Characterization of a peptide domain within the GB virus C NS5A phosphoprotein that inhibits HIV replication

Human Pegivirus Type 1: A Common Human Virus That Is Beneficial in Immune-Mediated Disease?

Two groups identified a novel human flavivirus in the mid-1990s. One group named the virus hepatitis G virus (HGV) and the other named it GB Virus type C (GBV-C). Sequence analyses found these two isolates to be the same virus, and subsequent studies found that the virus does not cause hepatitis despite sharing genome organization with hepatitis C virus. Although HGV/GBV-C infection is common and may cause persistent infection in humans, the virus does not appear to directly cause any other known disease state. Thus, the virus was renamed “human pegivirus 1” (HPgV-1) for “persistent G” virus. HPgV-1 is found primarily in lymphocytes and not hepatocytes, and several studies found HPgV-1 infection associated with prolonged survival in people living with HIV. Co-infection of human lymphocytes with HPgV-1 and HIV inhibits HIV replication. Although three viral proteins directly inhibit HIV replication in vitro, the major effects of HPgV-1 leading to reduced HIV-related mortality appear to result from a global reduction in immune activation. HPgV-1 specifically interferes with T cell receptor signaling (TCR) by reducing proximal activation of the lymphocyte specific Src kinase LCK. Although TCR signaling is reduced, T cell activation is not abolished and with sufficient stimulus, T cell functions are enabled. Consequently, HPgV-1 is not associated with immune suppression. The HPgV-1 immunomodulatory effects are associated with beneficial outcomes in other diseases including Ebola virus infection and possibly graft-versus-host-disease following stem cell transplantation. Better understanding of HPgV-1 immune escape and mechanisms of inflammation may identify novel therapies for immune-based diseases.

Clinical and molecular aspects of human pegiviruses in the interaction host and infectious agent

Background

Human pegivirus 1 (HPgV-1) is a Positive-sense single-stranded RNA (+ ssRNA) virus, discovered in 1995 as a Flaviviridae member, and the closest human virus linked to HCV. In comparison to HCV, HPgV-1 seems to be lymphotropic and connected to the viral group that infects T and B lymphocytes. HPgV-1 infection is not persuasively correlated to any known human disease; nevertheless, multiple studies have reported a connection between chronic HPgV-1 infection and improved survival in HPgV-1/HIV co-infected patients with a delayed and favorable impact on HIV infection development. While the process has not been thoroughly clarified, different mechanisms for these observations have been proposed. HPgV-1 is categorized into seven genotypes and various subtypes. Infection with HPgV-1 is relatively common globally. It can be transferred parenterally, sexually, and through vertical ways, and thereby its co-infection with HIV and HCV is common. In most cases, the clearance of HPgV-1 from the body can be achieved by developing E2 antibodies after infection.

Main body

In this review, we thoroughly discuss the current knowledge and recent advances in understanding distinct epidemiological, molecular, and clinical aspects of HPgV-1.

Conclusion

Due to the unique characteristics of the HPgV-1, so advanced research on HPgV-1, particularly in light of HIV co-infection and other diseases, should be conducted to explore the essential mechanisms of HIV clearance and other viruses and thereby suggest novel strategies for viral therapy in the future.

A Caulobacter crescentus Microbicide Protects from Vaginal Infection with HIV-1JR-CSF in Humanized Bone Marrow-Liver-Thymus Mice

Human immunodeficiency virus (HIV) disproportionally infects young women in sub-Saharan Africa. Current HIV-1 prevention options have had limited success among women, suggesting that alternative, female-controlled prevention options need to be developed. Microbicides that can be applied to the vaginal tract are a promising prevention option. In this study, we describe the testing of 15 potential candidates for inhibition of HIV-1 infection in a humanized mouse model of HIV-1 infection. Four of these candidates were able to provide significant protection from vaginal infection with HIV-1, with the most successful candidate protecting 75% of the mice from infection. This study describes the preclinical testing of a new strategy that could be a safe and effective option for HIV-1 prevention in women.

