Compartmentalization of HIV-1 in the central nervous system: role of the choroid plexus

Changes in cerebrospinal fluid proteins across the spectrum of untreated and treated chronic HIV-1 infection

Using the Olink Explore 1536 platform, we measured 1,463 unique proteins in 303 cerebrospinal fluid (CSF) specimens from four clinical centers contributed by uninfected controls and 12 groups of people living with HIV-1 infection representing the spectrum of progressive untreated and treated chronic infection. We present three initial analyses of these measurements: an overview of the CSF protein features of the sample; correlations of the CSF proteins with CSF HIV-1 RNA and neurofilament light chain protein (NfL) concentrations; and comparison of CSF proteins in HIV-associated dementia (HAD) and neurosymptomatic CSF escape (NSE). These reveal a complex but coherent picture of CSF protein changes with highest concentrations of many proteins during CNS injury in the HAD and NSE groups and variable protein changes across the course of systemic HIV-1 progression that included two common patterns, designated as lymphoid and myeloid patterns, related to principal involvement of their underlying inflammatory cell lineages. Antiretroviral therapy reduced CSF protein perturbations, though not always to control levels. The dataset of these CSF protein measurements, along with background clinical information, is posted online. Extended studies of this unique dataset will supplement this report to provide more detailed characterization of the dynamic impact of HIV-1 infection on the CSF proteome across the spectrum of HIV-1 infection, advancing the mechanistic understanding of HIV-1-related CNS pathobiology.

Changes in Cerebrospinal Fluid Proteins across the Spectrum of Untreated and Treated Chronic HIV-1 Infection

Using the Olink Explore 1536 platform, we measured 1,463 unique proteins in 303 cerebrospinal fluid (CSF) specimens from four clinical centers that included uninfected controls and 12 groups of people living with HIV-1 infection representing the spectrum of progressive untreated and treated chronic infection. We present three initial analyses of these measurements: an overview of the CSF protein features of the sample; correlations of the CSF proteins with CSF HIV-1 RNA and neurofilament light chain protein (NfL) concentrations; and comparison of the CSF proteins in HIV-associated dementia ( HAD ) and neurosymptomatic CSF escape ( NSE ). These reveal a complex but coherent picture of CSF protein changes that includes highest concentrations of many proteins during CNS injury in the HAD and NSE groups and variable protein changes across the course of neuroasymptomatic systemic HIV-1 progression, including two common patterns, designated as lymphoid and myeloid patterns, related to the principal involvement of their underlying inflammatory cell lineages. Antiretroviral therapy reduced CSF protein perturbations, though not always to control levels. The dataset of these CSF protein measurements, along with background clinical information, is posted online. Extended studies of this unique dataset will provide more detailed characterization of the dynamic impact of HIV-1 infection on the CSF proteome across the spectrum of HIV-1 infection, and further the mechanistic understanding of HIV-1-related CNS pathobiology.

Value of Radiomic Analysis Combined With Diffusion Tensor Imaging in Early Diagnosis of HIV-Associated Neurocognitive Disorders

BACKGROUND

The combination of radiomics and diffusion tensor imaging (DTI) may have potential clinical value in the early stage of HIV-associated neurocognitive disorders (HAND).

PURPOSE

To investigate the value of DTI-based radiomics in the early stage of HAND in people living with HIV (PLWH).

STUDY TYPE

Retrospective.

POPULATION

A total of 138 male PLWH were included, including 68 with intact cognition (IC) and 70 with asymptomatic neurocognitive impairment (ANI). Seventy healthy controls (HCs) were recruited for tract-based spatial statistics (TBSS) analysis. All PLWHs were randomly divided into training and validation cohorts at a 7:3 ratio.

FIELD STRENGTH/SEQUENCE

A 3 T, single-shot spin-echo echo planar imaging (EPI).

ASSESSMENT

The differences between the PLWH groups were compared using TBSS and region of interest (ROI) analysis. Radiomic features were extracted from the corpus callosum (CC) on DTI postprocessed images, including fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD). The performance of the radiomic signatures was evaluated by ROC curve analysis. The radiomic signature with the highest area under the curve (AUC) was combined with clinical characteristics to construct a nomogram. Decision curve analysis (DCA) was performed to evaluate the ability of different methods in discriminating ANI.

STATISTICAL TESTS

Chi-square test, independent-samples t test, Kruskal-Wallis test, Mann-Whitney U test, threshold-free cluster enhancement (TFCE), ROC curve analysis, DCA, multivariate logistic regression analysis, Hosmer-Lemeshow test. P < 0.05 with TFCE corrected and P < 0.0001 without TFCE corrected were considered statistically significant.

RESULTS

The ANI group showed lower FA and higher AD than the IC group. In the validation cohort, the AUCs of the FA-, AD-, MD- and RD-based radiomic signatures and the clinicoradiomic nomogram were 0.829, 0.779, 0.790, 0.864, and 0.874, respectively. DCA revealed that the nomogram was of greater clinical value than TBSS analysis, the clinical models, and the RD-based radiomic signature.

DATA CONCLUSION

The combination of DTI and radiomics is correlated with early stage of HAND in PLWH.

EVIDENCE LEVEL

3.

TECHNICAL EFFICACY

Stage 2.

The risk of drug resistance during long-acting antimicrobial therapy

The emergence of drug resistance during antimicrobial therapy is a major global health problem, especially for chronic infections like human immunodeficiency virus, hepatitis B and C, and tuberculosis. Sub-optimal adherence to long-term treatment is an important contributor to resistance risk. New long-acting drugs are being developed for weekly, monthly or less frequent dosing to improve adherence, but may lead to long-term exposure to intermediate drug levels. In this study, we analyse the effect of dosing frequency on the risk of resistance evolving during time-varying drug levels. We find that long-acting therapies can increase, decrease or have little effect on resistance, depending on the source (pre-existing or de novo) and degree of resistance, and rates of drug absorption and clearance. Long-acting therapies with rapid drug absorption, slow clearance and strong wild-type inhibition tend to reduce resistance caused by partially resistant strains in the early stages of treatment even if they do not improve adherence. However, if subpopulations of microbes persist and can reactivate during sub-optimal treatment, longer-acting therapies may substantially increase the resistance risk. Our results show that drug kinetics affect selection for resistance in a complicated manner, and that pathogen-specific models are needed to evaluate the benefits of new long-acting therapies.

Shock and kill within the CNS: A promising HIV eradication approach?

The most studied HIV eradication approach is the "shock and kill" strategy, which aims to reactivate the latent reservoir by latency reversing agents (LRAs) and allowing elimination of these cells by immune-mediated clearance or viral cytopathic effects. The CNS is an anatomic compartment in which (persistent) HIV plays an important role in HIV-associated neurocognitive disorder. Restriction of the CNS by the blood-brain barrier is important for maintenance of homeostasis of the CNS microenvironment, which includes CNS-specific cell types, expression of transcription factors, and altered immune surveillance. Within the CNS predominantly myeloid cells such as microglia and perivascular macrophages are thought to be a reservoir of persistent HIV infection. Nevertheless, infection of T cells and astrocytes might also impact HIV infection in the CNS. Genetic adaptation to this microenvironment results in genetically distinct, compartmentalized viral populations with differences in transcription profiles. Because of these differences in transcription profiles, LRAs might have different effects within the CNS as compared with the periphery. Moreover, reactivation of HIV in the brain and elimination of cells within the CNS might be complex and could have detrimental consequences. Finally, independent of activity on latent HIV, LRAs themselves can have adverse neurologic effects. We provide an extensive overview of the current knowledge on compartmentalized (persistent) HIV infection in the CNS and on the "shock and kill" strategy. Subsequently, we reflect on the impact and promise of the "shock and kill" strategy on the elimination of persistent HIV in the CNS.

