Microbial translocation is associated with increased monocyte activation and dementia in AIDS patients

Mechanisms underlying γδ T-cell subset perturbations in SIV-infected Asian rhesus macaques

T cells that express the γδ T-cell receptor, which recognize microbial or stress-induced antigens, represent a minority of blood T cells but constitute a major proportion of intraepithelial lymphocytes in the gastrointestinal mucosa. As microbial products have been shown to translocate from the gastrointestinal tract into circulation in chronically HIV/Simian immunodeficiency virus (SIV)-infected individuals, we conducted a study of Vδ1 and Vδ2 T-cell frequency, phenotype, and function in blood, spleen, lymph nodes, gastrointestinal mucosa, and bronchoalveolar lavage of uninfected and chronically SIVsmE543-infected rhesus macaques (RMs). We found: (1) SIV-associated inversion of Vδ1/Vδ2 T cells occurs in blood and in several tissues; (2) γδ T cells are not infected by SIV in vivo; (3) the Vδ1/Vδ2 inversion involves expansion of Vδ1 T cells; (4) expanded Vδ1 T cells are phenotypically and functionally different from Vδ1 T cells from uninfected RMs; and (5) the stimulus underlying expansion of Vδ1 T cells appears to be microbial translocation. These data highlight the importance of microbial translocation-induced immune activation in chronically infected individuals and provide new insights into an immune dysregulation phenomenon that is a hallmark of HIV/SIV infection. These findings may lead to novel therapeutic interventions that improve the immune responses against microbial antigens, and thus, decrease microbial translocation-induced immune activation.

Serological markers for inflammatory bowel disease in AIDS patients with evidence of microbial translocation

BACKGROUND

Breakdown of the gut mucosal barrier during chronic HIV infection allows translocation of bacterial products such as lipopolysaccharides (LPS) from the gut into the circulation. Microbial translocation also occurs in inflammatory bowel disease (IBD). IBD serological markers are useful in the diagnosis of IBD and to differentiate between Crohn's disease (CD) and ulcerative colitis (UC). Here, we evaluate detection of IBD serological markers in HIV-infected patients with advanced disease and their relationship to HIV disease markers.

METHODS

IBD serological markers (ASCA, pANCA, anti-OmpC, and anti-CBir1) were measured by ELISA in plasma from AIDS patients (n = 26) with low CD4 counts (<300 cells/µl) and high plasma LPS levels, and results correlated with clinical data. For meta-analysis, relevant data were abstracted from 20 articles.

RESULTS

IBD serological markers were detected in approximately 65% of AIDS patients with evidence of microbial translocation. An antibody pattern consistent with IBD was detected in 46%; of these, 75% had a CD-like pattern. Meta-analysis of data from 20 published studies on IBD serological markers in CD, UC, and non-IBD control subjects indicated that IBD serological markers are detected more frequently in AIDS patients than in non-IBD disease controls and healthy controls, but less frequently than in CD patients. There was no association between IBD serological markers and HIV disease markers (plasma viral load and CD4 counts) in the study cohort.

CONCLUSIONS

IBD serological markers may provide a non-invasive approach to monitor HIV-related inflammatory gut disease. Further studies to investigate their clinical significance in HIV-infected individuals are warranted.

A role for syndecan-1 and claudin-2 in microbial translocation during HIV-1 infection

Microbial translocation from the gastrointestinal tract has been implicated in chronic activation of the immune system during progressive HIV-1 infection by ill-defined mechanisms. We recently identified a gene encoding syndecan-1 (SYN1) in microarray studies of HIV-1 infection in lymphatic tissues and show here that increased expression of SYN1 in the gut of HIV-1-infected individuals is associated with increased microbial translocation. We further show that: (1) microbial access to SYN1 in the intestinal epithelium could be mediated by compromised barrier function through the upregulation of claudin-2; (2) increases in SYN1 and microbial translocation are associated with systemic immune activation; and (3) SYN1 expression and microbial translocation are inversely correlated with peripheral blood CD4 T-cell counts. We thus propose a new mechanism in which claudin-2 and SYN1 work in concert to enhance microbial translocation across the intestinal epithelial barrier to contribute to chronic immune activation and CD4 T-cell depletion.

Disruption of intestinal CD4+ T cell homeostasis is a key marker of systemic CD4+ T cell activation in HIV-infected individuals

HIV infection is associated with depletion of intestinal CD4(+) T cells, resulting in mucosal immune dysfunction, microbial translocation, chronic immune activation, and progressive immunodeficiency. In this study, we examined HIV-infected individuals with active virus replication (n = 15), treated with antiretroviral therapy (n = 13), and healthy controls (n = 11) and conducted a comparative analysis of T cells derived from blood and four gastrointestinal (GI) sites (terminal ileum, right colon, left colon, and sigmoid colon). As expected, we found that HIV infection is associated with depletion of total CD4(+) T cells as well as CD4(+)CCR5(+) T cells in all GI sites, with higher levels of these cells found in ART-treated individuals than in those with active virus replication. While the levels of both CD4(+) and CD8(+) T cell proliferation were higher in the blood of untreated HIV-infected individuals, only CD4(+) T cell proliferation was significantly increased in the gut of the same patients. We also noted that the levels of CD4(+) T cells and the percentages of CD4(+)Ki67(+) proliferating T cells are inversely correlated in both blood and intestinal tissues, thus suggesting that CD4(+) T cell homeostasis is similarly affected by HIV infection in these distinct anatomic compartments. Importantly, the level of intestinal CD4(+) T cells (both total and Th17 cells) was inversely correlated with the percentage of circulating CD4(+)Ki67(+) T cells. Collectively, these data confirm that the GI tract is a key player in the immunopathogenesis of HIV infection, and they reveal a strong association between the destruction of intestinal CD4(+) T cell homeostasis in the gut and the level of systemic CD4(+) T cell activation.

Microbial translocation in simian immunodeficiency virus (SIV)-infected rhesus monkeys (Macaca mulatta)

BACKGROUND

Chronic immune activation is a hallmark of HIV infection and has been postulated as major factor in the pathogenesis of AIDS. Recent evidence suggests that activation of immune cells is triggered by microbial translocation through the impaired gastrointestinal barrier.

METHODS

To determine the association between microbial translocation and disease progression, we have retrospectively analyzed microbial products, viral load and markers of immune activation in a cohort of 37 simian immunodeficiency virus-infected rhesus monkeys, divided in two groups with distinct disease courses.

RESULTS

As seen in HIV-infected patients, we found elevated levels of lipopolysaccharide (LPS) in infected animals. However, LPS levels or LPS control mechanisms like endotoxin core antibodies or LPS-binding protein did not differ between groups with different disease progression. In contrast, neopterin, a metabolic product of activated macrophages, was higher in fast progressors than in slow progressors.

CONCLUSION

Our data indicate that translocation of microbial products is not the major driving force of immune activation in HIV infection.

