HIV-induced TNF-alpha regulates arachidonic acid and PGE2 release from HIV-infected mononuclear phagocytes

Correlative Imaging to Detect Rare HIV Reservoirs and Associated Damage in Tissues

Correlative light-electron microscopy (CLEM) has evolved in the last decades, especially after significant developments in sample preparation, imaging acquisition, software, spatial resolution, and equipment, including confocal, live-cell, super-resolution, and electron microscopy (scanning, transmission, focused ion beam, and cryo-electron microscopy). However, the recent evolution of different laser-related techniques, such as mass spectrometry imaging (MSI) and laser capture microdissection, could further expand spatial imaging capabilities into high-resolution OMIC approaches such as proteomic, lipidomics, small molecule, and drug discovery. Here, we will describe a protocol to integrate the detection of rare viral reservoirs with imaging mass spectrometry.

Resistance to Prostaglandin E2 Promotes Monocyte Activation During Chronic HIV Infection

BACKGROUND

Monocyte activation is a driver of inflammation in the course of chronic HIV infection. Prostaglandin E2 (PGE2) is known to mediate anti-inflammatory effects, notably the inhibition of tumor necrosis factor- (TNF-) production by monocytes. We aim to investigate the effects of PGE2 on activation of monocytes in chronic HIV infection and the mechanisms through which PGE2 modulates their inflammatory signature.

METHODS

We recruited a group of people with HIV (PWH) and matched healthy uninfected persons. We compared plasma levels of PGE2, monocyte activation, and sensitivity of monocytes to the inhibitory actions mediated by PGE2.

RESULTS

We found increased plasma levels of PGE2 in PWH, and an activated phenotype in circulating monocytes, compared with uninfected individuals. Monocytes from PWH showed a significant resistance to the inhibitory actions mediated by PGE2; the concentration of PGE2 able to inhibit 50 of the production of TNF- by lipopolysaccharide-stimulated monocytes was 10 times higher in PWH compared with uninfected controls. Furthermore, the expression of phosphodiesterase 4B, a negative regulator of PGE2 activity, was significantly increased in monocytes from PWH.

CONCLUSIONS

Resistance to the inhibitory actions mediated by PGE2 could account, at least in part, for the inflammatory profile of circulating monocytes in PWH.

Intra-amygdala microinjection of TNF-α impairs the auditory fear conditioning of rats via glutamate toxicity

During an inflammatory or infectious process, innate immune cells produce large amount of pro-inflammatory cytokines that act on the brain to cause cognitive dysfunctions. Tumor necrosis factor alpha (TNF-α) is one of the main pro-inflammatory cytokines. Thus, it is important to study how the excessive TNF-α affects the cognitive functions of central nervous system and possible antagonists to its effects. In the present study, we conducted behavioral experiments of rats to determine whether murine TNF-α administered directly into the brain would elicit behavioral effects related to learning and memory impairments. Rats subjected to single-dose intra-amygdala TNF-α infusion showed a significant delay in the acquisition and extinction of auditory fear conditioning. Accordingly, the glutamate level of the tissue samples from amygdala was elevated after the TNF-α treatment. Furthermore, pharmacological blockade of NMDAR before the TNF-α treatment reversed the TNF-α induced impairments in fear learning. Our findings suggest that TNF-α can impair the learning and memory functions through glutamate-NMDAR neurotoxicity, and present the possibility to develop therapeutic modalities directing at glutamate transmission for the treatment of neuro-inflammative dysfunctions.

Investigating the effects of metabolic dysregulation on hair follicles: a comparison of HIV-infected women with and without central lipohypertrophy

BACKGROUND

Normal lipid metabolism and functioning of the peroxisome proliferator-activated receptor gamma (PPAR-gamma) in the sebaceous gland is critical to maintaining a normal hair follicle. Human immunodeficiency virus (HIV) infection affects lipid metabolism; some have hypothesized a link between PPAR-gamma function and lipodystrophy in HIV infection. Our objective was to determine whether lipodystrophy is associated with altered hair characteristics in HIV-infected women from the Women's Interagency HIV Study.

