Monocyte/macrophages and their role in HIV neuropathogenesis

Novel elvitegravir nanoformulation for drug delivery across the blood-brain barrier to achieve HIV-1 suppression in the CNS macrophages

The use of antiretroviral therapy (ART) has remarkably decreased the morbidity associated with HIV-1 infection, however, the prevalence of HIV-1-associated neurocognitive disorders (HAND) is still increasing. The blood-brain barrier (BBB) is the major impediment for penetration of antiretroviral drugs, causing therapeutics to reach only suboptimal level to the brain. Conventional antiretroviral drug regimens are not sufficient to improve the treatment outcomes of HAND. In our recent report, we have developed a poloxamer-PLGA nanoformulation loaded with elvitegravir (EVG), a commonly used antiretroviral drug. The nanoformulated EVG is capable of elevating intracellular drug uptake and simultaneously enhance viral suppression in HIV-1-infected macrophages. In this work, we identified the clinical parameters including stability, biocompatibility, protein corona, cellular internalization pathway of EVG nanoformulation for its potential clinical translation. We further assessed the ability of this EVG nanoformulation to cross the in vitro BBB model and suppress the HIV-1 in macrophage cells. Compared with EVG native drug, our EVG nanoformulation demonstrated an improved BBB model penetration cross the in vitro BBB model and an enhanced HIV-1 suppression in HIV-1-infected human monocyte-derived macrophages after crossing the BBB model without altering the BBB model integrity. Overall, this is an innovative and optimized treatment strategy that has a potential for therapeutic interventions in reducing HAND.

Plasma inflammatory biomarkers link to diffusion tensor imaging metrics in virally suppressed HIV-infected individuals

OBJECTIVE

Inflammation may contribute to brain white matter health in people living with HIV who report cognitive symptoms despite adherence to combination antiretroviral therapy and viral suppression. We explored relationships between diffusion tensor imaging (DTI) metrics of white matter, plasma biomarkers of immune activation, and cognitive function in the HIV-infected population.

DESIGN

Retrospective study of older adults living with HIV who are combination antiretroviral therapy adherent, virally suppressed, and self-report cognitive symptoms.

METHODS

MRI, blood draws, and standardized neuropsychological test scores were collected from HIV-infected individuals. DTI metrics (fractional anisotropy, mean diffusivity, radial diffusivity, axial diffusivity) and plasma biomarkers (soluble CD163, soluble CD14, neopterin, IFN γ-induced protein 10, monocyte chemoattractant protein 1) were quantified. Statistical analysis explored associations between biomarker levels or neuropsychological test scores and DTI metrics using region of interest analyses and a voxelwise approach.

RESULTS

A total of 43 participants with median (interquartile range) age of 64 (62-66 years), CD4 cell count of 600 (400-760 cell/μl) who were all virally suppressed (<100 copies/ml) were selected. Higher levels of monocyte chemoattractant protein 1 associated with lower fractional anisotropy and higher mean diffusivity (P < 0.05) across white matter tracts including corpus callosum, corona radiata, and superior longitudinal fasciculus. Higher neopterin associated with higher mean diffusivity in the genu of corpus callosum, and higher soluble CD14 associated with lower fractional anisotropy in the bilateral superior corona radiata (P < 0.05). Worse global performance and speed domain scores associated with higher mean diffusivity and lower fractional anisotropy, and worse executive domain scores associated with lower fractional anisotropy (P < 0.05).

CONCLUSION

Elevated inflammatory plasma biomarkers link to white matter abnormalities among virally suppressed individuals. DTI abnormalities associate to cognitive performance. We conclude that inflammatory processes impact clinically relevant brain health indices despite viral suppression.

New Potential Axes of HIV Neuropathogenesis with Relevance to Biomarkers and Treatment

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) affect approximately half of people living with HIV despite viral suppression with antiretroviral therapies and represent a major cause of morbidity. HAND affects activities of daily living including driving, using the Internet and, importantly, maintaining drug adherence. Whilst viral suppression with antiretroviral therapies (ART) has reduced the incidence of severe dementia, mild neurocognitive impairments continue to remain prevalent. The neuropathogenesis of HAND in the context of viral suppression remains ill-defined, but underlying neuroinflammation is likely central and driven by a combination of chronic intermittent low-level replication of whole virus or viral components, latent HIV infection, peripheral inflammation possibly from a disturbed gut microbiome or chronic cellular dysfunction in the central nervous system. HAND is optimally diagnosed by clinical assessment with imaging and neuropsychological testing, which can be difficult to perform in resource-limited settings. Thus, the identification of biomarkers of disease is a key focus of the field. In this chapter, recent advances in the pathogenesis of HAND and biomarkers that may aid its diagnosis and treatment will be discussed.

High Plasma Soluble CD163 During Infancy Is a Marker for Neurocognitive Outcomes in Early-Treated HIV-Infected Children

BACKGROUND

Monocyte activation may contribute to neuronal injury in aviremic HIV-infected adults; data are lacking in children. We examined the relation between monocyte activation markers and early and long-term neurodevelopmental outcomes in early-treated HIV-infected children.

SETTING

Prospective study of infant and child neurodevelopmental outcomes nested within a randomized clinical trial (NCT00428116) and extended cohort study in Kenya.

METHODS

HIV-infected infants (N = 67) initiated antiretroviral therapy (ART) at age <5 months. Plasma soluble (s) CD163 (sCD163), sCD14, and neopterin were measured before ART (entry) and 6 months later. Milestone attainment was ascertained monthly during 24 months, and neuropsychological tests were performed at 5.8-8.2 years after initiation of ART (N = 27). The relationship between neurodevelopment and sCD163, sCD14, and neopterin at entry and 6 months after ART was assessed using Cox proportional hazards models and linear regression.

RESULTS

Infants with high entry sCD163 had unexpected earlier attainment of supported sitting (5 vs 6 months; P = 0.006) and supported walking (10 vs 12 months; P = 0.02) with trends in adjusted analysis. Infants with high 6-month post-ART sCD163 attained speech later (17 vs 15 months; P = 0.006; adjusted hazard ratio, 0.47; P = 0.02), threw toys later (18 vs 17 months; P = 0.01; adjusted hazard ratio, 0.53; P = 0.04), and at median 6.8 years after ART, had worse neuropsychological test scores (adj. mean Z-score differences, cognition, -0.42; P = 0.07; short-term memory, -0.52; P = 0.08; nonverbal test performance, -0.39, P = 0.05).

CONCLUSIONS

Before ART, monocyte activation may reflect transient neuroprotective mechanisms in infants. After ART and viral suppression, monocyte activation may predict worse short- and long-term neurodevelopment outcomes.

Plasma concentration of neurofilament light chain protein decreases after switching from tenofovir disoproxil fumarate to tenofovir alafenamide fumarate

Background

Because tenofovir alafenamide (TAF) leads to significantly lower plasma tenofovir concentrations than tenofovir disoproxil fumarate (TDF) and is a stronger substrate for P-glycoprotein (P-gp) than TDF, TAF could lead to decreased central nervous system (CNS) tenofovir exposure than TDF. We aimed to determine if switching from TDF to TAF increases the risk of neuronal injury, by quantifying plasma levels of neurofilament light protein (NfL), a sensitive marker of neuronal injury in HIV CNS infection.

Methods

Plasma NfL concentration was measured at baseline, week 24, and week 84 in stored plasma samples from 416 participants (272 switching to elvitegravir (E)/cobicistat (C)/emtricitabine (F)/TAF and 144 continuing E/C/F/TDF) enrolled in the randomized, active-controlled, multicenter, open-label, noninferiority Gilead GS-US-292-0109 trial.

Results

While plasma NfL levels in both groups were within the normal range, we found a small but significant decrease in the E/C/F/TAF arm after 84 weeks from a geometric mean of 9.3 to 8.8 pg/mL (5.4% decline, 95% CI 2.0–8.4, p = 0.002). This change was significantly different (p = 0.001) from that of the E/C/F/TDF arm, in which plasma NfL concentration changed from 9.7 pg/mL at baseline to 10.2 pg/mL at week 84 (5.8% increase, 95% CI -0.8–12.9, p = 0.085). This increase is in line with what could be expected in normal ageing. Plasma NfL concentrations significantly correlated with age. No correlation was found between plasma NfL and serum creatinine.

Conclusions

We found no biomarker evidence of CNS injury when switching from TDF to TAF. It is unclear whether the small decrease in plasma NfL found after switch to TAF is of any clinical relevance, particularly with plasma NfL levels in both arms remaining within the limits found in HIV-negative controls. These results indicate that switching from TDF to TAF appears safe with regard to neuronal injury.