Over 2 million people are infected with HIV-1 annually. Approximately half of these new infections occur in women residing in low-income countries, where their access to and control over HIV-1 preventative measures are often limited, indicating that female-controlled prevention options for HIV-1 are urgently needed. Microbicides that can be topically applied to the vaginal tract in advance of sexual activity represent a promising female-controlled prevention option for HIV-1. We have previously described the development of an HIV-1-specific microbicide using the surface or S-layer recombinant protein display capabilities of the nonpathogenic, freshwater bacterium Caulobacter crescentus. Recombinant C. crescentus bacteria were created that displayed proteins that interfere with the HIV-1 attachment and entry process and that were able to provide significant protection of TZM-bl cells from infection with HIV-1 pseudovirus. These studies have been expanded to investigate if these recombinant C. crescentus bacteria are able to maintain efficacy with replication-competent HIV-1 and both TZM-bl cells and human peripheral blood mononuclear cells (PBMCs). In addition, we utilized the humanized bone marrow-liver-thymus (BLT) mouse model to determine if vaginal application of recombinant C. crescentus at the time of HIV-1_JR-CSF infection could provide protection from HIV-1 infection. Recombinant C. crescentus bacteria expressing Griffithsin, GB virus C E2 protein, elafin, α-1-antitrypsin, indolicidin, and the fusion inhibitor T-1249 were able to protect 40 to 75% of the BLT mice from vaginal infection with HIV-1_JR-CSF, with C. crescentus bacteria expressing Griffithsin being the most effective. Taken together, these data suggest that a C. crescentus-based microbicide could be a safe and effective method for HIV-1 prevention.

IMPORTANCE Human immunodeficiency virus (HIV) disproportionally infects young women in sub-Saharan Africa. Current HIV-1 prevention options have had limited success among women, suggesting that alternative, female-controlled prevention options need to be developed. Microbicides that can be applied to the vaginal tract are a promising prevention option. In this study, we describe the testing of 15 potential candidates for inhibition of HIV-1 infection in a humanized mouse model of HIV-1 infection. Four of these candidates were able to provide significant protection from vaginal infection with HIV-1, with the most successful candidate protecting 75% of the mice from infection. This study describes the preclinical testing of a new strategy that could be a safe and effective option for HIV-1 prevention in women.

Development of peptide inhibitors of HIV transmission

Treatment of HIV has long faced the challenge of high mutation rates leading to rapid development of resistance, with ongoing need to develop new methods to effectively fight the infection. Traditionally, early HIV medications were designed to inhibit RNA replication and protein production through small molecular drugs. Peptide based therapeutics are a versatile, promising field in HIV therapy, which continues to develop as we expand our understanding of key protein-protein interactions that occur in HIV replication and infection. This review begins with an introduction to HIV, followed by the biological basis of disease, current clinical management of the disease, therapeutics on the market, and finally potential avenues for improved drug development.

Classical swine fever virus NS5A protein changed inflammatory cytokine secretion in porcine alveolar macrophages by inhibiting the NF-κB signaling pathway

Background

Classical swine fever (CSF) caused by CSF virus (CSFV) is a highly contagious disease of the pigs. A number of studies have suggested that CSFV non-structural (NS) 5A protein is involved in CSFV-associated pathogenesis, but its mechanism is still uncertain. The aim of this study was to investigate the roles of NS5A protein in CSFV-associated pathogenesis in cultured porcine alveolar macrophages (PAMs).

Methods

After PAMs cultured in vitro were transfected with CSFV NS5A, the alterations in IL-1β, IL-6 and TNF-α expression were determined by ELISA, the RIG-I signaling activity related to inflammatory cytokine secretion was investigated by Western blot and Immunofluorescent staining.

Results

It was suggested that, the stable expressed CSFV NS5A solely had no influence on the expressions of inflammatory cytokines IL-1β, IL-6 and TNF-α in PAMs Moreover, NS5A protein could suppressed IL-1β, IL-6 and TNF-α expression induced by poly(I:C). It was also showed that NS5A protein did not impair the expressions of RIG-I, MDA5, IPS-1, NF-κB and IkBα in cells without poly(I:C) stimulation. Protein expressions of RIG-I, MDA5, IPS-1, NF-κB were not disrupted by NS5A protein in poly(I:C)-stimulated cells, while poly(I:C)-induced NF-κB nuclear translocation and activity was obviously suppressed by this protein. A suppression in poly(I:C)-induced IkBα degradation in NS5A-expressing cells was also observed.

