RNA landscapes of brain and brain-derived extracellular vesicles in simian immunodeficiency virus (SIV) infection and central nervous system pathology.

INTRODUCTION: Brain tissue-derived extracellular vesicles (bdEVs) act locally in the central nervous system (CNS) and may indicate molecular mechanisms in HIV CNS pathology. Using brain homogenate (BH) and bdEVs from a simian immunodeficiency virus (SIV) model of HIV disease, we identified RNA networks in SIV infection and neuroinflammation. METHODS: Postmortem occipital cortex samples were obtained from uninfected controls and SIV-infected subjects (acute and chronic phases with or without CNS pathology (SIV encephalitis). bdEVs were separated and characterized per international consensus guidelines. RNAs from bdEVs and BH were sequenced and qPCR-amplified to detect levels of small RNAs (sRNAs, including microRNAs (miRNAs)) and longer RNAs including messenger RNAs (mRNAs) and circular RNAs (circRNAs). RESULTS: Dysregulated RNAs in BH and bdEVs were identified in acute and chronic infection with pathology groups, including mRNAs, miRNAs, and circRNAs. Most dysregulated mRNAs in bdEVs reflected dysregulation in source BH. These mRNAs are disproportionately involved in inflammation and immune responses. Based on target prediction, several circRNAs that were differentially abundant in source tissue might be responsible for specific differences in sRNA levels in bdEVs during SIV infection. CONCLUSIONS: RNA profiling of bdEVs and source tissues reveals potential regulatory networks in SIV infection and SIV-related CNS pathology.

Progression and Resolution of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection in Golden Syrian Hamsters.

To catalyze severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) research, including development of novel interventive and preventive strategies, the progression of disease was characterized in a robust coronavirus disease 2019 (COVID-19) animal model. In this model, male and female golden Syrian hamsters were inoculated intranasally with SARS-CoV-2 USA-WA1/2020. Groups of inoculated and mock-inoculated uninfected control animals were euthanized at 2, 4, 7, 14, and 28 days after inoculation to track multiple clinical, pathology, virology, and immunology outcomes. SARS-CoV-2-inoculated animals consistently lost body weight during the first week of infection, had higher lung weights at terminal time points, and developed lung consolidation per histopathology and quantitative image analysis measurements. High levels of infectious virus and viral RNA were reliably present in the respiratory tract at days 2 and 4 after inoculation, corresponding with widespread necrosis and inflammation. At day 7, when the presence of infectious virus was rare, interstitial and alveolar macrophage infiltrates and marked reparative epithelial responses (type II hyperplasia) dominated in the lung. These lesions resolved over time, with only residual epithelial repair evident by day 28 after inoculation. The use of quantitative approaches to measure cellular and morphologic alterations in the lung provides valuable outcome measures for developing therapeutic and preventive interventions for COVID-19 using the hamster COVID-19 model.

Effect of Single Housing on Innate Immune Activation in Immunodeficiency Virus-Infected Pigtail Macaques ( Macaca nemestrina ) as a Model of Psychosocial Stress in Acute HIV Infection.

OBJECTIVE: Simian immunodeficiency virus (SIV) infection of macaques recapitulates many aspects of HIV pathogenesis and is similarly affected by both genetic and environmental factors. Psychosocial stress is associated with immune system dysregulation and worse clinical outcomes in people with HIV. This study assessed the impact of single housing, as a model of psychosocial stress, on innate immune responses of pigtailed macaques ( Macaca nemestrina ) during acute SIV infection. METHODS: A retrospective analysis of acute SIV infection of 2- to si6-year-old male pigtailed macaques was performed to compare the innate immune responses of socially ( n = 41) and singly ( n = 35) housed animals. Measures included absolute monocyte count and subsets, and in a subset ( n ≤ 18) platelet counts and activation data. RESULTS: SIV infection resulted in the expected innate immune parameter changes with a modulating effect from housing condition. Monocyte number increased after infection for both groups, driven by classical monocytes (CD14 + CD16 - ), with a greater increase in socially housed animals (227%, p < .001, by day 14 compared with preinoculation time points). Platelet numbers recovered more quickly in the socially housed animals. Platelet activation (P-selectin) increased by 65% ( p = .004) and major histocompatibility complex class I surface expression by 40% ( p = .009) from preinoculation only in socially housed animals, whereas no change in these measures occurred in singly housed animals. CONCLUSIONS: Chronic psychosocial stress produced by single housing may play an immunomodulatory role in the innate immune response to acute retroviral infection. Dysregulated innate immunity could be one of the pathways by which psychosocial stress contributes to immune suppression and increased disease severity in people with HIV.

