HIV-1 Tat protein binds to TLR4-MD2 and signals to induce TNF-α and IL-10

Altered Host microRNAomics in HIV Infections: Therapeutic Potentials and Limitations

microRNAs have emerged as essential regulators of health and disease, attracting significant attention from researchers across diverse disciplines. Following their identification as noncoding oligonucleotides intricately involved in post-transcriptional regulation of protein expression, extensive efforts were devoted to elucidating and validating their roles in fundamental metabolic pathways and multiple pathologies. Viral infections are significant modifiers of the host microRNAome. Specifically, the Human Immunodeficiency Virus (HIV), which affects approximately 39 million people worldwide and has no definitive cure, was reported to induce significant changes in host cell miRNA profiles. Identifying and understanding the effects of the aberrant microRNAome holds potential for early detection and therapeutic designs. This review presents a comprehensive overview of the impact of HIV on host microRNAome. We aim to review the cause-and-effect relationship between the HIV-induced aberrant microRNAome that underscores miRNA's therapeutic potential and acknowledge its limitations.

The expression of HIV-1 tat in Lactococcus lactis

Efficient expression of functional proteins in heterologous hosts has become the pivotal focus of modern biotechnology and biomedical research. To this end, multiple alternatives to E. coli are being explored for recombinant protein expression. L. lactis, being a gram-positive organism, circumvents the need for an endotoxin removal step during protein purification. We report here the optimisation of the expression of HIV-1 Tat, a notoriously difficult protein, in Lactococcus lactis system. We evaluated five different promoters in two different Lactococcus lactis strains and examined the effect of pH, glucose, and induction time on the yield and purity of Tat. Finally, the recombinant Tat was functionally competent in transactivating the HIV-1 promoter in HLM-1 reporter cells. Our work provides a scaffold for future work on the expression of toxic proteins in Lactococcus lactis.

The dangerous liaisons in innate immunity involving recombinant proteins and endotoxins: Examples from the literature and the Leptospira field

Endotoxins, also known as lipopolysaccharides (LPS), are essential components of cell walls of diderm bacteria such as Escherichia coli. LPS are microbe-associated molecular patterns that can activate pattern recognition receptors. While trying to investigate the interactions between proteins and host innate immunity, some studies using recombinant proteins expressed in E. coli reported interaction and activation of immune cells. Here, we set out to provide information on endotoxins that are highly toxic to humans and bind to numerous molecules, including recombinant proteins. We begin by outlining the history of the discovery of endotoxins, their receptors and the associated signaling pathways that confer extreme sensitivity to immune cells, acting alone or in synergy with other microbe-associated molecular patterns. We list the various places where endotoxins have been found. Additionally, we warn against the risk of data misinterpretation due to endotoxin contamination in recombinant proteins, which is difficult to estimate with the Limulus amebocyte lysate assay, and cannot be completely neutralized (e.g., treatment with polymyxin B or heating). We further illustrate our point with examples of recombinant heat-shock proteins and viral proteins from severe acute respiratory syndrome coronavirus 2, dengue and HIV, for which endotoxin contamination has eventually been shown to be responsible for the inflammatory roles previously ascribed. We also critically appraised studies on recombinant Leptospira proteins regarding their putative inflammatory roles. Finally, to avoid these issues, we propose alternatives to express recombinant proteins in nonmicrobial systems. Microbiologists wishing to undertake innate immunity studies with their favorite pathogens should be aware of these difficulties.

The mechanisms of nerve injury caused by viral infection in the occurrence of gastrointestinal motility disorder-related diseases

Gastrointestinal motility refers to the peristalsis and contractility of gastrointestinal muscles, including the force and frequency of gastrointestinal muscle contraction. Gastrointestinal motility maintains the normal digestive function of the human body and is a critical component of the physiological function of the digestive tract. At present, gastrointestinal motility disorder-related diseases are gradually affecting human production and life. In recent years, it has been consistently reported that the enteric nervous system has a coordinating and controlling role in gastrointestinal motility. Motility disorders are closely related to functional or anatomical changes in the gastrointestinal nervous system. At the same time, some viral infections, such as herpes simplex virus and varicella-zoster virus infections, can cause damage to the gastrointestinal nervous system. Therefore, this paper describes the mechanisms of viral infection in the gastrointestinal nervous system and the associated clinical manifestations. Studies have indicated that the means by which viruses can cause the infection of the enteric nervous system are various, including retrograde transport, hematogenous transmission and centrifugal transmission from the central nervous system. When viruses infect the enteric nervous system, they can cause clinical symptoms, such as abdominal pain, abdominal distension, early satiation, belching, diarrhea, and constipation, by recruiting macrophages, lymphocytes and neutrophils and regulating intestinal microbes. The findings of several case‒control studies suggest that viruses are the cause of some gastrointestinal motility disorders. It is concluded that one of the causes of gastrointestinal motility disorders is viral infection of the enteric nervous system. In such disorders, the relationships between viruses and nerves remain to be studied more deeply. Further studies are necessary to evaluate whether prophylactic antiviral therapy is feasible in gastrointestinal motility disorders.

HIV-1 subtype B Tat enhances NOTCH3 signaling in astrocytes to mediate oxidative stress, inflammatory response, and neuronal apoptosis

NOTCH receptors are relevant to multiple neurodegenerative diseases. However, the roles and mechanisms of NOTCH receptors in HIV-associated neurocognitive disorder (HAND) remain largely unclear. Transactivator of transcription (Tat) induces oxidative stress and inflammatory response in astrocytes, thereby leading to neuronal apoptosis in the central nervous system. We determined that NOTCH3 expression was upregulated during subtype B or C Tat expression in HEB astroglial cells. Moreover, bioinformatics analysis of the Gene Expression Omnibus (GEO) dataset revealed that NOTCH3 mRNA expression in the frontal cortex tissues of HIV encephalitis patients was higher than that of HIV control patients. Of note, subtype B Tat, rather than subtype C Tat, interacted with the extracellular domain of the NOTCH3 receptor, thus activating NOTCH3 signaling. Downregulation of NOTCH3 attenuated subtype B Tat-induced oxidative stress and reactive oxygen species generation. In addition, we demonstrated that NOTCH3 signaling facilitated subtype B Tat-activated NF-κB signaling pathway, thereby mediating pro-inflammatory cytokines IL-6 and TNF-α production. Furthermore, downregulation of NOTCH3 in HEB astroglial cells protected SH-SY5Y neuronal cells from astrocyte-mediated subtype B Tat neurotoxicity. Taken together, our study clarifies the potential role of NOTCH3 in subtype B Tat-induced oxidative stress and inflammatory response in astrocytes, which could be a novel therapeutic target for the relief of HAND.

HIV-1 Tat Upregulates TREM1 Expression in Human Microglia

Because microglia are a reservoir for HIV and are resistant to the cytopathic effects of HIV infection, they are a roadblock for any HIV cure strategy. We have previously identified that triggering receptor expressed on myeloid cells 1 (TREM1) plays a key role in human macrophage resistance to HIV-mediated cytopathogenesis. In this article, we show that HIV-infected human microglia express increased levels of TREM1 and are resistant to HIV-induced apoptosis. Moreover, upon genetic inhibition of TREM1, HIV-infected microglia undergo cell death in the absence of increased viral or proinflammatory cytokine expression or the targeting of uninfected cells. We also show that the expression of TREM1 is mediated by HIV Tat through a TLR4, TICAM1, PG-endoperoxide synthase 2, PGE synthase, and PGE2-dependent manner. These findings highlight the potential of TREM1 as a therapeutic target to eradicate HIV-infected microglia without inducing a proinflammatory response.

A C-type lectin induces NLRP3 inflammasome activation via TLR4 interaction in human peripheral blood mononuclear cells

Lectins are a large group of proteins found in many snake venoms. BjcuL is a C-type lectin from Bothrops jararacussu snake venom that does not present cytotoxicity action on human peripheral blood mononuclear cells (PBMCs) at concentrations of 5 and 10 μg/mL. BjcuL demonstrates an immunomodulatory role in PBMCs with the production of pro- and anti-inflammatory cytokines (IL-2, IL-10, IFN-γ, IL-6, TNF-α, and IL-17) in addition to stimulate T cells to produce reactive oxygen species (ROS) that could play a role in the acute inflammatory reaction observed in the victims. Inflammasomes are an essential arm in cells of innate immunity to detect and sense a range of endogenous or exogenous, sterile, or infectious stimuli to elicit cellular responses and effector mechanisms. NLRP3 inflammasome is a significant target for this study, because the lectin is responsible for leukocyte activation stimulating the release of inflammatory mediators, which results in dynamic cellular responses to remove the detrimental process to the body in snakebites. Thus, this study aimed to investigate how isolated BjcuL from B. jararacussu venom affects NLRP3 inflammasome activation on PBMCs. For this, the cells were isolated by density gradient and incubated with BjcuL at different periods and concentrations for the evaluation of the activation of the NLRP3 inflammasome through gene and protein expressions of ASC, CASPASE-1, and NLRP3 by RT-qPCR, Western blot, and immunofluorescence, as well as the participation of Toll-like receptor 4 (TLR4) and ROS in the IL-1β production, a product resultant of the NLRP3 inflammasome activation. Herein, BjcuL interacts with TLR4 as demonstrated by in vitro and in silico studies and induces cytokines release via NF-κB signaling. By genic and protein expression assays, BjcuL activates NLRP3 inflammasome, and the pharmacological modulation with LPS-RS, an antagonist of TLR4; LPS-SM, an agonist of TLR4; MCC950, a specific NLRP3 inhibitor, and rotenone, an inhibitor of mitochondrial ROS, confirmed the participation of TLR4 and ROS in the NLRP3 inflammasome activation and IL-1β liberation. The effects of BjcuL on the regulation and activation of the NLRP3 inflammasome complex via TLR4 activation with ROS participation may be determinant for the development of the inflammatory local effects seen in snakebite victims. In addition, in silico together with in vitro studies provide information that may be useful in the rational design of TLR agonists as well as new adjuvants for immunomodulatory therapy.