METHODS

Hair characteristics and scalp inflammation were assessed by an interviewer-administered questionnaire. Central lipohypertrophy and peripheral lipoatrophy were defined by self-report of moderate to severe fat gain in central body sites and fat loss in peripheral body sites, respectively confirmed by clinical examination. Additional covariates considered in the analyses included demographics, behavioral characteristics, medical history, and HIV-related factors.

RESULTS

There were 1037 women with data on all study variables; 76 women reported central lipohypertrophy, while only four women reported lipoatrophy. Women with central lipohypertrophy were more likely to be older, had a self-reported history of injection drug use, statin medication use, diabetes, elevated cholesterol, and have self-reported less hair and shorter eyelashes. After adjustment for age, central lipohypertrophy was associated with shorter eyelashes (OR 2.3; 95% CI 1.4-3.8).

CONCLUSIONS

Central lipohypertrophy was not associated with change in scalp hair texture or scalp inflammation in this cohort. Rather, we found an association between central lipohypertrophy and shorter eyelash length. This finding may be explained by an influence of prostaglandin E2 mediators on eyelash follicles.

Antiproliferative effect of hepatitis C virus on mitogen-stimulated peripheral blood mononuclear cells: potential role in viral persistence in Egyptian patients

OBJECTIVES

We aimed to study the effect of hepatitis C virus (HCV) and sera of chronic HCV patients on phytohemagglutinin (PHA)-stimulated normal donor PBMCs and to study the effect of chronic HCV infection on some cytokine profile.

SUBJECTS AND METHODS

(3)H-Thymidine uptake was utilized to study effect of pelleted virus and patients sera on PBMCs proliferation in vitro. The study included 337 Egyptian chronic liver patients from Ain Shams University Hospitals and 90 healthy control subjects. The patients' group included chronic hepatitis C (250 subjects), and other chronic liver diseases (87 subjects). All subjects' sera were subjected to RT-PCR for HCV RNA detection, IL-4, IL-1beta, and TNF-alpha measurement by EIA, and biochemical measurement of ALT and albumin.

RESULTS

Treatment of PHA-stimulated normal donor PBMCs with pelleted virus led to decrease (dose response) in their rate of proliferation. This was partially reversed after addition of HCV RNA positive patients' sera. HCV RNA positive patients were significantly higher in IL-4 and ALT, and lower in IL-1beta and albumin than HCV RNA negative patients.

CONCLUSION

HCV infection suppresses early immune response. This leads to increased IL-4 Th2 cytokine.

The Toll‐like receptor 7/8‐ligand resiquimod (R‐848) primes human neutrophils for leukotriene B4, prostaglandin E2and platelet‐activating factor biosynthesis

Toll-like receptors (TLR) recognize pathogen-associated molecular patterns and play important roles in the innate immune system. While single-stranded viral RNA is the natural ligand of TLR7/TLR8, the imidazoquinoline resiquimod (R-848) is recognized as a potent synthetic agonist of TLR7/TLR8. We investigated the effects of TLR7/8 activation on lipid mediator production in polymorphonuclear leukocytes exposed to R-848. Although R-848 had minimal effects by itself, it strongly enhanced leukotriene B4 formation on subsequent stimulation by fMLP, platelet-activating factor, and the ionophore A23187. R-848 acted via TLR8 but not TLR7 as shown by the lack of effect of the TLR7-specific ligand imiquimod. Priming with R-848 also resulted in enhanced arachidonic acid release and platelet-activating factor formation following fMLP stimulation, as well as enhanced prostaglandin E2 synthesis following the addition of arachidonic acid. Western blot analysis demonstrated that R-848 induced the phosphorylation of the cytosolic phospholipase A2alpha, promoted 5-lipoxygenase translocation and potently stimulated the expression of the type 2 cyclooxygenase. Bafilomycin A1, an inhibitor of endosomal acidification, efficiently inhibited all R-848-induced effects. These studies demonstrate that TLR8 signaling strongly promotes inflammatory lipid mediator biosynthesis and provide novel insights on innate immune response to viral infections.