Conclusion

These data indicated that CSFV NS5A protein could inhibit the secretion of inflammatory cytokine induced by poly(I:C) through the suppression of the NF-κB signaling pathway, indicating the participation of CSFV NS5A protein in the pathogenesis of CSFV.

Definition of an 18-mer Synthetic Peptide Derived from the GB virus C E1 Protein as a New HIV-1 Entry Inhibitor

BACKGROUND

A slower progression of AIDS and increased survival in GBV-C positive individuals, compared with GBV-C negative individuals has been demonstrated; while the loss of GBV-C viremia was closely associated with a rise in mortality and increased progression of AIDS. Following on from the previous reported studies that support the thesis that GBV-C E2 interferes with HIV-1 entry, in this work we try to determine the role of the GBV-C E1 protein in HIV-1 inhibition.

METHODS

The present work involves the construction of several overlapping peptide libraries scanning the GBV-C E1 protein and the evaluation of their anti-HIV activity.

RESULTS

Specifically, an 18-mer synthetic peptide from the GBV-C E1 protein, E1(139-156), showed similar antiviral activity against HIVs from viruses from clades A, B, C, D and AE. Competitive ELISA using specific gp41-targeting mAbs, fluorescence resonance energy transfer as well as haemolysis assays demonstrated that this E1 peptide sequence interacts with the highly conserved N-terminal region of the HIV-1 gp41 (the fusion peptide) which is essential for viral entry.

CONCLUSIONS

We have defined a novel peptide lead compound and described the inhibitory role of a highly conserved fragment of the E1 protein.

GENERAL SIGNIFICANCE

The results together allow us to consider the non-pathogenic E1 GBV-C protein as an attractive source of peptides for the development of novel anti-HIV therapies.

Human pegivirus (GB virus C) NS3 protease activity inhibits induction of the type I interferon response and is not inhibited by HCV NS3 protease inhibitors

We previously found that human pegivirus (HPgV; formerly GBV-C) NS3 protease activity inhibits Human Immunodeficiency Virus (HIV) replication in a CD4+ T cell line. Given the protease׳s similarity to the Hepatitis C virus (HCV) NS3 protease, we characterized HPgV protease activity and asked whether it affects the type I interferon response or is inhibited by HCV protease antagonists. We characterized the activity of proteases with mutations in the catalytic triad and demonstrated that the HCV protease inhibitors Telaprevir, Boceprevir, and Danoprevir do not affect HPgV protease activity. HPgV NS3 protease cleaved MAVS but not TRIF, and it inhibited interferon responses sufficiently to enhance growth of an interferon-sensitive virus. Therefore, HPgV׳s inhibition of the interferon response could help promote HPgV persistence, which is associated with clinical benefits in HIV-infected patients. Our results also imply that HCV protease inhibitors should not interfere with the beneficial effects of HPgV in HPgV/HCV/HIV infected patients.

Deep sequencing identifies two genotypes and high viral genetic diversity of human pegivirus (GB virus C) in rural Ugandan patients

Human pegivirus (HPgV), formerly 'GB virus C' or 'hepatitis G virus', is a member of the genus Flavivirus (Flaviviridae) that has garnered significant attention due to its inhibition of HIV, including slowing disease progression and prolonging survival in HIV-infected patients. Currently, there are six proposed HPgV genotypes that have roughly distinct geographical distributions. Genotypes 2 and 3 are the most comprehensively characterized, whereas those genotypes occurring on the African continent, where HPgV prevalence is highest, are less well studied. Using deep sequencing methods, we identified complete coding HPgV sequences in four of 28 patients (14.3%) in rural Uganda, east Africa. One of these sequences corresponds to genotype 1 and is the first complete genome of this genotype from east Africa. The remaining three sequences correspond to genotype 5, a genotype that was previously considered exclusively South African. All four positive samples were collected within a geographical area of less than 25 km(2), showing that multiple HPgV genotypes co-circulate in this area. Analysis of intra-host viral genetic diversity revealed that total single-nucleotide polymorphism frequency was approximately tenfold lower in HPgV than in hepatitis C virus. Finally, one patient was co-infected with HPgV and HIV, which, in combination with the high prevalence of HIV, suggests that this region would be a useful locale to study the interactions and co-evolution of these viruses.