Innate immunity against HIV: a priority target for HIV prevention research

This review summarizes recent advances and current gaps in understanding of innate immunity to human immunodeficiency virus (HIV) infection, and identifies key scientific priorities to enable application of this knowledge to the development of novel prevention strategies (vaccines and microbicides). It builds on productive discussion and new data arising out of a workshop on innate immunity against HIV held at the European Commission in Brussels, together with recent observations from the literature.

Increasing evidence suggests that innate responses are key determinants of the outcome of HIV infection, influencing critical events in the earliest stages of infection including the efficiency of mucosal HIV transmission, establishment of initial foci of infection and local virus replication/spread as well as virus dissemination, the ensuing acute burst of viral replication, and the persisting viral load established. They also impact on the subsequent level of ongoing viral replication and rate of disease progression. Modulation of innate immunity thus has the potential to constitute a powerful effector strategy to complement traditional approaches to HIV prophylaxis and therapy. Importantly, there is increasing evidence to suggest that many arms of the innate response play both protective and pathogenic roles in HIV infection. Consequently, understanding the contributions made by components of the host innate response to HIV acquisition/spread versus control is a critical pre-requisite for the employment of innate immunity in vaccine or microbicide design, so that appropriate responses can be targeted for up- or down-modulation. There is also an important need to understand the mechanisms via which innate responses are triggered and mediate their activity, and to define the structure-function relationships of individual innate factors, so that they can be selectively exploited or inhibited. Finally, strategies for achieving modulation of innate functions need to be developed and subjected to rigorous testing to ensure that they achieve the desired level of protection without stimulation of immunopathological effects. Priority areas are identified where there are opportunities to accelerate the translation of recent gains in understanding of innate immunity into the design of improved or novel vaccine and microbicide strategies against HIV infection.

Th17 cell dynamics in HIV infection

PURPOSE OF REVIEW

Th17 cells are a newly identified subtype of CD4 T cells that respond to bacterial and fungal antigens and are important in mucosal immunology. Because HIV infection results in loss of CD4 T cells as well as disruption to the gastrointestinal tract that causes microbial translocation and immune activation, Th17 cells potentially play an important role in HIV pathogenesis. Here we examine the relationship between Th17 cells and HIV disease pathogenesis.

RECENT FINDINGS

Th17 cells are preferentially lost from the gastrointestinal tract of HIV-infected individuals, which is not entirely due to direct infection, as Th17 cells can be infected in vivo, but are not preferentially infected. Long-term highly active antiretroviral therapy (HAART) can result in restoration of Th17 cells in the gastrointestinal, which may be associated with better disease prognosis. Furthermore, other cells, such as Vdelta1 T cells, can make IL-17 in vivo during HIV infection and may contribute to antibacterial immunity after loss of Th17 cells.

SUMMARY

Recent studies have improved our understanding of the role for Th17 cells during HIV infection; however, more studies are needed to discern better the detrimental consequences of loss of Th17 cells during HIV infection.

Th17 lineage commitment and HIV-1 pathogenesis

PURPOSE OF REVIEW

The present review emphasizes the requirement for functional genomic studies and studies in human immunology toward the identification of tissue-specific regulators of human Th17 lineage commitment and molecular determinants for HIV permissiveness in Th17 cells.

RECENT FINDINGS

Th17 cells play a beneficial role in immunity against bacteria and fungi and a deleterious role in autoimmune diseases. Commensal microbiota control Th17 differentiation in the gut. Th17 cells are depleted from the gut of HIV-infected individuals and their depletion is associated with microbial translocation, which is a cause for chronic immune activation and disease progression. Th17 cells are permissive to HIV infection and therefore play a dual role in HIV pathogenesis.

SUMMARY

The discovery of human Th17 lineage revised our thinking about CD4 T-cell heterogeneity and plasticity in the context of HIV pathogenesis. The present review highlights unsolved mysteries around the genetic control of differentiation and tissue-specific specialization of human Th17 cells. Systems biology studies are now required to provide a global view of transcriptional changes in Th17 subsets and mucosal tissues and to shed light on molecular mechanisms of Th17 depletion in HIV infection, with the final goal to identify new strategies to improve mucosal immunity in infected individuals.

Development of a novel self-microemulsifying drug delivery system for reducing HIV protease inhibitor-induced intestinal epithelial barrier dysfunction

The development of HIV protease inhibitors (PIs) has been one of the most significant advances of the past decade in controlling HIV infection. Unfortunately, the benefits of HIV PIs are compromised by serious side effects. One of the most frequent and deleterious side effects of HIV PIs is severe gastrointestinal (GI) disorders including mucosal erosions, epithelial barrier dysfunction, and leak-flux diarrhea, which occurs in 16-62% of patients on HIV PIs. Although the underlying mechanisms behind HIV PI-associated serious adverse side effects remain to be identified, our recent studies have shown that activation of endoplasmic reticulum (ER) stress response plays a critical role in HIV PI-induced GI complications. The objective of this study was to develop a novel self-microemulsifying drug delivery system (SMEDDS) using various antioxidants as surfactants and cosurfactants to reduce the GI side effects of the most commonly used HIV PI, ritonavir. The biological activities of this SMSDDS of ritonavir were compared with that of Norvir, which is currently used in the clinic. Rat normal intestinal epithelial cells (IEC-6) and mouse Raw 264.7 macrophages were used to examine the effect of new SMEDDS of ritonavir on activation of ER stress and oxidative stress. Sprague-Dawley rats and C57/BL6 mice were used for pharmacokinetic studies and in vivo studies. The intracellular and plasma drug concentrations were determined by HPLC analysis. Activation of ER stress was detected by Western blot analysis and secreted alkaline phosphatase (SEAP) reporter assay. Reactive oxygen species (ROS) was measured using dichlorodihydrofluorescein diacetate as a probe. Cell viability was determined by Roche's cell proliferation reagent WST-1. Protein levels of inflammatory cytokines (TNF-alpha and IL-6) were determined by enzyme-linked immunosorbent assays (ELISA). The intestinal permeability was assessed by luminal enteral administration of fluorescein isothiocyanate conjugated dextran (FITC-dextran, 4 kDa). The pathologic changes in intestine were determined by histological examination. The results indicated that incorporation of antioxidants in this new SMEDDS not only significantly reduced ritonavir-induced ER stress activation, ROS production and apoptosis in intestinal epithelial cells and macrophages, but also improved the solubility, stability and bioavailability of ritonavir, and significantly reduced ritonavir-induced disruption of intestinal barrier function in vivo. In conclusion, this new SMEDDS of ritonavir has less GI side effects compared to Norvir. This new SMEDDS can be used for other HIV PIs and any insoluble antiviral drug with serious GI side effects.