Role of the pro-inflammatory cytokines TNF-alpha and IL-1beta in HIV-associated dementia

Human immunodeficiency virus-1 (HIV-1)-infected and immune-activated macrophages and microglia secrete neurotoxins. Two of these neurotoxins are the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), which are thought to play a major role in inducing neuronal death. Both TNF-alpha and IL-1beta increase the permeability of the blood-brain barrier, through which subsequently HIV-infected monocytes can enter the brain. They both induce over-stimulation of the NMDA-receptor via several pathways, resulting in a lethal neuronal increase in Ca(2+) levels. Additionally, TNF-alpha co-operates with several other proinflammatory mediators to enhance their toxic effects. Although most research has focused on the neurotoxic effects of TNF-alpha and IL-1beta in HAD, there is also evidence that these cytokines can be neuroprotective. In this paper the effect of TNF-alpha and IL-1beta on neuronal life and death in HAD is discussed.

Autoantigen specific T cells inhibit glutamate uptake in astrocytes by decreasing expression of astrocytic glutamate transporter GLAST: a mechanism mediated by tumor necrosis factor‐α

Glutamate excitotoxicity is increasingly being recognized as a pathogenic mechanism in autoimmune inflammatory disorders of the central nervous system (CNS). Astrocytes are the predominant players in clearing the extracellular space from glutamate and normally have extensive spare capacities in terms of glutamate uptake. We asked what might be the basis of glutamate accumulation in T cell triggered autoimmune inflammation. In vitro, coculture of primary rat astrocytes with activated myelin basic protein (MBP)-specific T cells resulted in a decrease of astrocytic glutamate uptake rates (Vmax). In parallel, the amount of the Na+-dependent glutamate transporter GLAST was reduced within 48-60 h. Significant decreases of GLAST protein were observed in astrocytes harvested after incubation with T cells activated by MBP during coculture or after incubation with T cell blasts preactivated in the presence of splenocytes beforehand. Since exposure of astrocytes to cell-free supernatant of MBP-activated T cells also resulted in reduced expression of GLAST, a humoral factor appeared to be the driving agent. In blocking experiments using neutralizing antibodies and by incubation of astrocytes with recombinant cytokines, tumor necrosis factor-alpha (TNF-alpha) was identified as being responsible for the down-modulation of GLAST. GLAST was also down-regulated in the CNS of autoimmune encephalomyelitic rats but not in animals suffering from systemic inflammation. Since the loss of GLAST was not confined to inflammatory infiltrates, here too, a humoral factor seemed to be causative. In conclusion, T cell derived TNF-alpha impairs glutamate clearance capacity of astrocytes in vitro and probably also in vivo providing a pathogenic link to glutamate excitotoxicity that may contribute to early axonal dysfunction remote from active autoimmune inflammatory demyelination.

Cyclo-oxygenase type 2-dependent prostaglandin E2 secretion is involved in retrovirus-induced T-cell dysfunction in mice

MAIDS (murine AIDS) is caused by infection with the murine leukaemia retrovirus RadLV-Rs and is characterized by a severe immunodeficiency and T-cell anergy combined with a lymphoproliferative disease affecting both B- and T-cells. Hyperactivation of the cAMP-protein kinase A pathway is involved in the T-cell dysfunction of MAIDS and HIV by inhibiting T-cell activation through the T-cell receptor. In the present study, we show that MAIDS involves a strong and selective up-regulation of cyclo-oxygenase type 2 in the CD11b+ subpopulation of T- and B-cells of the lymph nodes, leading to increased levels of PGE2 (prostaglandin E2). PGE2 activates the cAMP pathway through G-protein-coupled receptors. Treatment with cyclo-oxygenase type 2 inhibitors reduces the level of PGE2 and thereby reverses the T-cell anergy, restores the T-cell immune function and ameliorates the lymphoproliferative disease.