Psychosocial Stress Alters the Immune Response and Results in Higher Viral Load During Acute Simian Immunodeficiency Virus Infection in a Pigtailed Macaque Model of Human Immunodeficiency Virus.

BACKGROUND: Although social distancing is a key public health response during viral pandemics, psychosocial stressors, such as social isolation, have been implicated in adverse health outcomes in general [1] and in the context of infectious disease, such as human immunodeficiency virus (HIV) [2, 3]. A comprehensive understanding of the direct pathophysiologic effects of psychosocial stress on viral pathogenesis is needed to provide strategic and comprehensive care to patients with viral infection. METHODS: To determine the effect of psychosocial stress on HIV pathogenesis during acute viral infection without sociobehavioral confounders inherent in human cohorts, we compared commonly measured parameters of HIV progression between singly (n = 35) and socially (n = 41) housed simian immunodeficiency virus (SIV)-infected pigtailed macaques (Macaca nemestrina). RESULTS: Singly housed macaques had a higher viral load in the plasma and cerebrospinal fluid and demonstrated greater CD4 T-cell declines and more CD4 and CD8 T-cell activation compared with socially housed macaques throughout acute SIV infection. CONCLUSIONS: These data demonstrate that psychosocial stress directly impacts the pathogenesis of acute SIV infection and imply that it may act as an integral variable in the progression of HIV infection and potentially of other viral infections.

Human immunodeficiency virus-1/simian immunodeficiency virus infection induces opening of pannexin-1 channels resulting in neuronal synaptic compromise: A novel therapeutic opportunity to prevent NeuroHIV.

In healthy conditions, pannexin-1 (Panx-1) channels are in a close state, but in several pathological conditions, including human immunodeficiency virus-1 (HIV) and NeuroHIV, the channel becomes open. However, the mechanism or contribution of Panx-1 channels to the HIV pathogenesis and NeuroHIV is unknown. To determine the contribution of Panx-1 channels to the pathogenesis of NeuroHIV, we used a well-established model of simian immunodeficiency virus (SIV) infection in macaques (Macaca mulatta) in the presence of and absence of a Panx-1 blocker to later examine the synaptic/axonal compromise induced for the virus. Using Golgi's staining, we demonstrated that SIV infection compromised synaptic and axonal structures, especially in the white matter. Blocking Panx-1 channels after SIV infection prevented the synaptic and axonal compromise induced by the virus, especially by maintaining the more complex synapses. Our data demonstrated that targeting Panx-1 channels can prevent and maybe revert brain synaptic compromise induced by SIV infection.

Infectious Virus Persists in CD4+ T Cells and Macrophages in Antiretroviral Therapy-Suppressed Simian Immunodeficiency Virus-Infected Macaques.