Distinct HIV-1 Population Structure across Meningeal and Peripheral T Cells and Macrophage Lineage Cells

HIV-1 sequence population structure among brain and nonbrain cellular compartments is incompletely understood. Here, we compared proviral pol and env high-quality consensus single-molecule real-time (SMRT) sequences derived from CD3⁺ T cells and CD14⁺ macrophage lineage cells from meningeal or peripheral (spleen, blood) tissues obtained at autopsy from two individuals with viral suppression on antiretroviral therapy (ART). Phylogenetic analyses showed strong evidence of population structure between CD3⁺ and CD14⁺ virus populations. Distinct env variable-region characteristics were also found between CD3⁺ and CD14⁺ viruses. Furthermore, shared macrophage-tropic amino acid residues (env) and drug resistance mutations (pol) between meningeal and peripheral virus populations were consistent with the meninges playing a role in viral gene flow across the blood-brain barrier. Overall, our results point toward potential functional differences among meningeal and peripheral CD3⁺ and CD14⁺ virus populations and a complex evolutionary history driven by distinct selection pressures and/or viral gene flow. IMPORTANCE Different cell types and/or tissues may serve as a reservoir for HIV-1 during ART-induced viral suppression. We compared proviral pol and env sequences from CD3⁺ T cells and CD14⁺ macrophage lineage cells from brain and nonbrain tissues from two virally suppressed individuals. We found strong evidence of viral population structure among cells/tissues, which may result from distinct selective pressures across cell types and anatomic sites.

The choroid plexus and its role in the pathogenesis of neurological infections

The choroid plexus is situated at an anatomically and functionally important interface within the ventricles of the brain, forming the blood-cerebrospinal fluid barrier that separates the periphery from the central nervous system. In contrast to the blood-brain barrier, the choroid plexus and its epithelial barrier have received considerably less attention. As the main producer of cerebrospinal fluid, the secretory functions of the epithelial cells aid in the maintenance of CNS homeostasis and are capable of relaying inflammatory signals to the brain. The choroid plexus acts as an immunological niche where several types of peripheral immune cells can be found within the stroma including dendritic cells, macrophages, and T cells. Including the epithelia cells, these cells perform immunosurveillance, detecting pathogens and changes in the cytokine milieu. As such, their activation leads to the release of homing molecules to induce chemotaxis of circulating immune cells, driving an immune response at the choroid plexus. Research into the barrier properties have shown how inflammation can alter the structural junctions and promote increased bidirectional transmigration of cells and pathogens. The goal of this review is to highlight our foundational knowledge of the choroid plexus and discuss how recent research has shifted our understanding towards viewing the choroid plexus as a highly dynamic and important contributor to the pathogenesis of neurological infections. With the emergence of several high-profile diseases, including ZIKA and SARS-CoV-2, this review provides a pertinent update on the cellular response of the choroid plexus to these diseases. Historically, pharmacological interventions of CNS disorders have proven difficult to develop, however, a greater focus on the role of the choroid plexus in driving these disorders would provide for novel targets and routes for therapeutics.

Pitfalls of Antiretroviral Therapy: Current Status and Long-Term CNS Toxicity

HIV can traverse the BBB using a Trojan horse-like mechanism. Hidden within infected immune cells, HIV can infiltrate the highly safeguarded CNS and propagate disease. Once integrated within the host genome, HIV becomes a stable provirus, which can remain dormant, evade detection by the immune system or antiretroviral therapy (ART), and result in rebound viraemia. As ART targets actively replicating HIV, has low BBB penetrance, and exposes patients to long-term toxicity, further investigation into novel therapeutic approaches is required. Viral proteins can be produced by latent HIV, which may play a synergistic role alongside ART in promoting neuroinflammatory pathophysiology. It is believed that the ability to specifically target these proviral reservoirs would be a vital driving force towards a cure for HIV infection. A novel drug design platform, using the in-tandem administration of several therapeutic approaches, can be used to precisely target the various components of HIV infection, ultimately leading to the eradication of active and latent HIV and a functional cure for HIV. The aim of this review is to explore the pitfalls of ART and potential novel therapeutic alternatives.

Compartmentalization of cerebrospinal fluid inflammation across the spectrum of untreated HIV-1 infection, central nervous system injury and viral suppression

OBJECTIVE

To characterize the evolution of central nervous system (CNS) inflammation in HIV-1 infection applying a panel of cerebrospinal fluid (CSF) inflammatory biomarkers to grouped subjects representing a broad spectrum of systemic HIV-1 immune suppression, CNS injury and viral control.

METHODS

This is a cross-sectional analysis of archived CSF and blood samples, assessing concentrations of 10 functionally diverse soluble inflammatory biomarkers by immunoassays in 143 HIV-1-infected subjects divided into 8 groups: untreated primary HIV-1 infection (PHI); four untreated groups defined by their blood CD4+ T lymphocyte counts; untreated patients presenting with subacute HIV-associated dementia (HAD); antiretroviral-treated subjects with ≥1 years of plasma viral suppression; and untreated elite controllers. Twenty HIV-1-uninfected controls were included for comparison. Background biomarkers included blood CD4+ and CD8+ T lymphocytes, CSF and blood HIV-1 RNA, CSF white blood cell (WBC) count, CSF/blood albumin ratio, CSF neurofilament light chain (NfL), and CSF t-tau.

FINDINGS

HIV-1 infection was associated with a broad compartmentalized CSF inflammatory response that developed early in its course and changed with systemic disease progression, development of neurological injury, and viral suppression. CSF inflammation in untreated individuals without overt HAD exhibited at least two overall patterns of inflammation as blood CD4+ T lymphocytes decreased: one that peaked at 200-350 blood CD4+ T cells/μL and associated with lymphocytic CSF inflammation and HIV-1 RNA concentrations; and a second that steadily increased through the full range of CD4+ T cell decline and associated with macrophage responses and increasing CNS injury. Subacute HAD was distinguished by a third inflammatory profile with increased blood-brain barrier permeability and robust combined lymphocytic and macrophage CSF inflammation. Suppression of CSF and blood HIV-1 infections by antiretroviral treatment and elite viral control were associated with reduced CSF inflammation, though not fully to levels found in HIV-1 seronegative controls.

The Paradox of HIV Blood-Brain Barrier Penetrance and Antiretroviral Drug Delivery Deficiencies

HIV attacks the body's immune cells, frequently compromises the integrity of the blood-brain barrier (BBB), and infects the CNS in the early stages of infection. Dysfunction of the BBB further potentiates viral replication within the CNS, which can lead to HIV-associated neuropathology. Antiretroviral therapy (ART) significantly improves HIV patient outcomes and reduces mortality rates. However, there has been limited progress in targeting latent viral reservoirs within the CNS, which may eventually lead to rebound viremia. While ART drugs are shown to be effective in attenuating HIV replication in the periphery, the protection of the brain by the BBB offers an isolated sanctuary to harbor HIV and maintains chronic and persistent replication within the CNS. In this review, we elucidate the pathology of the BBB, its ability to potentiate viral replication, as well as current therapies and insufficiencies in treating HIV-infected individuals.