Myeloid differentiation factor-2/LY96, a new predictive biomarker of metastasis in prostate cancer: Clinical implications as a potential therapeutic target

Relapsed prostate cancer (CaP), usually treated with androgen deprivation therapy, acquires resistance to develop into lethal metastatic castration-resistant CaP. The cause of resistance remains elusive, and the lack of biomarkers predictive of castration-resistance emergence is a stumbling block in managing the disease. We provide strong evidence that Myeloid differentiation factor-2 (MD2) plays a critical role in metastasis and CaP progression. Analysis of tumor genomic data and IHC of tumors showed a high frequency of MD2 amplification and association with poor overall survival in patients. The Decipher-genomic test validated the potential of MD2 in predicting metastasis. In vitro studies demonstrated that MD2 confers invasiveness by activating MAPK and NF-kB signaling pathways. Furthermore, we show that metastatic cells release MD2 (sMD2). We measured serum-sMD2 in patients and found that the level is correlated to disease extent. We determined the significance of MD2 as a therapeutic target and found that targeting MD2 significantly inhibited metastasis in a murine model. We conclude that MD2 predicts metastatic behavior and serum-MD2 is a non-invasive biomarker for tumor burden, whereas MD2 presence on prostate biopsy predicts adverse disease outcome. We suggest MD2-targeted therapies could be developed as potential treatments for aggressive metastatic disease.

Heme-Induced Macrophage Phenotype Switching and Impaired Endogenous Opioid Homeostasis Correlate with Chronic Widespread Pain in HIV

Chronic widespread pain (CWP) is associated with a high rate of disability and decreased quality of life in people with HIV-1 (PWH). We previously showed that PWH with CWP have increased hemolysis and elevated plasma levels of cell-free heme, which correlate with low endogenous opioid levels in leukocytes. Further, we demonstrated that cell-free heme impairs β-endorphin synthesis/release from leukocytes. However, the cellular mechanisms by which heme dampens β-endorphin production are inconclusive. The current hypothesis is that heme-dependent TLR4 activation and macrophage polarization to the M1 phenotype mediate this phenomenon. Our novel findings showed that PWH with CWP have elevated M1-specific macrophage chemokines (ENA-78, GRO-α, and IP-10) in plasma. In vitro, hemin-induced polarization of M0 and M2 macrophages to the M1 phenotype with low β-endorphins was mitigated by treating cells with the TLR4 inhibitor, TAK-242. Similarly, in vivo phenylhydrazine hydrochloride (PHZ), an inducer of hemolysis, injected into C57Bl/6 mice increased the M1/M2 cell ratio and reduced β-endorphin levels. However, treating these animals with the heme-scavenging protein hemopexin (Hx) or TAK-242 reduced the M1/M2 ratio and increased β-endorphins. Furthermore, Hx attenuated heme-induced mechanical, heat, and cold hypersensitivity, while TAK-242 abrogated hypersensitivity to mechanical and heat stimuli. Overall, these results suggest that heme-mediated TLR4 activation and M1 polarization of macrophages correlate with impaired endogenous opioid homeostasis and hypersensitivity in people with HIV.

Toll-like Receptor Response to Human Immunodeficiency Virus Type 1 or Co-Infection with Hepatitis B or C Virus: An Overview

Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that play important roles in the early detection of pathogen-associated molecular patterns and shaping innate and adaptive immune responses, which may influence the consequences of infection. Similarly to other viral infections, human immunodeficiency virus type 1 (HIV-1) also modulates the host TLR response; therefore, a proper understanding of the response induced by human HIV-1 or co-infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), due to the common mode of transmission of these viruses, is essential for understanding HIV-1 pathogenesis during mono- or co-infection with HBV or HCV, as well as for HIV-1 cure strategies. In this review, we discuss the host TLR response during HIV-1 infection and the innate immune evasion mechanisms adopted by HIV-1 for infection establishment. We also examine changes in the host TLR response during HIV-1 co-infection with HBV or HCV; however, this type of study is extremely scarce. Moreover, we discuss studies investigating TLR agonists as latency-reverting agents and immune stimulators towards new strategies for curing HIV. This understanding will help develop a new strategy for curing HIV-1 mono-infection or co-infection with HBV or HCV.

IRAK1 inhibition blocks the HIV-1 RNA mediated pro-inflammatory cytokine response from microglia

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) are a common source of morbidity in people living with HIV (PLWH). Although antiretroviral therapy (ART) has lessened the severity of neurocognitive disorders, cognitive impairment still occurs in PLWH receiving ART. The pathogenesis of HAND is likely multifaceted, but common factors include the persistence of HIV transcription within the central nervous system, higher levels of pro-inflammatory cytokines in the cerebrospinal fluid, and the presence of activated microglia. Toll-like receptor (TLR) 7 and TLR8 are innate pathogen recognition receptors located in microglia and other immune and non-immune cells that can recognise HIV RNA and trigger pro-inflammatory responses. IL-1 receptor-associated kinase (IRAK) 1 is key to these signalling pathways. Here, we show that IRAK1 inhibition inhibits the TLR7 and TLR8-dependent pro-inflammatory response to HIV RNA. Using genetic and pharmacological inhibition, we demonstrate that inhibition of IRAK1 prevents IRAK1 phosphorylation and ubiquitination, and the subsequent recruitment of TRAF6 and the TAK1 complex to IRAK1, resulting in the inhibition of downstream signalling and the suppression of pro-inflammatory cytokine and chemokine release.

SARS-CoV-2 Envelope (E) Protein Binds and Activates TLR2 Pathway: A Novel Molecular Target for COVID-19 Interventions

This paper presents a molecular characterization of the interaction between the SARS-CoV-2 envelope (E) protein and TLR2. We demonstrated that the E protein, both as a recombinant soluble protein and as a native membrane protein associated with SARS-CoV-2 viral particles, interacts physically with the TLR2 receptor in a specific and dose-dependent manner. Furthermore, we showed that the specific interaction with the TLR2 pathway activates the NF-κB transcription factor and stimulates the production of the CXCL8 inflammatory chemokine. In agreement with the importance of NF-κB in the TLR signaling pathway, we showed that the chemical inhibition of this transcription factor leads to significant inhibition of CXCL8 production, while the blockade of the P38 and ERK1/2 MAP kinases only results in partial CXCL8 inhibition. Overall, our findings propose the envelope (E) protein as a novel molecular target for COVID-19 interventions: either (i) by exploring the therapeutic effect of anti-E blocking/neutralizing antibodies in symptomatic COVID-19 patients, or (ii) as a promising non-spike SARS-CoV-2 antigen candidate for inclusion in the development of next-generation prophylactic vaccines against COVID-19 infection and disease.

Swine Enteric Coronavirus: Diverse Pathogen–Host Interactions

Swine enteric coronavirus (SeCoV) causes acute gastroenteritis and high mortality in newborn piglets. Since the last century, porcine transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) have swept farms all over the world and caused substantial economic losses. In recent years, porcine delta coronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV) have been emerging SeCoVs. Some of them even spread across species, which made the epidemic situation of SeCoV more complex and changeable. Recent studies have begun to reveal the complex SeCoV–host interaction mechanism in detail. This review summarizes the current advances in autophagy, apoptosis, and innate immunity induced by SeCoV infection. These complex interactions may be directly involved in viral replication or the alteration of some signal pathways.

Kaposi’s Sarcoma Lesion Progression in BKV-Tat Transgenic Mice Is Increased by Inflammatory Cytokines and Blocked by Treatment with Anti-Tat Antibodies

Kaposi’s sarcoma (KS) is an angioproliferative tumor showing an increased frequency and aggressiveness in HIV-infected subjects (AIDS-KS), due to the combined effects of inflammatory cytokines (IC), angiogenic factors, and the HIV-1 Tat protein. While the introduction of effective combined antiretroviral regimens greatly improved AIDS-KS incidence and course, it continues to be an incurable disease and the development of new rational targeted therapies is warranted. We used the BKV/Tat transgenic mouse model to evaluate the effects of IC and anti-Tat antibodies (Abs) treatment on KS-like lesions arising in BKV/Tat mice. We demonstrated here that IC-treatment increases the severity and delays the regression of KS-like lesions. Further, anti-Tat Abs reduced KS-like lesion severity developing in IC-treated mice when anti-Tat Abs were administered at an early-stage of lesion development as compared to more advanced lesions. Early anti-Tat Abs treatment also accelerated KS-like lesion regression and reduced the rate of severe-grade lesions. This effect was more evident in the first weeks after Ab treatment, suggesting that a longer treatment with anti-Tat Abs might be even more effective, particularly if administered just after lesion development. Although preliminary, these results are encouraging, and the approach deserves further studies for the development of anti-Tat Ab-based therapies for AIDS-KS. Clinical studies specifically addressing the effect of anti-Tat antibodies in treating AIDS-KS are not yet available. Nevertheless, the effectiveness of anti-Tat antibodies in controlling HIV/AIDS progression, likely due to the neutralization of extracellular Tat activities, is suggested by several cross-sectional and longitudinal clinical studies, indicating that anti-Tat Ab treatment or Tat-based vaccines may be effective to treat AIDS-KS patients or prevent the tumor in individuals at risk.