Understanding the cellular and anatomical sites of latent virus that contribute to human immunodeficiency virus (HIV) rebound is essential for eradication. In HIV-positive patients, CD4+ T lymphocytes comprise a well-defined functional latent reservoir, defined as cells containing transcriptionally silent genomes able to produce infectious virus once reactivated. However, the persistence of infectious latent virus in CD4+ T cells in compartments other than blood and lymph nodes is unclear. Macrophages (Mϕ) are infected by HIV/simian immunodeficiency virus (SIV) and are likely to carry latent viral genomes during antiretroviral therapy (ART), contributing to the reservoir. Currently, the gold standard assay used to measure reservoirs containing replication-competent virus is the quantitative viral outgrowth assay (QVOA). Using an SIV-macaque model, the CD4+ T cell and Mϕ functional latent reservoirs were measured in various tissues using cell-specific QVOAs. Our results showed that blood, spleen, and lung in the majority of suppressed animals contain latently infected Mϕs. Surprisingly, the numbers of CD4+ T cells, monocytes, and Mϕs carrying infectious genomes in blood and spleen were at comparable frequencies (∼1 infected cell per million). We also demonstrate that ex vivo viruses produced in the Mϕ QVOA are capable of infecting activated CD4+ T cells. These results strongly suggest that latently infected tissue Mϕs can reestablish productive infection upon treatment interruption. This study provides the first comparison of CD4+ T cell and Mϕ functional reservoirs in a macaque model. It is the first confirmation of the persistence of latent genomes in monocytes in blood and Mϕs in the spleen and lung of SIV-infected ART-suppressed macaques. Our results demonstrate that transcriptionally silent genomes in Mϕs can contribute to viral rebound after ART interruption and should be considered in future HIV cure strategies.IMPORTANCE This study suggests that CD4+ T cells found throughout tissues in the body can contain replication-competent SIV and contribute to rebound of the virus after treatment interruption. In addition, this study demonstrates that macrophages in tissues are another cellular reservoir for SIV and may contribute to viral rebound after treatment interruption. This new insight into the size and location of the SIV reservoir could have great implications for HIV-infected individuals and should be taken into consideration for the development of future HIV cure strategies.

Differential regulation of TREM2 and CSF1R in CNS macrophages in an SIV/macaque model of HIV CNS disease.

HIV-associated neuroinflammation is primarily driven by CNS macrophages including microglia. Regulation of these immune responses, however, remains to be characterized in detail. Using the SIV/macaque model of HIV, we evaluated CNS expression of triggering receptor expressed on myeloid cells 2 (TREM2) which is constitutively expressed by microglia and contributes to cell survival, proliferation, and differentiation. Loss-of-function mutations in TREM2 are recognized risk factors for neurodegenerative diseases including Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and Nasu-Hakola disease (NHD); recent reports have also indicated a role for TREM2 in HIV-associated neuroinflammation. Using in situ hybridization (ISH) and qRT-PCR, TREM2 mRNA levels were found to be significantly elevated in frontal cortex of macaques with SIV encephalitis compared with uninfected controls (P = 0.02). TREM2 protein levels were also elevated as measured by ELISA of frontal cortex tissue homogenates in these animals. Previously, we characterized the expression of CSF1R (colony-stimulating factor 1 receptor) in this model; the TREM2 and CSF1R promoters both contain a PU.1 binding site. While TREM2 and CSF1R mRNA levels in the frontal cortex were highly correlated (Spearman R = 0.79, P < 0.001), protein levels were not well correlated. In SIV-infected macaques released from ART to study viral rebound, neither TREM2 nor CSF1R mRNA increased with rebound viremia. However, CSF1R protein levels remained significantly elevated unlike TREM2 (P = 0.02). This differential expression suggests that TREM2 and CSF1R play unique, distinct roles in the pathogenesis of HIV CNS disease.

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.

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.

Marked Enteropathy in an Accelerated Macaque Model of AIDS.

