Density analysis of hepatitis C virus particle population in the circulation of infected hosts: implications for virus neutralization or persistence

Polarization of granulocytic myeloid-derived suppressor cells by hepatitis C core protein is mediated via IL-10/STAT3 signalling

Myeloid-derived suppressor cells (MDSCs) have been described as suppressors of T-cell function in many malignancies. Impaired T-cell responses have been observed in patients with chronic hepatitis C virus infection (CHC), which is reportedly associated with the establishment of persistent HCV infection. Therefore, we hypothesized that MDSCs also play a role in chronic HCV infection. MDSCs in the peripheral blood of 206 patients with CHC and 20 healthy donors were analyzed by flow cytometry. Peripheral blood mononuclear cells (PBMCs) of healthy donors cultured with hepatitis C virus core protein (HCVc) were stimulated with or without interleukin 10 (IL-10). Compared to healthy donors and certain CHC patients with sustained viral response (SVR), CHC patients without SVR presented with a dramatic elevation of G-MDSCs with the HLA-DR^-/low CD33⁺ CD14^- CD11b⁺ phenotype in peripheral blood. The frequency of G-MDSCs in CHC patients was positively correlated with serum HCVc, and G-MDSCs were induced from healthy PBMCs by adding exogenous HCVc. Furthermore, we revealed a potential mechanism by which HCVc mediates G-MDSC polarization; activation of ERK1/2 resulting in IL-10 production and IL-10-activated STAT3 signalling. Finally, we confirmed that HCVc-induced G-MDSCs suppress the proliferation and production of IFN-γ in autologous T-cells. We also found that the frequency of G-MDSCs in serum was associated with CHC prognosis. HCVc maintains immunosuppression by promoting IL-10/STAT3-dependent differentiation of G-MDSCs from PBMCs, resulting in the impaired functioning of T-cells. G-MDSCs may thus be a promising biomarker for predicting prognosis of CHC patients.

Substitution in Amino Acid 70 of Hepatitis C Virus Core Protein Changes the Adipokine Profile via Toll-Like Receptor 2/4 Signaling

Background & Aims

It has been suggested that amino acid (aa) substitution at position 70 from arginine (70R) to glutamine (70Q) in the genotype 1b hepatitis C virus (HCV) core protein is associated with insulin resistance and worse prognosis. However, the precise mechanism is still unclear. The aim of this study was to investigate the impact of the substitution at position 70 in HCV core protein on adipokine production by murine and human adipocytes.

Methods

The influence of treatment with HCV core protein (70R or 70Q) on adipokine production by both 3T3-L1 and human adipocytes were examined with real-time PCR and enzyme-linked immunosorbent assay (ELISA), and triglyceride content was also analyzed. The effects of toll-like receptor (TLR)2/4 inhibition on IL-6 production by 3T3-L1 induced by HCV core protein were examined.

Results

IL-6 production was significantly increased and adiponectin production was reduced without a change in triglyceride content by treatment with 70Q compared to 70R core protein in both murine and human adipocytes. IL-6 induction of 3T3-L1 cells treated by 70Q HCV core protein was significantly inhibited with anti-TLR2 antibody by 42%, and by TLR4 inhibitor by 40%.

Conclusions

Our study suggests that extracellular HCV core protein with substitution at position 70 enhanced IL-6 production and reduced adiponectin production from visceral adipose tissue, which can cause insulin resistance, hepatic steatosis, and ultimately development of HCC.

Role of the exogenous HCV core protein in the interaction of human hepatocyte proliferation and macrophage sub-populations

BACKGROUND

The core protein of hepatitis C virus (HCV) is found in the cytoplasm and nuclei of infected cells, including hepatocytes and other cells in the liver. The core protein could be secreted as well. Resident liver macrophages are dependent on the tissue micro-environment and external stimuli to differentiate M1 and M2 hypotypes with distinct functions, and increased expression of the nuclear transcription factor STAT3 was seen in M2-polarized macrophages. In contrast to proinflammatory M1 macrophages, M2 macrophages serve beneficial roles in chronic inflammation, immunosuppression, and tumorigenesis.

METHODS

Monocyte-derived human macrophage line (mTHP-1) was treated with the exogenous HCV core protein. Next, the mTHP-1 culture supernatant or cell pellets were added to culture media of normal human liver cell line (L02).