Cyclooxygenases and prostaglandins: shaping up the immune response

The relevance of cyclooxygenases (COX)-1 and -2 and their products to inflammation, thrombosis and gastroprotection are well known. Their importance in the immune response was first recognized more than 25 years ago, but has only gained widespread attention recently. In this review, we attempt to integrate information on prostanoids and both the innate and acquired immune responses, including effects on leukocytes, antigen presenting cells, dendritic cells, T and B lymphocytes. Prostanoids may be relevant to immunotolerance, autoimmune disorders, transplantation, immunologic defense against tumors, acquired immunodeficiencies and viral infections. Insight into the role of prostanoids in immune function may afford novel therapeutic opportunities.

Glutamate is a mediator of neurotoxicity in secretions of activated HIV-1-infected macrophages

We sought to identify neurotoxin(s) secreted by HIV-1-infected mononuclear phagocytes that could contribute to the pathophysiology of HIV-1-associated dementia (HAD). Neurotoxic factors were characterized in batches of conditioned media (CM) from human monocyte-derived macrophages (MDM) infected with HIV-1(ADA) and/or activated with lipopolysaccharide (LPS). All of the neurotoxicity was: present in the <3000-Da fraction; blocked by 5 microM MK801; and not trypsin sensitive or extractable into polar organic solvents. Glutamate measured in CM accounted for all neurotoxic effects observed from HIV/LPS CM in astrocyte-poor neuronal cultures and may contribute to the pathophysiology of HIV-1-associated dementia.

The effects of human immunodeficiency virus in the central nervous system

More than a decade after the first description of HIV DNA in the nervous system the pathophysiology of HIVD remains largely enigmatic, with data supporting a number of potential mechanisms for the development of neuronal dysfunction. Nevertheless, a few key findings have considerable support in the literature devoted to this subject: 1. HIV dementia is caused by HIV itself; no other pathogen has been consistently found in the brains of patients with HIVD. 2. In comparison with other viral encephalopathies, there appears to be a significant discordance between the amount of virus being produced in the brains of patients with HIVD and the degree of neurological deterioration. 3. The key cell types responsible for viral production within the CNS are the resident macrophages or microglial cells. 4. Other elements within the CNS, particularly astrocytes, are probably infected with HIV as well, but all of these infections are highly restricted in terms of production of virus or viral structural proteins. 5. At least one component of the pathogenesis of HIVD may be the generation of neurotoxins by infected microglia, although the type of neurotoxin, and the specific compound most likely to be involved, are quite controversial. Advances with combination antiviral therapy have successfully reduced plasma viral load in a high proportion of individuals, leading to the speculation (previously almost heretical) that it may be possible to eradicate HIV completely from the systemic immune system. If that were the case, potential "sanctuary" sites such as the immunologically protected CNS might remain as important reservoirs for reseeding of lymphoid tissues. Microglia may be particularly suited for this purpose because they are long lived, can produce HIV for several weeks (at least in culture), and they are apparently relatively immune to virus-induced cytopathology such as syncytium formation. One can speculate about several scenarios resulting from the continued presence of replication-competent HIV within brain. In the worst case, a smoldering infection of the nervous system could lead to neurological deterioration without reinfection of systemic immune cells. The epidemiological data indicating that HIVD is a disease primarily associated with immunodeficiency suggest that the systemic immune system plays a role in maintaining virus residing within the CNS under control. Thus it is quite possible that this scenario would not occur for many years after the systemic infection is controlled. Alternatively, virus could be transported from the CNS by circulating lymphocytes and monocytes and reinfect systemic organs. This would necessitate restarting therapy for those individuals who were previously thought to be cured, but presumably virus within the CNS would not have developed resistance to antivirals. In either case, the techniques currently available do not permit an accurate assessment of CNS HIV load in living people, and this question will remain unanswered until antivirals are discontinued in a few individuals with persistently negative tests for systemic virus. In addition to this most critical question, the relationship between viral levels and HIVD is largely unexplored, as is the possibility that some strains are particularly virulent or neuroinvasive. Furthermore, the potential contribution of host genotype in the development of dementia is unknown. In view of the strong influence of major chemokine receptor (CCR5) truncations on HIV replication, it is entirely possible that more discrete genetic polymorphisms have a subtle effect on either brain invasion or virulence.