HIV Tat-Mediated Induction of Monocyte Transmigration Across the Blood-Brain Barrier: Role of Chemokine Receptor CXCR3

HIV trans-activator of transcription (Tat), one of the cytotoxic proteins secreted from HIV-infected cells, is also known to facilitate chemokine-mediated transmigration of monocytes into the brain leading, in turn, to neuroinflammation and thereby contributing to the development of HIV-associated neurocognitive disorders (HAND). The mechanism(s) underlying HIV Tat-mediated enhancement of monocyte transmigration, however, remain largely unknown. CXC chemokine receptor 3 (CXCR3) that is expressed by the peripheral monocytes is known to play a role in the monocyte influx and accumulation. In the present study, we demonstrate for the first time that exposure of human monocytes to HIV Tat protein resulted in upregulated expression of CXCR3 leading, in turn, to increased monocyte transmigration across the blood–brain barrier (BBB) both in the in vitro and in vivo model systems. This process involved activation of toll-like receptor 4 (TLR4), with downstream phosphorylation and activation of TANK-binding kinase 1 (TBK1), and subsequent phosphorylation and nuclear translocation of interferon regulatory factor 3 (IRF3), ultimately leading to enhanced expression of CXCR3 in human monocytes. These findings imply a novel molecular mechanism underlying HIV Tat-mediated increase of monocyte transmigration across the BBB, while also implicating a novel role of CXCR3-dependent monocyte transmigration in HIV Tat-mediated neuroinflammation.

7,8-Dihydroxyflavone improves neuropathological changes in the brain of Tg26 mice, a model for HIV-associated neurocognitive disorder

The combined antiretroviral therapy era has significantly increased the lifespan of people with HIV (PWH), turning a fatal disease to a chronic one. However, this lower but persistent level of HIV infection increases the susceptibility of HIV-associated neurocognitive disorder (HAND). Therefore, research is currently seeking improved treatment for this complication of HIV. In PWH, low levels of brain derived neurotrophic factor (BDNF) has been associated with worse neurocognitive impairment. Hence, BDNF administration has been gaining relevance as a possible adjunct therapy for HAND. However, systemic administration of BDNF is impractical because of poor pharmacological profile. Therefore, we investigated the neuroprotective effects of BDNF-mimicking 7,8 dihydroxyflavone (DHF), a bioactive high-affinity TrkB agonist, in the memory-involved hippocampus and brain cortex of Tg26 mice, a murine model for HAND. In these brain regions, we observed astrogliosis, increased expression of chemokine HIV-1 coreceptors CXCR4 and CCR5, neuroinflammation, and mitochondrial damage. Hippocampi and cortices of DHF treated mice exhibited a reversal of these pathological changes, suggesting the therapeutic potential of DHF in HAND. Moreover, our data indicates that DHF increases the phosphorylation of TrkB, providing new insights about the role of the TrkB-Akt-NFkB signaling pathway in mediating these pathological hallmarks. These findings guide future research as DHF shows promise as a TrkB agonist treatment for HAND patients in adjunction to the current antiviral therapies.

HIV-1 Tat: An update on transcriptional and non-transcriptional functions

Over the past decades, much have been learned about HIV-1 virus and its molecular strategies for pathogenesis. However, HIV-1 still remains an enigmatic virus, particularly because of its unique proteins. Establishment of latency and reactivation is still a puzzling question and various temporal and spatial dynamics between HIV-1 proteins itself have given us new way of thinking about its pathogenesis. HIV-1 replication depends on Tat which is a small unstructured protein and subjected to various post-translational modifications for its myriad of functions. HIV-1 Tat protein modulates the functions of various strategic cellular pathways like proteasomal machinery and inflammatory pathways to aid in HIV-1 pathogenesis. Many of the recent findings have shown that Tat is associated with exosomes, cleared from HIV-1 infected cells through its degradation by diverse routes ranging from lysosomal to proteasomal pathways. HIV-1 Tat was also found to be associated with other HIV-1 proteins including Vpr, Nef, Nucleocapsid (NC) and Rev. Interaction of Tat with Vpr and Nef increases its transactivation function, whereas, interaction of Tat with NC or Rev leads to Tat protein degradation and hence suppression of Tat functions. Research in the recent years has established that Tat is not only important for HIV-1 promoter transactivation and virus replication but also modulating multiple cellular and molecular functions leading to HIV-1 pathogenicity. In this review we discussed various transcriptional and non-transcriptional HIV-1 Tat functions which modulate host cell metabolism during HIV-1 pathogenesis.

Targeting TLR4 Signaling to Blunt Viral-Mediated Acute Lung Injury

Respiratory viral infections have been a long-standing global burden ranging from seasonal recurrences to the unexpected pandemics. The yearly hospitalizations from seasonal viruses such as influenza can fluctuate greatly depending on the circulating strain(s) and the congruency with the predicted strains used for the yearly vaccine formulation, which often are not predicted accurately. While antiviral agents are available against influenza, efficacy is limited due to a temporal disconnect between the time of infection and symptom development and viral resistance. Uncontrolled, influenza infections can lead to a severe inflammatory response initiated by pathogen-associated molecular patterns (PAMPs) or host-derived danger-associated molecular patterns (DAMPs) that ultimately signal through pattern recognition receptors (PRRs). Overall, these pathogen-host interactions result in a local cytokine storm leading to acute lung injury (ALI) or the more severe acute respiratory distress syndrome (ARDS) with concomitant systemic involvement and more severe, life threatening consequences. In addition to traditional antiviral treatments, blocking the host's innate immune response may provide a more viable approach to combat these infectious pathogens. The SARS-CoV-2 pandemic illustrates a critical need for novel treatments to counteract the ALI and ARDS that has caused the deaths of millions worldwide. This review will examine how antagonizing TLR4 signaling has been effective experimentally in ameliorating ALI and lethal infection in challenge models triggered not only by influenza, but also by other ALI-inducing viruses.

An Immunoinformatics Approach for SARS-CoV-2 in Latam Populations and Multi-Epitope Vaccine Candidate Directed towards the World's Population

The coronavirus pandemic is a major public health crisis affecting global health systems with dire socioeconomic consequences, especially in vulnerable regions such as Latin America (LATAM). There is an urgent need for a vaccine to help control contagion, reduce mortality and alleviate social costs. In this study, we propose a rational multi-epitope candidate vaccine against SARS-CoV-2. Using bioinformatics, we constructed a library of potential vaccine peptides, based on the affinity of the most common major human histocompatibility complex (HLA) I and II molecules in the LATAM population to predict immunological complexes among antigenic, non-toxic and non-allergenic peptides extracted from the conserved regions of 92 proteomes. Although HLA-C, had the greatest antigenic peptide capacity from SARS-CoV-2, HLA-B and HLA-A, could be more relevant based on COVID-19 risk of infection in LATAM countries. We also used three-dimensional structures of SARS-CoV-2 proteins to identify potential regions for antibody production. The best HLA-I and II predictions (with increased coverage in common alleles and regions evoking B lymphocyte responses) were grouped into an optimized final multi-epitope construct containing the adjuvants Beta defensin-3, TpD, and PADRE, which are recognized for invoking a safe and specific immune response. Finally, we used Molecular Dynamics to identify the multi-epitope construct which may be a stable target for TLR-4/MD-2. This would prove to be safe and provide the physicochemical requirements for conducting experimental tests around the world.

Differential recognition of HIV-stimulated IL-1β and IL-18 secretion through NLR and NAIP signalling in monocyte-derived macrophages

Macrophages are important drivers of pathogenesis and progression to AIDS in HIV infection. The virus in the later phases of the infection is often predominantly macrophage-tropic and this tropism contributes to a chronic inflammatory and immune activation state that is observed in HIV patients. Pattern recognition receptors of the innate immune system are the key molecules that recognise HIV and mount the inflammatory responses in macrophages. The innate immune response against HIV-1 is potent and elicits caspase-1-dependent pro-inflammatory cytokine production of IL-1β and IL-18. Although, NLRP3 has been reported as an inflammasome sensor dictating this response little is known about the pattern recognition receptors that trigger the “priming” signal for inflammasome activation, the NLRs involved or the HIV components that trigger the response. Using a combination of siRNA knockdowns in monocyte derived macrophages (MDMs) of different TLRs and NLRs as well as chemical inhibition, it was demonstrated that HIV Vpu could trigger inflammasome activation via TLR4/NLRP3 leading to IL-1β/IL-18 secretion. The priming signal is triggered via TLR4, whereas the activation signal is triggered by direct effects on Kv1.3 channels, causing K⁺ efflux. In contrast, HIV gp41 could trigger IL-18 production via NAIP/NLRC4, independently of priming, as a one-step inflammasome activation. NAIP binds directly to the cytoplasmic tail of HIV envelope protein gp41 and represents the first non-bacterial ligand for the NAIP/NLRC4 inflammasome. These divergent pathways represent novel targets to resolve specific inflammatory pathologies associated with HIV-1 infection in macrophages.