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

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

In Silico Insights into HIV-1 Vpu-Tetherin Interactions and Its Mutational Counterparts

Tetherin, an interferon-induced host protein encoded by the bone marrow stromal antigen 2 (BST2/CD317/HM1.24) gene, is involved in obstructing the release of many retroviruses and other enveloped viruses by cross-linking the budding virus particles to the cell surface. This activity is antagonized in the case of human immunodeficiency virus (HIV)-1 wherein its accessory protein Viral Protein U (Vpu) interacts with tetherin, causing its downregulation from the cell surface. Vpu and tetherin connect through their transmembrane (TM) domains, culminating into events leading to tetherin degradation by recruitment of β-TrCP2. However, mutations in the TM domains of both proteins are reported to act as a resistance mechanism to Vpu countermeasure impacting tetherin's sensitivity towards Vpu but retaining its antiviral activity. Our study illustrates the binding aspects of blood-derived, brain-derived, and consensus HIV-1 Vpu with tetherin through protein-protein docking. The analysis of the bound complexes confirms the blood-derived Vpu-tetherin complex to have the best binding affinity as compared to other two. The mutations in tetherin and Vpu are devised computationally and are subjected to protein-protein interactions. The complexes are tested for their binding affinities, residue connections, hydrophobic forces, and, finally, the effect of mutation on their interactions. The single point mutations in tetherin at positions L23Y, L24T, and P40T, and triple mutations at {L22S, F44Y, L37I} and {L23T, L37T, T45I}, while single point mutations in Vpu at positions A19H and W23Y and triplet of mutations at {V10K, A11L, A19T}, {V14T, I18T, I26S}, and {A11T, V14L, A15T} have revealed no polar contacts with minimal hydrophobic interactions between Vpu and tetherin, resulting in reduced binding affinity. Additionally, we have explored the aggregation potential of tetherin and its association with the brain-derived Vpu protein. This work is a possible step toward an understanding of Vpu-tetherin interactions.

Ultradeep single-molecule real-time sequencing of HIV envelope reveals complete compartmentalization of highly macrophage-tropic R5 proviral variants in brain and CXCR4-using variants in immune and peripheral tissues

Despite combined antiretroviral therapy (cART), HIV+ patients still develop neurological disorders, which may be due to persistent HIV infection and selective evolution in brain tissues. Single-molecule real-time (SMRT) sequencing technology offers an improved opportunity to study the relationship among HIV isolates in the brain and lymphoid tissues because it is capable of generating thousands of long sequence reads in a single run. Here, we used SMRT sequencing to generate ~ 50,000 high-quality full-length HIV envelope sequences (> 2200 bp) from seven autopsy tissues from an HIV+/cART+ subject, including three brain and four non-brain sites. Sanger sequencing was used for comparison with SMRT data and to clone functional pseudoviruses for in vitro tropism assays. Phylogenetic analysis demonstrated that brain-derived HIV was compartmentalized from HIV outside the brain and that the variants from each of the three brain tissues grouped independently. Variants from all peripheral tissues were intermixed on the tree but independent of the brain clades. Due to the large number of sequences, a clustering analysis at three similarity thresholds (99, 99.5, and 99.9%) was also performed. All brain sequences clustered exclusive of any non-brain sequences at all thresholds; however, frontal lobe sequences clustered independently of occipital and parietal lobes. Translated sequences revealed potentially functional differences between brain and non-brain sequences in the location of putative N-linked glycosylation sites (N-sites), V1 length, V3 charge, and the number of V4 N-sites. All brain sequences were predicted to use the CCR5 co-receptor, while most non-brain sequences were predicted to use CXCR4 co-receptor. Tropism results were confirmed by in vitro infection assays. The study is the first to use a SMRT sequencing approach to study HIV compartmentalization in tissues and supports other reports of limited trafficking between brain and non-brain sequences during cART. Due to the long sequence length, we could observe changes along the entire envelope gene, likely caused by differential selective pressure in the brain that may contribute to neurological disease.

Identification of Emerging Macrophage-Tropic HIV-1 R5 Variants in Brain Tissue of AIDS Patients without Severe Neurological Complications

Untreated HIV-positive (HIV-1⁺) individuals frequently suffer from HIV-associated neurocognitive disorders (HAND), with about 30% of AIDS patients suffering severe HIV-associated dementias (HADs). Antiretroviral therapy has greatly reduced the incidence of HAND and HAD. However, there is a continuing problem of milder neurocognitive impairments in treated HIV⁺ patients that may be increasing with long-term therapy. In the present study, we investigated whether envelope (env) genes could be amplified from proviral DNA or RNA derived from brain tissue of 12 individuals with normal neurology or minor neurological conditions (N/MC individuals). The tropism and characteristics of the brain-derived Envs were then investigated and compared to those of Envs derived from immune tissue. We showed that (i) macrophage-tropic R5 Envs could be detected in the brain tissue of 4/12 N/MC individuals, (ii) macrophage-tropic Envs in brain tissue formed compartmentalized clusters distinct from non-macrophage-tropic (non-mac-tropic) Envs recovered from the spleen or brain, (iii) the evidence was consistent with active viral expression by macrophage-tropic variants in the brain tissue of some individuals, and (iv) Envs from immune tissue of the N/MC individuals were nearly all tightly non-mac-tropic, contrasting with previous data for neuro-AIDS patients where immune tissue Envs mediated a range of macrophage infectivities, from background levels to modest infection, with a small number of Envs from some patients mediating high macrophage infection levels. In summary, the data presented here show that compartmentalized and active macrophage-tropic HIV-1 variants are present in the brain tissue of individuals before neurological disease becomes overt or serious.IMPORTANCE The detection of highly compartmentalized macrophage-tropic R5 Envs in the brain tissue of HIV patients without serious neurological disease is consistent with their emergence from a viral population already established there, perhaps from early disease. The detection of active macrophage-tropic virus expression, and probably replication, indicates that antiretroviral drugs with optimal penetration through the blood-brain barrier should be considered even for patients without neurological disease (neuro-disease). Finally, our data are consistent with the brain forming a sanctuary site for latent virus and low-level viral replication in the absence of neuro-disease.

Genetic analyses of HIV env associated with uveitis in antiretroviral-naive individuals

OBJECTIVE

To analyze and compare HIV-1 env sequences from the eye to those from the blood of individuals with uveitis attributed to HIV with the goal of gaining insight into the pathogenesis of HIV-associated eye disease.

DESIGN

A prospective case series of five HIV-infected antiretroviral-naive individuals with uveitis negative for other pathogens.

METHODS

RNA from blood plasma and ocular aqueous humor was reverse transcribed using random hexamers. HIV env C2-V5 (HXB2: 6990-7668) sequences were generated by single-genome amplification using nested polymerase chain reaction followed by bidirectional Sanger sequencing. Sequence analyses by Geneious, Geno2Pheno, N-GLYCOSITE, DIVEIN, and HyPhy evaluated relationships between HIV in plasma and aqueous humor.

RESULTS

A median of 20 (range: 13-22) plasma and 15 (range: 9-18) aqueous humor sequences were generated from each individual. The frequencies of sequences with predicted-N-linked-glycosylation sites and C-X-C chemokine receptor type 4 were comparable in aqueous humor and plasma of all five patients. Aqueous humor sequences had lower median genetic diversity compared with plasma across all patients, but similar divergence, in four of five patients. Aqueous humor HIV sequences were compartmentalized from plasma across subjects by Critchlow correlation coefficient, Slatkin and Maddison, nearest-neighbor statistic, and Fixation index.