RESULTS

Only the culture supernatant stimulated L02 cells proliferation, which was associated with phosphorylated ERK expression. Core protein activated mTHP-1 cells showed enhanced pro- and anti-inflammatory cytokines secretion, which was accompanied by high expression of phosphorylated NF-κB105 and NF-κB65. However, phosphorylated STAT1, and STAT3, which are normally associated with M1 and M2 macrophage polarization, and cell surface expression of CD206, CD14, CD16, and CD86, were unaltered. A transwell co-culture system showed that only in mTHP-1 co-cultured with L02 in the presence of exogenous core protein, were higher levels of phosphorylated STAT3 and CD206 seen.

CONCLUSIONS

We showed L02 cells proliferation was accelerated by the culture supernatant of mTHP-1 cells treated with the exogenous HCV core protein. The exogenous core protein mediated the interaction between macrophages and hepatocytes in co-culture, which enhanced the expression of phosphorylated STAT3 and CD206 in macrophages.

Phenotypic and functional alterations of primary human PBMCs induced by HCV non-enveloped capsid-like particles uptake

Hepatitis C virus non-enveloped particles circulate in the serum of HCV-infected patients and are believed to be involved in viral persistence. It was previously demonstrated that recombinant HCVne particles can efficiently enter T cells. In this study we investigated the effect of this entry on the phenotype and function of PBMCs, focused on the CD4+ and CD8+ T-cells. We have generated recombinant HCVne in the absence of other viral proteins. PBMCs from healthy donors were sampled after incubation either with HCVne or the control at different time points. Levels of expression of CD107a, CD25, CTLA-4, and T regulatory cells were estimated and cytokine expression and secretion were also monitored. Peripheral T cells expressed elevated CD127. The intracellular expression of the inhibitory marker CTLA-4 (CD152) increased significantly on peripheral T cells at late hours post-treatment, compared to the respective non-treated group. Despite the fact that there was an initial immune response due to HCVne uptake, T cells were driven to a partial exhausted phenotype. A significant induction of CD4+CD25+(hi)CD127-regulatory T cells at late hours was observed. Consistently, Foxp3+CD4+ T cells were also increased. In parallel, a significant transcriptional activation and increased secretion of IL-2, IL-10, and IFN-γ, was recorded. Moreover, mRNA transcription of TGF-β was considerably elevated. HCVne particles have the potential to shape the immune response by modifying specific phenotypic and functional markers mainly on CD4+ T cells and driving them to partial exhaustion as well as to Treg expansion.

Hepatitis C virus entry

Hepatitis C virus (HCV) is a hepatotropic virus and a major cause of chronic hepatitis and liver disease worldwide. Initial interactions between HCV virions and hepatocytes are required for productive viral infection and initiation of the viral life cycle. Furthermore, HCV entry contributes to the tissue tropism and species specificity of this virus. The elucidation of these interactions is critical, not only to understand the pathogenesis of HCV infection, but also to design efficient antiviral strategies and vaccines. This review summarizes our current knowledge of the host factors required for the HCV-host interactions during HCV binding and entry, our understanding of the molecular mechanisms underlying HCV entry into target cells, and the relevance of HCV entry for the pathogenesis of liver disease, antiviral therapy, and vaccine development.

Hepatitis C virus, cholesterol and lipoproteins--impact for the viral life cycle and pathogenesis of liver disease

Hepatitis C virus (HCV) is a leading cause of chronic liver disease, including chronic hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Hepatitis C infection associates with lipid and lipoprotein metabolism disorders such as hepatic steatosis, hypobetalipoproteinemia, and hypocholesterolemia. Furthermore, virus production is dependent on hepatic very-low-density lipoprotein (VLDL) assembly, and circulating virions are physically associated with lipoproteins in complexes termed lipoviral particles. Evidence has indicated several functional roles for the formation of these complexes, including co-opting of lipoprotein receptors for attachment and entry, concealing epitopes to facilitate immune escape, and hijacking host factors for HCV maturation and secretion. Here, we review the evidence surrounding pathogenesis of the hepatitis C infection regarding lipoprotein engagement, cholesterol and triglyceride regulation, and the molecular mechanisms underlying these effects.