It has been previously shown that inflammasome activation can be triggered during viral infection to produce the active cytokines IL-1β and IL-18. Our study represents a significant advance, as we now show that in fact there are distinct NLR inflammasome complexes and viral ligands for IL-1β secretion (Vpu) compared to IL-18 secretion (gp41) in response to HIV-1.

Most importantly, we show that the HIV envelope protein gp41 represents the first non-bacterial ligand for the assembly of the NAIP/NLRC4 inflammasome. HIV gp41 is a viroporin, and thus our data demonstrates for the first time that the NAIP/NLRC4 inflammasome assembles for all pore-forming proteins, irrespective of whether they have a viral or bacterial origin. This is critical for the host antiviral response and has broad implications for innate immunity in general.

Mini review: Promotion of substance abuse in HIV patients: Biological mediation by HIV-1 Tat protein

Despite successful viral suppression by combinatorial anti-retroviral therapy, HIV infection continues to negatively impact the quality of life of patients by promoting neuropathy and HIV-Associated Neurocognitive Disorders (HAND), where substance use disorder (SUD) is highly comorbid and known to worsen health outcomes. While substance abuse exacerbates the progression of HIV, emerging evidence also suggests the virus may potentiate the rewarding effect of abused substances. As HIV does not infect neurons, these effects are theorized to be mediated by viral proteins. Key among these proteins are HIV-1 Tat, which can continue to be produced under viral suppression in patients. This review will recap the behavioral evidence for HIV-1 Tat mediation of a potentiation of cocaine, opioid and alcohol reward, and explore the neurochemical dysfunction associated by Tat as potential mechanisms underlying changes in reward. Targeting rampant oxidative stress, inflammation and excitotoxicity associated with HIV and Tat protein exposure may prove useful in combating persistent substance abuse comorbid with HIV in the clinic.

Hippocampal blood-brain barrier of methamphetamine self-administering HIV-1 transgenic rats

Combined antiretroviral therapy for HIV infection reduces plasma viral load and prolongs life. However, the brain is a viral reservoir, and pathologies such as cognitive decline and blood-brain barrier (BBB) disruption persist. Methamphetamine abuse is prevalent among HIV-infected individuals. Methamphetamine and HIV toxic proteins can disrupt the BBB, but it is unclear if there exists a common pathway by which HIV proteins and methamphetamine induce BBB damage. Also unknown are the BBB effects imposed by chronic exposure to HIV proteins in the comorbid context of chronic methamphetamine abuse. To evaluate these scenarios, we trained HIV-1 transgenic (Tg) and non-Tg rats to self-administer methamphetamine using a 21-day paradigm that produced an equivalency dose range at the low end of the amounts self-titrated by humans. Markers of BBB integrity were measured for the hippocampus, a brain region involved in cognitive function. Outcomes revealed that tight junction proteins, claudin-5 and occludin, were reduced in Tg rats independent of methamphetamine, and this co-occurred with increased levels of lipopolysaccharide, albumin (indicating barrier breakdown) and matrix metalloproteinase-9 (MMP-9; indicating barrier matrix disruption); reductions in GFAP (indicating astrocytic dysfunction); and microglial activation (indicating inflammation). Evaluations of markers for two signaling pathways that regulate MMP-9 transcription, NF-κB and ERK/∆FosB revealed an overall genotype effect for NF-κB. Methamphetamine did not alter measurements from Tg rats, but in non-Tg rats, methamphetamine reduced occludin and GFAP, and increased MMP-9 and NF-κB. Study outcomes suggest that BBB dysregulation resulting from chronic exposure to HIV-1 proteins or methamphetamine both involve NF-κB/MMP-9.

Strong Association of the rs4986790 Single Nucleotide Polymorphism (SNP) of the Toll-Like Receptor 4 (TLR4) Gene with Human Immunodeficiency Virus (HIV) Infection: A Meta-Analysis

Human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS) and enters the host cell via CD4 and either CC-chemokine receptor 5 (CCR) or CXC-chemokine receptor 4 (CXCR4). HIV is directly recognized by toll-like receptor 4 (TLR4) and affects downstream immune-related signal pathways. In addition, stimulated TLR4 inhibits HIV-1 invasion, and the rs4986790 single nucleotide polymorphism (SNP) (D299G) of the TLR4 gene contributes to the risk of HIV-1 infection in an Indian population. To evaluate whether the rs4986790 SNP of the TLR4 gene is related to vulnerability to HIV-1 infection, we collected genetic information from HIV-1 patients in previous studies and performed an association analysis with a matched control population obtained from the 1000 Genomes Project. In addition, to strengthen the results of association analysis, we performed a meta-analysis. We identified a strong association between the rs4986791 SNP and susceptibility to HIV infection in HIV-infected patients in previous studies and a matched control population obtained from the 1000 Genomes Project. In addition, we found that the G allele of the rs4986791 SNP in the TLR4 gene is strongly related to susceptibility to HIV infection in three Caucasian populations (odd ratio = 2.29, 95% confidence interval: 1.72–3.07, p = 1.438 × 10⁻⁷) and all four populations (odd ratio = 2.22, 95% confidence interval: 1.74–2.84, p = 2 × 10⁻¹⁰) in a meta-analysis. To the best our knowledge, this was the first meta-analysis on the association between the rs4986791 SNP of the TLR4 gene and susceptibility to HIV infection.

The Tat Protein of HIV-1 Prevents the Loss of HSV-Specific Memory Adaptive Responses and Favors the Control of Viral Reactivation

The development of therapeutic strategies to control the reactivation of the Herpes Simplex Virus (HSV) is an unaddressed priority. In this study, we evaluated whether Tat, a HIV-1 protein displaying adjuvant functions, could improve previously established HSV-specific memory responses and prevent viral reactivation. To this aim, mice were infected with non-lethal doses of HSV-1 and, 44 days later, injected or not with Tat. Mice were then monitored to check their health status and measure memory HSV-specific cellular and humoral responses. The appearance of symptoms associated with HSV-reactivation was observed at significantly higher frequencies in the control group than in the Tat-treated mice. In addition, the control animals experienced a time-dependent decrease in HSV-specific Immunoglobulin G (IgG), while the Tat-treated mice maintained antibody titers over time. IgG levels were directly correlated with the number of HSV-specific CD8⁺ T cells, suggesting an effect of Tat on both arms of the adaptive immunity. Consistent with the maintenance of HSV-specific immune memory, Tat-treated mice showed a better control of HSV-1 re-infection. Although further studies are necessary to assess whether similar effects are observed in other models, these results indicate that Tat exerts a therapeutic effect against latent HSV-1 infection and re-infection by favoring the maintenance of adaptive immunity.

HIV-1 Tat - TLR4/MD2 interaction drives the expression of IDO-1 in monocytes derived dendritic cells through NF-κB dependent pathway

In the present study we showed that HIV-1 Tat protein stimulated the expression of Indoleamine 2,3 dioxygenase (IDO) -1 in human monocytes derived dendritic cells (MoDC) but not IDO-2 by acting directly at the cell membrane level. This induction of IDO-1 is dependent on the secondary structure of Tat protein, since stimulation with a chemically oxidized Tat protein loses its capacity to induce the production of IDO-1. Among the variety of candidate receptors described for Tat, we demonstrated that Tat protein interacted physically with TLR4/MD2 complex. Strikingly, blockade of Tat-TLR4 interaction by anti-TLR4 antibodies (clone HTA125), LPS-RS, a known TLR4 antagonist, or by soluble recombinant TLR4/MD2 complex inhibited strongly or totally the capacity of Tat to induce IDO-1 in MoDC while such treatments had no effect on IFN-γ-induced IDO-1. Furthermore, we showed that the activation of the transcription factor NF-κB by Tat is essential for the production of IDO-1 by human MoDC. Indeed, Tat activated NF-κB pathway in MoDC as demonstrated by the phosphorylation of p65 in Tat-treated MoDC. Further, we demonstrate that the stimulation of IDO-1 by Tat or by IFN-γ was totally or partially inhibited in the presence of NF-κB inhibitor respectively. These results suggest that Tat and IFN-γ act probably by two distinct mechanisms to induce the production of IDO-1. Our results clearly demonstrated that, although TLR4 pathway is necessary for Tat-induced IDO-1 in MoDC, it seems not to be sufficient since stable transfection of a functional TLR4/MD2 pathway in HEK or HeLa cell lines which are endogenously defectives for TLR4, did not restore the capacity of Tat to induce IDO-1 while IFN-γ treatment induces IDO-1 in HeLa cells independently of TLR4 pathway. These results suggest the involvement of additional stimuli in addition to TLR4 pathway which remain to be identified. Altogether our results demonstrated that, in human MoDC, HIV-1 Tat protein induced IDO-1 expression and activity in a NF-κB dependent-manner by recruiting TLR4 pathway.