CONCLUSION

Among antiretroviral-naive individuals with uveitis attributed to HIV, the universal compartmentalization and decreased diversity of eye compared with blood sequences suggests time-limited passage of a small subset of variants from each patient's viral population into the eye tissues, followed by limited immune selection despite the inflammatory uveitis.

Feline Immunodeficiency Virus Neuropathogenesis: A Model for HIV-Induced CNS Inflammation and Neurodegeneration

Feline Immunodeficiency virus (FIV), similar to its human analog human immunodeficiency virus (HIV), enters the central nervous system (CNS) soon after infection and establishes a protected viral reservoir. The ensuing inflammation and damage give rise to varying degrees of cognitive decline collectively known as HIV-associated neurocognitive disorders (HAND). Because of the similarities to HIV infection and disease, FIV has provided a useful model for both in vitro and in vivo studies of CNS infection, inflammation and pathology. This mini review summarizes insights gained from studies of early infection, immune cell trafficking, inflammation and the mechanisms of neuropathogenesis. Advances in our understanding of these processes have contributed to the development of therapeutic interventions designed to protect neurons and regulate inflammatory activity.

Modelling the HIV persistence through the network of lymphocyte recirculation in vivo

Human Immunodeficiency Virus (HIV) is able to persist in cellular and/or anatomical viral reservoirs, despite the effective inhibition of virus replication by the antiretroviral therapy (ART). Here we develop a mathematical model to gain some insights of HIV persistence relevant to the lymphocyte recirculation network of immune system and the central nervous system (CNS). Our simulations and analyses illustrate the role of the CNS as a virus reservoir to prevent antiretroviral drugs from penetrating the blood-brain (or blood-testis) barrier, and we examine the long-term impact of this reservoir on the transmissibility of an infected individual. We observe numerically that level of HIV in peripheral blood may not accurately reflect the true mechanisms occurring within other organs.

Treatment of perinatal viral infections to improve neurologic outcomes

Viral infections in the fetus or newborn often involve the central nervous system (CNS) and can lead to significant morbidity and mortality. Substantial progress has been made in identifying interventions decreasing adverse neurodevelopmental outcomes in this population. This review highlights progress in treatment of important viruses affecting the CNS in these susceptible hosts, focusing on herpes simplex virus (HSV), cytomegalovirus (CMV), human immunodeficiency virus (HIV), and enteroviruses. The observation that high-dose acyclovir improves mortality in neonatal HSV disease culminated decades of antiviral research for this disease. More recently, prolonged oral acyclovir was found to improve neurologic morbidity after neonatal HSV encephalitis. Ganciclovir, and more recently its oral prodrug valganciclovir, is effective in improving hearing and neurodevelopment after congenital CMV infection. Increasing evidence suggests early control of perinatal HIV infection has implications for neurocognitive functioning into school age. Lastly, the antiviral pleconaril has been studied for nearly two decades for treating severe enteroviral infections, with newer data supporting a role for this drug in neonates. Identifying common mechanisms for pathogenesis of viral CNS disease during this critical period of brain development is an important research goal, highlighted by the recent emergence of Zika virus as a potential cause of fetal neurodevelopmental abnormalities.

Compartmentalization, Viral Evolution, and Viral Latency of HIV in the CNS

Human immunodeficiency virus type 1 (HIV-1) infection occurs throughout the body and can have dramatic physical effects, such as neurocognitive impairment in the central nervous system (CNS). Furthermore, examining the virus that resides in the CNS is challenging due to its location and can only be done using samples collected either at autopsy, indirectly form the cerebral spinal fluid (CSF), or through the use of animal models. The unique milieu of the CNS fosters viral compartmentalization as well as evolution of viral sequences, allowing for new cell types, such as macrophages and microglia, to be infected. Treatment must also cross the blood-brain barrier adding additional obstacles in eliminating viral populations in the CNS. These long-lived infected cell types and treatment barriers may affect functional cure strategies in people on highly active antiretroviral therapy (HAART).

RIG-I detects HIV-1 infection and mediates type I interferon response in human macrophages from patients with HIV-1-associated neurocognitive disorders

The aim of this study was to explore the precise role of retinoic acid-inducible gene-I (RIG-I) signaling in human immunodeficiency virus type 1 (HIV-1)-infected macrophages from patients with HIV-1-associated neurocognitive disorders (HAND). Postmortem brain tissues were collected from patients with HIV-1-associated dementia and were compared to samples collected from HIV serum-positive patients without dementia and HIV serum-negative patients. A human monocyte-derived macrophage (MDM) primary culture system was established to evaluate the expression of RIG-I in these samples. Knockdown of RIG-I pathways genes was employed and STAT1 expression and phosphorylation levels were examined to explore the molecular mechanisms of HAND. The expression of RIG-I in postmortem brain tissue from HAND patients was significantly higher than in patients who were HIV serum-positive without dementia or HIV serum-negative. Moreover, we demonstrated that HIV-1 infection could result in a significant increase in the level of RIG-I in human MDMs. Moreover, a correlation was found between the increase in RIG-I expression and STAT1 expression and phosphorylation. Accordingly, knockdown of RIG-I decreased the phosphorylation of STAT1 and downregulated interferon-related genes. These observations highlight the importance of RIG-I signaling in anti-HIV innate immunity in macrophages, which may be beneficial for the treatment of HIV and aid in the understanding of the neuropathogenesis of HAND.

SIV encephalitis lesions are composed of CD163(+) macrophages present in the central nervous system during early SIV infection and SIV-positive macrophages recruited terminally with AIDS

Macrophage recruitment to the central nervous system (CNS) during AIDS pathogenesis is poorly understood. We measured the accumulation of brain perivascular (CD163(+)) and inflammatory (MAC387(+)) macrophages in SIV-infected monkeys. Monocyte progenitors were 5-bromo-2'-deoxyuridine (BrdU) labeled in bone marrow, and CNS macrophages were labeled serially with fluorescent dextrans injected into the cisterna magna. MAC387(+) macrophages accumulated in the meninges and choroid plexus in early inflammation and in the perivascular space and SIV encephalitis (SIVE) lesions late. CD163(+) macrophages accumulated in the perivascular space and SIVE lesions with late inflammation. Most of the BrdU(+) cells were MAC387(+); however, CD163(+)BrdU(+) macrophages were present in the meninges and choroid plexus with AIDS. Most (81.6% ± 1.8%) of macrophages in SIVE lesions were present in the CNS before SIVE lesion formation. There was a 2.9-fold increase in SIVp28(+) macrophages entering the CNS late compared with those entering early (P < 0.05). The rate of CD163(+) macrophage recruitment to the CNS inversely correlated with time to death (P < 0.03) and increased with SIVE. In SIVE animals, soluble CD163 correlated with CD163(+) macrophage recruitment (P = 0.02). Most perivascular macrophages that comprise SIVE lesions and multinucleated giant cells are present in the CNS early, before SIVE lesions are formed. Most SIV-infected macrophages traffic to the CNS terminally with AIDS.