Effects of dietary arachidonic acid on human immune response

Arachidonic acid (AA) is a precursor of eicosanoids, which influence human health and the in vitro activity of immune cells. We therefore examined the effects of dietary AA on the immune response (IR) of 10 healthy men living at our metabolic suite for 130 d. All subjects were fed a basal diet containing 27 energy percentage (en%) fat, 57 en% carbohydrate, and 16 en% protein (AA, 200 mg/d) for the first and last 15 d of the study. Additional AA (1.5 g/d) was incorporated into the diet of six men from day 16 to 65 while the remaining four subjects continued to eat the basal diet. The diets of the two groups were crossed-over from day 66 to 115. In vitro indexes of IR were examined using the blood samples drawn on days 15, 58, 65, 108, 115, and 127. The subjects were immunized with the measles/mumps/rubella vaccine on day 35 and with the influenza vaccine on day 92. Dietary AA did not influence many indexes of IR (peripheral blood mononuclear cell proliferation in response to phytohemagglutinin, Concanavalin A, pokeweed, measles/mumps/rubella, and influenza vaccines prior to immunization, and natural killer cell activity). The post-immunization proliferation in response to influenza vaccine was about fourfold higher in the group receiving high-AA diet compared to the group receiving low-AA diet (P = 0.02). Analysis of variance of the data pooled from both groups showed that the number of circulating granulocytes was significantly (P = 0.03) more when the subjects were fed the high-AA diet than when they were fed the low-AA diet. The small increases in granulocyte count and the in vitro proliferation in response to influenza vaccine caused by dietary AA may not be of clinical significance. However, the lack of any adverse effects on IR indicates that supplementation with AA may be done safely when needed for other health reasons.

Epstein-Barr Virus Modulates 5-Lipoxygenase Product Synthesis in Human Peripheral Blood Mononuclear Cells

The effect of short-term coincubations of Epstein-Barr virus (EBV) with mononuclear cells on the synthesis of leukotrienes (LT) by monocytes was investigated. Although treatment of mononuclear cells with EBV alone had no significant effect on LT synthesis by monocytes, the preincubation of mononuclear cells with EBV before the further stimulation of the cells with either the ionophore A23187, the chemoattractant formyl-Met-Leu-Phe, or the phagocytic particles zymosan strikingly enhanced the formation of both LTB4 and LTC4 above the levels of synthesis observed with the stimuli alone. Such priming effect of EBV on LT synthesis was maximal after 15 minutes of preincubation of mononuclear cells with EBV and slowly declined at longer preincubation times; the priming effect of EBV was observed both in Hank's Balanced Salt Solution and plasma. The effect of EBV was abolished by prior treatment of viral particles by heat or by antibody raised against the glycoprotein gp350 of the viral envelope, but not by UV irradiation of the viral particles. Exposure of mononuclear cells to EBV was shown to strongly enhance the activation of the 5-lipoxygenase and the release of arachidonic acid induced upon cell stimulation with a second agonist. The release of arachidonic acid by the EBV-treated mononuclear cells was inhibitable by arachidonyl trifluoromethyl ketone, an inhibitor of the 80-kD cytosolic phospholipase A2 . Furthermore, EBV was shown to rapidly increase (maximum effect within 15 minutes) the levels of phosphorylated form of the cytosolic phospholipase A2 (as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis), a process related to the activation of this enzyme. These data show that the interaction of EBV with monocytes upregulates the formation of important lipid mediators of inflammation.