Lipoprotein receptors and lipid enzymes in hepatitis C virus entry and early steps of infection

Viruses are obligate intracellular agents that depend on host cells for successful propagation, hijacking cellular machineries to their own profit. The molecular interplay between host factors and invading viruses is a continuous coevolutionary process that determines viral host range and pathogenesis. The hepatitis C virus (HCV) is a strictly human pathogen, causing chronic liver injuries accompanied by lipid disorders. Upon infection, in addition to protein-protein and protein-RNA interactions usual for such a positive-strand RNA virus, HCV relies on protein-lipid interactions at multiple steps of its life cycle to establish persistent infection, making use of hepatic lipid pathways. This paper focuses on lipoproteins in HCV entry and on receptors and enzymes involved in lipid metabolism that HCV exploits to enter hepatocytes.

Myeloid suppressor cells induced by hepatitis C virus suppress T-cell responses through the production of reactive oxygen species

Impaired T-cell responses in chronic hepatitis C virus (HCV) patients have been reported to be associated with the establishment of HCV persistent infection. However, the mechanism for HCV-mediated T-cell dysfunction is yet to be defined. Myeloid-derived suppressor cells (MDSCs) play a pivotal role in suppressing T-cell responses. In this study we examined the accumulation of MDSCs in human peripheral blood mononuclear cells (PBMCs) following HCV infection. We found that CD33(+) mononuclear cells cocultured with HCV-infected hepatocytes, or with HCV core protein, suppress autologous T-cell responses. HCV core-treated CD33(+) cells exhibit a CD14(+) CD11b(+/low) HLADR(-/low) phenotype with up-regulated expression of p47(phox) , a component of the NOX2 complex critical for reactive oxygen species (ROS) production. In contrast, immunosuppressive factors, arginase-1 and inducible nitric oxide synthase (iNOS), were not up-regulated. Importantly, treatment with an inactivator of ROS reversed the T-cell suppressive function of HCV-induced MDSCs. Lastly, PBMCs of chronic HCV patients mirror CD33(+) cells following treatment with HCV core where CD33(+) cells are CD14(+) CD11b(+) HLADR(-/low) , and up-regulate the expression of p47(phox).

CONCLUSION

These results suggest that HCV promotes the accumulation of CD33(+) MDSC, resulting in ROS-mediated suppression of T-cell responsiveness. Thus, the accumulation of MDSCs during HCV infection may facilitate and maintain HCV persistent infection.

HCV and the hepatic lipid pathway as a potential treatment target

Atherosclerosis has been described as a liver disease of the heart [1]. The liver is the central regulatory organ of lipid pathways but since dyslipidaemias are major contributors to cardiovascular disease and type 2 diabetes rather than liver disease, research in this area has not been a major focus for hepatologists. Virus-host interaction is a continuous co-evolutionary process [2] involving the host immune system and viral escape mechanisms [3]. One of the strategies HCV has adopted to escape immune clearance and establish persistent infection is to make use of hepatic lipid pathways. This review aims to: • update the hepatologist on lipid metabolism • review the evidence that HCV exploits hepatic lipid pathways to its advantage • discuss approaches to targeting host lipid pathways as adjunctive therapy.

Extracellular hepatitis C virus core protein activates STAT3 in human monocytes/macrophages/dendritic cells via an IL-6 autocrine pathway

Hepatitis C virus (HCV) infection is highly efficient in the establishment of persistent infection, which leads to the development of chronic liver disease and hepatocellular carcinoma. Impaired T cell responses with reduced IFN-γ production have been reported to be associated with persistent HCV infection. Extracellular HCV core is a viral factor known to cause HCV-induced T cell impairment via its suppressive effect on the activation and induction of pro-inflammatory responses by antigen-presenting cells (APCs). The activation of STAT proteins has been reported to regulate the inflammatory responses and differentiation of APCs. To further characterize the molecular basis for the regulation of APC function by extracellular HCV core, we examined the ability of extracellular HCV core to activate STAT family members (STAT1, -2, -3, -5, and -6). In this study, we report the activation of STAT3 on human monocytes, macrophages, and dendritic cells following treatment with extracellular HCV core as well as treatment with a gC1qR agonistic monoclonal antibody. Importantly, HCV core-induced STAT3 activation is dependent on the activation of the PI3K/Akt pathway. In addition, the production of multifunctional cytokine IL-6 is essential for HCV core-induced STAT3 activation. These results suggest that HCV core-induced STAT3 activation plays a critical role in the alteration of inflammatory responses by APCs, leading to impaired anti-viral T cell responses during HCV infection.