GB virus type C E2 protein inhibits human immunodeficiency virus type 1 assembly through interference with HIV-1 gag plasma membrane targeting

GB virus type C (GBV-C) is a single-stranded positive-sense RNA virus classified in the Flaviviridae family. Persistent coinfection with GBV-C is associated with lower human immunodeficiency virus type 1 (HIV-1) load, higher CD4(+) T-cell count, and prolonged survival in HIV-1 coinfected patients. The GBV-C envelope glycoprotein E2 has been reported to interfere with HIV-1 entry. In this study, we showed that the expression of GBV-C E2 inhibited HIV-1 Gag assembly and release. Expression of glycosylated GBV-C E2 inhibited HIV-1 Gag precursor processing, resulting in lower production of CAp24 and MAp17, while the overall expression level of the Gag precursor Pr55 remained unchanged. Membrane floatation gradient and indirect immunofluorescence confocal microscopy analysis showed that glycosylated E2 disrupted HIV-1 Gag trafficking to the plasma membrane, resulting in Gag accumulation in subcellular compartments. This interference in HIV-1 Gag trafficking led to diminished HIV-1 particle production, which is a critical step for HIV-1 to infect new host cells. These findings shed light on a novel mechanism used by GBV-C E2 to inhibit HIV-1 replication and may provide insight into new approaches for suppressing HIV-1 replication.

Chimpanzee GB virus C and GB virus A E2 envelope glycoproteins contain a peptide motif that inhibits human immunodeficiency virus type 1 replication in human CD4⁺ T-cells

GB virus type C (GBV-C) is a lymphotropic virus that can cause persistent infection in humans. GBV-C is not associated with any disease, but is associated with reduced mortality in human immunodeficiency virus type 1 (HIV-1)-infected individuals. Related viruses have been isolated from chimpanzees (GBV-Ccpz) and from New World primates (GB virus type A, GBV-A). These viruses are also capable of establishing persistent infection. We determined the nucleotide sequence encoding the envelope glycoprotein (E2) of two GBV-Ccpz isolates obtained from the sera of captive chimpanzees. The deduced GBV-Ccpz E2 protein differed from human GBV-C by 31 % at the amino acid level. Similar to human GBV-C E2, expression of GBV-Ccpz E2 in a tet-off human CD4(+) Jurkat T-cell line significantly inhibited the replication of diverse HIV-1 isolates. This anti-HIV-replication effect of GBV-Ccpz E2 protein was reversed by maintaining cells in doxycycline to reduce E2 expression. Previously, we found a 17 aa region within human GBV-C E2 that was sufficient to inhibit HIV-1. Although GBV-Ccpz E2 differed by 3 aa differences in this region, the chimpanzee GBV-C 17mer E2 peptide inhibited HIV-1 replication. Similarly, the GBV-A peptide that aligns with this GBV-C E2 region inhibited HIV-1 replication despite sharing only 5 aa with the human GBV-C E2 sequence. Thus, despite amino acid differences, the peptide region on both the GBV-Ccpz and the GBV-A E2 protein inhibit HIV-1 replication similar to human GBV-C. Consequently, GBV-Ccpz or GBV-A infection of non-human primates may provide an animal model to study GB virus-HIV interactions.

Role of GB virus C in modulating HIV disease

GB virus C (GBV-C) is a member of the Flaviviridae family and the most closely related human virus to HCV. However, GBV-C does not replicate in hepatocytes, but rather in lymphocytes. GBV-C has a worldwide distribution and is transmitted sexually, parenterally and through mother-to-child transmission. Thus, co-infection with HCV and HIV is common. Until now, no human disease has been associated with GBV-C infection. However, there are several reports of a beneficial effect of GBV-C on HIV disease progression in vivo. Different mechanisms to explain these observations have been proposed, including modification of antiviral cytokine production, HIV co-receptor expression, direct inhibition of HIV-1 entry, T-cell activation and Fas-mediated apoptosis. Further understanding of these mechanisms may open new strategies for the treatment of HIV/AIDS.