Brain macrophages harbor latent, infectious simian immunodeficiency virus

: The current review examines the role of brain macrophages, that is perivascular macrophages and microglia, as a potential viral reservoir in antiretroviral therapy (ART) treated, simian immunodeficiency virus (SIV)-infected macaques. The role, if any, of latent viral reservoirs of HIV and SIV in the central nervous system during ART suppression is an unresolved issue. HIV and SIV infect both CD4 lymphocytes and myeloid cells in blood and tissues during acute and chronic infection. HIV spread to the brain occurs during acute infection by the infiltration of activated CD4 lymphocytes and monocytes from blood and is established in both embryonically derived resident microglia and monocyte-derived perivascular macrophages. ART controls viral replication in peripheral blood and cerebrospinal fluid in HIV-infected individuals but does not directly eliminate infected cells in blood, tissues or brain. Latently infected resting CD4 lymphocytes in blood and lymphoid tissues are a well recognized viral reservoir that can rebound once ART is withdrawn. In contrast, central nervous system resident microglia and perivascular macrophages in brain have not been examined as potential reservoirs for HIV during suppressive ART. Macrophages in tissues are long-lived cells that are HIV and SIV infected in tissues such as gut, lung, spleen, lymph node and brain and contribute to ongoing inflammation in tissues. However, their potential role in viral persistence and latency or their potential to rebound in the absence ART has not been examined. It has been shown that measurement of HIV latency by HIV DNA PCR in CD4 lymphocytes overestimates the size of the latent reservoirs of HIV that contribute to rebound that is cells containing the genomes of replicative viruses. Thus, the quantitative viral outgrowth assay has been used as a reliable measure of the number of latent cells that harbor infectious viral DNA and, may constitute a functional latent reservoir. Using quantitative viral outgrowth assays specifically designed to quantitate latently infected CD4 lymphocytes and myeloid cells in an SIV macaque model, we demonstrated that macrophages in brain harbor SIV genomes that reactivate and produce infectious virus in this assay, demonstrating that these cells have the potential to be a reservoir.

SLAM Family Receptor Signaling in Viral Infections: HIV and Beyond

The signaling lymphocytic activation molecule (SLAM) family of receptors are expressed on the majority of immune cells. These receptors often serve as self-ligands, and play important roles in cellular communication and adhesion, thus modulating immune responses. SLAM family receptor signaling is differentially regulated in various immune cell types, with responses generally being determined by the presence or absence of two SLAM family adaptor proteins-Ewing's sarcoma-associated transcript 2 (EAT-2) and SLAM-associated adaptor protein (SAP). In addition to serving as direct regulators of the immune system, certain SLAM family members have also been identified as direct targets for specific microbes and viruses. Here, we will discuss the known roles for these receptors in the setting of viral infection, with special emphasis placed on HIV infection. Because HIV causes such complex dysregulation of the immune system, studies of the roles for SLAM family receptors in this context are particularly exciting.

Microglial Cells: The Main HIV-1 Reservoir in the Brain

Despite efficient combination of the antiretroviral therapy (cART), which significantly decreased mortality and morbidity of HIV-1 infection, a definitive HIV cure has not been achieved. Hidden HIV-1 in cellular and anatomic reservoirs is the major hurdle toward a functional cure. Microglial cells, the Central Nervous system (CNS) resident macrophages, are one of the major cellular reservoirs of latent HIV-1. These cells are believed to be involved in the emergence of drugs resistance and reseeding peripheral tissues. Moreover, these long-life reservoirs are also involved in the development of HIV-1-associated neurocognitive diseases (HAND). Clearing these infected cells from the brain is therefore crucial to achieve a cure. However, many characteristics of microglial cells and the CNS hinder the eradication of these brain reservoirs. Better understandings of the specific molecular mechanisms of HIV-1 latency in microglial cells should help to design new molecules and new strategies preventing HAND and achieving HIV cure. Moreover, new strategies are needed to circumvent the limitations associated to anatomical sanctuaries with barriers such as the blood brain barrier (BBB) that reduce the access of drugs.

Pathology of inflammatory diseases of the nervous system: Human disease versus animal models

Numerous recent studies have been performed to elucidate the function of microglia, macrophages, and astrocytes in inflammatory diseases of the central nervous system. Regarding myeloid cells a core pattern of activation has been identified, starting with the activation of resident homeostatic microglia followed by recruitment of blood borne myeloid cells. An initial state of proinflammatory activation is at later stages followed by a shift toward an‐anti‐inflammatory and repair promoting phenotype. Although this core pattern is similar between experimental models and inflammatory conditions in the human brain, there are important differences. Even in the normal human brain a preactivated microglia phenotype is evident, and there are disease specific and lesion stage specific differences in the contribution between resident and recruited myeloid cells and their lesion state specific activation profiles. Reasons for these findings reside in species related differences and in differential exposure to different environmental cues. Most importantly, however, experimental rodent studies on brain inflammation are mainly focused on autoimmune encephalomyelitis, while there is a very broad spectrum of human inflammatory diseases of the central nervous system, triggered and propagated by a variety of different immune mechanisms.

Zika virus enhances monocyte adhesion and transmigration favoring viral dissemination to neural cells

Zika virus (ZIKV) invades and persists in the central nervous system (CNS), causing severe neurological diseases. However the virus journey, from the bloodstream to tissues through a mature endothelium, remains unclear. Here, we show that ZIKV-infected monocytes represent suitable carriers for viral dissemination to the CNS using human primary monocytes, cerebral organoids derived from embryonic stem cells, organotypic mouse cerebellar slices, a xenotypic human-zebrafish model, and human fetus brain samples. We find that ZIKV-exposed monocytes exhibit higher expression of adhesion molecules, and higher abilities to attach onto the vessel wall and transmigrate across endothelia. This phenotype is associated to enhanced monocyte-mediated ZIKV dissemination to neural cells. Together, our data show that ZIKV manipulates the monocyte adhesive properties and enhances monocyte transmigration and viral dissemination to neural cells. Monocyte transmigration may represent an important mechanism required for viral tissue invasion and persistence that could be specifically targeted for therapeutic intervention.

Zika virus (ZIKV) can infect the central nervous system, but it is not clear how it reaches the brain. Here, Ayala-Nunez et al. show in ex vivo and in vivo models that ZIKV can hitch a ride in monocytes in a Trojan Horse manner to cross the endothelium and disseminate the virus.

Tat expression led to increased histone 3 tri-methylation at lysine 27 and contributed to HIV latency in astrocytes through regulation of MeCP2 and Ezh2 expression

Astrocytes are susceptible to HIV infection and potential latent HIV reservoirs. Tat is one of three abundantly expressed HIV early genes in HIV-infected astrocytes and has been shown to be a major pathogenic factor for HIV/neuroAIDS. In this study, we sought to determine if and how Tat expression would affect HIV infection and latency in astrocytes. Using the glycoprotein from vesicular stomatitis virus-pseudotyped red-green HIV (RGH) reporter viruses, we showed that HIV infection was capable of establishing HIV latency in astrocytes. We also found that Tat expression decreased the generation of latent HIV-infected cells. Activation of latent HIV-infected astrocytes showed that treatment of GSK126, a selective inhibitor of methyltransferase enhancer of zeste homolog 2 (Ezh2) that is specifically responsible for tri-methylation of histone 3 lysine 27 (H3K27me3), led to activation of significantly more latent HIV-infected Tat-expressing astrocytes. Molecular analysis showed that H3K27me3, Ezh2, MeCP2, and Tat all exhibited a similar bimodal expression kinetics in the course of HIV infection and latency in astrocytes, although H3K27me3, Ezh2, and MeCP2 were expressed higher in Tat-expressing astrocytes and their expression were peaked immediately preceding Tat expression. Subsequent studies showed that Tat expression alone was sufficient to induce H3K27me3 expression, likely through its regulation of Ezh2 and MeCP2 expression. Taken together, these results showed for the first time that Tat expression induced H3K27me3 expression and contributed to HIV latency in astrocytes and suggest a new role and novel mechanism for Tat in HIV latency.

Fluctuating Sensorineural Hearing Loss

BACKGROUND

Several otologic conditions can present with fluctuating sensorineural hearing loss, including Ménière's disease, autoimmune inner ear disease, and enlarged vestibular aqueduct. Although these 3 etiologies vary greatly, distinguishing between these conditions at initial presentation can be challenging. Furthermore, initial treatment of these conditions is often similar. In this review, we discuss historical and current perspectives on diagnosis and treatment of these conditions.

SUMMARY

A literature search was performed regarding fluctuating hearing loss, and current treatment of these etiologies of fluctuating hearing loss was summarized. Immediate measures at the onset of acute hearing loss include corticosteroid therapy, while preventative and chronic therapies, which can limit disease severity and frequency, vary based on the specific condition treated. Key Messages: Fluctuating hearing loss can represent a range of pathologies, but the precise etiology may not be clear at initial presentation. Timely treatment and long-term follow-up, along with appropriate diagnostics, are necessary to optimize long-term hearing.