Modeling the Function of TATA Box Binding Protein in Transcriptional Changes Induced by HIV-1 Tat in Innate Immune Cells and the Effect of Methamphetamine Exposure

Innate immune cells are targets of HIV-1 infection in the Central Nervous System (CNS), generating neurological deficits. Infected individuals with substance use disorders as co-morbidities, are more likely to have aggravated neurological disorders, higher CNS viral load and inflammation. Methamphetamine (Meth) is an addictive stimulant drug, commonly among HIV+ individuals. The molecular basis of HIV direct effects and its interactions with Meth in host response, at the gene promoter level, are not well understood. The main HIV-1 peptide acting on transcription is the transactivator of transcription (Tat), which promotes replication by recruiting a Tata-box binding protein (TBP) to the virus long-terminal repeat (LTR). We tested the hypothesis that Tat can stimulate host gene expression through its ability to increase TBP, and thus promoting its binding to promoters that bear Tata-box binding motifs. Genes with Tata-box domains are mainly inducible, early response, and involved in inflammation, regulation and metabolism, relevant in HIV pathogenesis. We also tested whether Tat and Meth interact to trigger the expression of Tata-box bearing genes. The THP1 macrophage cell line is a well characterized innate immune cell system for studying signal transduction in inflammation. These cells are responsive to Tat, as well as to Meth, by recruiting RNA Polymerase (RNA Pol) to inflammatory gene promoters, within 15 min of stimulation (1). THP-1 cells, including their genetically engineered derivatives, represent valuable tools for investigating monocyte structure and function in both health and disease, as a consistent system (2). When differentiated, they mimic several aspects of the response of macrophages, and innate immune cells that are the main HIV-1 targets within the Central Nervous System (CNS). THP1 cells have been used to characterize the impact of Meth and resulting neurotransmitters on HIV entry (1), mimicking the CNS micro-environment. Integrative consensus sequence analysis in genes with enriched RNA Pol, revealed that TBP was a major transcription factor in Tat stimulation, while the co-incubation with Meth shifted usage to a distinct and diversified pattern. For validating these findings, we engineered a THP1 clone to be deficient in the expression of all major TBP splice variants, and tested its response to Tat stimulation, in the presence or absence of Meth. Transcriptional patterns in TBP-sufficient and deficient clones confirmed TBP as a dominant transcription factor in Tat stimulation, capable of inducing genes with no constitutive expression. However, in the presence of Meth, TBP was no longer necessary to activate the same genes, suggesting promoter plasticity. These findings demonstrate TBP as mechanism of host-response activation by HIV-1 Tat, and suggest that promoter plasticity is a challenge imposed by co-morbid factors such as stimulant drug addiction. This may be one mechanism responsible for limited efficacy of therapeutic approaches in HIV+ Meth abusers.

HIV-1 Envelope Glycoproteins Induce the Production of TNF-α and IL-10 in Human Monocytes by Activating Calcium Pathway

Human HIV-1 infection leads inevitably to a chronic hyper-immune-activation. However, the nature of the targeted receptors and the pathways involved remain to be fully elucidated. We demonstrate that X4-tropic gp120 induced the production of TNF-α and IL-10 by monocytes through activation of a cell membrane receptor, distinct from the CD4, CXCR4, and MR receptors. Gp120 failed to stimulate IL-10 and TNF-α production by monocytes in Ca²⁺ free medium. This failure was total for IL-10 and partial for TNF-α. However, IL-10 and TNF-α production was fully restored following the addition of exogenous calcium. Accordingly, addition of BAPTA-AM and cyclosporine-A, fully and partially inhibited IL-10 and TNF-α respectively. The PKA pathway was crucial for IL-10 production but only partially involved in gp120-induced TNF-α. The PLC pathway was partially and equivalently involved in gp120-induced TNF-α and IL-10. Moreover, the inhibition of PI3K, ERK1/2, p38 MAP-kinases and NF-κB pathways totally abolished the production of both cytokines. In conclusion, this study revealed the crucial calcium signaling pathway triggered by HIV-1 gp120 to control the production of these two cytokines: TNF-α and IL-10. The finding could help in the development of a new therapeutic strategy to alleviate the chronic hyper-immune-activation observed in HIV-1 infected patients.

A high-resolution mass cytometry analysis reveals a delay of cytokines production after TLR4 or TLR7/8 engagements in HIV-1 infected humans

HIV infection is associated with chronic inflammation in both non-treated and treated patients. TLR-dependent mechanisms are strongly involved in the maintenance of this inflammation. Indeed, the residual replication of HIV, the potential viral co-infections, or the products issued from microbial translocation provide TLR ligands, which contribute to trigger innate immune responses. Maintaining this chronic inflammation leads to an exhaustion of the immune system. Therefore, the TLR-dependent responses could be altered in HIV-infected patients. To investigate this hypothesis, we performed high-resolution phenotyping using a mass cytometry panel of 34 cell markers. Whole blood cells from healthy, non-treated HIV-infected and ART-treated HIV-infected subjects were stimulated with LPS, R848 or Poly(I:C). We observed the immune responses induced in T-cells, B-cells, polymorphonuclear cells, NK cells, basophils, monocytes and dendritic cells. We observed that, for either LPS or R848 stimulations, the production of cytokines in monocytes and conventional dendritic cells was delayed in treated or non-treated HIV-infected patients, compared to healthy individuals. These results suggest that leukocytes from chronic HIV-infected patients are slower to respond following the sensing of pathogens and danger signals, which may be an important feature of HIV infection.

Tat is a multifunctional viral protein that modulates cellular gene expression and functions

The human immunodeficiency virus type I (HIV-1) has developed several strategies to condition the host environment to promote viral replication and spread. Viral proteins have evolved to perform multiple functions, aiding in the replication of the viral genome and modulating the cellular response to the infection. Tat is a small, versatile, viral protein that controls transcription of the HIV genome, regulates cellular gene expression and generates a permissive environment for viral replication by altering the immune response and facilitating viral spread to multiple tissues. Studies carried out utilizing biochemical, cellular, and genomic approaches show that the expression and activity of hundreds of genes and multiple molecular networks are modulated by Tat via multiple mechanisms.

HIV and HIV-Tat inhibit LPS-induced IL-27 production in human macrophages by distinct intracellular signaling pathways

Monocyte-derived Mϕs (MDMs) from HIV-infected patients and MDM infected in vitro with HIV exhibit a reduced ability to secrete various cytokines, including IL-12. Recently, IL-27, an IL-12 family cytokine, was shown to inhibit HIV replication in Mϕ. Whether HIV infection or HIV accessory protein(s) impact IL-27 production in Mϕs remains unknown. Herein, we show that in vitro HIV infection, as well as intracellular HIV-Tat (Tat) and Tat peptides, inhibit LPS-induced IL-27 production in human MDMs, suggesting impairment of the TLR4 signaling pathway. To understand the signaling pathways governing HIV or Tat-mediated inhibition of LPS-induced IL-27 production, we first demonstrated that p38 MAPK, PI3K, Src-homology region 2 domain-containing tyrosine phosphatase 1 (SHP-1), and Src kinases regulate LPS-induced IL-27 production in MDMs. Tat caused down-regulation of TNFR-associated factor (TRAF)-6 and inhibitor of apoptosis 1 (cIAP-1) and subsequently decreased phosphorylation of downstream PI3K and p38 MAPKs, which were implicated in LPS-induced IL-27 production. Whereas SHP-1 and Src kinases regulated LPS-induced IL-27 production, Tat did not inhibit these kinases, suggesting that they were not involved in Tat-mediated inhibition of LPS-induced IL-27 production. In contrast to Tat, in vitro HIV infection of MDM inhibited LPS-induced IL-27 production via inhibition of p38 MAPK activation. Overall, HIV and Tat inhibit LPS-induced IL-27 production in human macrophages via distinct mechanisms: Tat through the inhibition of cIAP-1-TRAF-6 and subsequent inhibition of PI3K and p38 MAPKs, whereas HIV through the inhibition of p38 MAPK activation.

PKC-δ isoform plays a crucial role in Tat-TLR4 signalling pathway to activate NF-κB and CXCL8 production

HIV-1 Tat protein induces the production of CXCL8 chemokine in a TLR4/MD2 and PKC dependent manner. The objective of this study was to understand whether these two pathways were distinct or constituted a single common pathway, and to determine the nature of the PKC isoforms involved and their interrelation with the activation of NF-κB and CXCL8 gene product expression. Here, we show that Tat-induced CXCL8 production is essentially dependent on the activation of PKC delta isoform, as shown a) by the capacity of PKC delta dominant negative (DN), and Rottlerin, a selective PKC delta pharmacological inhibitor, to inhibit Tat-induced CXCL8 production and b) by the ability of the constitutively active (CAT) isoform of PKC delta to induce CXCL8 production in a HEK cell line in the absence of Tat stimulation. The finding that comparable amounts of CXCL8 were produced following stimulation with either Tat protein, PKC-delta CAT transfection, or both, argue for the implication of one common pathway where PKC delta is activated downstream of TLR4 recruitment and leads to the activation of NF-κB. Altogether, our results underline the crucial role of PKC delta isoform in activating gene expression of CXCL8, a cytokine largely implicated in the physiopathology of HIV-1 infection.

