-1 replication

Chemokines play critical roles in HIV-1 infection, serving both to modulate viral replication and to recruit target cells to sites of infection. Interferon-gamma-inducible protein 10 (IP-10/CXCL10) is a C-X-C chemokine that acts specifically upon activated T cells and macrophages and attracts T cells into the cerebrospinal fluid (CSF) in HIV-associated neurological disease. We now demonstrate that IP-10 stimulates HIV-1 replication in monocyte-derived macrophages and peripheral blood lymphocytes. We further demonstrate that neutralization of endogenous IP-10 or blocking the function of its receptor, CXCR3, reduces HIV-1 replication in these same cells. Therefore, blocking the interaction between IP-10 and CXCR3 represents a possible new target for anti-retroviral therapy.

CXC chemokine receptors in the central nervous system: Role in cerebellar neuromodulation and development

Chemokines and their receptors are constitutively present in the central nervous system (CNS), expressed in neurons and glial cells. Much evidence suggests that, beyond their involvement in neuroinflammation, these proteins play a role in neurodevelopment and neurophysiological signaling. The goal of this review is to summarize recent information concerning expression, signaling, and function of CXC chemokine receptor in the CNS, with the main focus on the developmental and neuromodulatory actions of chemokines in the cerebellum.

Characterization of chemokines and their receptors in the central nervous system: physiopathological implications

Chemokines represent key factors in the outburst of the immune response, by activating and directing the leukocyte traffic, both in lymphopoiesis and in immune surveillance. Neurobiologists took little interest in chemokines for many years, until their link to acquired immune deficiency syndrome-associated dementia became established, and thus their importance in this field has been neglected. Nevertheless, the body of data on their expression and role in the CNS has grown in the past few years, along with a new vision of brain as an immunologically competent and active organ. A large number of chemokines and chemokine receptors are expressed in neurons, astrocytes, microglia and oligodendrocytes, either constitutively or induced by inflammatory mediators. They are involved in many neuropathological processes in which an inflammatory state persists, as well as in brain tumor progression and metastasis. Moreover, there is evidence for a crucial role of CNS chemokines under physiological conditions, similar to well known functions in the immune system, such as proliferation and developmental patterning, but also peculiar to the CNS, such as regulation of neural transmission, plasticity and survival.