In vitro Infection of Primary Human Monocytes with HIV-1

Monocyte infection by HIV-1 is an important component of chronic HIV pathogenesis. Following infection by HIV-1, monocytes are able to cross the blood brain barrier and set up a viral reservoir in the central nervous system. Additionally, in the setting of chronic HIV-1 infection, monocytes can become activated either directly through HIV-1 infection or indirectly via HIV-1-mediated systemic immune activation. Currently, there are few studies looking at HIV-1 infection of primary human monocytes in vitro. Furthermore, detection of successful HIV-1 infection of monocytes can be laborious requiring an ELISA for p24 or assessing levels of HIV-1 mRNA or DNA. This protocol utilizes an HIV-1 strain expressing GFP to allow for easy quantification of HIV-1 infection by fluorescence-assisted cell sorting (FACS). By determining HIV-1 infection by FACS one can take advantage of its multiparametric nature allowing for the use of less cells and the ability to assess the expression of other markers on HIV-1⁺ and HIV-1^- cells in the same experiment. Additionally, this protocol could be modified to study HIV-1 infection of other cells including CD4⁺ T cells.

SIV-Mediated Synaptic Dysfunction Is Associated with an Increase in Synapsin Site 1 Phosphorylation and Impaired PP2A Activity

Although the reduction of viral loads in people with HIV undergoing combination antiretroviral therapy has mitigated AIDS-related symptoms, the prevalence of neurological impairments has remained unchanged. HIV-associated CNS dysfunction includes impairments in memory, attention, memory processing, and retrieval. Here, we show a significant site-specific increase in the phosphorylation of Syn I serine 9, site 1, in the frontal cortex lysates and synaptosome preparations of male rhesus macaques infected with simian immunodeficiency virus (SIV) but not in uninfected or SIV-infected antiretroviral therapy animals. Furthermore, we found that a lower protein phosphatase 2A (PP2A) activity, a phosphatase responsible for Syn I (S9) dephosphorylation, is primarily associated with the higher S9 phosphorylation in the frontal cortex of SIV-infected macaques. Comparison of brain sections confirmed higher Syn I (S9) in the frontal cortex and greater coexpression of Syn I and PP2A A subunit, which was observed as perinuclear aggregates in the somata of the frontal cortex of SIV-infected macaques. Synaptosomes from SIV-infected animals were physiologically tested using a synaptic vesicle endocytosis assay and FM4-64 dye showing a significantly higher baseline depolarization levels in synaptosomes of SIV⁺-infected than uninfected control or antiretroviral therapy animals. A PP2A-activating FDA-approved drug, FTY720, decreased the higher synaptosome depolarization in SIV-infected animals. Our results suggest that an impaired distribution and lower activity of serine/threonine phosphatases in the context of HIV infection may cause an indirect effect on the phosphorylation levels of essential proteins involving in synaptic transmission, supporting the occurrence of specific impairments in the synaptic activity during SIV infection.SIGNIFICANCE STATEMENT Even with antiretroviral therapy, neurocognitive deficits, including impairments in attention, memory processing, and retrieval, are still major concerns in people living with HIV. Here, we used the rhesus macaque simian immunodeficiency virus model with and without antiretroviral therapy to study the dynamics of phosphorylation of key amino acid residues of synapsin I, which critically impacts synaptic vesicle function. We found a significant increase in synapsin I phosphorylation at serine 9, which was driven by dysfunction of serine/threonine protein phosphatase 2A in the nerve terminals. Our results suggest that an impaired distribution and lower activity of serine/threonine phosphatases in the context of HIV infection may cause an indirect effect on the phosphorylation levels of essential proteins involved in synaptic transmission.

Heterogeneity in neurocognitive change trajectories among people with HIV starting antiretroviral therapy in Rakai, Uganda

Considerable heterogeneity exists in patterns of neurocognitive change in people with HIV (PWH). We examined heterogeneity in neurocognitive change trajectories from HIV diagnosis to 1-2 years post-antiretroviral therapy (ART). In an observational cohort study in Rakai, Uganda, 312 PWH completed a neuropsychological (NP) test battery at two-time points (ART-naïve, 1-2 years post-ART initiation). All NP outcomes were used in a latent profile analysis to identify subgroups of PWH with similar ART-related neurocognitive change profiles. In a subset, we examined subgroup differences pre-ART on cytokine and neurodegenerative biomarkers CSF levels. We identified four ART-related change subgroups: (1) decline-only (learning, memory, fluency, processing speed, and attention measures), (2) mixed (improvements in learning and memory but declines in attention and executive function measures), (3) no-change, or (4) improvement-only (learning, memory, and attention measures). ART-related NP outcomes that are most likely to change included learning, memory, and attention. Motor function measures were unchanged. Subgroups differed on eight of 34 pre-ART biomarker levels including interleukin (IL)-1β, IL-6, IL-13, interferon-γ, macrophage inflammatory protein-1β, matrix metalloproteinase (MMP)-3, MMP-10, and platelet-derived growth factor-AA. The improvement-only and mixed subgroups showed lower levels on these markers versus the no-change subgroup. These findings provide support for the need to disentangle heterogeneity in ART-related neurocognitive changes, to focus on higher-order cognitive processes (learning, memory, attention) as they were most malleable to change, and to better understand why motor function remained unchanged despite ART treatment. Group differences in pre-ART CSF levels provide preliminary evidence of biological plausibility of neurocognitive phenotyping.

Overexpression and activation of colony-stimulating factor 1 receptor in the SIV/macaque model of HIV infection and neuroHIV

In the present study, we investigated whether colony-stimulating factor 1 receptor (CSF1R) is expressed on brain macrophages and microglia in the human and macaque brain and whether it is upregulated and activated after lentivirus infection in vivo and contributes to development of encephalitic lesions. We examined, using multi-label and semi-quantitative immunofluorescence microscopy, the protein expression level and cellular localization of CSF1R in brain tissues from uninfected controls and SIV-infected adult macaques with or without encephalitis and also from uninfected controls, HIV-infected encephalitic subjects and virally suppressed subjects. In the normal uninfected brain, CSF1R protein was detected only on microglia and brain macrophages but not on neurons, astrocytes or oligodendrocytes. Microglia constitutively expressed CSF1R at low levels, and its expression was largely unchanged in non-encephalitic and encephalitic animals. Brain macrophages, including perivascular macrophages (PVMs), expressed higher levels of CSF1R compared to microglia. Interestingly, we found significantly increased expression of CSF1R on the infected PVMs and lesional macrophages in the brains of encephalitic macaques. Moreover, the per cell expression of CSF1R determined by its mean pixel intensity (MPI) correlated positively with the MPI of SIV Gag p28 in SIV-infected PVMs. Using phosphorylated CSF1R at tyrosine residue 723 and phosphorylated signal transducer and activator of transcription 5 at tyrosine reside 694 as markers for CSF1R activation, we found selective activation of CSF1R signaling in infected brain macrophages in encephalitis. We also found colocalization of CSF1R and its ligand CSF1 in PVMs and lesional macrophages in the brains of encephalitic macaques and humans. Notably, elevated brain CSF1R expression was found in virally suppressed subjects. These findings point to opportunities for developing a specific approach targeting infected brain macrophages, with several brain-penetrant CSF1R inhibitors that are available now, in order to eliminate central nervous system macrophage reservoirs, while not affecting resting uninfected microglia and PVMs that show no CSF1R activation.

The SIV Envelope Glycoprotein, Viral Tropism, and Pathogenesis: Novel Insights from Nonhuman Primate Models of AIDS

BACKGROUND

Cellular tropism of human immunodeficiency virus (HIV-1) is closely linked to interactions between the viral envelope glycoprotein (Env) with CD4 and chemokine receptor family members, CCR5 and CXCR4. This interaction plays a key role in determining anatomic sites that are infected in vivo and the cascade of early and late events that result in chronic immune activation, immunosuppression and ultimately, AIDS. CD4+ T cells are critical to adaptive immune responses, and their early and rapid infection in gut lamina propria and secondary lymphoid tissues in susceptible hosts likely contributes to viral persistence and progression to disease. CD4+ macrophages are also infected, although their role in HIV-1 pathogenesis is more controversial.

METHODS

Pathogenic infection by simian immunodeficiency viruses (SIV) in Asian macaques as models of HIV-1 infection has enabled the impact of cellular tropism on pathogenesis to be directly probed. This review will highlight examples in which experimental interventions during SIV infection or the introduction of viral mutations have altered cellular tropism and, subsequently, pathogenesis.

RESULTS

Alterations to the interaction of Env and its cellular receptors has been shown to result in changes to CD4 dependence, coreceptor specificity, and viral tropism for gut CD4+ T cells and macrophages.

CONCLUSION

Collectively, these findings have yielded novel insights into the critical role of the viral Env and tropism as a driver of pathogenesis and host control and have helped to identify new areas for targeted interventions in therapy and prevention of HIV-1 infection.

Editor's Commentary for Special Issue: "The Role of Macrophages in HIV Persistence"

Macrophages as reservoirs for persistent HIV infection has gained renewed importance, with an intense research focus dedicated to eradication strategies. Clearance of both latent and productive HIV from these important reservoirs is essential for successful eradication. This spe cial theme issue contains 11 papers, including 6 Invited Reviews, 1 Brief Report and 4 Original Articles, that focus on the various aspects of the macrophage as pertains to HIV persistence, latency and cure. These topics include: functional latency of macrophages and microglia, the link between peripheral monocytes and pathogenesis, macrophages as sources of HIV RNA and DNA in virally suppressed patients, brain imaging of neuroinflammation, macrophages as drug delivery vehicles, therapeutic strategies of infected macrophages for cure, and the role of drugs of abuse in enhancing macrophage viral persistence.