HIV-1 Tat Primes and Activates Microglial NLRP3 Inflammasome-Mediated Neuroinflammation

Neuroinflammation associated with HIV-1 infection is a problem affecting ∼50% of HIV-infected individuals. NLR family pyrin domain containing 3 (NLRP3) inflammasome has been implicated in HIV-induced microglial activation, but the mechanism(s) remain unclear. Because HIV-1 Transactivator of Transcription (Tat) protein continues to be present despite antiretroviral therapy and activates NF-kB, we hypothesized that Tat could prime the NLRP3 inflammasome. We found a dose- and time-dependent induction of NLRP3 expression in microglia exposed to Tat compared with control. Tat exposure also time-dependently increased the mature caspase-1 and IL-1β levels and enhanced the IL-1β secretion. These in vitro findings were validated in archival brain tissues from Simian Immunodeficiency Virus (SIV)-infected and uninfected rhesus macaques. Further validation of NLRP3 priming in vivo involved administration of lipopolysaccharide (LPS) to HIV transgenic (Tg) rats followed by assessment of IL-1β mRNA expression and inflammasome activation (ASC oligomers and mature IL-1β). Intriguingly, LPS potentiated upregulation of IL-1β mRNA and inflammasome activation in HIV-Tg rats compared with the wild-type controls. Interestingly, we found an inverse relationship in the expression of NLRP3 and its negative regulator, miR-223, suggesting a miR-223-mediated mechanism for Tat-induced NLRP3 priming. Furthermore, blockade of NLRP3 resulted in decreased IL-1β secretion. Collectively, these findings suggest a novel role of Tat in priming and activating the NLRP3 inflammasome. Therefore, NLRP3 can be envisioned as a therapeutic target for ameliorating Tat-mediated neuroinflammation.SIGNIFICANCE STATEMENT Despite successful suppression of viremia with increased longevity in the era of combined antiretroviral therapy, chronic inflammation with underlying neurocognitive impairment continues to afflict almost 50% of infected individuals. Viral, bacterial, and cellular products have all been implicated in promoting the chronic inflammation found in these individuals. Understanding the molecular mechanism(s) by which viral proteins such as HIV-1 Transactivator of Transcription (Tat) protein can activate microglia is thus of paramount importance. Herein, we demonstrate a novel role of Tat in priming and activating NLR family pyrin domain containing 3 (NLRP3) inflammasomes in microglial cells and in HIV-Tg rats administered lipopolysaccharide. Targeting NLRP3 inflammasome pathway mediators could thus be developed as therapeutic interventions to alleviate or prevent neuroinflammation and subsequent cognitive impairment in HIV-positive patients.

In Vivo and in Vitro Proteome Analysis of Human Immunodeficiency Virus (HIV)-1-infected, Human CD4+ T Cells

Host-directed therapies against HIV-1 are thought to be critical for long term containment of the HIV-1 pandemic but remain elusive. Because HIV-1 infects and manipulates important effectors of both the innate and adaptive immune system, identifying modulations of the host cell systems in humans during HIV-1 infection may be crucial for the development of immune based therapies. Here, we quantified the changes of the proteome in human CD4⁺ T cells upon HIV-1 infection, both in vitro and in vivo A SWATH-MS approach was used to measure the proteome of human primary CD4⁺ T cells infected with HIV-1 in vitro as well as CD4⁺ T cells from HIV-1-infected patients with paired samples on and off antiretroviral treatment. In the in vitro experiment, the proteome of CD4⁺ T cells was quantified over a time course following HIV-1 infection. 1,725 host cell proteins and 4 HIV-1 proteins were quantified, with 145 proteins changing significantly during the time course. Changes in the proteome peaked 24 h after infection, concomitantly with significant HIV-1 protein production. In the in vivo branch of the study, CD4⁺ T cells from viremic patients and those with no detectable viral load after treatment were sorted, and the proteomes were quantified. We consistently detected 895 proteins, 172 of which were considered to be significantly different between the viremic patients and patients undergoing successful treatment. The proteome of the in vitro-infected CD4⁺ T cells was modulated on multiple functional levels, including TLR-4 signaling and the type 1 interferon signaling pathway. Perturbations in the type 1 interferon signaling pathway were recapitulated in CD4⁺ T cells from patients. The study shows that proteome maps generated by SWATH-MS indicate a range of functionally significant changes in the proteome of HIV-infected human CD4⁺ T cells. Exploring these perturbations in more detail may help identify new targets for immune based interventions.

Genetic variations of NOD2 and MD2 genes in hepatitis B virus infection

OBJECTIVES

Nucleotide oligomerization domain 2 (NOD2) and myeloid differentiation protein 2 (MD-2) have crucial roles in the innate immune system. NOD2 is a member of the NOD-like receptor (NLR) family of pattern recognition receptors (PRRs), while MD-2 is a co-receptor for Toll-like receptor 4 (TLR4), which comprises another group of PRRs. Genetic variations in the NOD2 and MD-2 genes may be susceptibility factors to viral pathogens including hepatitis B virus (HBV). We investigated whether polymorphisms at NOD2 (rs2066845 and rs2066844) or at MD-2 (rs6472812 and rs11466004) were associated with susceptibility to HBV infection and advancement to related liver complications in a Saudi Arabian population. Methods: A total of 786 HBV-infected patients and 600 healthy uninfected controls were analyzed in the present study. HBV-infected patients were categorized into three groups based on the clinical stage of the infection: inactive HBV carriers, active HBV carriers, and patients with liver cirrhosis + hepatocellular carcinoma (HCC). Results: All four SNPs were significantly associated with susceptibility to HBV infection although none of the SNPs tested in NOD2 and MD-2 were significantly associated with persistence of HBV infection. We found that HBV-infected patients that were homozygous CC for rs2066845 in the NOD2 gene were at a significantly increased risk of progression to HBV-related liver complications (Odds Ratio = 7.443 and P = 0.044). Furthermore, haplotype analysis found that the rs2066844-rs2066845 C-G and T-G haplotypes at the NOD2 gene and four rs6472812-rs11466004 haplotypes (G-C, G-T, A-C, and A-T) at the MD-2 gene were significantly associated with HBV infection in the affected cohort compared to those found in our control group. Conclusion: We found that the single nucleotide polymorphisms rs2066844 and rs2066845 at NOD2 and rs6472812 and rs11466004 at MD-2 were associated with susceptibility to HBV infection in a Saudi population.

HIV-1 Tat exacerbates lipopolysaccharide-induced cytokine release via TLR4 signaling in the enteric nervous system

The loss of gut epithelium integrity leads to translocation of microbes and microbial products resulting in immune activation and drives systemic inflammation in acquired immunodeficiency syndrome (AIDS) patients. Although viral loads in HIV patients are significantly reduced in the post-cART era, inflammation and immune activation persist and can lead to morbidity. Here, we determined the interactive effects of the viral protein HIV-1 Tat and lipopolysaccharide (LPS) on enteric neurons and glia. Bacterial translocation was significantly enhanced in Tat-expressing (Tat+) mice. Exposure to HIV-1 Tat in combination with LPS enhanced the expression and release of the pro-inflammatory cytokines IL-6, IL-1β and TNF-α in the ilea of Tat+ mice and by enteric glia. This coincided with enhanced NF-κB activation in enteric glia that was abrogated in glia from TLR4 knockout mice and by knockdown (siRNA) of MyD88 siRNA in wild type glia. The synergistic effects of Tat and LPS resulted in a reduced rate of colonic propulsion in Tat+ mice treated with LPS. These results show that HIV-1 Tat interacts with the TLR4 receptor to enhance the pro-inflammatory effects of LPS leading to gastrointestinal dysmotility and enhanced immune activation.

Human Coronaviruses: A Review of Virus-Host Interactions

Human coronaviruses (HCoVs) are known respiratory pathogens associated with a range of respiratory outcomes. In the past 14 years, the onset of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) have thrust HCoVs into spotlight of the research community due to their high pathogenicity in humans. The study of HCoV-host interactions has contributed extensively to our understanding of HCoV pathogenesis. In this review, we discuss some of the recent findings of host cell factors that might be exploited by HCoVs to facilitate their own replication cycle. We also discuss various cellular processes, such as apoptosis, innate immunity, ER stress response, mitogen-activated protein kinase (MAPK) pathway and nuclear factor kappa B (NF-κB) pathway that may be modulated by HCoVs.

HIV-1 Tat Protein Activates both the MyD88 and TRIF Pathways To Induce Tumor Necrosis Factor Alpha and Interleukin-10 in Human Monocytes

In this study, we show that the HIV-1 Tat protein interacts with rapid kinetics to engage the Toll-like receptor 4 (TLR4) pathway, leading to the production of proinflammatory and anti-inflammatory cytokines. The pretreatment of human monocytes with Tat protein for 10 to 30 min suffices to irreversibly engage the activation of the TLR4 pathway, leading to the production of tumor necrosis factor alpha (TNF-α) and interleukin-10 (IL-10), two cytokines strongly implicated in the chronic activation and dysregulation of the immune system during HIV-1 infection. Therefore, this study analyzed whether the HIV-1 Tat protein is able to activate these two pathways separately or simultaneously. Using three complementary approaches, including mice deficient in the MyD88, TIRAP/MAL, or TRIF adaptor, biochemical analysis, and the use of specific small interfering RNAs (siRNAs), we demonstrated (i) that Tat was able to activate both the MyD88 and TRIF pathways, (ii) the capacity of Tat to induce TIRAP/MAL degradation, (iii) the crucial role of the MyD88 pathway in the production of Tat-induced TNF-α and IL-10, (iv) a reduction but not abrogation of IL-10 and TNF-α by Tat-stimulated macrophages from mice deficient in TIRAP/MAL, and (v) the crucial role of the TRIF pathway in Tat-induced IL-10 production. Further, we showed that downstream of the MyD88 and TRIF pathways, the Tat protein activated the protein kinase C (PKC) βII isoform, the mitogen-activated protein (MAP) kinases p38 and extracellular signal-regulated kinase 1/2 (ERK1/2), and NF-κB in a TLR4-dependent manner. Collectively, our data show that by recruiting the TLR4 pathway with rapid kinetics, the HIV-1 Tat protein leads to the engagement of both the MyD88 and TRIF pathways and to the activation of PKC, MAP kinase, and NF-κB signaling to induce the production of TNF-α and IL-10.