Adaptive immunity to the hepatitis C virus

The hepatitis C virus (HCV) is a global public health problem affecting approximately 2% of the human population. The majority of HCV infections (more than 70%) result in life-long persistence of the virus that substantially increases the risk of serious liver diseases, including cirrhosis and hepatocellular carcinoma. The remainder (less than 30%) resolves spontaneously, often resulting in long-lived protection from persistence upon reexposure to the virus. To persist, the virus must replicate and this requires effective evasion of adaptive immune responses. In this review, the role of humoral and cellular immunity in preventing HCV persistence, and the mechanisms used by the virus to subvert protective host responses, are considered.

Cellular models for the screening and development of anti-hepatitis C virus agents

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Characterization of hepatitis C RNA-containing particles from human liver by density and size

Hepatitis C virus (HCV) particles found in vivo are heterogeneous in density and size, but their detailed characterization has been restricted by the low titre of HCV in human serum. Previously, our group has found that HCV circulates in blood in association with very-low-density lipoprotein (VLDL). Our aim in this study was to characterize HCV RNA-containing membranes and particles in human liver by both density and size and to identify the subcellular compartment(s) where the association with VLDL occurs. HCV was purified by density using iodixanol gradients and by size using gel filtration. Both positive-strand HCV RNA (present in virus particles) and negative-strand HCV RNA (an intermediate in virus replication) were found with densities below 1.08 g ml⁻¹. Viral structural and non-structural proteins, host proteins ApoB, ApoE and caveolin-2, as well as cholesterol, triglyceride and phospholipids were also detected in these low density fractions. After fractionation by size with Superose gel filtration, HCV RNA and viral proteins co-fractionated with endoplasmic reticulum proteins and VLDL. Fractionation on Toyopearl, which separates particles with diameters up to 200 nm, showed that 78 % of HCV RNA from liver was >100 nm in size, with a positive-/negative-strand ratio of 6 : 1. Also, 8 % of HCV RNA was found in particles with diameters between 40 nm and 70 nm and a positive-/negative-strand ratio of 45 : 1. This HCV was associated with ApoB, ApoE and viral glycoprotein E2, similar to viral particles circulating in serum. Our results indicate that the association between HCV and VLDL occurs in the liver.

Hepatitis C virus entry and neutralization

The processes of hepatitis C virus (HCV) entry and antibody-mediated neutralization are intimately linked. The high frequency of neutralizing antibodies (nAbs) that inhibit E2-CD81 interaction(s) suggests that this is a major target for the humoral immune response. The observation that HCV can transmit to naive cells by means of CD81-dependent and -independent routes in vitro awaits further investigation to assess the significance in vivo but may offer new strategies for HCV to escape nAbs. The identification of claudins in the entry process highlights the importance of cell polarity in defining routes of HCV entry and release, with recent experiments suggesting a polarized route of viral entry into cells in vitro. In this review, the authors summarize the current understanding of the mechanism(s) defining HCV entry and the role of nAbs in controlling HCV replication.

Role of complement in immune regulation and its exploitation by virus

Complement is activated during the early phase of viral infection and promotes destruction of virus particles as well as the initiation of inflammatory responses. Recently, complement and complement receptors have been reported to play an important role in the regulation of innate as well as adaptive immune responses during infection. The regulation of host immune responses by complement involves modulation of dendritic cell activity in addition to direct effects on T-cell function. Intriguingly, many viruses encode homologs of complement regulatory molecules or proteins that interact with complement receptors on antigen-presenting cells and lymphocytes. The evolution of viral mechanisms to alter complement function may augment pathogen persistence and limit immune-mediated tissue destruction. These observations suggest that complement may play an important role in both innate and adaptive immune responses to infection as well as virus-mediated modulation of host immunity.