Damaged intestinal epithelial integrity linked to microbial translocation in pathogenic simian immunodeficiency virus infections

The chronic phase of HIV infection is marked by pathological activation of the immune system, the extent of which better predicts disease progression than either plasma viral load or CD4(+) T cell count. Recently, translocation of microbial products from the gastrointestinal tract has been proposed as an underlying cause of this immune activation, based on indirect evidence including the detection of microbial products and specific immune responses in the plasma of chronically HIV-infected humans or SIV-infected Asian macaques. We analyzed tissues from SIV-infected rhesus macaques (RMs) to provide direct in situ evidence for translocation of microbial constituents from the lumen of the intestine into the lamina propria and to draining and peripheral lymph nodes and liver, accompanied by local immune responses in affected tissues. In chronically SIV-infected RMs this translocation is associated with breakdown of the integrity of the epithelial barrier of the gastrointestinal (GI) tract and apparent inability of lamina propria macrophages to effectively phagocytose translocated microbial constituents. By contrast, in the chronic phase of SIV infection in sooty mangabeys, we found no evidence of epithelial barrier breakdown, no increased microbial translocation and no pathological immune activation. Because immune activation is characteristic of the chronic phase of progressive HIV/SIV infections, these findings suggest that increased microbial translocation from the GI tract, in excess of capacity to clear the translocated microbial constituents, helps drive pathological immune activation. Novel therapeutic approaches to inhibit microbial translocation and/or attenuate chronic immune activation in HIV-infected individuals may complement treatments aimed at direct suppression of viral replication.

Compromised gastrointestinal integrity in pigtail macaques is associated with increased microbial translocation, immune activation, and IL-17 production in the absence of SIV infection

Pigtail macaques (PTMs) rapidly progress to AIDS after simian immunodeficiency virus (SIV) infection. Given the strong association between human immunodeficiency virus (HIV) and SIV disease progression and microbial translocation and immune activation, we assessed whether high basal levels of immune activation and microbial translocation exist in PTMs. We found that before SIV infection, PTMs had high levels of microbial translocation that correlated with significant damage to the structural barrier of the gastrointestinal tract. Moreover, this increased microbial translocation correlated with high levels of immune activation and was associated with high frequencies of interleukin-17-producing T cells. These data highlight the relationship among mucosal damage, microbial translocation and systemic immune activation in the absence of SIV replication, and underscore the importance of microbial translocation in the rapid course of disease progression in SIV-infected PTMs. Furthermore, these data suggest that PTM may be an ideal model to study therapeutic interventions aimed at decreasing microbial translocation-induced immune activation.

Interferon-alpha drives monocyte gene expression in chronic unsuppressed HIV-1 infection

OBJECTIVES

HIV-1 infection dysregulates the innate immune system and alters leukocyte-gene expression. The objectives were two fold: to characterize the impact of HIV-1 infection on peripheral monocyte gene expression and to identify the predominant factor(s) responsible for altered gene expression.

DESIGN AND METHODS

In a cross-sectional study (n = 55), CD14 monocytes were isolated from 11 HIV-1 seronegative controls, 22 HIV-1 seropositive individuals with low-viral loads (LVL) and 22 HIV-1 seropositive individuals with high-viral loads (HVL). Monocyte gene expression data were collected for control, LVL and HVL individuals using high-density microarrays. We evaluated three HIV-1 disease-related peripheral factors, interferon (IFN)-alpha, IFN-gamma and lipopolysaccharide (LPS) as candidates causing monocyte dysregulation, by comparing gene expression profiles between study individuals and monocytes treated with these factors in vitro. Plasma from HIV-1 positive individuals was quantified for LPS and soluble CD14.

RESULTS

Monocytes from HIV-1-infected individuals with viral loads above 10,000 RNA copies/ml (HVL) displayed an activated phenotype. Characterization of gene expression revealed an ongoing immune response to viral infection including inflammation and chemotaxis. Gene expression analysis of in-vitro-treated HIV-1 seronegative monocytes with IFN-alpha, IFN-gamma or LPS demonstrated that IFN-alpha most accurately recapitulated the HIV-1 HVL profile. No LPS-induced gene expression signature was detected even in HIV-1 individuals with the highest LPS and sCD14 levels.

CONCLUSION

Monocyte gene expression in individuals with HIV-1 viremia is predominantly due to IFN-alpha, whereas individuals with LVL have a nonactivated phenotype. In monocytes, there was no discernible expression profile linked to LPS exposure.

Immunopathogenesis of AIDS

Twenty-five years after the discovery of HIV as the cause of AIDS, tremendous progress has been made in reducing the morbidity and mortality associated with this disease. However, there is still neither a cure nor a vaccine for HIV infection. This shortcoming is likely a consequence of our incomplete understanding of the mechanisms of AIDS pathogenesis, particularly with regard to the interaction between the virus and the host immune system. In this article we review a series of recent advances in specific areas of HIV immunopathogenesis research: virus-host cell interactions; immune responses to HIV; chronic immune activation; and natural simian immunodeficiency virus infections. Finally, we discuss the potential implications of these findings for HIV/AIDS therapy and vaccines.

Microbial translocation induces persistent macrophage activation unrelated to HIV-1 levels or T-cell activation following therapy

OBJECTIVE

HIV-1 replication and microbial translocation occur concomitant with systemic immune activation. This study delineates mechanisms of immune activation and CD4 T-cell decline in pediatric HIV-1 infection.

DESIGN

Cross-sectional and longitudinal cellular and soluble plasma markers for inflammation were evaluated in 14 healthy and 33 perinatally HIV-1-infected pediatric study volunteers prior to and over 96 weeks of protease-inhibitor-containing combination antiretroviral therapy (ART). All HIV-1-infected patients reconstituted CD4 T cells either with suppression of viremia or rebound of drug-resistant virus.

METHODS

Systemic immune activation was determined by polychromatic flow cytometry of blood lymphocytes and ELISA for plasma soluble CD27, soluble CD14, and tumor necrosis factor. Microbial translocation was evaluated by limulus amebocyte lysate assay to detect bacterial lipopolysaccharide (LPS) and ELISA for antiendotoxin core antigen immunoglobulin M (IgM) antibodies. Immune activation markers were compared with viral load, CD4 cell percentage, and LPS by regression models. Comparisons between healthy and HIV-1-infected or between different viral outcome groups were performed by nonparametric rank sum.

RESULTS

Microbial translocation was detected in healthy infants but resolved with age (P < 0.05). LPS and soluble CD14 levels were elevated in all HIV-1-infected patients (P < 0.05 and P < 0.0001, respectively) and persisted even if CD4 T cells were fully reconstituted, virus optimally suppressed, and lymphocyte activation resolved by ART. Children with CD4 T-cell reconstitution but viral rebound following ART continued to display high levels of soluble CD27.

CONCLUSION

Microbial translocation in pediatric HIV-1 infection is associated with persistent monocyte/macrophage activation independent of viral replication or T-cell activation.