Cerebrospinal fluid viral escape in aviremic HIV-infected patients receiving antiretroviral therapy: prevalence, risk factors and neurocognitive effects

BACKGROUND

During antiretroviral therapy, HIV RNA can be detected in cerebrospinal fluid (CSF) when it is undetectable in plasma, a condition termed 'CSF viral escape'. The aim of the current study was to determine the prevalence and risk factors for CSF viral escape in two large cohorts in the USA.

METHODS

A total of 1264 HIV-infected volunteers enrolled in two US cohorts at their most recent visit between 2003 and 2011 were included in this cross-sectional analysis if their HIV RNA level in plasma was less than 50 copies/ml while receiving stable antiretroviral therapy (ART) (>6 months) and if they had HIV RNA measured in CSF at their most recent visit between 2003 and 2011. Potential risk factors were identified using univariable and multivariable regression.

RESULTS

CSF viral escape was detected in 55 adults (4.4%; 95% CI: 3.4-5.6), who had a median CSF HIV RNA of 155 copies/ml [interquartile range (IQR: 80-283)]. Patients with or without CSF viral escape had similar rates of neurocognitive impairment (38.2 vs. 37.7%; P = 0.91). CSF viral escape was independently associated with the use of ritonavir-boosted protease inhibitors [odds ratio (OR): 2.0; 95% CI: 1.1-3.8] or unboosted atazanavir (OR: 5.1; 95% CI: 1.3-16.1), CSF pleocytosis (OR: 7.6; 95% CI: 4.2-13.7) and abnormal CSF total protein (OR: 2.1; 95% CI: 1.1-3.7).

CONCLUSIONS

In this large study of aviremic patients receiving ART, CSF viral escape was uncommon and was linked to evidence of central nervous system inflammation and the use of protease inhibitors, but not with worse neurocognitive performance.

A Quantitative Approach to SIV Functional Latency in Brain Macrophages

Lentiviruses are retroviruses that primarily infect myeloid cells, leading to acute inflammatory infections in many tissues particularly, lung, joints and the central nervous system (CNS). Acute infection by lentiviruses is followed by persistent/latent infections that are not cleared by the host immune system. HIV and SIV are lentiviruses that also infect CD4+ lymphocytes as well as myeloid cells in blood and multiple tissues. HIV infection of myeloid cells in brain, lung and heart cause tissue specific diseases as well as infect cells in gut, lymph nodes and spleen. AIDS dementia and other tissue specific disease are observed when infected individuals are immunosuppressed and the number of circulating CD4+ T cells declines to low levels. Antiretroviral therapy (ART) controls viral spread and dramatically changes the course of immunodeficiency and AIDS dementia. However, ART does not eliminate virus-infected cells. Brain macrophages contain HIV DNA and may represent a latent reservoir that persists. HIV latency in CD4+ lymphocytes is the main focus of current research and concern in efforts to eradicate HIV. However, a number of studies have demonstrated that myeloid cells in blood and tissues of ART suppressed individuals harbor HIV DNA. The resident macrophages in tissues such as brain (microglia), spleen (red pulp macrophages) and alveolar macrophages in lung are derived from the yolk sac and can self renew. The question of the latent myeloid reservoir in HIV has not been rigorously examined and its potential as a barrier to eradication been considered. Using a well characterized SIV ART suppressed, non-human primate (NHP) model, our laboratory developed the first quantitative viral outgrowth assay (QVOA) designed to evaluate latently infected CD4+ lymphocytes and more recently developed a similar protocol for the assessment of latently infected myeloid cells in blood and brain. Using an SIV ART model, it was demonstrated that myeloid cells in blood and brain harbor latent SIV that can be reactivated and produce infectious virus in vitro. These studies demonstrate for the first time that myeloid cells have the potential to be a latent reservoir of HIV that produces infectious virus that can be reactivated in the absence of ART and during HIV eradication strategies. Graphical Abstract.

Cerebrospinal fluid levels of glial marker YKL-40 strongly associated with axonal injury in HIV infection

BACKGROUND

HIV-1 infects the central nervous system (CNS) shortly after transmission. This leads to a chronic intrathecal immune activation. YKL-40, a biomarker that mainly reflects activation of astroglial cells, has not been thoroughly investigated in relation to HIV. The objective of our study was to characterize cerebrospinal fluid (CSF) YKL-40 in chronic HIV infection, with and without antiretroviral treatment (ART).

METHODS

YKL-40, neopterin, and the axonal marker neurofilament light protein (NFL) were analyzed with ELISA in archived CSF samples from 120 HIV-infected individuals (85 untreated neuroasymptomatic patients, 7 with HIV-associated dementia, and 28 on effective ART) and 39 HIV-negative controls.

RESULTS

CSF YKL-40 was significantly higher in patients with HIV-associated dementia compared to all other groups. It was also higher in untreated neuroasymptomatic individuals with CD4 cell count < 350 compared to controls. Significant correlations were found between CSF YKL-40 and age (r = 0.38, p < 0.001), CD4 (r = - 0.36, p < 0.001), plasma HIV RNA (r = 0.35, p < 0.001), CSF HIV RNA (r = 0.35, p < 0.001), CSF neopterin (r = 0.40, p < 0.001), albumin ratio (r = 0.44, p < 0.001), and CSF NFL (r = 0.71, p < 0.001). Age, CD4 cell count, albumin ratio, and CSF HIV RNA were found as independent predictors of CSF YKL-40 concentrations in multivariable analysis. In addition, CSF YKL-40 was revealed as a strong independent predictor of CSF NFL together with age, CSF neopterin, and CD4 cell count.

CONCLUSIONS

CSF YKL-40 is a promising biomarker candidate for understanding the pathogenesis of HIV in the CNS. The strong correlation between CSF YKL-40 and NFL suggests a pathogenic association between astroglial activation and axonal injury, and implies its utility in assessing the prognostic value of YKL-40.

Microglial Cells: The Main HIV-1 Reservoir in the Brain

Despite efficient combination of the antiretroviral therapy (cART), which significantly decreased mortality and morbidity of HIV-1 infection, a definitive HIV cure has not been achieved. Hidden HIV-1 in cellular and anatomic reservoirs is the major hurdle toward a functional cure. Microglial cells, the Central Nervous system (CNS) resident macrophages, are one of the major cellular reservoirs of latent HIV-1. These cells are believed to be involved in the emergence of drugs resistance and reseeding peripheral tissues. Moreover, these long-life reservoirs are also involved in the development of HIV-1-associated neurocognitive diseases (HAND). Clearing these infected cells from the brain is therefore crucial to achieve a cure. However, many characteristics of microglial cells and the CNS hinder the eradication of these brain reservoirs. Better understandings of the specific molecular mechanisms of HIV-1 latency in microglial cells should help to design new molecules and new strategies preventing HAND and achieving HIV cure. Moreover, new strategies are needed to circumvent the limitations associated to anatomical sanctuaries with barriers such as the blood brain barrier (BBB) that reduce the access of drugs.

Human immunodeficiency virus Type-1 single-stranded RNA activates the NLRP3 inflammasome and impairs autophagic clearance of damaged mitochondria in human microglia

Despite the availability of antiretroviral therapy (ART) that fully suppresses human immunodeficiency virus type-1 (HIV), markers of inflammation and minor neurocognitive impairment are frequently identified in HIV-infected persons. Increasing data support that low-level replication defective viral RNA is made by infected cells despite the absence of infectious virus. Specific GU-rich single-stranded RNA from the HIV long terminal repeat region (ssRNA40) signaling through toll-like receptor (TLR)-7 and -8 has been shown to induce the secretion of interleukin-1β (IL-1β) in primary monocytes. Here, we examined the activation of microglial cells by HIV ssRNA40 and the potential subsequent neurotoxicity. Our findings show that exposure of human primary microglia to ssRNA40 activates the NLR family pyrin domain containing 3 (NLRP3) inflammasome. Following exposure to ssRNA40, pro-inflammatory cytokines IL-1β, IL-18, and neurotoxic cytokines TNF-α, IL-1α, and C1q expression and extracellular secretion are increased. The released cytokines are functional since culture supernatants from ssRNA40 exposed microglia-induced toxicity of human primary neurons. Moreover, inflammasome activation of microglia increased ROS generation with a loss of mitochondrial membrane potential and mitochondrial integrity. Treatment with ssRNA40 resulted in a blockade of autophagy/mitophagy mediated negative regulation of NLRP3 inflammasome activity with the release of inflammatory cytokines, caspase-1 activation, and pyroptotic microglial cell death. Thus, HIV ssRNA mediated activation of microglial cells can contribute to neurotoxicity and neurodegeneration via secretion of inflammatory and neurotoxic cytokines. These findings provide a potential mechanism that explains the frequent minor cognitive deficits and chronic inflammation that persist in HIV-infected persons despite treatment with suppressive ART.