The scavenger receptor BI and its ligand, HDL: partners in crime against HCV neutralizing antibodies

Better knowledge of the viral and host factors that determine HCV clearance vs. persistence at the acute stage of infection is needed in order to improve antiviral therapy and develop efficient vaccines. Spontaneous HCV clearance is associated with a strong, early and broad cellular immune response. Yet, several observations suggest that antibody-mediated neutralisation occurs during HCV infection in vivo and that polyclonal antibodies to HCV can be protective. The recent development of HCV infection assays has confirmed that sera from HCV-infected patients neutralise infection in vitro. Recent studies have demonstrated that Nt-antibodies, of narrow specificity, are induced during the early phase of infection and could play a role in controlling viral infection or clearance. Yet, high-titre, broadly cross-reacting Nt-antibodies are readily detected in chronically infected patients, suggesting that their effectiveness is limited in patients who do not resolve the disease. The factors that mitigate the impact of the Nt-antibody response need to be clarified. Here we review some essential features of the Nt-antibody responses to HCV. We then discuss an original mechanism that HCV may use in vivo to attenuate Nt-antibodies, which involves the hyper-variable region-1 of the HCV-E2 glycoprotein, high-density lipoprotein (HDL) and the physiologic activity of the scavenger receptor BI, a receptor shared by both HCV and HDL.

Serum-derived hepatitis C virus infection of primary human hepatocytes is tetraspanin CD81 dependent

Hepatitis C virus-positive serum (HCVser, genotypes 1a to 3a) or HCV cell culture (JFH1/HCVcc) infection of primary normal human hepatocytes was assessed by measuring intracellular HCV RNA strands. Anti-CD81 antibodies and siRNA-CD81 silencing markedly inhibited (>90%) HCVser infection irrespective of HCV genotype, viral load, or liver donor, while hCD81-large intracellular loop (LEL) had no effect. However, JFH1/HCVcc infection of hepatocytes was modestly inhibited (40 to 60%) by both hCD81-LEL and anti-CD81 antibodies. In conclusion, CD81 is involved in HCVser infection of human hepatocytes, and comparative studies of HCVser versus JFH1/HCVcc infection of human hepatocytes and Huh-7.5 cells revealed that the cell-virion combination is determinant of the entry process.

Human apolipoprotein e is required for infectivity and production of hepatitis C virus in cell culture

Recent advances in reverse genetics of hepatitis C virus (HCV) made it possible to determine the properties and biochemical compositions of HCV virions. Sedimentation analysis and characterization of HCV RNA-containing particles produced in the cultured cells revealed that HCV virions cover a large range of heterogeneous densities in sucrose gradient. The fractions of low densities are infectious, while the higher-density fractions containing the majority of HCV virion RNA are not. HCV core protein and apolipoprotein B and apolipoprotein E (apoE) were detected in the infectious HCV virions. The level of apoE correlates very well with HCV infectivity. Both apoE- and HCV E2-specific monoclonal antibodies precipitated HCV, demonstrating that HCV virions contain apoE and E2 proteins. apoE-specific monoclonal antibodies efficiently neutralized HCV infectivity in a dose-dependent manner, resulting in a reduction of infectious HCV by nearly 4 orders of magnitude. The knockdown of apoE expression by specific small interfering RNAs (siRNAs) remarkably reduced the levels of intracellular as well as secreted HCV virions. The apoE siRNA suppressed HCV production by more than 100-fold at 50 nM. These findings demonstrate that apoE is required for HCV virion infectivity and production, suggesting that HCV virions are assembled as apoE-enriched lipoprotein particles. Our findings also identified apoE as a novel target for discovery and development of antiviral drugs and monoclonal antibodies to suppress HCV virion formation and infection.

The exchangeable apolipoprotein ApoC-I promotes membrane fusion of hepatitis C virus

Cell entry of hepatitis C virus (HCV) is strikingly linked to lipoproteins and their receptors. Particularly, high density lipoprotein (HDL) enhances infectivity of HCV by involving the lipid-transfer function of the scavenger receptor BI, a receptor for both HDL and HCV. Here, we demonstrate that apoC-I, an exchangeable apolipoprotein that predominantly resides in HDL, specifically enhances HCVcc and HCVpp infectivity and increases the fusion rates between viral and target membranes via a direct interaction with the HCV surface. We identify the hypervariable region 1, located at the N terminus of the HCV E2 glycoprotein, as an essential viral component that modulates apoC-I-mediated enhancement of HCV fusion properties. The affinity of apoC-I for the HCV membrane may predispose it for fusion with a target membrane via alterations of its outer phospholipid layer. Conversely, we found that excess apoC-I provided as lipoprotein-free protein induces the disruption of the HCV membrane and subsequent loss of infectivity. Furthermore, our data indicate that HDL neither interacts nor spontaneously exchanges apoC-I with HCV virions. Because apoC-I is not present in serum as a lipoprotein-free form, our results suggest that HDL-embedded apoC-I could be released from the lipoprotein particle through a fine-tuned mechanism regulated via a triple interplay between hypervariable region 1, HDL, and scavenger receptor BI, resulting in optimal apoC-I recruitment on the viral membrane. These results provide the first description of a host serum factor helping the fusion process of an enveloped virus.