Inadequate clearance of translocated bacterial products in HIV-infected humanized mice

Bacterial translocation from the gut and subsequent immune activation are hallmarks of HIV infection and are thought to determine disease progression. Intestinal barrier integrity is impaired early in acute retroviral infection, but levels of plasma lipopolysaccharide (LPS), a marker of bacterial translocation, increase only later. We examined humanized mice infected with HIV to determine if disruption of the intestinal barrier alone is responsible for elevated levels of LPS and if bacterial translocation increases immune activation. Treating uninfected mice with dextran sodium sulfate (DSS) induced bacterial translocation, but did not result in elevated plasma LPS levels. DSS-induced translocation provoked LPS elevation only when phagocytic cells were depleted with clodronate liposomes (clodrolip). Macrophages of DSS-treated, HIV-negative mice phagocytosed more LPS ex vivo than those of control mice. In HIV-infected mice, however, LPS phagocytosis was insufficient to clear the translocated LPS. These conditions allowed higher levels of plasma LPS and CD8+ cell activation, which were associated with lower CD4+/CD8+ cell ratios and higher viral loads. LPS levels reflect both intestinal barrier and LPS clearance. Macrophages are essential in controlling systemic bacterial translocation, and this function might be hindered in chronic HIV infection.

HIV-associated neurocognitive disorder: pathogenesis and therapeutic opportunities

Human immunodeficiency virus type 1 (HIV) infection presently affects more that 40 million people worldwide, and is associated with central nervous system (CNS) disruption in at least 30% of infected individuals. The use of highly active antiretroviral therapy has lessened the incidence, but not the prevalence of mild impairment of higher cognitive and cortical functions (HIV-associated neurocognitive disorders) as well as substantially reduced a more severe form dementia (HIV-associated dementia). Furthermore, improving neurological outcomes will require novel, adjunctive therapies that are targeted towards mechanisms of HIV-induced neurodegeneration. Identifying such molecular and pharmacological targets requires an understanding of the events preceding irreversible neuronal damage in the CNS, such as actions of neurotoxins (HIV proteins and cellular factors), disruption of ion channel properties, synaptic damage, and loss of adult neurogenesis. By considering the specific mechanisms and consequences of HIV neuropathogenesis, unified approaches for neuroprotection will likely emerge using a tailored, combined, and non-invasive approach.

Increased monocyte turnover from bone marrow correlates with severity of SIV encephalitis and CD163 levels in plasma

Cells of the myeloid lineage are significant targets for human immunodeficiency virus (HIV) in humans and simian immunodeficiency virus (SIV) in monkeys. Monocytes play critical roles in innate and adaptive immunity during inflammation. We hypothesize that specific subsets of monocytes expand with AIDS and drive central nervous system (CNS) disease. Additionally, there may be expansion of cells from the bone marrow through blood with subsequent macrophage accumulation in tissues driving pathogenesis. To identify monocytes that recently emigrated from bone marrow, we used 5-bromo-2′-deoxyuridine (BrdU) labeling in a longitudinal study of SIV-infected CD8+ T lymphocyte depleted macaques. Monocyte expansion and kinetics in blood was assessed and newly migrated monocyte/macrophages were identified within the CNS. Five animals developed rapid AIDS with differing severity of SIVE. The percentages of BrdU+ monocytes in these animals increased dramatically, early after infection, peaking at necropsy where the percentage of BrdU+ monocytes correlated with the severity of SIVE. Early analysis revealed changes in the percentages of BrdU+ monocytes between slow and rapid progressors as early as 8 days and consistently by 27 days post infection. Soluble CD163 (sCD163) in plasma correlated with the percentage of BrdU+ monocytes in blood, demonstrating a relationship between monocyte activation and expansion with disease. BrdU+ monocytes/macrophages were found within perivascular spaces and SIVE lesions. The majority (80–90%) of the BrdU+ cells were Mac387+ that were not productively infected. There was a minor population of CD68+BrdU+ cells (<10%), very few of which were infected (<1% of total BrdU+ cells). Our results suggest that an increased rate of monocyte recruitment from bone marrow into the blood correlates with rapid progression to AIDS, and the magnitude of BrdU+ monocytes correlates with the severity of SIVE.

Human immunodeficiency virus (HIV) and the closely related simian immunodeficiency virus (SIV) can infect monocyte/macrophages, which enter and accumulate in the brain leading to neuronal dysfunction. Monocyte/macrophages exit the bone marrow, transit through the blood and enter the central nervous system (CNS). What triggers these cells to traffic is undefined, but it occurs in normal non-infected conditions at a rate that is accelerated with viral infection. Here, we used 5-bromo-2′-deoxyuridine (BrdU) injection and incorporation into the DNA of monocytes prior to their departure from the bone marrow. We found that the percentage of BrdU+ monocytes leaving the bone marrow 24 hours after injection increased in animals that rapidly succumbed to AIDS and correlated with the severity of SIV encephalitis (SIVE). Differences in BrdU labeled monocytes in slow and rapid progressors were revealed as early as 8 days and were consistent by 27 days post infection. Soluble CD163, shed by activated monocyte/macrophages, directly correlated with BrdU+ monocyte expansion. Our study provides new insights into the development of HIV-related CNS disease and underscores the importance of monocyte/macrophage recruitment from the bone marrow as an AIDS defining event.

Host hindrance to HIV-1 replication in monocytes and macrophages

Monocytes and macrophages are targets of HIV-1 infection and play critical roles in multiple aspects of viral pathogenesis. HIV-1 can replicate in blood monocytes, although only a minor proportion of circulating monocytes harbor viral DNA. Resident macrophages in tissues can be infected and function as viral reservoirs. However, their susceptibility to infection, and their capacity to actively replicate the virus, varies greatly depending on the tissue localization and cytokine environment. The susceptibility of monocytes to HIV-1 infection in vitro depends on their differentiation status. Monocytes are refractory to infection and become permissive upon differentiation into macrophages. In addition, the capacity of monocyte-derived macrophages to sustain viral replication varies between individuals. Host determinants regulate HIV-1 replication in monocytes and macrophages, limiting several steps of the viral life-cycle, from viral entry to virus release. Some host factors responsible for HIV-1 restriction are shared with T lymphocytes, but several anti-viral mechanisms are specific to either monocytes or macrophages. Whilst a number of these mechanisms have been identified in monocytes or in monocyte-derived macrophages in vitro, some of them have also been implicated in the regulation of HIV-1 infection in vivo, in particular in the brain and the lung where macrophages are the main cell type infected by HIV-1. This review focuses on cellular factors that have been reported to interfere with HIV-1 infection in monocytes and macrophages, and examines the evidences supporting their role in vivo, highlighting unique aspects of HIV-1 restriction in these two cell types.

Molecular mechanisms of neuroinvasion by monocytes-macrophages in HIV-1 infection

HIV associated neurocognitive disorders and their histopathological correlates largely depend on the continuous seeding of the central nervous system with immune activated leukocytes, mainly monocytes/macrophages from the periphery. The blood-brain-barrier plays a critical role in this never stopping neuroinvasion, although it appears unaltered until the late stage of HIV encephalitis. HIV flux that moves toward the brain thus relies on hijacking and exacerbating the physiological mechanisms that govern blood brain barrier crossing rather than barrier disruption. This review will summarize the recent data describing neuroinvasion by HIV with a focus on the molecular mechanisms involved.