Unique monocyte subset in patients with AIDS dementia

BACKGROUND

15-30% of patients infected with HIV will develop a debilitating dementia. Whilst HIV enters the brain soon after infection, presumably within monocyte-derived macrophages, not all patients with HIV become demented. Blood monocytes probably cross the blood-brain barrier and give rise ultimately to parenchyma macrophages. We looked for a specific monocyte subset in AIDS patients with dementia.

METHODS

Peripheral blood monocytes from three groups were compared: AIDS patients with (n = 12) and without (n = 11) dementia, and ten HIV seronegative healthy controls. We used flow cytometry to analyse monocytes, and cell lysis and apoptosis assays to examine monocyte effects on human brain cells in vitro.

FINDINGS

We found a unique subset of monocytes in patients with AIDS dementia. These monocytes were more dense and granular and expressed CD14/CD16 and CD14/CD69. Means (SD) for CD14/CD16 in HIV-negative controls and in AIDS non-dementia and AIDS dementia patients were 6.5% (4), 16% (13), and 37% (21), respectively (p = 0.008 between the two groups of patients). The corresponding means for CD14/CD69 were 7% (6), 8% (10), and 69% (18) (p < 0.0001).

INTERPRETATION

CD69 is a member of the natural-killer-cell gene complex that is expressed after activation. Supernatants from cultures containing these dense cells can trigger apoptosis of human brain cells in vitro. The monocyte subset we found in patients with AIDS dementia might enter the brain and expose neural cells to toxic factors.

AIDS Dementia and HIV-1-Induced Neurotoxicity: Possible Pathogenic Associations and Mechanisms

AIDS Dementia Complex (ADC) is a syndrome of cognitive, behavioral, and motor deficits resulting from HIV-1 infection within the brain. ADC is characterized by variable degrees of neuronal cell death and gliosis that likely result, at least, in part from release of metabolic products, cytokines, and viral proteins from infected macrophages, although a unifying explanation for the neurological dysfunction has yet to be established. Major unanswered questions include: (i) do neurologic symptoms result from neuronal cell death and/or dysfunction in surviving neurons?; (ii) are viral genomic sequences determinants of neurotoxicity?; (iii) is HIV infection of neurons and astrocytes relevant to pathogenesis?, and (iv) what circulating factors within the brain affect neuronal cell survival and function? This review addresses the association between HIV-1 replication within the brain, production of potential neurotoxins and possible mechanisms of induction of neurotoxicity and neuronal dysfunction contributing to the pathogenesis of ADC. Copyright 1996 S. Karger AG, Basel

Tumor necrosis factor alpha inhibits glutamate uptake by primary human astrocytes. Implications for pathogenesis of HIV-1 dementia

Human immunodeficiency virus (HIV) infection is commonly associated with neurological disease that occurs in the apparent absence of extensive infection of brain cells by HIV, suggesting that indirect mechanisms account for neuropathogenesis in the CNS, perhaps including changes in the normal neuroprotective functions of astrocytes. To test this hypothesis, we examined the effect of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFalpha), produced by HIV-1-infected macrophages and microglia, on glutamate transport by primary human fetal astrocytes (PHFAs). A dose-dependent inhibition of high affinity glutamate uptake sites was observed 12-24 h after addition of exogenous recombinant human TNFalpha to PHFAs. This effect was specific since it was blocked by a neutralizing monoclonal antibody directed against TNFalpha. Furthermore, the inhibitory effect was reproduced by a monoclonal antibody that is an agonist at the 55-kDa TNF receptor. These results suggest that the neurotoxic effects of TNFalpha may be due in part to its ability to inhibit glutamate uptake by astrocytes, which in turn may result in excitotoxic concentrations of glutamate in synapses.