Recent contributions of in vitro models to our understanding of hepatitis C virus life cycle

Hepatitis C virus is a human pathogen responsible for liver diseases including acute and chronic hepatitis, cirrhosis and hepatocellular carcinoma. Its high prevalence, the absence of a prophylactic vaccine and the poor efficiency of current therapies are huge medical problems. Since the discovery of the hepatitis C virus, our knowledge of its biology has been largely punctuated by the development of original models of research. At the end of the 1980s, the chimpanzee model led to cloning of the viral genome and the definition of infectious molecular clones. In 1999, a breakthrough was achieved with the development of a robust in vitro replication model named 'replicon'. This system allowed intensive research into replication mechanisms and drug discovery. Later, in 2003, pseudotyped retroviruses harbouring surface proteins of hepatitis C virus were produced to specifically investigate the viral entry process. It was only in 2005 that infectious viruses were produced in vitro, enabling intensive investigations into the entire life cycle of the hepatitis C virus. This review describes the different in vitro models developed to study hepatitis C virus, their contribution to current knowledge of the virus biology and their future research applications.

Evidence for cellular uptake of recombinant hepatitis C virus non-enveloped capsid-like particles

Although the hepatitis C virus (HCV) is an enveloped virus, naked nucleocapsids have been reported in the serum of infected patients, and most recently novel HCV subgenomes with deletions of the envelope proteins have been identified. However the significance of these findings remains unclear. In this study, we used the baculovirus expression system to generate recombinant HCV capsid-like particles, and investigated their possible interactions with cells. We show that expression of HCV core in insect cells can sufficiently direct the formation of capsid-like particles in the absence of the HCV envelope glycoproteins and of the 5' untranslated region. By confocal microscopy analysis, we provide evidence that the naked capsid-like particles could be uptaken by human hepatoma cells. Moreover, our findings suggest that they have the potential to produce cell-signaling effects.

The low-density lipoprotein receptor plays a role in the infection of primary human hepatocytes by hepatitis C virus

BACKGROUND/AIMS

The direct implication of low-density lipoprotein receptor (LDLR) in hepatitis C virus (HCV) infection of human hepatocyte has not been demonstrated. Normal primary human hepatocytes infected by serum HCV were used to document this point.

METHODS

Expression and activity of LDLR were assessed by RT-PCR and LDL entry, in the absence or presence of squalestatin or 25-hydroxycholesterol that up- or down-regulates LDLR expression, respectively. Infection was performed in the absence or presence of LDL, HDL, recombinant soluble LDLR peptides encompassing full-length (r-shLDLR4-292) or truncated (r-shLDLR4-166) LDL-binding domain, monoclonal antibodies against r-shLDLR4-292, squalestatin or 25-hydroxycholesterol. Intracellular amounts of replicative and genomic HCV RNA strands used as end point of infection were assessed by RT-PCR.

RESULTS

r-shLDLR4-292, antibodies against r-shLDLR4-292 and LDL inhibited viral RNA accumulation, irrespective of genotype, viral load or liver donor. Inhibition was greatest when r-shLDLR4-292 was present at the time of inoculation and gradually decreased as the delay between inoculation and r-shLDLR4-292 treatment increased. In hepatocytes pre-treated with squalestatin or 25-hydroxycholesterol before infection, viral RNA accumulation increased or decreased in parallel with LDLR mRNA expression and LDL entry.

CONCLUSIONS

LDLR is involved at an early stage in infection of normal human hepatocytes by serum-derived HCV virions.