IMPORTANCE

In this study, we demonstrate that by recruiting the TLR4 pathway with rapid kinetics, the HIV-1 Tat protein leads to the engagement of both the MyD88 and TRIF pathways and to the activation of PKC-βII, MAP kinase, and NF-κB signaling to induce the production of TNF-α and IL-10, two cytokines strongly implicated in the chronic activation and dysregulation of the immune system during HIV-1 infection. Thus, it may be interesting to target Tat as a pathogenic factor early after HIV-1 infection. This could be achieved either by vaccination approaches including Tat as an immunogen in potential candidate vaccines or by developing molecules capable of neutralizing the effect of the Tat protein.

TB/HIV pleurisy reduces Th17 lymphocyte proportion independent of the cytokine microenvironment

T-helper (Th) 17 cells are a pro-inflammatory subset of CD4(+) effector T-cells critical in mucosal immunity. Imbalances in Th17 cell proportion have been implicated in the pathogenesis of several diseases; however, this has not been adequately explored in tuberculosis (TB) and human immunodeficiency virus (HIV) co-infection. Since Th17 cells are predominantly mucosally associated, we assessed Th17 proportion and associated microenvironment in pleural effusions from patients co-infected with TB/HIV. Our results show that TB(+)HIV(+) pleurisy results in significantly reduced frequency of CD4(+)IL-17(+)RORC(+)STAT3(+) Th17 cells compared to TB(-)HIV(-)ex vivo (p = 0.0054) and was confirmed in conditioned media studies in vitro (p = 0.0001). This was not associated with alterations in Th17 polarising cytokines IL-6, IL-21 and IL-23 or changes in Th17 signature cytokines IL-17A and F. However, the mRNA expression of Th17 signalling molecules, IL-6 (p = 0.0022), IL-6R (p = 0.0247), IL-1β (p = 0.0022) and signal transducer and activator (STAT) 3 (p = 0.0022) were significantly upregulated. Notably, TB(+)HIV(+) pleural fluid contained significantly higher concentrations of IL-1β (p = 0.0008), IL-22 (p = 0.0115), IL-31 (p = 0.0210), TNF-α (p = 0.0251) and IFN-γ (p = 0.0026) than TB(-)HIV(-) pleural fluid ex vivo. Taken together, this suggests a reduced portion of Th17 lymphocytes in TB/HIV pleurisy is independent of locally mediated cytokine polarisation.

Human immunodeficiency virus-associated disruption of mucosal barriers and its role in HIV transmission and pathogenesis of HIV/AIDS disease

Oral, intestinal and genital mucosal epithelia have a barrier function to prevent paracellular penetration by viral, bacterial and other pathogens, including human immunodeficiency virus (HIV). HIV can overcome these barriers by disrupting the tight and adherens junctions of mucosal epithelia. HIV-associated disruption of epithelial junctions may also facilitate paracellular penetration and dissemination of other viral pathogens. This review focuses on possible molecular mechanisms of HIV-associated disruption of mucosal epithelial junctions and its role in HIV transmission and pathogenesis of HIV and acquired immune deficiency syndrome (AIDS).

HIV-1 Tat protein enhances the intracellular growth of Leishmania amazonensis via the ds-RNA induced protein PKR

HIV-1 co-infection with human parasitic diseases is a growing public health problem worldwide. Leishmania parasites infect and replicate inside macrophages, thereby subverting host signaling pathways, including the response mediated by PKR. The HIV-1 Tat protein interacts with PKR and plays a pivotal role in HIV-1 replication. This study shows that Tat increases both the expression and activation of PKR in Leishmania-infected macrophages. Importantly, the positive effect of Tat addition on parasite growth was dependent on PKR signaling, as demonstrated in PKR-deficient macrophages or macrophages treated with the PKR inhibitor. The effect of HIV-1 Tat on parasite growth was prevented when the supernatant of HIV-1-infected macrophages was treated with neutralizing anti-HIV-1 Tat prior to Leishmania infection. The addition of HIV-1 Tat to Leishmania-infected macrophages led to inhibition of iNOS expression, modulation of NF-kB activation and enhancement of IL-10 expression. Accordingly, the expression of a Tat construct containing mutations in the basic region (49–57aa), which is responsible for the interaction with PKR, favored neither parasite growth nor IL-10 expression in infected macrophages. In summary, we show that Tat enhances Leishmania growth through PKR signaling.

Myeloid differentiation protein 2 facilitates pollen- and cat dander-induced innate and allergic airway inflammation

BACKGROUND

The National Health and Nutrition Examination Survey identified several pollens and cat dander as among the most common allergens that induce allergic sensitization and allergic diseases. We recently reported that ragweed pollen extract (RWPE) requires Toll-like receptor 4 (TLR4) to stimulate CXCL-mediated innate neutrophilic inflammation, which in turn facilitates allergic sensitization and airway inflammation. Myeloid differentiation protein 2 (MD2) is a TLR4 coreceptor, but its role in pollen- and cat dander-induced innate and allergic inflammation has not been critically evaluated.

OBJECTIVE

We sought to elucidate the role of MD2 in inducing pollen- and cat dander-induced innate and allergic airway inflammation.

METHODS

TCM(Null) (TLR4(Null), CD14(Null), MD2(Null)), TLR4(Hi), and TCM(Hi) cells and human bronchial epithelial cells with small interfering RNA-induced downregulation of MD2 were stimulated with RWPE, other pollen allergic extracts, or cat dander extract (CDE), and activation of nuclear factor κB (NF-κB), secretion of the NF-κB-dependent CXCL8, or both were quantified. Wild-type mice or mice with small interfering RNA knockdown of lung MD2 were challenged intranasally with RWPE or CDE, and innate and allergic inflammation was quantified.

RESULTS

RWPE stimulated MD2-dependent NF-κB activation and CXCL secretion. Likewise, Bermuda, rye, timothy, pigweed, Russian thistle, cottonwood, walnut, and CDE stimulated MD2-dependent CXCL secretion. RWPE and CDE challenge induced MD2-dependent and CD14-independent innate neutrophil recruitment. RWPE induced MD2-dependent allergic sensitization and airway inflammation.

CONCLUSIONS

MD2 plays an important role in induction of allergic sensitization to cat dander and common pollens relevant to human allergic diseases.

Phenotype and Polyfunctional Deregulation Involving Interleukin 6 (IL-6)- and IL-10-Producing Monocytes in HIV-Infected Patients Receiving Combination Antiretroviral Therapy Differ From Those in Healthy Older Individuals

BACKGROUND

Despite the relevance of monocytes as promoters of the inflammatory response, whether human immunodeficiency virus (HIV) infection induces premature age-related changes to the phenotype and function of monocytes or whether these alterations are different and/or specifically driven by HIV remains to be mechanistically determined.

METHODS

We assayed the activation phenotype and the responsiveness in vitro to Toll-like receptor (TLR) agonists in classical, intermediate, and nonclassical subsets of monocytes by assessing intracellular interleukin 1α (IL-1α), IL-1β, interleukin 6 (IL-6), interleukin 8, tumor necrosis factor α, and interleukin 10 (IL-10) production in 20 HIV-infected patients receiving combination antiretroviral therapy (cART) and 2 groups of uninfected controls (20 age-matched young individuals and 20 older individuals aged >65 years).

RESULTS

HIV-infected patients showed a more activated phenotype of monocytes than older controls. Regarding functionality, under unstimulated conditions HIV-infected patients showed a higher percentage of classical monocytes producing IL-6 and IL-10 than control subjects. The percentage of cells with production of multiple cytokines (polyfunctionality), including IL-10, in response to TLR agonists was greater among HIV-infected patients than among control subjects.

CONCLUSIONS

Inflammatory alterations associated with monocytes during HIV infection are different from those in aging individuals. This monocyte dysfunction, mainly characterized by high levels of IL-6- and IL-10-producing monocytes, may have clinical implications in HIV-infected patients that are different from those in aging individuals.

Vpr Enhances Tumor Necrosis Factor Production by HIV-1-Infected T Cells

The HIV-1 accessory protein Vpr displays different activities potentially impacting viral replication, including the arrest of the cell cycle in the G2 phase and the stimulation of apoptosis and DNA damage response pathways. Vpr also modulates cytokine production by infected cells, but this property remains partly characterized. Here, we investigated the effect of Vpr on the production of the proinflammatory cytokine tumor necrosis factor (TNF). We report that Vpr significantly increases TNF secretion by infected lymphocytes. De novo production of Vpr is required for this effect. Vpr mutants known to be defective for G2 cell cycle arrest induce lower levels of TNF secretion, suggesting a link between these two functions. Silencing experiments and the use of chemical inhibitors further implicated the cellular proteins DDB1 and TAK1 in this activity of Vpr. TNF secreted by HIV-1-infected cells triggers NF-κB activity in bystander cells and allows viral reactivation in a model of latently infected cells. Thus, the stimulation of the proinflammatory pathway by Vpr may impact HIV-1 replication in vivo.