Characterization of a peptide domain within the GB virus C envelope glycoprotein (E2) that inhibits HIV replication

GB virus C (GBV-C) infection is associated with prolonged survival in HIV-infected cohorts, and GBV-C E2 protein inhibits HIV entry when added to CD4+ T cells. To further characterize E2 effects on HIV replication, stably transfected Jurkat cell lines expressing GBV-C E2 or control sequences were infected with HIV and replication was measured. HIV replication (all 6 isolates studied) was inhibited in all cell lines expressing a region of 17 amino acids of GBV-C E2, but not in cell lines expressing E2 without this region. In contrast, mumps and yellow fever virus replication was not inhibited by E2 protein expression. Synthetic GBV-C E2 17mer peptides did not inhibit HIV replication unless they were fused to a tat-protein-transduction-domain (TAT) for cellular uptake. These data identify the region of GBV-C E2 protein involved in HIV inhibition, and suggest that this GBV-C E2 peptide must gain entry into the cell to inhibit HIV.

The GB virus C (GBV-C) NS3 serine protease inhibits HIV-1 replication in a CD4+ T lymphocyte cell line without decreasing HIV receptor expression

INTRODUCTION

Persistent infection with GBV-C (GB Virus C), a non-pathogenic virus related to hepatitis C virus (HCV), prolongs survival in HIV infection. Two GBV-C proteins, NS5A and E2, have been shown previously to inhibit HIV replication in vitro. We investigated whether the GBV-C NS3 serine protease affects HIV replication.

RESULTS

GBV-C NS3 protease expressed in a human CD4+ T lymphocyte cell line significantly inhibited HIV replication. Addition of NS4A or NS4A/4B coding sequence to GBV-C NS3 increased the effect on HIV replication. Inhibition of HIV replication was dose-dependent and was not mediated by increased cell toxicity. Mutation of the NS3 catalytic serine to alanine resulted in loss of both HIV inhibition and protease activity. GBV-C NS3 expression did not measurably decrease CD4 or CXCR4 expression.

CONCLUSION

GBV-C NS3 serine protease significantly inhibited HIV replication without decreasing HIV receptor expression. The requirement for an intact catalytic serine at the active site indicates that inhibition was mediated by proteolytic cleavage of an unidentified target(s).

Peptides derived from a distinct region of GB virus C glycoprotein E2 mediate strain-specific HIV-1 entry inhibition

The nonpathogenic human GB virus C (GBV-C), a member of the Flaviviridae, is highly prevalent in individuals with HIV-1 infections or with parenteral and sexual risk factors. Long-term GBV-C viremia has been associated with better survival or improved diagnosis in several epidemiological studies. In a previous study we reported that the E2 glycoprotein of GBV-C interferes with HIV-1 entry in vitro. To address the question what region of the E2 protein is involved in suppression of HIV-1 replication, we performed an E2-derived peptide scanning and determined the HIV-inhibitory activity of each peptide in HIV replication assays. We demonstrate here that peptides representing the N-terminal part of the E2 protein from amino acids (aa) 29 to 72 are able to inhibit efficiently HIV-1 replication in vitro. In particular, the peptides P6-2 (representing the E2-region from aa 45 to 64) and P4762 (aa 37 to 64) showed the highest potency in HIV replication assays performed on TZM-bl cells with 50% inhibitory concentrations between 0.1 and 2 μM. However, primary HIV-1 isolates representing clades A to H showed a high variability in their sensitivity to E2 peptides. Pseudovirus inhibition assays revealed that the sensitivity is determined by the gp120/gp41 envelope proteins. Using HIV-1 BlaM-Vpr-based fusion assays, we demonstrate that the E2-derived peptides prevent HIV-1 binding or fusion, presumably via interaction with the HIV-1 particle. Together, these findings reveal a new mechanism of viral interference, suggesting that the envelope protein E2 of GBV-C target directly HIV-1 particles to avoid entry of these virions.