Enteropathy in HIV infection is not eliminated with combination antiretroviral therapy and is possibly linked to microbial translocation. We used a rapidly progressing SIV/pigtailed macaque model of HIV to examine enteropathy and microbial translocation. Histologic evidence of intestinal disease was observed in only half of infected macaques during late-stage infection (LSI). Combination antiretroviral therapy initiated during acute infection prevented intestinal disease. In the ileum and colon, enteropathy was associated with increased caspase-3 staining, decreased CD3+ T cells, and increased SIV-infected cells. CD3+ T cells were preserved in LSI animals without intestinal disease, and levels of CD3 staining in all LSI animals strongly correlated with the number of infected cells in the intestine and plasma viral load. Unexpectedly, there was little evidence of microbial translocation as measured by soluble CD14, soluble CD163, lipopolysaccharide binding protein, and microbial 16s ribosomal DNA. Loss of epithelial integrity indicated by loss of the tight junction protein claudin-3 was not observed during acute infection despite significantly fewer T cells. Claudin-3 was reduced in LSI animals with severe intestinal disease but did not correlate with increased microbial translocation. LSI animals that did not develop intestinal disease had increased T-cell intracytoplasmic antigen 1-positive cytotoxic T lymphocytes, suggesting a robust adaptive cytotoxic T-lymphocyte response may, in part, confer resilience to SIV-induced intestinal damage.

An SIV/macaque model targeted to study HIV-associated neurocognitive disorders.

Simian immunodeficiency virus (SIV) infection of pigtailed macaques is a highly representative and well-characterized animal model for HIV neuropathogenesis studies that provides an excellent opportunity to study and develop prognostic markers of HIV-associated neurocognitive disorders (HAND) for HIV-infected individuals. SIV studies can be performed in a controlled setting that enhances reproducibility and offers high-translational value. Similar to observations in HIV-infected patients receiving antiretroviral therapy (ART), ongoing neurodegeneration and inflammation are present in SIV-infected pigtailed macaques treated with suppressive ART. By developing quantitative viral outgrowth assays that measure both CD4+ T cells and macrophages harboring replication competent SIV as well as a highly sensitive mouse-based viral outgrowth assay, we have positioned the SIV/pigtailed macaque model to advance our understanding of latent cellular reservoirs, including potential CNS reservoirs, to promote HIV cure. In addition to contributing to our understanding of the pathogenesis of HAND, the SIV/pigtailed macaque model also provides an excellent opportunity to test innovative approaches to eliminate the latent HIV reservoir in the brain.

Quantitation of Productively Infected Monocytes and Macrophages of Simian Immunodeficiency Virus-Infected Macaques.

UNLABELLED: Despite the success of combined antiretroviral therapy (ART), human immunodeficiency virus (HIV) infection remains a lifelong infection because of latent viral reservoirs in infected patients. The contribution of CD4(+) T cells to infection and disease progression has been extensively studied. However, during early HIV infection, macrophages in brain and other tissues are infected and contribute to tissue-specific diseases, such as encephalitis and dementia in brain and pneumonia in lung. The extent of infection of monocytes and macrophages has not been rigorously assessed with assays comparable to those used to study infection of CD4(+) T cells and to evaluate the number of CD4(+) T cells that harbor infectious viral genomes. To assess the contribution of productively infected monocytes and macrophages to HIV- and simian immunodeficiency virus (SIV)-infected cells in vivo, we developed a quantitative virus outgrowth assay (QVOA) based on similar assays used to quantitate CD4(+) T cell latent reservoirs in HIV- and SIV-infected individuals in whom the infection is suppressed by ART. Myeloid cells expressing CD11b were serially diluted and cocultured with susceptible cells to amplify virus. T cell receptor ß RNA was measured as a control to assess the potential contribution of CD4(+) T cells in the assay. Virus production in the supernatant was quantitated by quantitative reverse transcription-PCR. Productively infected myeloid cells were detected in blood, bronchoalveolar lavage fluid, lungs, spleen, and brain, demonstrating that these cells persist throughout SIV infection and have the potential to contribute to the viral reservoir during ART. IMPORTANCE: Infection of CD4(+) T cells and their role as latent reservoirs have been rigorously assessed; however, the frequency of productively infected monocytes and macrophages in vivo has not been similarly studied. Myeloid cells, unlike lymphocytes, are resistant to the cytopathic effects of HIV. Moreover, tissue-resident macrophages have the ability to self-renew and persist in the body for months to years. Thus, tissue macrophages, once infected, have the characteristics of a potentially stable viral reservoir. A better understanding of the number of productively infected macrophages is crucial to further evaluate the role of infected myeloid cells as a potential viral reservoir. In the study described here we compared the frequency of productively infected CD4(+) T cells and macrophages in an SIV-infected macaque model. We developed a critical assay that will allow us to quantitate myeloid cells containing viral genomes that lead to productive infection in SIV-infected macaques and assess the role of macrophages as potential reservoirs.