Activation of CD8 T cells predicts progression of HIV infection in women coinfected with hepatitis C virus

BACKGROUND

Because activation of T cells is associated with human immunodeficiency virus (HIV) pathogenesis, CD4 and CD8 activation levels in patients coinfected with HIV and hepatitis C virus (HCV) may explain conflicting reports regarding effects of HCV on HIV disease progression.

METHODS

Kaplan-Meier and multivariate Cox regression models were used to study the risk of incident clinical AIDS and AIDS-related deaths among 813 HCV-negative women with HIV infection, 87 HCV-positive nonviremic women with HIV coinfection, and 407 HCV-positive viremic women with HIV coinfection (median follow-up time, 5.2 years). For 592 women, the percentages of activated CD4 and CD8 T cells expressing HLA-DR (DR) and/or CD38 were evaluated.

RESULTS

HCV-positive viremic women had a statistically significantly higher percentage of activated CD8 T cells (P < .001) and a statistically significantly higher incidence of AIDS compared with HCV-negative women (P < .001 [log-rank test]). The AIDS risk was greater among HCV-positive viremic women in the highest tertile compared with the lowest tertile (>43% vs <26%) of CD8(+)CD38(+)DR(+) T cells (hazard ratio, 2.94 [95% confidence interval, 1.50-5.77]; P = .001). This difference was not observed in the HCV-negative women (hazard ratio, 1.87 [95% confidence interval, 0.80-4.35]; P = .16). In contrast, CD4 activation predicted AIDS in both groups similarly. Increased percentages of CD8(+)CD38(-)DR(+), CD4(+)CD38(-)DR(-), and CD8(+)CD38(-)DR(-) T cells were associated with a >60% decreased risk of AIDS for HCV-positive viremic women and HCV-negative women.

CONCLUSION

HCV-positive viremic women with HIV coinfection who have high levels of T cell activation may have increased risk of AIDS. Earlier treatment of HIV and HCV infection may be beneficial.

Alcohol, inflammation, and gut-liver-brain interactions in tissue damage and disease development

Chronic inflammation is often associated with alcohol-related medical conditions. The key inducer of such inflammation, and also the best understood, is gut microflora-derived lipopolysaccharide (LPS). Alcohol can significantly increase the translocation of LPS from the gut. In healthy individuals, the adverse effects of LPS are kept in check by the actions and interactions of multiple organs. The liver plays a central role in detoxifying LPS and producing a balanced cytokine milieu. The central nervous system contributes to anti-inflammatory regulation through neuroimmunoendocrine actions. Chronic alcohol use impairs not only gut and liver functions, but also multi-organ interactions, leading to persistent systemic inflammation and ultimately, to organ damage. The study of these interactions may provide potential new targets for therapeutic intervention.

High systemic levels of interleukin-10, interleukin-22 and C-reactive protein in Indian patients are associated with low in vitro replication of HIV-1 subtype C viruses

BACKGROUND

HIV-1 subtype C (HIV-1C) accounts for almost 50% of all HIV-1 infections worldwide and predominates in countries with the highest case-loads globally. Functional studies suggest that HIV-1C is unique in its biological properties, and there are contradicting reports about its replicative characteristics. The present study was conducted to evaluate whether the host cytokine environment modulates the in vitro replication capacity of HIV-1C viruses.

METHODS

A small subset of HIV-1C isolates showing efficient replication in peripheral blood mononuclear cells (PBMC) is described, and the association of in vitro replication capacity with disease progression markers and the host cytokine response was evaluated. Viruses were isolated from patient samples, and the corresponding in vitro growth kinetics were determined by monitoring for p24 production. Genotype, phenotype and co-receptor usage were determined for all isolates, while clinical category, CD4 cell counts and viral loads were recorded for all patients. Plasmatic concentrations of cytokines and, acute-phase response, and microbial translocation markers were determined; and the effect of cytokine treatment on in vitro replication rates was also measured.

RESULTS

We identified a small number of viral isolates showing high in vitro replication capacity in healthy-donor PBMC. HIV-1C usage of CXCR4 co-receptor was rare; therefore, it did not account for the differences in replication potential observed. There was also no correlation between the in vitro replication capacity of HIV-1C isolates and patients' disease status. Efficient virus growth was significantly associated with low interleukin-10 (IL-10), interleukin-22 (IL-22), and C-reactive protein (CRP) levels in plasma (p < .0001). In vitro, pretreatment of virus cultures with IL-10 and CRP resulted in a significant reduction of virus production, whereas IL-22, which lacks action on immune cells appears to mediate its anti-HIV effect through interaction with both IL-10 and CRP, and its own protective effect on mucosal membranes.

CONCLUSIONS

These results indicate that high systemic levels of IL-10, CRP and IL-22 in HIV-1C-infected Indian patients are associated with low viral replication in vitro, and that the former two have direct inhibitory effects whereas the latter acts through downstream mechanisms that remain uncertain.

Differential inhibition of human immunodeficiency virus type 1 in peripheral blood mononuclear cells and TZM-bl cells by endotoxin-mediated chemokine and gamma interferon production

Bacterial lipopolysaccharide (endotoxin) is a frequent contaminant of biological specimens and is also known to be a potent inducer of beta-chemokines and other soluble factors that inhibit HIV-1 infection in vitro. Though lipopolysaccharide (LPS) has been shown to stimulate the production of soluble HIV-1 inhibitors in cultures of monocyte-derived macrophages, the ability of LPS to induce similar inhibitors in other cell types is poorly characterized. Here we show that LPS exhibits potent anti-HIV activity in phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMCs) but has no detectable anti-HIV-1 activity in TZM-bl cells. The anti-HIV-1 activity of LPS in PBMCs was strongly associated with the production of beta-chemokines from CD14-positive monocytes. Culture supernatants from LPS-stimulated PBMCs exhibited potent anti-HIV-1 activity when added to TZM-bl cells but, in this case, the antiviral activity appeared to be related to IFN-gamma rather than to beta-chemokines. These observations indicate that LPS stimulates PBMCs to produce a complex array of soluble HIV-1 inhibitors, including beta-chemokines and IFN-gamma, that differentially inhibit HIV-1 depending on the target cell type. The results also highlight the need to use endotoxin-free specimens to avoid artifacts when assessing HIV-1-specific neutralizing antibodies in PBMC-based assays.