Contrasting roles for TLR ligands in HIV-1 pathogenesis

The first line of a host's response to various pathogens is triggered by their engagement of cellular pattern recognition receptors (PRRs). Binding of microbial ligands to these receptors leads to the induction of a variety of cellular factors that alter intracellular and extracellular environment and interfere directly or indirectly with the life cycle of the triggering pathogen. Such changes may also affect any coinfecting microbe. Using ligands to Toll-like receptors (TLRs) 5 and 9, we examined their effect on human immunodeficiency virus (HIV)-1 replication in lymphoid tissue ex vivo. We found marked differences in the outcomes of such treatment. While flagellin (TLR5 agonist) treatment enhanced replication of CC chemokine receptor 5 (CCR 5)-tropic and CXC chemokine receptor 4 (CXCR4)-tropic HIV-1, treatment with oligodeoxynucleotide (ODN) M362 (TLR9 agonist) suppressed both viral variants. The differential effects of these TLR ligands on HIV-1 replication correlated with changes in production of CC chemokines CCL3, CCL4, CCL5, and of CXC chemokines CXCL10, and CXCL12 in the ligand-treated HIV-1-infected tissues. The nature and/or magnitude of these changes were dependent on the ligand as well as on the HIV-1 viral strain. Moreover, the tested ligands differed in their ability to induce cellular activation as evaluated by the expression of the cluster of differentiation markers (CD) 25, CD38, CD39, CD69, CD154, and human leukocyte antigen D related (HLA)-DR as well as of a cell proliferation marker, Ki67, and of CCR5. No significant effect of the ligand treatment was observed on apoptosis and cell death/loss in the treated lymphoid tissue ex vivo. Our results suggest that binding of microbial ligands to TLRs is one of the mechanisms that mediate interactions between coinfected microbes and HIV-1 in human tissues. Thus, the engagement of appropriate TLRs by microbial molecules or their mimetic might become a new strategy for HIV therapy or prevention.

Viruses within the Flaviviridae decrease CD4 expression and inhibit HIV replication in human CD4+ cells

Viral infections alter host cell homeostasis and this may lead to immune evasion and/or interfere with the replication of other microbes in coinfected hosts. Two flaviviruses are associated with a reduction in HIV replication or improved survival in HIV-infected people (dengue virus (DV) and GB virus type C (GBV-C)). GBV-C infection and expression of the GBV-C nonstructural protein 5A (NS5A) and the DV NS5 protein in CD4(+) T cells inhibit HIV replication in vitro. To determine whether the inhibitory effect on HIV replication is conserved among other flaviviruses and to characterize mechanism(s) of HIV inhibition, the NS5 proteins of GBV-C, DV, hepatitis C virus, West Nile virus, and yellow fever virus (YFV; vaccine strain 17D) were expressed in CD4(+) T cells. All NS5 proteins inhibited HIV replication. This correlated with decreased steady-state CD4 mRNA levels and reduced cell surface CD4 protein expression. Infection of CD4(+) T cells and macrophages with YFV (17D vaccine strain) also inhibited HIV replication and decreased CD4 gene expression. In contrast, mumps virus was not inhibited by the expression of flavivirus NS5 protein or by YFV infection, and mumps infection did not alter CD4 mRNA or protein levels. In summary, CD4 gene expression is decreased by all human flavivirus NS5 proteins studied. CD4 regulation by flaviviruses may interfere with innate and adaptive immunity and contribute to in vitro HIV replication inhibition. Characterization of the mechanisms by which flaviviruses regulate CD4 expression may lead to novel therapeutic strategies for HIV and immunological diseases.

Inhibition of HIV-1 replication in human monocyte-derived macrophages by parasite Trypanosoma cruzi

BACKGROUND

Cells of monocyte/macrophage lineage are one of the major targets of HIV-1 infection and serve as reservoirs for viral persistence in vivo. These cells are also the target of the protozoa Trypanosoma cruzi, the causative agent of Chagas disease, being one of the most important endemic protozoonoses in Latin America. It has been demonstrated in vitro that co-infection with other pathogens can modulate HIV replication. However, no studies at cellular level have suggested an interaction between T. cruzi and HIV-1 to date.