Role of Macrophage Dopamine Receptors in Mediating Cytokine Production: Implications for Neuroinflammation in the Context of HIV-Associated Neurocognitive Disorders

Despite the success of combination anti-retroviral therapy (cART), around 50% of HIV-infected individuals still display a variety of neuropathological and neurocognitive sequelae known as NeuroHIV. Current research suggests these effects are mediated by long-term changes in CNS function in response to chronic infection and inflammation, and not solely due to active viral replication. In the post-cART era, drug abuse is a major risk-factor for the development of NeuroHIV, and increases extracellular dopamine in the CNS. Our lab has previously shown that dopamine can increase HIV infection of primary human macrophages and increase the production of inflammatory cytokines, suggesting that elevated dopamine could enhance the development of HIV-associated neuropathology. However, the precise mechanism(s) by which elevated dopamine could exacerbate NeuroHIV, particularly in chronically-infected, virally suppressed individuals remain unclear. To determine the connection between dopaminergic alterations and HIV-associated neuroinflammation, we have examined the impact of dopamine exposure on macrophages from healthy and virally suppressed, chronically infected HIV patients. Our data show that dopamine treatment of human macrophages isolated from healthy and cART-treated donors promotes production of inflammatory mediators including IL-1β, IL-6, IL-18, CCL2, CXCL8, CXCL9, and CXCL10. Furthermore, in healthy individuals, dopamine-mediated modulation of specific cytokines is correlated with macrophage expression of dopamine-receptor transcripts, particularly DRD5, the most highly-expressed dopamine-receptor subtype. Overall, these data will provide more understanding of the role of dopamine in the development of NeuroHIV, and may suggest new molecules or pathways that can be useful as therapeutic targets during HIV infection.

Cerebrospinal Fluid Ceruloplasmin, Haptoglobin, and Vascular Endothelial Growth Factor Are Associated with Neurocognitive Impairment in Adults with HIV Infection

Dysregulated iron transport and a compromised blood-brain barrier are implicated in HIV-associated neurocognitive disorders (HAND). We quantified the levels of proteins involved in iron transport and/or angiogenesis-ceruloplasmin, haptoglobin, and vascular endothelial growth factor (VEGF)-as well as biomarkers of neuroinflammation, in cerebrospinal fluid (CSF) from 405 individuals with HIV infection and comprehensive neuropsychiatric assessments. Associations with HAND [defined by a Global Deficit Score (GDS) ≥ 0.5, GDS as a continuous measure (cGDS), or by Frascati criteria] were evaluated for the highest versus lowest tertile of each biomarker, adjusting for potential confounders. Higher CSF VEGF was associated with GDS-defined impairment [odds ratio (OR) 2.17, p = 0.006] and cGDS in unadjusted analyses and remained associated with GDS impairment after adjustment (p = 0.018). GDS impairment was also associated with higher CSF ceruloplasmin (p = 0.047) and with higher ceruloplasmin and haptoglobin in persons with minimal comorbidities (ORs 2.37 and 2.13, respectively; both p = 0.043). In persons with minimal comorbidities, higher ceruloplasmin and haptoglobin were associated with HAND by Frascati criteria (both p < 0.05), and higher ceruloplasmin predicted worse impairment (higher cGDS values, p < 0.01). In the subgroup with undetectable viral load and minimal comorbidity, CSF ceruloplasmin and haptoglobin were strongly associated with GDS impairment (ORs 5.57 and 2.96, respectively; both p < 0.01) and HAND (both p < 0.01). Concurrently measured CSF IL-6 and TNF-α were only weakly correlated to these three biomarkers. Higher CSF ceruloplasmin, haptoglobin, and VEGF are associated with a significantly greater likelihood of HAND, suggesting that interventions aimed at disordered iron transport and angiogenesis may be beneficial in this disorder.

A single low dose of hydrocortisone enhances cognitive functioning in HIV-infected women

OBJECTIVE

Low-dose hydrocortisone (LDH) enhances aspects of learning and memory in select populations including patients with posttraumatic stress disorder and HIV-infected men. HIV-infected women show impairments in learning and memory, but the cognitive effects of LDH in HIV-infected women are unknown.

DESIGN

Double-blind, placebo-controlled, cross-over study examining the time-dependent effects of a single low-dose administration of hydrocortisone (10 mg oral) on cognition in 36 HIV-infected women. Participants were first randomized to LDH or placebo and then received the opposite treatment one month later.

METHODS

Cognitive performance was assessed 30 min and 4 h after pill administration to assess, respectively, nongenomic and genomic effects. Self-reported stress/anxiety and salivary cortisol were assessed throughout sessions.

RESULTS

LDH significantly increased salivary cortisol levels versus placebo; levels returned to baseline 4-h postadministration. At the 30-min assessment, LDH enhanced verbal learning and delayed memory, working memory, behavioral inhibition, and visuospatial abilities. At the 4-h assessment, LDH enhanced verbal learning and delayed memory compared with placebo. LDH-induced cognitive benefits related to reductions in cytokines and to a lesser extent to increases in cortisol.

CONCLUSION

The extended benefits from 30 min to 4 h of a single administration of LDH on learning and delayed memory suggest that targeting the hypothalamic-pituitary-adrenal axis may have potential clinical utility in HIV-infected women. These findings contrast with our findings in HIV-infected men who showed improved learning only at the 30-min assessment. Larger, longer term studies are underway to verify possible cognitive enhancing effects of LDH and the clinical significance of these effects in HIV.

Neuropathogenesis of human immunodeficiency virus infection

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) remain a common end-organ manifestation of viral infection. Subclinical and mild symptoms lead to neurocognitive and behavioral abnormalities. These are associated, in part, with viral penetrance and persistence in the central nervous system. Infections of peripheral blood monocytes, macrophages, and microglia are the primary drivers of neuroinflammation and neuronal impairments. While current antiretroviral therapy (ART) has reduced the incidence of HIV-associated dementia, milder forms of HAND continue. Depression, comorbid conditions such as infectious liver disease, drugs of abuse, antiretroviral drugs themselves, age-related neurodegenerative diseases, gastrointestinal maladies, and concurrent social and economic issues can make accurate diagnosis of HAND challenging. Increased life expectancy as a result of ART clearly creates this variety of comorbid conditions that often blur the link between the virus and disease. With the discovery of novel biomarkers, neuropsychologic testing, and imaging techniques to better diagnose HAND, the emergence of brain-penetrant ART, adjunctive therapies, longer life expectancy, and better understanding of disease pathogenesis, disease elimination is perhaps a realistic possibility. This review focuses on HIV-associated disease pathobiology with an eye towards changing trends in the face of widespread availability of ART.

Characterization of Cellular Immune Responses in Thai Individuals With and Without HIV-Associated Neurocognitive Disorders

HIV-associated neurocognitive disorder (HAND) remains a challenge despite antiretroviral therapy (ART), and has been linked to monocyte/macrophage (M/M) migration to the brain. Due to the potential impact of T cell effector mechanisms in eliminating activated/HIV-infected M/M, T cell activation may play a role in the development of HAND. We sought to investigate the relationship between cognition and both CD8⁺ T cell activation (HLA-DR⁺/CD38⁺) and HIV-specific CD8⁺ T cell responses at the time of HIV diagnosis and 12 months postinitiation of ART. CD8⁺ T cell activation was increased in HAND compared to cognitive normal (NL) individuals and correlated directly with plasma viral load and inversely with the cognitive status. In addition, Gag-specific cytolytic activity (CD107a/b⁺) was decreased in HAND compared with NL individuals and correlated with their neurological testing, suggesting a potential role of cytotoxic CD8⁺ T cells in the mechanism of HAND development.

Microglial activation is inversely associated with cognition in individuals living with HIV on effective antiretroviral therapy

OBJECTIVE

Despite viral suppression, HIV-associated cognitive impairment persists and may be partially due to persistent immune signalling by cells of the myeloid-lineage. Here, we aimed to understand the contribution of activated microglia located in vulnerable brain regions (e.g. frontal, subcortical) of HIV-infected, virally suppressed (HIV+VS) individuals in relation to cognitive and motor function.

DESIGN

Twenty-one HIV+VS individuals underwent PET with [11C]DPA-713 to image the translocator protein 18 kDa (TSPO), a marker of microglial activation, and completed a comprehensive neuropsychological test battery.

METHODS

Multivariable linear regressions were used to examine the contribution of [11C]DPA-713 binding to cognitive performance.

RESULTS

Higher [11C]DPA-713 binding was associated with lower cognition among HIV+VS individuals. [11C]DPA-713 binding in middle frontal gyrus/frontal cortex, hippocampus/temporal cortex and occipital cortex was inversely associated with performance on a number of cognitive domains, including verbal memory, processing speed/attention/concentration, executive function, working memory and motor function. [C]DPA-713 binding in parietal cortex, cerebellum and thalamus was associated with only specific cognitive domains including visual construction and verbal memory. Binding was not associated with global cognitive performance.