Splenic Damage during SIV Infection: Role of T-Cell Depletion and Macrophage Polarization and Infection.

The effects of HIV infection on spleen and its cellular subsets have not been fully characterized, particularly for macrophages in which diverse populations exist. We used an accelerated SIV-infected macaque model to examine longitudinal effects on T-cell and macrophage populations and their susceptibilities to infection. Substantial lymphoid depletion occurred, characterized by follicular burn out and a loss of CD3 T lymphocytes, which was associated with cellular activation and transient dysregulations in CD4/CD8 ratios and memory effector populations. In contrast, the loss of CD68 and CD163(+)CD68(+) macrophages and increase in CD163 cells was irreversible, which began during acute infection and persisted until terminal disease. Mac387 macrophages and monocytes were transiently recruited into spleen, but were not sufficient to mitigate the changes in macrophage subsets. Type I interferon, M2 polarizing genes, and chemokine-chemokine receptor signaling were up-regulated in spleen and drove macrophage alterations. SIV-infected T cells were numerous within the white pulp during acute infection, but were rarely observed thereafter. CD68, CD163, and Mac387 macrophages were highly infected, which primarily occurred in the red pulp independent of T cells. Few macrophages underwent apoptosis, indicating that they are a long-lasting target for HIV/SIV. Our results identify macrophages as an important contributor to HIV/SIV infection in spleen and in promoting morphologic changes through the loss of specific macrophage subsets that mediate splenic organization.

Central nervous system-specific consequences of simian immunodeficiency virus Gag escape from major histocompatibility complex class I-mediated control.

In the fourth decade of the HIV epidemic, the relationship between host immunity and HIV central nervous system (CNS) disease remains incompletely understood. Using a simian immunodeficiency virus (SIV)/macaque model, we examined CNS outcomes in pigtailed macaques expressing the MHC class I allele Mane-A1*084:01 which confers resistance to SIV-induced CNS disease and induces the prototypic viral escape mutation Gag K165R. Insertion of gag K165R into the neurovirulent clone SIV/17E-Fr reduced viral replication in vitro compared to SIV/17E-Fr. We also found lower cerebrospinal fluid (CSF), but not plasma, viral loads in macaques inoculated with SIV/17E-Fr K165R versus those inoculated with wildtype. Although escape mutation K165R was genotypically stable in plasma, it rapidly reverted to wildtype Gag KP9 in both CSF and in microglia cultures. We induced robust Gag KP9-specific CTL tetramer responses by vaccinating Mane-A*084:01-positive pigtailed macaques with a Gag KP9 virus-like particle (VLP) vaccine. Upon SIV/17E-Fr challenge, vaccinated animals had lower SIV RNA in CSF compared to unvaccinated controls, but showed no difference in plasma viral loads. These data clearly demonstrate that viral fitness in the CNS is distinct from the periphery and underscores the necessity of understanding the consequences of viral escape in CNS disease with the advent of new therapeutic vaccination strategies.

A Murine Viral Outgrowth Assay to Detect Residual HIV Type 1 in Patients With Undetectable Viral Loads.