Genetic diversity and proviral DNA load in different neural compartments of HIV-1 subtype C infection

In India, the low prevalence of HIV-associated dementia (HAD) in the Human immunodeficiency virus type 1 (HIV-1) subtype C infection is quite paradoxical given the high-rate of macrophage infiltration into the brain. Whether the direct viral burden in individual brain compartments could be associated with the variability of the neurologic manifestations is controversial. To understand this paradox, we examined the proviral DNA load in nine different brain regions and three different peripheral tissues derived from ten human subjects at autopsy. Using a highly sensitive TaqMan probe-based real-time PCR, we determined the proviral load in multiple samples processed in parallel from each site. Unlike previously published reports, the present analysis identified uniform proviral distribution among the brain compartments examined without preferential accumulation of the DNA in any one of them. The overall viral DNA burden in the brain tissues was very low, approximately 1 viral integration per 1000 cells or less. In a subset of the tissue samples tested, the HIV DNA mostly existed in a free unintegrated form. The V3-V5 envelope sequences, demonstrated a brain-specific compartmentalization in four of the ten subjects and a phylogenetic overlap between the neural and non-neural compartments in three other subjects. The envelope sequences phylogenetically belonged to subtype C and the majority of them were R5 tropic. To the best of our knowledge, the present study represents the first analysis of the proviral burden in subtype C postmortem human brain tissues. Future studies should determine the presence of the viral antigens, the viral transcripts, and the proviral DNA, in parallel, in different brain compartments to shed more light on the significance of the viral burden on neurologic consequences of HIV infection.

Different levels of HIV DNA copy numbers in cerebrospinal fluid cellular subsets

Inequities in the incidence of HIV infection and AIDS with continued persistence of HIV-associated neurocognitive disorders (HAND) exist in populations in Hawaii (HI) and Puerto Rico (PR). We previously reported that peripheral monocyte HIV DNA levels are high in patients in Hawaii with HAND and we now hypothesize that similar findings would be observed in the cerebrospinal fluid (CSF) cellular subsets. Cerebrospinal fluid cells were obtained from patients from PR and HI undergoing neurocognitive testing and sorted into monocytes (CD14+) and lymphocytes (CD14-) and HIV DNA was measured. From six PR subjects (three HAND, three normal cognition, NC) and six HI subjects (three HAND, three NC), HIV DNA burden in CD14+ cells was higher in HAND than NC patients; NC patients had higher HIV DNA burden in CD14-cells versus HAND. Differences in HIV DNA burden in particular CSF cellular subsets suggest that HIV DNA burden may play a role in HAND neuropathogenesis.

Virus infection, antiviral immunity, and autoimmunity

As a group of disorders, autoimmunity ranks as the third most prevalent cause of morbidity and mortality in the Western World. However, the etiology of most autoimmune diseases remains unknown. Although genetic linkage studies support a critical underlying role for genetics, the geographic distribution of these disorders as well as the low concordance rates in monozygotic twins suggest that a combination of other factors including environmental ones are involved. Virus infection is a primary factor that has been implicated in the initiation of autoimmune disease. Infection triggers a robust and usually well-coordinated immune response that is critical for viral clearance. However, in some instances, immune regulatory mechanisms may falter, culminating in the breakdown of self-tolerance, resulting in immune-mediated attack directed against both viral and self-antigens. Traditionally, cross-reactive T-cell recognition, known as molecular mimicry, as well as bystander T-cell activation, culminating in epitope spreading, have been the predominant mechanisms elucidated through which infection may culminate in an T-cell-mediated autoimmune response. However, other hypotheses including virus-induced decoy of the immune system also warrant discussion in regard to their potential for triggering autoimmunity. In this review, we discuss the mechanisms by which virus infection and antiviral immunity contribute to the development of autoimmunity.

Chemokine CXCL8 promotes HIV-1 replication in human monocyte-derived macrophages and primary microglia via nuclear factor-κB pathway

BACKGROUND

Chemokine CXCL8 is an important neutrophil chemoattractant implicated in various neurodegenerative disorders. Cytokine/chemokine imbalance, with an increase in proinflammatory cytokines like interleukin-1β and tumor necrosis factor-α within the central nervous system, is a hallmark of human immunodeficiency virus (HIV)-1 infection. We previously reported that HIV-1 infection is linked to upregulation of CXCL8 in brain tissues and human astrocytes. Chemokines play crucial roles in trafficking of leukocytes and trafficking of HIV-1-infected across the blood-brain barrier play an important role in HIV-1 central nervous system disease. In the post-antiretroviral therapy era, low level of productive replication of HIV-1 in brain is a critical component of neuropathogenesis regulation. The present study investigated the effect of CXCL8 on productive infection of HIV-1 in human monocytes-derived macrophages (MDM) and primary human microglia.

RESULTS

Human MDM and microglia were infected with the blood or brain derived HIV-1 isolates, HIV-1ADA or HIV-1JRFL. Treatment with CXCL8 significantly upregulated HIV-1p24 levels in supernatants of both HIV-1-infected MDM as well as microglia. In addition, the formation of 2-long terminal repeat (LTR) circles, a measure of viral genome integration, was significantly higher in CXCL8-treated, HIV-1-infected MDM and microglia. Transient transfection of U937 cells with HIV-1 LTR luciferase reporter construct resulted in increased promoter activity when treated with CXCL8. Moreover, increased nuclear translocation of nuclear factor-κB was seen in HIV-1-infected MDM following CXCL8 treatment. Blocking CXCL8 receptors CXCR1 and CXCR2 abrogated the CXCL8-mediated enhanced HIV-1 replication.

CONCLUSION

Our results show that CXCL8 mediates productive infection of HIV-1 in MDM and microglia via receptors CXCR1 and CXCR2. These results demonstrate that CXCL8 exerts its downstream effects by increasing translocation of nuclear factor-κB into the nucleus, thereby promoting HIV-1 LTR activity.

Phenotypically heterogeneous populations in spatially heterogeneous environments

The spatial expansion of a population in a nonuniform environment may benefit from phenotypic heterogeneity with interconverting subpopulations using different survival strategies. We analyze the crossing of an antibiotic-containing environment by a bacterial population consisting of rapidly growing normal cells and slow-growing, but antibiotic-tolerant persister cells. The dynamics of crossing is characterized by mean first arrival times and is found to be surprisingly complex. It displays three distinct regimes with different scaling behavior that can be understood based on an analytical approximation. Our results suggest that a phenotypically heterogeneous population has a fitness advantage in nonuniform environments and can spread more rapidly than a homogeneous population.

Identification of nitrated immunoglobulin variable regions in the HIV-infected human brain: implications in HIV infection and immune response

HIV can infiltrate the brain and lead to HIV-associated neurocognitive disorders (HAND). The pathophysiology of HAND is poorly understood, and there are no diagnostic biomarkers for it. Previously, an increase in inducible nitric oxide synthase levels and protein tyrosine nitration in the brain were found to correlate with the severity of HAND.1,2 In this study, we analyzed human brains from individuals who had HIV infection without encephalitis and with encephalitis/HAND and compared them to the brains of healthy individuals. We identified the nitrated proteins and determined the sites of modification using affinity enrichment followed by high-resolution and high-mass-accuracy nanoLC–MS/MS. We found that nitrated proteins were predominantly present in the HIV-infected individuals with encephalitis, and, interestingly, the modifications were predominantly located on immunoglobulin variable regions. Our molecular model indicated potential interactions with HIV envelope proteins and changes on the heavy and light chain interface upon the nitration and nitrohydroxylation of these residues. Therefore, our findings suggest a role for these modifications in the immune response, which may have implications in disease pathogenesis.