Repression of interferon regulatory factor 1 by hepatitis C virus core protein results in inhibition of antiviral and immunomodulatory genes

Hepatitis C virus (HCV) proteins are known to interfere at several levels with both innate and adaptive responses of the host. A key target in these effects is the interferon (IFN) signaling pathway. While the effects of nonstructural proteins are well established, the role of structural proteins remains controversial. We investigated the effect of HCV structural proteins on the expression of interferon regulatory factor 1 (IRF-1), a secondary transcription factor of the IFN system responsible for inducing several key antiviral and immunomodulatory genes. We found substantial inhibition of IRF-1 expression in cells expressing the entire HCV replicon. Suppression of IRF-1 synthesis was mainly mediated by the core structural protein and occurred at the transcriptional level. The core protein in turn exerted a transcriptional repression of several interferon-stimulated genes, targets of IRF-1, including interleukin-15 (IL-15), IL-12, and low-molecular-mass polypeptide 2. These data recapitulate in a unifying mechanism, i.e., repression of IRF-1 expression, many previously described pathogenetic effects of HCV core protein and suggest that HCV core-induced IRF-1 repression may play a pivotal role in establishing persistent infection by dampening an effective immune response.

Differential biophysical properties of infectious intracellular and secreted hepatitis C virus particles

The recent development of a cell culture infection model for hepatitis C virus (HCV) permits the production of infectious particles in vitro. In this report, we demonstrate that infectious particles are present both within the infected cells and in the supernatant. Kinetic analysis indicates that intracellular particles constitute precursors of the secreted infectious virus. Ultracentrifugation analyses indicate that intracellular infectious viral particles are similar in size (approximately 65 to 70 nm) but different in buoyant density (approximately 1.15 to 1.20 g/ml) from extracellular particles (approximately 1.03 to 1.16 g/ml). These results indicate that infectious HCV particles are assembled intracellularly and that their biochemical composition is altered during viral egress.

High Density Lipoprotein Inhibits Hepatitis C Virus-neutralizing Antibodies by Stimulating Cell Entry via Activation of the Scavenger Receptor BI

Hepatitis C virus (HCV) exploits serum-dependent mechanisms that inhibit neutralizing antibodies. Here we demonstrate that high density lipoprotein (HDL) is a key serum factor that attenuates neutralization by monoclonal and HCV patient-derived polyclonal antibodies of infectious pseudo-particles (HCVpp) harboring authentic E1E2 glycoproteins and cell culture-grown genuine HCV (HCVcc). Over 10-fold higher antibody concentrations are required to neutralize either HCV-enveloped particles in the presence of HDL or human serum, and less than 3-5-fold reduction of infectious titers are obtained at saturating antibody concentrations, in contrast to complete inhibition in serum-free conditions. We show that HDL interaction with the scavenger receptor BI (SR-BI), a proposed cell entry co-factor of HCV and a receptor mediating lipid transfer with HDL, strongly reduces neutralization of HCVpp and HCVcc. We found that HDL activation of target cells strongly stimulates cell entry of viral particles by accelerating their endocytosis, thereby suppressing a 1-h time lag during which cell-bound virions are not internalized and can be targeted by antibodies. Compounds that inhibit lipid transfer functions of SR-BI fully restore neutralization by antibodies in human serum. We demonstrate that this functional HDL/SR-BI interaction only interferes with antibodies blocking HCV-E2 binding to CD81, a major HCV receptor, reflecting its prominent role during the cell entry process. Moreover, we identify monoclonal antibodies targeted to epitopes in the E1E2 complex that are not inhibited by HDL. Consistently, we show that antibodies targeted to HCV-E1 efficiently neutralize HCVpp and HCVcc in the presence of human serum.

Association between hepatitis C virus and very-low-density lipoprotein (VLDL)/LDL analyzed in iodixanol density gradients

Hepatitis C virus (HCV) RNA circulates in the blood of persistently infected patients in lipoviroparticles (LVPs), which are heterogeneous in density and associated with host lipoproteins and antibodies. The variability and lability of these virus-host complexes on fractionation has hindered our understanding of the structure of LVP and determination of the physicochemical properties of the HCV virion. In this study, HCV from an antibody-negative immunodeficient patient was analyzed using three fractionation techniques, NaBr gradients, isotonic iodixanol, and sucrose gradient centrifugation. Iodixanol gradients were shown to best preserve host lipoprotein-virus complexes, and all HCV RNA was found at densities below 1.13 g/ml, with the majority at low density, < or =1.08 g/ml. Immunoprecipitation with polyclonal antibodies against human ApoB and ApoE precipitated 91.8% and 95.0% of HCV with low density, respectively, suggesting that host lipoprotein is closely associated with HCV in a particle resembling VLDL. Immunoprecipitation with antibodies against glycoprotein E2 precipitated 25% of HCV with low density, providing evidence for the presence of E2 in LVPs. Treatment of serum with 0.5% deoxycholic acid in the absence of salt produced HCV with a density of 1.12 g/ml and a sedimentation coefficient of 215S. The diameters of these particles were calculated as 54 nm. Treatment of serum with 0.18% NP-40 produced HCV with a density of 1.18 g/ml, a sedimentation coefficient of 180S, and a diameter of 42 nm. Immunoprecipitation analysis showed that ApoB remained associated with HCV after treatment of serum with deoxycholic acid or NP-40, whereas ApoE was removed from HCV with these detergents.