Regulation of lentivirus neurovirulence by lipopolysaccharide conditioning: suppression of CXCL10 in the brain by IL-10

Lentivirus infections including HIV and feline immunodeficiency virus (FIV) cause neurovirulence, which is largely mediated by innate immunity. To investigate the interactions between neurovirulence and repeated conditioning by innate immune activation, models of lentivirus infection were exposed to LPS. Gene expression in HIV-infected (HIV+) and control (HIV-) patient brains was compared by real time RT-PCR and immunocytochemistry. Supernatants from mock and HIV-infected monocyte-derived macrophages exposed to LPS were applied to human neurons. FIV-infected (FIV+) and control (FIV-) animals were exposed repeatedly to LPS postinfection together with concurrent neurobehavioral testing, viral load, and host gene analyses. Brains from HIV+ individuals exhibited induction of CD3epsilon, CXCL10, and granzyme A expression (p < 0.05). Supernatants from HIV+ monocyte-derived macrophages induced CXCL10 expression in neurons, which was diminished by IL-10 treatment (p < 0.05). LPS-exposed FIV+ animals demonstrated lower plasma and brain viral loads (p < 0.05). Neuronal CXCL10 expression was increased in FIV+ animals but was suppressed by LPS exposure, together with reduced brain CD3epsilon and granzyme A expression (p < 0.05). In conjunction with preserved NeuN-positive neuronal counts in parietal cortex (p < 0.05), FIV+ animals exposed to LPS also showed less severe neurobehavioral deficits (p < 0.05). Repeated LPS exposures suppressed CXCL10 in the brain and ensuing T cell infiltration with a concomitant reduction in neurovirulence. Thus, innate immune chronic conditioning exerted beneficial effects on neurovirulence through suppression of a specific chemotactic factor, CXCL10, mediated by IL-10, leading to reduced leukocyte infiltration and release of neurotoxic factors.

The macrophage: the intersection between HIV infection and atherosclerosis

HIV-infected individuals are at increased risk of coronary artery disease (CAD) with underlying mechanisms including chronic immune activation and inflammation secondary to HIV-induced microbial translocation and low-grade endotoxemia; direct effects of HIV and viral proteins on macrophage cholesterol metabolism; and dyslipidemia related to HIV infection and specific antiretroviral therapies. Monocytes are the precursors of the lipid-laden foam cells within the atherosclerotic plaque and produce high levels of proinflammatory cytokines such as IL-6. The minor CD14+/CD16+ "proinflammatory" monocyte subpopulation is preferentially susceptible to HIV infection and may play a critical role in the pathogenesis of HIV-related CAD. In this review, the central role of monocytes/macrophages in HIV-related CAD and the importance of inflammation and cholesterol metabolism are discussed.

CNS inflammation and macrophage/microglial biology associated with HIV-1 infection

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS) can result in neurological dysfunction with devastating consequences in a significant proportion of individuals with acquired immune deficiency syndrome. HIV-1 does not infect neurons directly but induces damage indirectly through the accumulation of activated macrophage/microglia (M/M) cells, some of which are infected, that release neurotoxic mediators including both cellular activation products and viral proteins. One mechanism for the accumulation of activated M/M involves the development in infected individuals of an activated peripheral blood monocyte population that traffics through the blood-brain barrier, a process that also serves to carry virus into CNS and establish local infection. A second mechanism involves the release by infected and activated M/M in the CNS of chemotactic mediators that recruit additional monocytes from the periphery. These activated M/M, some of which are infected, release a number of cytokines and small molecule mediators as well as viral proteins that act on bystander cells and in turn activate them, thus amplifying the cascade. These viral proteins and cellular products have neurotoxic properties as well, both directly and through induction of astrocyte dysfunction, which ultimately lead to neuronal injury and death. In patients effectively treated with antiretroviral therapy, frank dementia is now uncommon and has been replaced by milder forms of neurocognitive impairment, with less frequent and more focal neuropathology. This review summarizes key findings that support the critical role and mechanisms of monocyte/macrophage activation and inflammation as a major component for HIV-1 encephalitis or HIV-1 associated dementia.

Microbial translocation is associated with residual viral replication in HAART-treated HIV+ subjects with <50copies/ml HIV-1 RNA

BACKGROUND

Recent data have shown that plasma levels of lipopolysaccharide (LPS) are a quantitative indicator of microbial translocation in HIV infected individuals.

OBJECTIVES

To assess the impact of residual viral replication on plasma LPS in HAART-treated HIV+ subjects with <50copies/ml HIV-1 RNA and to evaluate LPS changes during repeated HAART interruptions not exceeding 2-month duration.

STUDY DESIGN

LPS was measured in 44 HIV+ subjects at T0 (during HAART) and at day 15 of the first and fourth HAART interruption. Ten uninfected, healthy donors were studied as well. Residual plasma HIV-1 RNA was measured at T0 by an ultra-ultrasensitive method with limit of detection of 2.5copies HIV-1 RNA/ml. Subjects with less than 2.5copies/ml (fully suppressed - FS) were compared to those with 2.5-50copies/ml (partially suppressed - PS).

RESULTS

At T0, plasma LPS levels were comparable in FS and uninfected subjects, whereas in PS they were higher than in uninfected subjects (p=0.049). After 4 HAART interruptions, they did not change significantly. However, LPS values were lower in FS than in PS (p=0.020). An inverse correlation was found between CD4 and LPS levels (p=0.044) in PS group only.

CONCLUSIONS

A reduced degree of microbial translocation was seen in subjects with a more complete suppression of viral replication. Repeated HAART interruptions had no significant impact on plasma LPS levels.

The blood-brain barrier and immune function and dysfunction

The blood-brain barrier (BBB) is the monocellular interface that divides the peripheral circulation from direct contact with the central nervous system (CNS). This interface consists of several parallel barriers that include most notably the capillary bed of the CNS and the choroid plexus. These barriers at one level create the dichotomy between the circulating factors of the immune system and the components of the CNS only to regulate interactions between the immune and central nervous systems at other levels. The BBB is thus an integral part of the neuroimmune axis. Here, we will consider four aspects of BBB-neuroimmune interactions: BBB disruption as mediated by LPS and cytokines, cytokine transport across the BBB, immune cell trafficking, and effects of lipopolysaccharide (LPS) on various functions of the BBB.

HIV-1 Tat dysregulation of lipopolysaccharide-induced cytokine responses: microbial interactions in HIV infection

OBJECTIVE

To examine whether the HIV-1 Tat protein impairs the lipopolysaccharide (LPS)-induced cytokine responses.

DESIGN

Concurrent infections with pathogens including bacteria and viruses are common in AIDS patients. However, cytokine and interferon responses during infection with or translocation from the gut of these pathogens in HIV-infected patients are not well studied. As HIV-1 Tat contributes partly to the HIV-induced immune dysregulation, we investigated whether the protein may play a role in perturbing the LPS-induced cytokine responses.

METHODS

Expression levels of cytokines in human primary blood monocytes/macrophages were determined by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Expression level of the cell surface Toll-like receptor 4 was examined by flow cytometry. Activations of signaling molecules were assayed by western blot and immunofluorescence.

RESULTS

We demonstrated that HIV-1 Tat downregulated the LPS-induction of IFN-beta and concomitantly upregulated IL-6 expression in primary blood monocytes/macrophages, whereas the viral protein had no significant effects on TNF-alpha expression. To delineate the underlying mechanism, we showed that Tat inhibited the LPS-activation of ERK1/2 but not the p38 mitogen-activated protein kinases. The viral protein suppressed the LPS-induced activation of NFkappaB p65 via its induction of IkappaBalpha expression, which resulted in retention of NFkappaB p65 in the cytosol.

CONCLUSION

These findings suggest that Tat may play a role in modulating the immune responses triggered by other coinfecting pathogens and thus providing a permissive environment for both HIV and other opportunistic microbes.