Monocyte/macrophages and their role in HIV neuropathogenesis

Neurological sequelae of human immunodeficiency virus (HIV) infection have been and remain a significant problem. Monocytes and macrophages in humans and monkeys are susceptible to infection by HIV and simian immunodeficiency virus (SIV), and are considered to be a main mechanism by which the central nervous system (CNS) is infected. Within the infected CNS, perivascular macrophages and, in some cases, parenchymal microglia are infected as are multinucleated giant cells when present. While neurons are not themselves directly infected, neuronal damage occurs within the infected CNS. Despite the success of antiretroviral therapy (ART) in limiting virus in plasma to non-detectable levels, neurological deficits persist. This review discusses the continued neurological dysfunctions that persist in the era of ART, focusing on the roles of monocyte and macrophage as targets of continued viral infection and as agents of pathogenesis in what appears to be emergent macrophage-mediated disease resulting from long-term HIV infection of the host. Data discussed include the biology of monocyte/macrophage activation with HIV and SIV infection, traffic of cells into and out of the CNS with infection, macrophage-associated biomarkers of CNS and cardiac disease, the role of antiretroviral therapy on these cells and CNS disease, as well as the need for effective adjunctive therapies targeting monocytes and macrophages.

Small ruminant lentiviruses: genetic variability, tropism and diagnosis

Small ruminant lentiviruses (SRLV) cause a multisystemic chronic disease affecting animal production and welfare. SRLV infections are spread across the world with the exception of Iceland. Success in controlling SRLV spread depends largely on the use of appropriate diagnostic tools, but the existence of a high genetic/antigenic variability among these viruses, the fluctuant levels of antibody against them and the low viral loads found in infected individuals hamper the diagnostic efficacy. SRLV have a marked in vivo tropism towards the monocyte/macrophage lineage and attempts have been made to identify the genome regions involved in tropism, with two main candidates, the LTR and env gene, since LTR contains primer binding sites for viral replication and the env-encoded protein (SU ENV), which mediates the binding of the virus to the host’s cell and has hypervariable regions to escape the humoral immune response. Once inside the host cell, innate immunity may interfere with SRLV replication, but the virus develops counteraction mechanisms to escape, multiply and survive, creating a quasi-species and undergoing compartmentalization events. So far, the mechanisms of organ tropism involved in the development of different disease forms (neurological, arthritic, pulmonary and mammary) are unknown, but different alternatives are proposed. This is an overview of the current state of knowledge on SRLV genetic variability and its implications in tropism as well as in the development of alternative diagnostic assays.

On the rapidity of antibiotic resistance evolution facilitated by a concentration gradient

The rapid emergence of bacterial strains resistant to multiple antibiotics is posing a growing public health risk. The mechanisms underlying the rapid evolution of drug resistance are, however, poorly understood. The heterogeneity of the environments in which bacteria encounter antibiotic drugs could play an important role. E.g., in the highly compartmentalized human body, drug levels can vary substantially between different organs and tissues. It has been proposed that this could facilitate the selection of resistant mutants, and recent experiments support this. To study the role of spatial heterogeneity in the evolution of drug resistance, we present a quantitative model describing an environment subdivided into relatively isolated compartments with various antibiotic concentrations, in which bacteria evolve under the stochastic processes of proliferation, migration, mutation and death. Analytical and numerical results demonstrate that concentration gradients can foster a mode of adaptation that is impossible in uniform environments. It allows resistant mutants to evade competition and circumvent the slow process of fixation by invading compartments with higher drug concentrations, where less resistant strains cannot subsist. The speed of this process increases sharply with the sensitivity of the growth rate to the antibiotic concentration, which we argue to be generic. Comparable adaptation rates in uniform environments would require a high selection coefficient (s > 0.1) for each forward mutation. Similar processes can occur if the heterogeneity is more complex than just a linear gradient. The model may also be applicable to other adaptive processes involving environmental heterogeneity and range expansion.

Transmigration of macrophages across the choroid plexus epithelium in response to the feline immunodeficiency virus

Although lentiviruses such as human, feline and simian immunodeficiency viruses (HIV, FIV, SIV) rapidly gain access to cerebrospinal fluid (CSF), the mechanisms that control this entry are not well understood. One possibility is that the virus may be carried into the brain by immune cells that traffic across the blood-CSF barrier in the choroid plexus. Since few studies have directly examined macrophage trafficking across the blood-CSF barrier, we established transwell and explant cultures of feline choroid plexus epithelium and measured trafficking in the presence or absence of FIV. Macrophages in co-culture with the epithelium showed significant proliferation and robust trafficking that was dependent on the presence of epithelium. Macrophage migration to the apical surface of the epithelium was particularly robust in the choroid plexus explants where 3-fold increases were seen over the first 24 h. Addition of FIV to the cultures greatly increased the number of surface macrophages without influencing replication. The epithelium in the transwell cultures was also permissive to PBMC trafficking, which increased from 17 to 26% of total cells after exposure to FIV. Thus, the choroid plexus epithelium supports trafficking of both macrophages and PBMCs. FIV significantly enhanced translocation of macrophages and T cells indicating that the choroid plexus epithelium is likely to be an active site of immune cell trafficking in response to infection.

Study of compartmentalization in the visna clinical form of small ruminant lentivirus infection in sheep

Background

A central nervous system (CNS) disease outbreak caused by small ruminant lentiviruses (SRLV) has triggered interest in Spain due to the rapid onset of clinical signs and relevant production losses. In a previous study on this outbreak, the role of LTR in tropism was unclear and env encoded sequences, likely involved in tropism, were not investigated. This study aimed to analyze heterogeneity of SRLV Env regions - TM amino terminal and SU V4, C4 and V5 segments - in order to assess virus compartmentalization in CNS.

Results

Eight Visna (neurologically) affected sheep of the outbreak were used. Of the 350 clones obtained after PCR amplification, 142 corresponded to CNS samples (spinal cord and choroid plexus) and the remaining to mammary gland, blood cells, bronchoalveolar lavage cells and/or lung. The diversity of the env sequences from CNS was 11.1-16.1% between animals and 0.35-11.6% within each animal, except in one animal presenting two sequence types (30% diversity) in the CNS (one grouping with those of the outbreak), indicative of CNS virus sequence heterogeneity. Outbreak sequences were of genotype A, clustering per animal and compartmentalizing in the animal tissues. No CNS specific signature patterns were found.

Conclusions

Bayesian approach inferences suggested that proviruses from broncoalveolar lavage cells and peripheral blood mononuclear cells represented the common ancestors (infecting viruses) in the animal and that neuroinvasion in the outbreak involved microevolution after initial infection with an A-type strain. This study demonstrates virus compartmentalization in the CNS and other body tissues in sheep presenting the neurological form of SRLV infection.

Glutaminase dysregulation in HIV-1-infected human microglia mediates neurotoxicity: relevant to HIV-1-associated neurocognitive disorders

Microglia represent the main cellular targets of HIV-1 in the brain. Infected and/or activated microglia play a pathogenic role in HIV-associated neurocognitive disorders (HAND) by instigating primary dysfunction and subsequent death of neurons. Although microglia are known to secrete neurotoxins when infected with HIV-1, the detailed mechanism of neurotoxicity remains unclear. Using a human microglia primary culture system and macrophage-tropic HIV-1 strains, we have now demonstrated that HIV-1 infection of microglia resulted in a significant increase in extracellular glutamate concentrations and elevated levels of neurotoxicity. RNA and protein analysis revealed upregulation of the glutamate-generating enzyme glutaminase isoform glutaminase C in HIV-1-infected microglia. The clinical relevance of these findings was further corroborated with investigation of postmortem brain tissues. The glutaminase C levels in the brain tissues of HIV dementia individuals were significantly higher than HIV serum-negative control and correlated with elevated concentrations of glutamate. When glutaminase was subsequently inhibited by siRNA or by a small molecular inhibitor, the HIV-induced glutamate production and the neuronal loss was diminished. In conclusion, these findings support glutaminase as a potential component of the HAND pathogenic process as well as a novel therapeutic target in their treatment.