BACKGROUND: Sensitive assays are needed for detection of residual human immunodeficiency virus (HIV) in patients with undetectable plasma viral loads to determine whether eradication strategies are effective. The gold standard quantitative viral outgrowth assay (QVOA) underestimates the magnitude of the viral reservoir. We sought to determine whether xenograft of leukocytes from HIV type 1 (HIV)-infected patients with undetectable plasma viral loads into immunocompromised mice would result in viral amplification. METHODS: Peripheral blood mononuclear cells or purified CD4(+) T cells from HIV or simian immunodeficiency virus (SIV)-infected subjects with undetectable plasma viral loads were adoptively transferred into NOD.Cg-Prkdc(scid)Il2rg(tm1Wjl)/SzJ (NSG) mice. The mice were monitored for viremia following depletion of human CD8(+) T cells to minimize antiviral activity. In some cases, humanized mice were also treated with activating anti-CD3 antibody. RESULTS: With this murine viral outgrowth assay (MVOA), we successfully amplified replication-competent HIV or SIV from all subjects tested, including 5 HIV-positive patients receiving suppressive antiretroviral therapy (ART) and 6 elite controllers or suppressors who were maintaining undetectable viral loads without ART, including an elite suppressor from whom we were unable to recover virus by QVOA. CONCLUSIONS: Our results suggest that the MVOA has the potential to serve as a powerful tool to identify residual HIV in patients with undetectable viral loads.

Loss of corneal sensory nerve fibers in SIV-infected macaques: an alternate approach to investigate HIV-induced PNS damage.

Peripheral neuropathy is the most frequent neurological complication of HIV infection, affecting more than one-third of infected patients, including patients treated with antiretroviral therapy. Although emerging noninvasive techniques for corneal nerve assessments are increasingly being used to diagnose and monitor peripheral neuropathies, corneal nerve alterations have not been characterized in HIV. Here, to determine whether SIV infection leads to corneal nerve fiber loss, we immunostained corneas for the nerve fiber marker ßIII tubulin. We developed and applied both manual and automated methods to measure nerves in the corneal subbasal plexus. These counting methods independently indicated significantly lower subbasal corneal nerve fiber density among SIV-infected animals that rapidly progressed to AIDS compared with slow progressors. Concomitant with decreased corneal nerve fiber density, rapid progressors had increased levels of SIV RNA and CD68-positive macrophages and expression of glial fibrillary acidic protein by glial satellite cells in the trigeminal ganglia, the location of the neuronal cell bodies of corneal sensory nerve fibers. In addition, corneal nerve fiber density was directly correlated with epidermal nerve fiber length. These findings indicate that corneal nerve assessment has great potential to diagnose and monitor HIV-induced peripheral neuropathy and to set the stage for introducing noninvasive techniques to measure corneal nerve fiber density in HIV clinical settings.

Macaque species susceptibility to simian immunodeficiency virus: increased incidence of SIV central nervous system disease in pigtailed macaques versus rhesus macaques.

Immune pressure exerted by MHC class I-restricted cytotoxic T cells drives the development of viral escape mutations, thereby regulating HIV disease progression. Nonetheless, the relationship between host immunity and HIV central nervous system (CNS) disease remains poorly understood. The simian immunodeficiency virus (SIV) macaque model recapitulates key features of HIV infection including development of AIDS and CNS disease. To investigate cell-mediated immunity regulating SIV CNS disease progression, we compared the incidence of SIV encephalitis and the influence of MHC class I allele expression on the development of CNS disease in rhesus macaques (Macaca mulatta) versus pigtailed macaques (Macaca nemestrina). After inoculation with the immunosuppressive swarm SIV/DeltaB670 and the neurovirulent molecular clone SIV/17E-Fr, pigtailed macaques progressed more rapidly to AIDS, had higher plasma and cerebrospinal fluid (CSF) viral loads, and were more likely to progress to SIV-associated encephalitis (SIVE) compared to rhesus macaques. In addition, MHC class I alleles were neuroprotective in both species (Mamu-A*001 in rhesus macaques and Mane-A1*084:01:01 in pigtailed macaques); animals expressing these alleles were less likely to develop SIV encephalitis and correspondingly had lower viral replication in the brain. Species-specific differences in susceptibility to SIV disease demonstrated that cell mediated immune responses are critical to SIV CNS disease progression.