CONCLUSION

The findings add to the growing body of evidence that immune-mediated brain injury may contribute to domain specific, HIV-associated, cognitive vulnerabilities despite viral suppression.

EcoHIV infection of mice establishes latent viral reservoirs in T cells and active viral reservoirs in macrophages that are sufficient for induction of neurocognitive impairment

Suppression of HIV replication by antiretroviral therapy (ART) or host immunity can prevent AIDS but not other HIV-associated conditions including neurocognitive impairment (HIV-NCI). Pathogenesis in HIV-suppressed individuals has been attributed to reservoirs of latent-inducible virus in resting CD4+ T cells. Macrophages are persistently infected with HIV but their role as HIV reservoirs in vivo has not been fully explored. Here we show that infection of conventional mice with chimeric HIV, EcoHIV, reproduces physiological conditions for development of disease in people on ART including immunocompetence, stable suppression of HIV replication, persistence of integrated, replication-competent HIV in T cells and macrophages, and manifestation of learning and memory deficits in behavioral tests, termed here murine HIV-NCI. EcoHIV established latent reservoirs in CD4+ T lymphocytes in chronically-infected mice but could be induced by epigenetic modulators ex vivo and in mice. In contrast, macrophages expressed EcoHIV constitutively in mice for up to 16 months; murine leukemia virus (MLV), the donor of gp80 envelope in EcoHIV, did not infect macrophages. Both EcoHIV and MLV were found in brain tissue of infected mice but only EcoHIV induced NCI. Murine HIV-NCI was prevented by antiretroviral prophylaxis but once established neither persistent EcoHIV infection in mice nor NCI could be reversed by long-acting antiretroviral therapy. EcoHIV-infected, athymic mice were more permissive to virus replication in macrophages than were wild-type mice, suffered cognitive dysfunction, as well as increased numbers of monocytes and macrophages infiltrating the brain. Our results suggest an important role of HIV expressing macrophages in HIV neuropathogenesis in hosts with suppressed HIV replication.

The role of catecholamines in HIV neuropathogenesis

The success of anti-retroviral therapy has improved the quality of life and lifespan of HIV + individuals, transforming HIV infection into a chronic condition. These improvements have come with a cost, as chronic HIV infection and long-term therapy have resulted in the emergence of a number of new pathologies. This includes a variety of the neuropathological and neurocognitive effects collectively known as HIVassociated neurocognitive disorders (HAND) or NeuroHIV. These effects persist even in the absence of viral replication, suggesting that they are mediated the long-term changes in the CNS induced by HIV infection rather than by active replication. Among these effects are significant changes in catecholaminergic neurotransmission, especially in dopaminergic brain regions. In HIV-infected individuals not treated with ARV show prominent neuropathology is common in dopamine-rich brain regions and altered autonomic nervous system activity. Even infected individuals on therapy, there is significant dopaminergic neuropathology, and elevated stress and norepinephrine levels correlate with a decreased effectiveness of antiretroviral drugs. As catecholamines function as immunomodulatory factors, the resultant dysregulation of catecholaminergic tone could substantially alter the development of HIVassociated neuroinflammation and neuropathology. In this review, we discuss the role of catecholamines in the etiology of HIV neuropathogenesis. Providing a comprehensive examination of what is known about these molecules in the context of HIV-associated disease demonstrates the importance of further studies in this area, and may open the door to new therapeutic strategies that specifically ameliorate the effects of catecholaminergic dysregulation on NeuroHIV.

Applications of the FIV Model to Study HIV Pathogenesis

Feline immunodeficiency virus (FIV) is a naturally-occurring retrovirus that infects domestic and non-domestic feline species, producing progressive immune depletion that results in an acquired immunodeficiency syndrome (AIDS). Much has been learned about FIV since it was first described in 1987, particularly in regard to its application as a model to study the closely related lentivirus, human immunodeficiency virus (HIV). In particular, FIV and HIV share remarkable structure and sequence organization, utilize parallel modes of receptor-mediated entry, and result in a similar spectrum of immunodeficiency-related diseases due to analogous modes of immune dysfunction. This review summarizes current knowledge of FIV infection kinetics and the mechanisms of immune dysfunction in relation to opportunistic disease, specifically in regard to studying HIV pathogenesis. Furthermore, we present data that highlight changes in the oral microbiota and oral immune system during FIV infection, and outline the potential for the feline model of oral AIDS manifestations to elucidate pathogenic mechanisms of HIV-induced oral disease. Finally, we discuss advances in molecular biology, vaccine development, neurologic dysfunction, and the ability to apply pharmacologic interventions and sophisticated imaging technologies to study experimental and naturally occurring FIV, which provide an excellent, but often overlooked, resource for advancing therapies and the management of HIV/AIDS.

In vivo characterization of macrophage-tropic simian immunodeficiency virus molecular clones in rhesus macaques

Macrophages are a major target of HIV/SIV infection and play an important role in pathogenesis by serving as viral reservoirs in the central nervous system. Previously, a unique early SIVmac251 envelope (Env) variant, deSIV147 was cloned from blood of a rhesus macaque with rapid disease progression and SIV-associated encephalitis. Here, we show that infectious molecular clone deSIV147 caused systemic infection in rhesus macaques following intravenous or intrarectal exposure. Next, we inoculated deSIV147 into macaques depleted of CD4+ T cells and found that animals were SIV-positive, with high plasma and CSF viral loads. These macaques also showed SIVp17-positive macrophages in brain, lymph nodes, colon, lung, and liver. Furthermore, accumulation of perivascular macrophages, multinucleated giant cells, and microgliosis was detected. These findings suggest that the neurotropic deSIV147 clone will be useful to study macrophage infection in HIV/SIV-associated neurocognitive disorders, gain insights into myeloid cell reservoirs in brain and other anatomical sites, as well as test strategies for eradication.

Effects of HIV infection and ART on phenotype and function of circulating monocytes, natural killer, and innate lymphoid cells

HIV infection causes upregulation of markers of inflammation, immune activation and apoptosis of host adaptive, and innate immune cells particularly monocytes, natural killer (NK) and innate lymphoid cells (ILCs). Although antiretroviral therapy (ART) restores CD4 T-cell counts, the persistent aberrant activation of monocytes, NK and ILCs observed likely contributes to the incomplete recovery of T-cell effector functions. A better understanding of the effects of HIV infection and ART on the phenotype and function of circulating monocytes, NK, and ILCs is required to guide development of novel therapeutic interventions to optimize immune recovery.

Methylglyoxal-bis-guanylhydrazone inhibits osteopontin expression and differentiation in cultured human monocytes

Monocyte activation and polarization play essential roles in many chronic inflammatory diseases. An imbalance of M1 and M2 macrophage activation (pro-inflammatory and alternatively activated, respectively) is believed to be a key aspect in the etiology of these diseases, thus a therapeutic approach that regulates macrophage activation could be of broad clinical relevance. Methylglyoxal-bis-guanylhydrazone (MGBG), a regulator of polyamine metabolism, has recently been shown to be concentrated in monocytes and macrophages, and interfere with HIV integration into the DNA of these cells in vitro. RNA expression analysis of monocytes from HIV+ and control donors with or without MGBG treatment revealed the only gene to be consistently down regulated by MGBG to be osteopontin (OPN). The elevated expression of this pro-inflammatory cytokine and monocyte chemoattractant is associated with various chronic inflammatory diseases. We demonstrate that MGBG is a potent inhibitor of secreted OPN (sOPN) in cultured monocytes with 50% inhibition achieved at 0.1 μM of the drug. Furthermore, inhibition of OPN RNA transcription in monocyte cultures occurs at similar concentrations of the drug. During differentiation of monocytes into macrophages in vitro, monocytes express cell surface CD16 and the cells undergo limited DNA synthesis as measured by uptake of BrdU. MGBG inhibited both activities at similar doses to those regulating OPN expression. In addition, monocyte treatment with MGBG inhibited differentiation into both M1 and M2 classes of macrophages at non-toxic doses. The inhibition of differentiation and anti-OPN effects of MGBG were specific for monocytes in that differentiated macrophages were nearly resistant to MGBG activities. Thus MGBG may have potential therapeutic utility in reducing or normalizing OPN levels and regulating monocyte activation in diseases that involve chronic inflammation.

An SIV macaque model of SIV and HAND: the need for adjunctive therapies in HIV that target activated monocytes and macrophages

Non-human primate models of AIDS and neuroAIDS are critical to study HIV infection of the CNS, neuropathology, and immune activation and macrophage accumulation that occurs in HAND. SIV, similar to HIV, infects CD4⁺ T lymphocytes and monocytes/macrophages. Virus enters the CNS early, and macrophage activation correlates with CNS disease, as well as inflammation outside of the CNS. Antiretroviral in HIV+ humans and SIV+ Rhesus macaques results in non-detectable plasma virus, decreased or non-detectable viral RNA or protein in the CNS. But, viral DNA rebounds following therapy interruption, demonstrating the presence of replication competent virus in the CNS within myeloid cells. In this brief review, we discuss our findings using a Rhesus macaque model of SIV-associated CNS infection and pathology, focusing on monocyte/macrophage activation and the link between CNS and cardiac disease. We conclude with recent studies using adjunctive therapy targeting monocytes/macrophages with ART to prevent or diminish CNS pathology that may be associated with HAND.