Viral determinants of HIV-1 macrophage tropism

Macrophages are important target cells for HIV-1 infection that play significant roles in the maintenance of viral reservoirs and other aspects of pathogenesis. Understanding the determinants of HIV-1 tropism for macrophages will inform HIV-1 control and eradication strategies. Tropism for macrophages is both qualitative (infection or not) and quantitative (replication capacity). For example many R5 HIV-1 isolates cannot infect macrophages, but for those that can the macrophage replication capacity can vary by up to 1000-fold. Some X4 viruses are also capable of replication in macrophages, indicating that cellular tropism is partially independent of co-receptor preference. Preliminary data obtained with a small number of transmitted/founder viruses indicate inefficient macrophage infection, whereas isolates from later in disease are more frequently tropic for macrophages. Thus tropism may evolve over time, and more macrophage tropic viruses may be implicated in the pathogenesis of advanced HIV-1 infection. Compartmentalization of macrophage-tropic brain-derived envelope glycoproteins (Envs), and non-macrophage tropic non-neural tissue-derived Envs points to adaptation of HIV-1 quasi-species in distinct tissue microenvironments. Mutations within and adjacent to the Env-CD4 binding site have been identified that determine macrophage tropism at the entry level, but post-entry molecular determinants of macrophage replication capacity involving HIV-1 accessory proteins need further definition.

HIV-1 clade B and C isolates exhibit differential replication: relevance to macrophage-mediated neurotoxicity

HIV-associated neurocognitive disorders (HAND) continue to be a consequence of HIV-1 infection among clade B-infected individuals. In contrast, the incidence of severe neurological impairment is lower among clade C-infected patients in regions of Sub-Saharan Africa and India. Biological aspects such as replication, cytopathicity, inflammatory response, and neurotoxicity unique to each clade influence neuropathogenicity and ultimately affect the clinical outcome of the disease. We hypothesize that productive infection by clade C isolates leads to macrophage-mediated neurotoxicity, although to a lesser extent than clade B isolates. Using a panel of primary isolates of clades B and C we demonstrated that clade B has higher replication efficiency in monocyte-derived macrophages (MDM) through reverse transcriptase activity assay and HIV-1 p24 antigen ELISA. To test the neurotoxicity of clades B and C, we used an in vitro neurotoxicity model. Conditioned medium from clade B-infected MDM was neurotoxic to rat and human neuron cultures. In contrast, clade C isolates mediated neurotoxicity when a higher initial viral titer was used for MDM infection. Furthermore, neurotoxicity mediated by isolates of both clades correlated with virus replication in MDM. Together, these results suggest that in comparison to clade B, primary isolates of clade C have slower replication kinetics in primary MDM, leading to lower levels of macrophage-mediated neurotoxicity. Elucidating the differences in replication and macrophage-mediated neurotoxicity between isolates of HIV-1 clades B and C will provide important insights needed to clarify the disparity seen in HAND incidence.

The distributional nexus of choroid plexus to cerebrospinal fluid, ependyma and brain: toxicologic/pathologic phenomena, periventricular destabilization, and lesion spread

Bordering the ventricular cerebrospinal fluid (CSF) are epithelial cells of choroid plexus (CP), ependyma and circumventricular organs (CVOs) that contain homeostatic transporters for mediating secretion/reabsorption. The distributional pathway ("nexus") of CP-CSF-ependyma-brain furnishes peptides, hormones, and micronutrients to periventricular regions. In disease/toxicity, this nexus becomes a conduit for infectious and xenobiotic agents. The sleeping sickness trypanosome (a protozoan) disrupts CP and downstream CSF-brain. Piperamide is anti-trypanosomic but distorts CP epithelial ultrastructure by engendering hydropic vacuoles; this reflects phospholipidosis and altered lysosomal metabolism. CP swelling by vacuolation may occlude CSF flow. Toxic drug tools delineate injuries to choroidal compartments: cyclophosphamide (vasculature), methylcellulose (interstitium), and piperazine (epithelium). Structurally perturbed CP allows solutes to penetrate the ventricles. There, CSF-borne pathogens and xenobiotics may permeate the ependyma to harm neurogenic stem cell niches. Amoscanate, an anti-helmintic, potently injures rodent ependyma. Ependymal/brain regions near CP are vulnerable to CSF-borne toxicants; this proximity factor links regional barrier breakdown to nearby periventricular pathology. Diverse diseases (e.g., African sleeping sickness, multiple sclerosis) take early root in choroidal, circumventricular, or perivascular loci. Toxicokinetics informs on pathogen, anti-parasitic agent, and auto-antibody distribution along the CSF nexus. CVOs are susceptible to plasma-borne toxicants/pathogens. Countering the physico-chemical and pathogenic insults to the homeostasis-mediating ventricle-bordering cells sustains brain health and fluid balance.

The neuropathogenesis of feline immunodeficiency virus infection: barriers to overcome

Feline immunodeficiency virus (FIV), like human immunodeficiency virus (HIV)-1, is a neurotropic lentivirus, and both natural and experimental infections are associated with neuropathology. FIV enters the brain early following experimental infection, most likely via the blood-brain and blood-cerebrospinal fluid barriers. The exact mechanism of entry, and the factors that influence this entry, are not fully understood. As FIV is a recognised model of HIV-1 infection, understanding such mechanisms is important, particularly as HIV enters the brain early in infection. Furthermore, the development of strategies to combat this central nervous system (CNS) infection requires an understanding of the interactions between the virus and the CNS. In this review the results of both in vitro and in vivo FIV studies are assessed in an attempt to elucidate the mechanisms of viral entry into the brain.

Reduced genetic diversity in lymphoid and central nervous system tissues and selection-induced tissue-specific compartmentalization of neuropathogenic SIVsmmFGb during acute infection

The simian lentivirus strain SIVsmmFGb is a viral swarm population inducing neuropathology in over 90% of infected pigtailed macaques and serves as a reliable model for HIV neuropathogenesis. However, little is understood about the genetic diversity of this virus, how said diversity influences the initial seeding of the central nervous system and lymph nodes, or whether the virus forms distinct genetic compartments between tissues during acute infection. In this study, we establish that our SIVsmmFGb stock virus contains four genetically distinct envelope V1 region groups, three distinct integrase groups, and two Nef groups. We demonstrate that initial central nervous system and lymph node seeding reduces envelope V1 and integrase genetic diversity but has a variable effect on Nef diversity. SIVsmmFGb envelope V1 region genes from the basal ganglia, cerebellum, and hippocampus form distinct genetic compartments from each other, the midfrontal cortex, and the lymph nodes. Basal ganglia, cerebellum, hippocampus, and midfrontal cortex-derived nef genes all form distinct genetic compartments from each other, as well as from the lymph nodes. We also find basal ganglia, hippocampus, and midfrontal cortex-derived integrase sequences forming distinct compartments from both of the lymph nodes and that the hippocampus and midfrontal cortex form separate compartments from the cerebellum, while the axillary and mesenteric lymph nodes compartmentalize separately from each other. Compartmentalization of the envelope V1 genes resulted from positive selection, and compartmentalization of the nef and integrase genes from negative selection. These results indicate restrictions on virus genetic diversity during initial tissue seeding in neuropathogenic SIV infection.