METHODOLOGY/PRINCIPAL FINDINGS

By using a fully replicative wild-type virus, our study showed that T. cruzi inhibits HIV-1 antigen production by nearly 100% (p<0.001) in monocyte-derived macrophages (MDM). In different infection schemes with luciferase-reporter VSV-G or BaL pseudotyped HIV-1 and trypomastigotes, T. cruzi induced a significant reduction of luciferase level for both pseudotypes in all the infection schemes (p<0.001), T. cruzi-HIV (>99%) being stronger than HIV-T. cruzi (approximately 90% for BaL and approximately 85% for VSV-G) infection. In MDM with established HIV-1 infection, T. cruzi significantly inhibited luciferate activity (p<0.01). By quantifying R-U5 and U5-gag transcripts by real time PCR, our study showed the expression of both transcripts significantly diminished in the presence of trypomastigotes (p<0.05). Thus, T. cruzi inhibits viral post-integration steps, early post-entry steps and entry into MDM. Trypomastigotes also caused a approximately 60-70% decrease of surface CCR5 expression on MDM. Multiplication of T. cruzi inside the MDM does not seem to be required for inhibiting HIV-1 replication since soluble factors secreted by trypomastigotes have shown similar effects. Moreover, the major parasite antigen cruzipain, which is secreted by the trypomastigote form, was able to inhibit viral production in MDM over 90% (p<0.01).

CONCLUSIONS/SIGNIFICANCE

Our study showed that T. cruzi inhibits HIV-1 replication at several replication stages in macrophages, a major cell target for both pathogens.

GB virus type C interactions with HIV: the role of envelope glycoproteins

GB virus C/hepatitis G virus (GBV-C/HGV) is the most closely related human virus to hepatitis C virus (HCV). GBV-C is lymphotropic and not associated with any known disease, although it is associated with improved survival in HIV-infected individuals. In peripheral blood mononuclear cells, GBV-C induces the release of soluble ligands for HIV entry receptors (RANTES, MIP-1a, MIP-1b and SDF-1), suggesting that GBV-C may interact with lymphocytes to induce a chemokine and/or cytokine milieu that is inhibitory to HIV infection. Expression of GBV-C envelope glycoprotein E2 in CD4+ T cells or addition of recombinant E2 to CD4 cells recapitulates the HIV inhibition seen with GBV-C infection. Like HCV E2, GBV-C E2 is predicted to be post-translationally processed in the endoplasmic reticulum and is involved with cell binding. The C-termini of GBV-C E1 and E2 proteins contain predicted transmembrane domains sharing features with HCV TM domains. To date, cellular receptor(s) for GBV-C E2 have not been identified. GBV-C E2-mediated HIV inhibition is dose-dependent and HIV replication is blocked at the binding and/or entry step. In addition, a putative GBV-C E2 fusion peptide interferes with HIV gp41 peptide oligomerization required for HIV-1 fusion, further suggesting that GBV-C E2 may inhibit HIV entry. Additional work is needed to identify the GBV-C E2 cellular receptor, characterize GBV-C E2 domains responsible for HIV inhibition, and to examine GBV-C E2-mediated fusion in the context of the entire envelope protein or viral-particles. Understanding the mechanisms of action may identify novel approaches to HIV therapy.

RNA interference effectively degrades mRNA and inhibits protein expression of GBV-C E2 gene in Huh7 cells

The GB virus C/hepatitis G virus (GBV-C/HGV) is a Flaviviridae member that despite its nonpathogenicity, has become of great interest given that it could inhibit the replication of the human immunodeficiency virus (HIV). Therefore, a better knowledge of the viral protein E2 has become our aim. In this study, a GBV-C model cell system (HuhEG) which expressing a fusion protein of the GBV-C E2 protein and enhanced green fluorescent protein (EGFP) stably was established. And the expression of these proteins was silenced effectively by the two E2 gene-specific siRNAs and an EGFP gene-specific siRNA. This inhibition is sequence-specific and extensive (90%). This HuhEG/specific siRNAs system can provide an approach for investigating the association between GBV-C E2 and HIV replication, which may be of potential value in the development of novel prophylactic or therapeutic agents for HIV infection.