Variability in C-reactive protein is associated with cognitive impairment in women living with and without HIV: a longitudinal study

Despite the availability of effective antiretroviral therapies, cognitive impairment (CI) remains prevalent in HIV-infected (HIV+) individuals. Evidence from primarily cross-sectional studies, in predominantly male samples, implicates monocyte- and macrophage-driven inflammatory processes linked to HIV-associated CI. Thus, peripheral systemic inflammatory markers may be clinically useful biomarkers in tracking HIV-associated CI. Given sex differences in immune function, we focused here on whether mean and intra-individual variability in inflammatory marker-predicted CI in HIV+ and HIV- women. Seventy-two HIV+ (36 with CI) and 58 HIV- (29 with CI) propensity-matched women participating in the Women's Interagency HIV Study completed a neuropsychological battery once between 2009 and 2011, and performance was used to determine CI status. Analysis of 13 peripheral immune markers was conducted on stored biospecimens at three time points (7 and 3.5 years before neuropsychological data collection and concurrent with data collection). HIV+ women showed alterations in 8 immune markers compared to HIV- women. The strongest predictors of CI across HIV+ and HIV- women were lower mean soluble tumor necrosis factor receptor I (sTNFRI) levels, higher mean interleukin (IL)-6 levels, and greater variability in C-reactive protein (CRP) and matrix metalloproteinase (MMP)-9 (p values < 0.05). Stratified by HIV, the only significant predictor of CI was greater variability in CRP for both HIV+ and HIV- women (p values < 0.05). This variability predicted lower executive function, attention/working memory, and psychomotor speed in HIV+ but only learning in HIV- women (p values < 0.05). Intra-individual variability in CRP levels over time may be a good predictor of CI in predominately minority low-socioeconomic status midlife women.

Receptor-interacting protein kinase 3 mediates macrophage/monocyte activation in autoimmune hepatitis and regulates interleukin-6 production

Background

The mechanisms of macrophages/monocytes in autoimmune hepatitis (AIH) remain unclear. We investigated the role of receptor-interacting protein kinase 3 (RIP3), a key inflammatory signal adapter, in macrophage/monocyte activation in AIH.

Methods

Liver tissues and monocytes from patients were collected to evaluate the relationship between macrophage activation and RIP3 by double-immunofluorescence and Western blotting. RAW264.7 macrophages were used to study the regulation of RIP3 signaling on inflammatory cytokines.

Results

Compared to the hepatic cyst, the majority of accumulated macrophages expressed RIP3 in AIH liver tissues. Moreover, RIP3 expression of monocytes was correlated with the levels of serum hepatic enzyme in AIH. Furthermore, RIP3 signaling was activated by lipopolysaccharide in RAW264.7 macrophages, which was accompanied with upregulated interleukin (IL)-1β, IL-6, and IL-10 and downregulated IL-4 and transforming growth factor-β. Notably, necrostatin-1, the specific inhibitor of the RIP3 signaling pathway, and 6-thioguanine (6-TG), the active metabolite of azathioprine, predominantly reduced IL-6 production compared to other cytokines. Moreover, the gene level of IL-6 was dramatically increased in AIH liver tissues.

Conclusions

RIP3 signaling is involved in macrophage/monocyte activation in AIH and mediates IL-6 production, and is a novel molecular mechanism of 6-TG, indicating that it might be a promising therapeutic target for AIH treatment.

HIV-associated neurocognitive disorder

PURPOSE OF REVIEW

HIV-associated neurocognitive disease is the most active topic for neuroAIDS investigations at present. Although impairment is mild in patients successfully treated with modern antiviral regimens, it remains an ongoing problem for HIV patients. It is important to update the emerging research concerning HIV-associated neurocognitive disease.

RECENT FINDINGS

The virus enters the brain during acute infection, with evidence for abnormal functioning that may occur early and often persists. Direct relationships with ongoing viral infection continue to be monitored, but chronic inflammation often associated with monocytes and macrophages appears to be the most likely driver of cognitive dysfunction. Appreciation for cerebrovascular disease as a significant comorbidity that is associated with cognitive deficits is increasing. Neuroimaging is actively being developed to address detection and measurement of changes in the brain. Optimal combined antiretroviral treatment therapy has vastly improved neurologic outcomes, but so far has not been demonstrated to reverse the remaining mild impairment. Inflammatory and vascular mechanisms of cerebral dysfunction may need to be addressed to achieve better outcomes.

SUMMARY

Ongoing research is required to improve neurological outcomes for persons living with HIV. It is likely that interventions beyond antiviral approaches will be required to control or reverse HIV-associated neurocognitive disease.

SIV Latency in Macrophages in the CNS

Lentiviruses infect myeloid cells, leading to acute infection followed by persistent/latent infections not cleared by the host immune system. HIV and SIV are lentiviruses that infect CD4+ lymphocytes in addition to myeloid cells in blood and tissues. HIV infection of myeloid cells in brain, lung, and heart causes tissue-specific diseases that are mostly observed during severe immunosuppression, when the number of circulating CD4+ T cells declines to exceeding low levels. Antiretroviral therapy (ART) controls viral replication but does not successfully eliminate latent virus, which leads to viral rebound once ART is interrupted. HIV latency in CD4+ lymphocytes is the main focus of research and concern when HIV eradication efforts are considered. However, myeloid cells in tissues are long-lived and have not been routinely examined as a potential reservoir. Based on a quantitative viral outgrowth assay (QVOA) designed to evaluate latently infected CD4+ lymphocytes, a similar protocol was developed for the assessment of latently infected myeloid cells in blood and tissues. Using an SIV ART model, it was demonstrated that myeloid cells in blood and brain harbor latent SIV that can be reactivated and produce infectious virus in vitro, demonstrating that myeloid cells have the potential to be an additional latent reservoir of HIV that should be considered during HIV eradication strategies.

Lymphocyte-Dominant Encephalitis and Meningitis in Simian Immunodeficiency Virus-Infected Macaques Receiving Antiretroviral Therapy

A retrospective neuropathologic review of 30 SIV-infected pigtailed macaques receiving combination antiretroviral therapy (cART) was conducted. Seventeen animals with lymphocyte-dominant inflammation in the brain and/or meninges that clearly was morphologically distinct from prototypic SIV encephalitis and human immunodeficiency virus encephalitis were identified. Central nervous system (CNS) infiltrates in cART-treated macaques primarily comprised CD20⁺ B cells and CD3⁺ T cells with fewer CD68⁺ macrophages. Inflammation was associated with low levels of SIV RNA in the brain as shown by in situ hybridization, and generally was observed in animals with episodes of cerebrospinal fluid (CSF) viral rebound or sustained plasma and CSF viremia during treatment. Although the lymphocytic CNS inflammation in these macaques shared morphologic characteristics with uncommon immune-mediated neurologic disorders reported in treated HIV patients, including CNS immune reconstitution inflammatory syndrome and neurosymptomatic CSF escape, the high prevalence of CNS lesions in macaques suggests that persistent adaptive immune responses in the CNS also may develop in neuroasymptomatic or mildly impaired HIV patients yet remain unrecognized given the lack of access to CNS tissue for histopathologic evaluation. Continued investigation into the mechanisms and outcomes of CNS inflammation in cART-treated, SIV-infected macaques will advance our understanding of the consequences of residual CNS HIV replication in patients on cART, including the possible contribution of adaptive immune responses to HIV-associated neurocognitive disorders.

T Cell-Macrophage Fusion Triggers Multinucleated Giant Cell Formation for HIV-1 Spreading

HIV-1-infected macrophages participate in virus dissemination and establishment of virus reservoirs in host tissues, but the mechanisms for virus cell-to-cell transfer to macrophages remain unknown. Here, we reveal the mechanisms for cell-to-cell transfer from infected T cells to macrophages and virus spreading between macrophages. We show that contacts between infected T lymphocytes and macrophages lead to cell fusion for the fast and massive transfer of CCR5-tropic viruses to macrophages. Through the merge of viral material between T cells and macrophages, these newly formed lymphocyte-macrophage fused cells acquire the ability to fuse with neighboring noninfected macrophages. Together, these two-step envelope-dependent cell fusion processes lead to the formation of highly virus-productive multinucleated giant cells reminiscent of the infected multinucleated giant macrophages detected in HIV-1-infected patients and simian immunodeficiency virus-infected macaques. These mechanisms represent an original mode of virus transmission for viral spreading and a new model for the formation of macrophage virus reservoirs during infection.IMPORTANCE We reveal a very efficient mechanism involved in cell-to-cell transfer from infected T cells to macrophages and subsequent virus spreading between macrophages by a two-step cell fusion process. Infected T cells first establish contacts and fuse with macrophage targets. The newly formed lymphocyte-macrophage fused cells then acquire the ability to fuse with surrounding uninfected macrophages, leading to the formation of infected multinucleated giant cells that can survive for a long time, as evidenced in vivo in lymphoid organs and the central nervous system. This route of infection may be a major determinant for virus dissemination and the formation of macrophage virus reservoirs in host tissues during HIV-1 infection.