TLR3 and TLR4 are innate antiviral immune receptors in human microglia: role of IRF3 in modulating antiviral and inflammatory response in the CNS

In the CNS, microglia are the primary targets of HIV infection. In this study, we investigated the effect of activation of the innate antiviral receptors TLR3 and TLR4 on HIV infection of primary human microglia, as well as microglial cell signaling and gene expression. Ligands for both TLR3 and TLR4 potently inhibited HIV replication in microglia through a pathway requiring IRF3. Surprisingly, a remarkably similar pattern of cell signaling and gene expression was observed in TLR3- and TLR4-activated microglia, suggesting a relatively minor role for MyD88 following TLR4 activation in these cells. HIV did not activate IRF3 but rather decreased IRF3 protein, indicating that HIV does not activate TLR3 or RIG-like helicases in microglia. Taken together, these results indicate that activation of TLR3 or TLR4 will elicit antiviral immunity, in addition to inducing proinflammatory responses. We suggest that a balanced expression between inflammatory and innate immune genes might be achieved by IRF3 over-expression.

Evidence for translocation of microbial products in patients with idiopathic CD4 lymphocytopenia

Translocation of microbial products has been described in chronic human immunodeficiency virus (HIV) infection and correlates with activation of the immune system. We investigated the potential translocation of microbial products in idiopathic CD4 lymphocytopenia (ICL), a rare disorder characterized by low CD4 T cell counts in the absence of HIV infection. Plasma lipopolysaccharide (LPS) levels and T cell activation were measured in a cross-sectional cohort study of patients with ICL and HIV infection and healthy control subjects. Increases in CD4 T cell proliferation but not CD8 T cell proliferation were observed in patients with ICL. LPS levels were significantly elevated both in patients with ICL and in patients with HIV infection, and they were strongly correlated with the proportion of proliferating CD4 T cells in the cohort of patients with ICL (r = 0.88; P= .003). The proportions of T helper (Th) 17 and Th1 CD4 cells in peripheral blood were similar between patients with ICL, patients with HIV infection, and control subjects. These findings suggest a potential association of translocation of microbial products with perturbed CD4 T cell homeostasis in individuals with CD4 lymphopenic states other than HIV infection.

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.

CD4 downregulation by memory CD4+ T cells in vivo renders African green monkeys resistant to progressive SIVagm infection

African green monkeys (genus Chlorocebus) can be infected with SIVagm, but do not develop AIDS. This natural host of SIV, like sooty mangabeys, maintains high levels of SIV replication but has evolved to avoid immunodeficiency. Elucidating the mechanisms that allow the natural hosts to co-exist with SIV without overt disease may provide crucial information to understand AIDS pathogenesis. Here we show: (1) many CD4⁺ T cells from African green monkeys down-regulate CD4 in vivo as they enter the memory pool, (2) down regulation of CD4 by memory T cells is independent of SIV infection, (3) the CD4⁻ memory T cells maintain functions which are normally attributed to CD4 T cells including production of IL-2, production of IL-17, expression of FoxP3 and expression of CD40L (4) loss of CD4 expression protects these T cells from infection by SIVagm in vivo, and (5) these CD4⁻ T cells can maintain MHC-II restriction. These data demonstrate that the absence of SIV-induced disease progression in natural hosts species may be partially explained by preservation of a subset of T cells that maintain CD4 T cell function while being resistant to SIV-infection in vivo.

HIV and SIV infection: the role of cellular restriction and immune responses in viral replication and pathogenesis

The human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) have a long biological history. Both viruses evolved from Africa and remnants of them can be found in the 'fossil record' of several species in which they are not endemic. SIV remains endemic in several species of monkeys in Africa where it does not cause immune deficiency. HIV and SIV actively replicate within humans and Asian non-human primates, despite cellular and genetic viral restriction factors and genes, and at times robust innate and adaptive immune responses. While Lentiviruses are considered 'slow viruses' it is clear in humans and susceptible Asian monkeys that virus production is rapid and highly active. This results in a massive loss of CD4+ memory effector T cells early after infection and a continued race between viral evolution, cytotoxic lymphocytes, and failed neutralizing antibody responses. Concurrently, HIV and SIV can infect monocyte/macrophage populations in blood and more importantly in tissues, including the central nervous system, where the virus can remain sequestered and not cleared by anti-retroviral therapy, and hide for years. This review will discuss species and cellular barriers to infection, and the role of innate and acquired immunity with infection and pathogenesis of HIV and SIV in select species.

Disturbance of the gut-associated lymphoid tissue is associated with disease progression in chronic HIV infection

Why and how HIV makes people sick is highly debated. Recent evidence implicates heightened immune activation due to breakdown of the gastrointestinal barrier as a determining factor of lentiviral pathogenesis. HIV-mediated loss of Th17 cells from the gut-associated lymphoid tissue (GALT) impairs mucosal integrity and innate defense mechanisms against gut microbes. Translocation of microbial products from the gut, in turn, correlates with increased immune activation in chronic HIV infection and may further damage the immune system by increasing viral and activation-induced T cell death, by reducing T cell reconstitution due to tissue scarring, and by impairing the function of other cell types, such as gammadelta T cells and epithelial cells. Maintaining a healthy GALT may be the key to reducing the pathogenic potential of HIV.

HIV-1 RNA dysregulates the natural TLR response to subclinical endotoxemia in Kenyan female sex-workers

Background

Subclinical endotoxemia has been reported in HIV-1 infected persons and may drive systemic immune activation and pathogenesis. Proinflammatory responsiveness to endotoxin (LPS) is mediated by Toll-like receptor 4 (TLR4). We therefore examined the association between plasma LPS levels, HIV RNA, and TLR4 expression and cytokine responses in the blood of HIV infected and uninfected participants in a cohort of female sex-workers in Kenya.

Methodology/Principal Findings

Ex vivo plasma and peripheral blood mononuclear cells (PBMC) were assessed for LPS and TLR mRNA, respectively. The effects of HIV single stranded RNA, a TLR8 ligand, on TLR4 and LPS signaling were further assessed in short term PBMC culture. Both HIV uninfected and infected subjects frequently had low detectable LPS levels in their plasmas. Significantly increased LPS levels were associated with chronic HIV-1 infection, both treated and untreated, but not with other acute or semi-chronic conditions reported. In HIV-uninfected subjects, TLR4 mRNA expression levels correlated inversely with plasma LPS levels, suggesting chronic endotoxin ‘tolerance’ in vivo. A similar effect of reduced TLR4 mRNA was seen in short term PBMC culture after stimulation with LPS. Interestingly, the apparent in vivo tolerance effect was diminished in subjects with HIV infection. Additionally, pre-stimulation of PBMC with LPS lead to proinflammatory (TNF-α) tolerance to subsequent LPS stimulation; however, pre-treatment of PBMC with HIV single-stranded RNA40, could enhance TLR4-mediated LPS responsiveness in vitro.

Conclusions/Significance

Thus, dysregulation of endotoxin tolerance by HIV-1 RNA may exacerbate HIV chronic immune activation and pathogenesis.