Major coexisting human immunodeficiency virus type 1 env gene subpopulations in the peripheral blood are produced by cells with similar turnover rates and show little evidence of genetic compartmentalization

A distinctive feature of chronic human immunodeficiency virus type 1 (HIV-1) infection is the presence of multiple coexisting genetic variants, or subpopulations, that comprise the HIV-1 population detected in the peripheral blood. Analysis of HIV-1 RNA decay dynamics during the initiation of highly active antiretroviral therapy (HAART) has been a valuable tool for modeling the life span of infected cells that produce the bulk HIV-1 population. However, different HIV-1 target cells may have different turnover rates, and it is not clear whether the bulk HIV-1 RNA decay rate actually represents a composite of the decay rates of viral subpopulations compartmentalized in different cellular subsets with different life spans. Using heteroduplex tracking assays targeting the highly variable V3 or V4-V5 regions of the HIV-1 env gene in eight subjects, we found that all detectable coexisting HIV-1 variants in the peripheral blood generally decayed at similar rates during the initiation of HAART, suggesting that all of the variants were produced by cells with similar life spans. Furthermore, single genome amplification and coreceptor phenotyping revealed that in two subjects coexisting HIV-1 variants with distinct CXCR4 or CCR5 coreceptor phenotypes decayed with similar rates. Also, in nine additional subjects, recombination and a lack of genetic compartmentalization between X4 and R5 variants were observed, suggesting an overlap in host cell range. Our results suggest that the HIV-1 env subpopulations detectable in the peripheral blood are produced by cells with similar life spans and are not genetically isolated within particular cell types.

Exceptional molecular and coreceptor-requirement properties of molecular clones isolated from an Human Immunodeficiency Virus Type-1 subtype C infection

BACKGROUND

The pathogenic significance of coreceptor switch in the viral infection of HIV-1 is not completely understood. This situation is more complex in subtype C infection where coreceptor switch is either absent or extremely rare. To gain insights into the mechanisms that underlie coreceptor requirement of subtype C, we screened several primary viral isolates and identified a clinical sample that demonstrated a potential to grow on standard T-cell lines with no detectable CCR5 expression. The subject was diagnosed with HIV-1 associated dementia in the absence of opportunistic infections of the brain. To isolate molecular clones from this virus, we devised a novel strategy based on anchor primers that target a sequence in the reverse transcriptase, highly conserved among diverse subtypes of HIV-1.

RESULTS

Using this strategy, we isolated 8 full-length molecular clones from the donor. Two of the eight molecular clones, 03In94_D17 and 03In94_D24, (D17 and D24) generated replication-competent viruses. Phylogenetic analysis of the full-length viral sequences revealed that both clones were non-recombinant subtype C viruses. They contain intact open reading frames in all the viral proteins. Both the viral clones are endowed with several unique molecular and biological properties. The viral promoter of the clones is characterized by the presence of four NF-kB binding elements, a feature rarely seen in the subtype C HIV-1 LTR. Interestingly, we identified the coexistence of two different forms of Rev, a truncated form common to subtype C and a full-length form less common for this subtype, in both proviral and plasma virus compartments. An exceptional property of the viruses, atypical of subtype C, is their ability to use a wide range of coreceptors including CCR5, CXCR4, and several others tested. Sequence analysis of Env of D17 and D24 clones identified differences within the variable loops providing important clues for the expanded coreceptor use. The V1, V2 and V4 loops in both of the molecular clones are longer due to the insertion of several amino acid residues that generated potential N-linked glycosylation sites.

CONCLUSION

The exceptional biological and molecular properties of these clones make them invaluable tools to understand the unique pathogenic characteristics of subtype C.

Characterization of peripheral blood human immunodeficiency virus isolates from Hispanic women with cognitive impairment

Human immunodeficiency virus type 1 (HIV-1) tropism plays an important role in HIV-associated dementia. In this study, aimed at determining if the tropism and coreceptor usage of circulating viruses correlates with cognitive function, the authors isolated and characterized HIV from the peripheral blood of 21 Hispanic women using antiretroviral therapy. Macrophage tropism was determined by inoculation of HIV isolates onto monocyte-derived macrophages and lymphocyte cultures. To define coreceptor usage, the HIV isolates were inoculated onto the U87.CD4 glioma cell lines with specific CCR5 and CXCR4 coreceptors. HIV isolates from cognitively impaired patients showed higher levels of replication in mitogen-stimulated peripheral blood mononuclear cells than did isolates from patients with normal cognition (P < .05). The viral growth of HIV primary isolates in macrophages and lymphocytes did not differ between patients with and those without cognitive impairment. However, isolates from the cognitively impaired women preferentially used the X4 coreceptor (P < .05). These phenotypic studies suggest that cognitively impaired HIV-infected women receiving treatment may have a more highly replicating and more pathogenic X4 virus in the circulation that could contribute to their neuropathogenesis.

Comparative study of methods for detecting sequence compartmentalization in human immunodeficiency virus type 1

Human immunodeficiency virus (HIV) infects different organs and tissues. During these infection events, subpopulations of HIV type 1 (HIV-1) develop and, if viral trafficking is restricted between subpopulations, the viruses can follow independent evolutionary histories, i.e., become compartmentalized. This phenomenon is usually detected via comparative sequence analysis and has been reported for viruses isolated from the central nervous system (CNS) and the genital tract. Several approaches have been proposed to study the compartmentalization of HIV sequences, but to date, no rigorous comparison of the most commonly employed methods has been made. In this study, we systematically compared inferences made by six different methods for detecting compartmentalization based on three data sets: (i) a sample of 45 patients with sequences gathered from the CNS, (ii) sequences from the female genital tract of 18 patients, and (iii) a set of simulated sequences. We found that different methods often reached contradictory conclusions. Methods based on the topology of a phylogenetic tree derived from clonal sequences were generally more sensitive in detecting compartmentalization than those that relied solely upon pairwise genetic distances between sequences. However, as the branching structure in a phylogenetic tree is often uncertain, especially for short, low-diversity, or recombinant sequences, tree-based approaches may need to be modified to take phylogenetic uncertainty into account. Given the frequently discordant predictions of different methods and the strengths and weaknesses of each particular methodology, we recommend that a suite of several approaches be used for reliable inference of compartmentalized population structure.

Compartmentalization and evolution of feline immunodeficiency virus between the central nervous system and periphery following intracerebroventricular or systemic inoculation

The emergence of distinct neuropathogenic strains resulting from the adaptation and the unique evolution of human immunodeficiency virus (HIV) in the brain may contribute to the development of HIV-induced neurological diseases. In this study, the authors tracked early changes in virus evolution and compartmentalization between peripheral tissues and the central nervous system (CNS) after intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) inoculation of animals with cell-free feline immunodeficiency virus (FIV). Using the FIV-NCSU1 envelope V3-V4 heteroduplex tracking assay (HTA), the authors observed a rapid compartmentalization of envelope variants between the CNS and periphery. Animals receiving the i.c.v. inoculation showed two peaks of viral RNA in the cerebrospinal fluid (CSF) with very different HTA patterns. Compared to the initial viral peak in CSF, the second peak showed an increased compartmentalization from plasma, reduced viral diversity, and more divergence from the proviral DNA in peripheral blood mononuclear cells (PBMCs) and the choroid plexus. In contrast, changes in plasma over the same time period were small. Different animals harbored different FIV DNA genotypes with varied regional compartmentalization within the brain. These results demonstrated that the virus within the CNS experienced a relatively independent but variable evolution from the periphery. Initial penetration of virus into the CSF facilitated the development of brain-specific reservoirs and viral diversification within the CNS.