IMPORTANCE

The role of the HIV-1 accessory protein Vpr remains only partially characterized. This protein is important for viral pathogenesis in infected individuals but is dispensable for viral replication in most cell culture systems. Some of the functions described for Vpr remain controversial. In particular, it remains unclear whether Vpr promotes or instead prevents proinflammatory and antiviral immune responses. In this report, we show that Vpr promotes the release of TNF, a proinflammatory cytokine associated with rapid disease progression. Using Vpr mutants or inhibiting selected cellular genes, we show that the cellular proteins DDB1 and TAK1 are involved in the release of TNF by HIV-infected cells. This report provides novel insights into how Vpr manipulates TNF production and helps clarify the role of Vpr in innate immune responses and inflammation.

Impairment of T cell development and acute inflammatory response in HIV-1 Tat transgenic mice

Immune activation and chronic inflammation are hallmark features of HIV infection causing T-cell depletion and cellular immune dysfunction in AIDS. Here, we addressed the issue whether HIV-1 Tat could affect T cell development and acute inflammatory response by generating a transgenic mouse expressing Tat in lymphoid tissue. Tat-Tg mice showed thymus atrophy and the maturation block from DN4 to DP thymic subpopulations, resulting in CD4⁺ and CD8⁺ T cells depletion in peripheral blood. In Tat-positive thymus, we observed the increased p65/NF-κB activity and deregulated expression of cytokines/chemokines and microRNA-181a-1, which are involved in T-lymphopoiesis. Upon LPS intraperitoneal injection, Tat-Tg mice developed an abnormal acute inflammatory response, which was characterized by enhanced lethality and production of inflammatory cytokines. Based on these findings, Tat-Tg mouse could represent an animal model for testing adjunctive therapies of HIV-1-associated inflammation and immune deregulation.

Interplay between HIV-1 and Toll-like receptors in human myeloid cells: friend or foe in HIV-1 pathogenesis?

The Toll-like receptors are the first line of the host response to pathogens, representing an essential component of the innate and adaptive immune response. They recognize different pathogens and trigger responses directed at eliminating the invader and at developing immunologic long-term memory, ultimately affecting viral pathogenesis. In viral infections, sensing of nucleic acids and/or viral structural proteins generally induces a protective immune response. Thus, it is not surprising that many viruses have developed strategies to evade or counteract signaling through the Toll-like receptor pathways, to survive the host defense machinery and ensure propagation. Thus, Toll-like receptor engagement can also be part of viral pathogenic mechanisms. Evidence for a direct interaction of Toll-like receptors with human immunodeficiency virus type 1 (HIV-1) structures has started to be achieved, and alterations of their expression and function have been described in HIV-1-positive subjects. Furthermore, Toll-like receptor triggering by bacterial and viral ligands have been described to modulate HIV-1 replication and host response, leading to protective or detrimental effects. This review covers major advances in the field of HIV-1 interplay with Toll-like receptors, focusing on human myeloid cells (e.g., monocytes/macrophages and dendritic cells). The role of this interaction in the dysregulation of myeloid cell function and in dictating aspects of the multifaceted pathogenesis of acquired immunodeficiency syndrome will be discussed.

Chronic morphine and HIV-1 Tat promote differential central nervous system trafficking of CD3+ and Ly6C+ immune cells in a murine Streptococcus pneumoniae infection model

Background

Persistent systemic infection results in excessive trafficking of peripheral immune cells into the central nervous system (CNS), thereby contributing to sustained neuroinflammation that leads to neurocognitive deficits. In this study, we explored the role of opportunistic systemic infection with Streptococcus pneumoniae in the recruitment of peripheral leukocytes into the CNS and its contribution to HIV-1-associated neurocognitive disorders in opioid-dependent individuals.

Methods

Wild-type B6CBAF1 (wt), μ-opioid receptor knockout (MORKO), FVB/N luciferase transgenic, and Toll-like receptor 2 and 4 knockout (TLR2KO and TLR4KO) mice were subcutaneously implanted with morphine/placebo pellet followed by HIV-1 Transactivator of transcription (Tat) protein injection intravenously and S. pneumoniae administration intraperitoneally. On postoperative day 5, brains perfused with phosphate-buffered saline were harvested and subjected to immunohistochemistry (for bacterial trafficking and chemokine ligand generation), flow cytometry (for phenotypic characterization of CNS trafficked immune cells), Western blot, and real-time PCR (for ligand expression).

Results

Our results show differential leukocyte trafficking of T lymphocytes (CD3+) and inflammatory monocytes (Ly6C+) into the CNS of mice treated with morphine, HIV-1 Tat, and/or S. pneumoniae. In addition, we demonstrate a Trojan horse mechanism for bacterial dissemination across the blood-brain barrier into the CNS by monocytes. Activation of TLRs on microglia induced a chemokine gradient that facilitated receptor-dependent trafficking of peripheral immune cells into the CNS. HIV-1 Tat induced trafficking of Ly6C+ and CD3+ cells into the CNS; infection with S. pneumoniae facilitated infiltration of only T lymphocytes into the CNS. We also observed differential chemokine secretion in the CNS, with CCL5 being the predominant chemokine following HIV-1 Tat treatment, which was potentiated further with morphine. S. pneumoniae alone led to preferential induction of CXCL12. Furthermore, we attributed a regulatory role for TLRs in the chemokine-mediated trafficking of leukocytes into the CNS. Chronic morphine and HIV-1 Tat, in the context of systemic S. pneumoniae co-infection, differentially modulated induction of TLR2/4, which consequently facilitated trafficking of TLR2 → CD3 + CCR5+ and TLR4 → Ly6C+(CCR5+/CXCR4+) immune cells into the CNS.

Conclusion

Our murine study suggests that secondary infection in opioid-dependent individuals infected with HIV-1 augments peripheral leukocyte trafficking as a consequence of sustained chemokine gradients in the CNS.

HIV-1 Tat Protein Induces Production of Proinflammatory Cytokines by Human Dendritic Cells and Monocytes/Macrophages through Engagement of TLR4-MD2-CD14 Complex and Activation of NF-κB Pathway

We recently reported that the human immunodeficiency virus type-1 (HIV-1) Tat protein induced the expression of programmed death ligand-1 (PD-L1) on dendritic cells (DCs) through a TLR4 pathway. However, the underlying mechanisms by which HIV-1 Tat protein induces the abnormal hyper-activation of the immune system seen in HIV-1 infected patients remain to be fully elucidated. In the present study, we report that HIV-1 Tat protein induced the production of significant amounts of the pro-inflammatory IL-6 and IL-8 cytokines by DCs and monocytes from both healthy and HIV-1 infected patients. Such production was abrogated in the presence of anti-TLR4 blocking antibodies or soluble recombinant TLR4-MD2 as a decoy receptor, suggesting TLR4 was recruited by Tat protein. Tat-induced murine IL-6 and CXCL1/KC a functional homologue of human IL-8 was abolished in peritoneal macrophages derived from TLR4 KO but not from Wt mice, confirming the involvement of the TLR4 pathway. Furthermore, the recruitment of TLR4-MD2-CD14 complex by Tat protein was demonstrated by the activation of TLR4 downstream pathways including NF-κB and SOCS-1 and by down-modulation of cell surface TLR4 by endocytosis in dynamin and lipid-raft-dependent manners. Collectively, these findings demonstrate, for the first time, that HIV-1 Tat interacts with TLR4-MD2-CD14 complex and activates the NF-κB pathway, leading to overproduction of IL-6 and IL-8 pro-inflammatory cytokines by myeloid cells from both healthy and HIV-1 infected patients. This study reveals a novel mechanism by which HIV-1, via its early expressed Tat protein, hijacks the TLR4 pathway, hence establishing abnormal hyper-activation of the immune system.

Mycobacterium tuberculosis RpfE promotes simultaneous Th1- and Th17-type T-cell immunity via TLR4-dependent maturation of dendritic cells

Reciprocal induction of the Th1 and Th17 immune responses is essential for optimal protection against Mycobacterium tuberculosis (Mtb); however, only a few Mtb antigens are known to fulfill this task. A functional role for resuscitation-promoting factor (Rpf) E, a latency-associated member of the Rpf family, in promoting naïve CD4(+) T-cell differentiation toward both Th1 and Th17 cell fates through interaction with dendritic cells (DCs) was identified in this study. RpfE induces DC maturation by increasing expression of surface molecules and the production of IL-6, IL-1β, IL-23p19, IL-12p70, and TNF-α but not IL-10. This induction is mediated through TLR4 binding and subsequent activation of ERK, p38 MAPKs, and NF-κB signaling. RpfE-treated DCs effectively caused naïve CD4(+) T cells to secrete IFN-γ, IL-2, and IL-17A, which resulted in reciprocal expansions of the Th1 and Th17 cell response along with activation of T-bet and RORγt but not GATA-3. Furthermore, lung and spleen cells from Mtb-infected WT mice but not from TLR4(-/-) mice exhibited Th1 and Th17 polarization upon RpfE stimulation. Taken together, our data suggest that RpfE has the potential to be an effective Mtb vaccine because of its ability to activate DCs that simultaneously induce both Th1- and Th17-polarized T-cell expansion.