Combination fluconazole/paroxetine treatment is neuroprotective despite ongoing neuroinflammation and viral replication in an SIV model of HIV neurological disease.

Effective combined antiretroviral therapy (cART) in HIV-infected patients has made HIV a treatable infection; however, debilitating HIV-associated neurocognitive disorders (HAND) can still affect approximately 50% of HIV-infected individuals even under cART. While cART has greatly reduced the prevalence of the most severe form of HAND, milder forms have increased in prevalence, leaving the total proportion of HIV-infected individuals suffering from HAND relatively unchanged. In this study, an in vitro drug screen identified fluconazole and paroxetine as protective compounds against HIV gp120 and Tat neurotoxicity. Using an accelerated, consistent SIV/macaque model of HIV-associated CNS disease, we tested the in vivo neuroprotective capabilities of combination fluconazole/paroxetine (FluPar) treatment. FluPar treatment protected macaques from SIV-induced neurodegeneration, as measured by neurofilament light chain in the CSF, APP accumulation in axons, and CaMKIIα in the frontal cortex, but did not significantly reduce markers of neuroinflammation or plasma or CNS viral loads. Since HIV and SIV neurodegeneration is often attributed to accompanying neuroinflammation, this study provides proof of concept that neuroprotection can be achieved even in the face of ongoing neuroinflammation and viral replication.

Platelet activation and platelet-monocyte aggregate formation contribute to decreased platelet count during acute simian immunodeficiency virus infection in pig-tailed macaques.

Platelets are key participants in innate immune responses to pathogens. As a decrease in circulating platelet count is one of the initial hematologic indicators of human immunodeficiency virus (HIV) infection, we sought to determine whether decline in platelet number during acute infection results from decreased production, increased antibody-mediated destruction, or increased platelet activation in a simian immunodeficiency virus (SIV)/macaque model. During acute SIV infection, circulating platelets were activated with increased surface expression of P-selection, CD40L and major histocompatibility complex class I. Platelet production was maintained and platelet autoantibodies were not detected during acute infection. Concurrent with a decrease in platelet numbers and an increase in circulating monocytes, platelets were found sequestered in platelet-monocyte aggregates, thereby contributing to the decline in platelet counts. Because the majority of circulating CD16(+) monocytes formed complexes with platelets during acute SIV infection, a decreased platelet count may represent platelet participation in the innate immune response to HIV.

A Switch from Glial to Neuronal Gene Expression Alterations in the Spinal Cord of SIV-infected Macaques on Antiretroviral Therapy.

Despite antiretroviral therapy (ART), HIV-associated peripheral neuropathy remains one of the most prevalent neurologic manifestations of HIV infection. The spinal cord is an essential component of sensory pathways, but spinal cord sampling and evaluation in people with HIV has been very limited, especially in those on ART. The SIV/macaque model allows for assessment of the spinal cord at key time points throughout infection with and without ART. In this study, RNA was isolated from the spinal cord of uninfected, SIV+, and SIV + ART animals to track alterations in gene expression using global RNA-seq. Next, the SeqSeek platform was used to map changes in gene expression to specific cell types. Pathway analysis of differentially expressed genes demonstrated that highly upregulated genes in SIV-infected spinal cord aligned with interferon and viral response pathways. Additionally, this upregulated gene set significantly overlapped with those expressed in myeloid-derived cells including microglia. Downregulated genes were involved in cholesterol and collagen biosynthesis, and TGF-b regulation of extracellular matrix. In contrast, enriched pathways identified in SIV + ART animals included neurotransmitter receptors and post synaptic signaling regulators, and transmission across chemical synapses. SeqSeek analysis showed that upregulated genes were primarily expressed by neurons rather than glia. These findings indicate that pathways activated in the spinal cord of SIV + ART macaques are predominantly involved in neuronal signaling rather than proinflammatory pathways. This study provides the basis for further evaluation of mechanisms of SIV infection + ART within the spinal cord with a focus on therapeutic interventions to maintain synaptodendritic homeostasis.