Peripheral immune tolerance alleviates the intracranial lipopolysaccharide injection-induced neuroinflammation and protects the dopaminergic neurons from neuroinflammation-related neurotoxicity

BACKGROUND

Neuroinflammation plays a critical role in the onset and development of neurodegeneration disorders such as Parkinson's disease. The immune activities of the central nervous system are profoundly affected by peripheral immune activities. Immune tolerance refers to the unresponsiveness of the immune system to continuous or repeated stimulation to avoid excessive inflammation and unnecessary by-stander injury in the face of continuous antigen threat. It has been proved that the immune tolerance could suppress the development of various peripheral inflammation-related diseases. However, the role of immune tolerance in neuroinflammation and neurodegenerative diseases was not clear.

METHODS

Rats were injected with repeated low-dose lipopolysaccharide (LPS, 0.3 mg/kg) intraperitoneally for 4 days to induce peripheral immune tolerance. Neuroinflammation was produced using intracranial LPS (15 μg) injection. Inflammation cytokines were measured using enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). Microglial activation were measured using immunostaining of Iba-1 and ED-1. Dopaminergic neuronal damage was evaluated using immunochemistry staining and stereological counting of TH-positive neurons. Behavioral impairment was evaluated using amphetamine-induced rotational behavioral assessment.

RESULTS

Compared with the non-immune tolerated animals, pre-treatment of peripheral immune tolerance significantly decreased the production of inflammatory cytokines, suppressed the microglial activation, and increased the number of dopaminergic neuronal survival in the substantia nigra.

CONCLUSIONS

Our results indicated that peripheral immune tolerance attenuated neuroinflammation and inhibited neuroinflammation-induced dopaminergic neuronal death.

Wnt7a induces a unique phenotype of monocyte-derived macrophages with lower phagocytic capacity and differential expression of pro- and anti-inflammatory cytokines

The variation of macrophage functions suggests the involvement of multiple signalling pathways in fine tuning their differentiation. Macrophages that originate from monocytes in the blood migrate to tissue in response to homeostatic or 'danger' signals and undergo substantial morphological and functional modifications to meet the needs of the dominant signals in the microenvironment. Wnts are secreted glycoproteins that play a significant role in organ and cell differentiation, yet their impact on monocyte differentiation is not clear. In this study, we assessed the role of Wnt1 and Wnt7a on the differentiation of monocytes and the subsequent phenotype and function of monocyte-derived macrophages (MDMs). We show that Wnt7a decreased the expression of CD14, CD11b, CD163 and CD206, whereas Wnt1 had no effect. The Wnt7a effect on CD11b was also observed in the brain and spleen of Wnt7a^-/- adult brain mouse tissue and in embryonic Wnt7a^-/- tissue. Wnt7a reduced the phagocytic capacity of M-MDMs, decreased interleukin-10 (IL-10) and IL-12 secretion and increased IL-6 secretion. Collectively, these findings demonstrate that Wnt7a generates an MDM phenotype with both pro-inflammatory and alternative MDM cytokine profiles and reduced phagocytic capacity. As such, Wnt7a can have a significant impact on macrophage responses in health and disease.

HIV-infected macrophages and microglia that survive acute infection become viral reservoirs by a mechanism involving Bim

While HIV kills most of the cells it infects, a small number of infected cells survive and become latent viral reservoirs, posing a significant barrier to HIV eradication. However, the mechanism by which immune cells resist HIV-induced apoptosis is still incompletely understood. Here, we demonstrate that while acute HIV infection of human microglia/macrophages results in massive apoptosis, a small population of HIV-infected cells survive infection, silence viral replication, and can reactivate viral production upon specific treatments. We also found that HIV fusion inhibitors intended for use as antiretroviral therapies extended the survival of HIV-infected macrophages. Analysis of the pro- and anti-apoptotic pathways indicated no significant changes in Bcl-2, Mcl-1, Bak, Bax or caspase activation, suggesting that HIV blocks a very early step of apoptosis. Interestingly, Bim, a highly pro-apoptotic negative regulator of Bcl-2, was upregulated and recruited into the mitochondria in latently HIV-infected macrophages both in vitro and in vivo. Together, these results demonstrate that macrophages/microglia act as HIV reservoirs and utilize a novel mechanism to prevent HIV-induced apoptosis. Furthermore, they also suggest that Bim recruitment to mitochondria could be used as a biomarker of viral reservoirs in vivo.

The role of human dopamine transporter in NeuroAIDS

HIV-associated neurocognitive disorder (HAND) remains highly prevalent in HIV infected individuals and represents a special group of neuropathological disorders, which are associated with HIV-1 viral proteins, such as transactivator of transcription (Tat) protein. Cocaine abuse increases the incidence of HAND and exacerbates its severity by enhancing viral replication. Perturbation of dopaminergic transmission has been implicated as a risk factor of HAND. The presynaptic dopamine (DA) transporter (DAT) is essential for DA homeostasis and dopaminergic modulation of the brain function including cognition. Tat and cocaine synergistically elevate synaptic DA levels by acting directly on human DAT (hDAT), ultimately leading to dysregulation of DA transmission. Through integrated computational modeling and experimental validation, key residues have been identified in hDAT that play a critical role in Tat-induced inhibition of DAT and induce transporter conformational transitions. This review presents current information regarding neurological changes in DAT-mediated dopaminergic system associated with HIV infection, DAT-mediated adaptive responses to Tat as well as allosteric modulatory effects of novel compounds on hDAT. Understanding the molecular mechanisms by which Tat induces DAT-mediated dysregulation of DA system is of great clinical interest for identifying new targets for an early therapeutic intervention for HAND.

Cocaine dependence modulates the effect of HIV infection on brain activation during intertemporal decision making

BACKGROUND

Both HIV infection and chronic cocaine use alter the neural circuitry of decision making, but the interactive effects of these commonly comorbid conditions have not been adequately examined. This study tested how cocaine moderates HIV-related neural activation during an intertemporal decision-making task.

METHODS

The sample included 73 participants who differed on cocaine and HIV status (18 COC+/HIV+, 19 COC+/HIV-, 19 COC-/HIV+, 17 COC-/HIV-). Participants made choices between smaller, sooner and larger, delayed rewards while undergoing functional MRI. Choices varied in difficulty based on subjective value: hard (equivalently valued), easy (disparately valued), and control choices. A mixed-effects model controlling for education and smoking identified main and interactive effects of HIV and COC during hard relative to easy choices (difficulty contrast).

RESULTS

COC+ status was associated with lower activation in bilateral frontal gyri and right insular and posterior parietal cortices. HIV+ status was associated with higher activation in the visual cortex, but lower activation in bilateral prefrontal cortices and cerebellum and left posterior parietal cortex. COC moderated the effects of HIV in several clusters centered in the bilateral prefrontal cortices and cerebellum. In post-hoc analyses, there were significant effects of HIV status on activation for COC+, but not COC-, participants; interaction effects remained after controlling for polysubstance use.

CONCLUSION

Cocaine use may diminish the compensatory neural activation often seen among HIV+ samples during decision making. Our results highlight the importance of examining the neuropsychiatric effects of comorbid medical conditions to identify potential neural targets for cognitive remediation interventions.

Common gene-network signature of different neurological disorders and their potential implications to neuroAIDS

The neurological complications of AIDS (neuroAIDS) during the infection of human immunodeficiency virus (HIV) are symptomized by non-specific, multifaceted neurological conditions and therefore, defining a specific diagnosis/treatment mechanism(s) for this neuro-complexity at the molecular level remains elusive. Using an in silico based integrated gene network analysis we discovered that HIV infection shares convergent gene networks with each of twelve neurological disorders selected in this study. Importantly, a common gene network was identified among HIV infection, Alzheimer's disease, Parkinson's disease, multiple sclerosis, and age macular degeneration. An mRNA microarray analysis in HIV-infected monocytes showed significant changes in the expression of several genes of this in silico derived common pathway which suggests the possible physiological relevance of this gene-circuit in driving neuroAIDS condition. Further, this unique gene network was compared with another in silico derived novel, convergent gene network which is shared by seven major neurological disorders (Alzheimer's disease, Parkinson's disease, Multiple Sclerosis, Age Macular Degeneration, Amyotrophic Lateral Sclerosis, Vascular Dementia, and Restless Leg Syndrome). These networks differed in their gene circuits; however, in large, they involved innate immunity signaling pathways, which suggests commonalities in the immunological basis of different neuropathogenesis. The common gene circuits reported here can provide a prospective platform to understand how gene-circuits belonging to other neuro-disorders may be convoluted during real-time neuroAIDS condition and it may elucidate the underlying-and so far unknown-genetic overlap between HIV infection and neuroAIDS risk. Also, it may lead to a new paradigm in understanding disease progression, identifying biomarkers, and developing therapies.