TLR2 and TLR4 triggering exerts contrasting effects with regard to HIV-1 infection of human dendritic cells and subsequent virus transfer to CD4+ T cells

BACKGROUND

Recognition of microbial products through Toll-like receptors (TLRs) initiates inflammatory responses orchestrated by innate immune cells such as dendritic cells (DCs). As these cells are patrolling mucosal surfaces, a portal of entry for various pathogens including human immunodeficiency virus type-1 (HIV-1), we investigated the impact of TLR stimulation on productive HIV-1 infection of DCs and viral spreading to CD4+ T cells.

RESULTS

We report here that engagement of TLR2 on DCs increases HIV-1 transmission toward CD4+ T cells by primarily affecting de novo virus production by DCs. No noticeable and consistent effect was observed following engagement of TLR5, 7 and 9. Additional studies indicated that both HIV-1 infection of DCs and DC-mediated virus transmission to CD4+ T cells were reduced upon TLR4 triggering due to secretion of type-I interferons.

CONCLUSION

It can thus be proposed that exposure of DCs to TLR2-binding bacterial constituents derived, for example, from pathogens causing sexually transmissible infections, might influence the process of DC-mediated viral dissemination, a phenomenon that might contribute to a more rapid disease progression.

Host and viral factors influencing the pathogenesis of HIV-associated neurocognitive disorders

The human immunodeficiency virus (HIV) invades the central nervous system early in the course of infection and establishes a protected viral reservoir. However, neurocognitive consequences of HIV infection, known collectively as HIV-associated neurocognitive disorders (HAND), develop in only a small portion of infected patients. The precise mechanisms of pathogenesis involved in HIV-induced central nervous system injury are still not completely understood. In particular, most theories of HAND pathogenesis cannot account for either the selective vulnerability of specific neuronal populations to HIV-induced neurodegeneration or why only a subset of patients develop clinically detectable nervous system disease. Epidemiological and virological studies have identified a variety of host and viral factors that are associated with increased risk of developing HAND. Some host factors that predispose HIV-infected patients to HAND overlap with those associated with Alzheimer's disease (AD), suggesting the possibility that common pathogenic mechanisms may participate in both diseases. Here, we will review reports of host and viral factors associated with HAND and place these studies in the context of the data employed to support current theories regarding the molecular and cellular mechanisms that lead to HIV-induced neurodegeneration with additional focus on mechanisms common to AD pathogenesis.

Microbial translocation, the innate cytokine response, and HIV-1 disease progression in Africa

Reports from the United States have demonstrated that elevated markers of microbial translocation from the gut may be found in chronic and advanced HIV-1 infection and are associated with an increase in immune activation. However, this phenomenon's role in HIV-1 disease in Africa is unknown. This study examined the longitudinal relationship between microbial translocation and circulating inflammatory cytokine responses in a cohort of people with varying rates of HIV-1 disease progression in Rakai, Uganda. Multiple markers for microbial translocation (lipopolysaccharide, endotoxin antibody, and sCD14) did not change significantly during HIV-1 disease progression. Moreover, circulating immunoreactive cytokine levels either decreased or remained virtually unchanged throughout disease progression. These data suggest that microbial translocation and its subsequent inflammatory immune response do not have a causal relationship with HIV-1 disease progression in Africa.

Characteristics of Activated Monocyte Phenotype Support R5-Tropic Human Immunodeficiency Virus

BACKGROUND: Microbial translocation has been recognized as an important factor in monocyte activation and contributing to AIDS pathogenesis with elevated plasma lipopolysaccharide (LPS) levels, as a marker for microbial translocation, seen in advanced HIV disease. Therefore, the current study was undertaken to assess monocyte activation in vitro by LPS and to determine its impact on monocyte phenotype. METHODS: Monocytes from non-HIV-infected donors were analyzed for CD14, CD16, CD69, TNFα, and CCR5 by flow cytometry pre- and post-stimulation with LPS. In-vitro cultures were then set up to expose non-activated and activated monocytes to R5-, X4-, and dual (R5/X4)-tropic viruses; and the amount of HIV present on the cells was assayed. RESULTS: Non-HIV-infected monocytes, after LPS stimulation, were confirmed to have an activated phenotype with increase in CD16 and CD69 surface expressions (p<0.05). The activation phenotype was supported by increase in TNFα production, p<0.05. The activated monocytes had increased surface CCR5 (from 21% to 98%; p=0.05); and were found to have more R5-tropic virus than non-activated monocytes (p<0.05). CONCLUSIONS: Following activation by LPS, non-HIV-infected monocytes were found to have increase in surface CCR5. These activated monocytes, when exposed to R5-tropic virus, were found to have more virus compared to non-activated monocytes. The significance of the findings could lie in explaining how microbial translocation plays a role in HIV progression; and possibly promoting CCR5-directed strategies in treating HIV.

Neurodegeneration and ageing in the HAART era

Cognitive impairment and neurodegeneration still occur despite highly active antiretroviral therapy (HAART). While there are many potential reasons for this, there is increasing evidence that such impairment occurs in the absence of a clear cause. Furthermore, there are data that some neurodegenerative diseases, especially Alzheimer's or an Alzheimer-like illness, are becoming more common in the context of HAART-treated human immunodeficiency virus (HIV) disease. This review will critically examine the evidence underpinning these observations. Potential mechanisms will be discussed with particular emphasis on the effect of ageing and how it overlaps with the effects of HIV disease itself thereby leading to neurodegeneration. The nature of this overlap will then be explored for its potential role in the facilitated expression and development of neurodegenerative diseases. Lastly, there will be a brief discussion of interventions to minimize such neurodegeneration including optimization of HAART for brain entry.

Expression and regulation of antiviral protein APOBEC3G in human neuronal cells

Apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G (APOBEC3G) has recently been identified as a potent antiviral protein. Here, we examined the expression and regulation of APOBEC3G in human brain tissues and the cells of central nervous system (CNS). Similar to the immune cells, human brain tissue and the CNS cells expressed APOBEC3G at both mRNA and protein levels. The expression of APOBEC3G could be up-regulated in human neuronal cells (NT2-N) and astrocytes (U87-MG) by interferons (IFN-alpha, beta and gamma), interleukin-1 (IL-1), and tumor necrosis factor. Other cytokines (IL-4, IL-6 and transforming growth factor beta1) and CC-chemokines (CCL3, 4 and 5), however, had little impact on the expression of APOBEC3G. In addition, pseudotyped HIV-1 infection and cytokine/chemokine-enriched supernatants from lipopolysaccharide-stimulated macrophage cultures induced APOBEC3G expression in NT2-N cells. APOBEC3G expressed in the neuronal cells and astrocytes was biologically functional, as the suppression of APOBEC3G expression by the specific siRNA led to increase of pseudotyped HIV-1 replication in these cells. These findings provide direct and compelling evidence that there is intracellular expression and regulation of functional APOBEC3G in the neuronal cells, which may be one of innate defense mechanisms involved in the neuronal protection in the CNS.