Activation of Refractory T Cell Responses against Hepatitis C Virus Core Protein by Ablation of Interfering Hydrophobic Domains

Hepatitis C virus (HCV) is the major pathogen of chronic hepatitis and liver disease, but currently there are no prophylactic HCV vaccines available. The HCV core protein-encoding sequence is among the most conserved genes in the HCV genome, making it a prime candidate for a component of a vaccine. The core protein localizes to the endoplasmic reticulum (ER) through a C-terminal hydrophobic region that is cotranslationally inserted into the ER membrane. Here we show that removal of the C-terminal hydrophobic region confers nuclear localization and enhances proteasomal degradation of the core protein in mammalian cells. This efficient protein proteolysis induces enhanced core-specific CD8(+) T cell responses in BALB/c mice immunized with plasmids expressing C-terminal deletions of the HCV core protein. These results suggest that more potent HCV vaccines can be achieved by targeting the core protein for proteasomal degradation by deletion of its C-terminal hydrophobic domain.

Signal peptide peptidase promotes the formation of hepatitis C virus non-enveloped particles and is captured on the viral membrane during assembly

The maturation of the core protein (C) of Hepatitis C virus (HCV) is controlled by the signal peptidase (sp) and signal peptide peptidase (spp) of the host. To date, it remains unknown whether spp cleavage influences viral infectivity and/or the assembly process. Here, evidence is provided that cleavage by spp is not required for assembly of nucleocapsid-like particles (NLPs) in yeast (Pichia pastoris). The immature NLPs (not processed by spp) show a density of 1.11 g ml(-1) on sucrose gradients and a diameter of 50 nm. Co-expression of human spp (hspp) with C generates the 21 kDa mature form of the protein and promotes the accumulation of non-enveloped particles. The amount of non-enveloped particles accumulating in the cell was correlated directly with the expression level of hspp. Furthermore, immunocapture studies showed that hspp was embedded in the membranes of enveloped particles. These results suggest that maturation of the C protein can occur after formation of the enveloped particles and that the abundance of hspp influences the types of particle accumulating in the cells.

Enveloped particles in the serum of chronic hepatitis C patients

HCV particles were isolated from the plasma of chronically infected patients. The virus was analysed by sucrose density gradient centrifugation. The fractions were tested for viral RNA, core antigen and envelope proteins by using a monoclonal antibody directed against the natural E1E2 complex (D32.10). Two populations of particles containing RNA plus core antigen were separated: the first with a density of 1.06-1.08 g/ml did not contain the envelope proteins; the second with a density between 1.17 and 1.21 g/ml expressed both E1 and E2 glycoproteins. Electron microscopy of the enveloped population after immunoprecipitation with D32.10 showed spherical particles with a rather featureless surface and with a diameter around 40 nm. Immuno-gold staining gave evidence that the E1E2 complex was indeed positioned at the surface of these particles.

Interaction of immune complexes isolated from hepatitis C virus-infected individuals with human cell lines

We investigated the interaction of immune complexes (IC) isolated from hepatitis C virus (HCV)-infected individuals with several cell lines that differentially express Fc receptors, and analyzed viral infection by the presence of HCV RNA sequences. Monocytic (U937 and Monomac-6) and lymphocytic (MOLT-4 and Jurkat) cell lines were incubated with interferon- plus phorbol myristate acetate to stimulate the expression of Fc receptors before addition of IC. Cell interaction with IC was monitored by flow cytometry. Positive cell fluorescence was detected in U937 and Monomac-6 cells [mean fluorescence intensity (MFI) 10.56+/-0.8 and 11.60+/-0.8, respectively]. Incubation of cells with monoclonal antibodies against Fc receptors for IgG before addition of IC decreased MFI in both cell lines (U937 2.1+/-0.5, Monomac-6 4.4+/-0.8, P<0.001), indicating that cell-IC interaction through these receptors was inhibited. In particular, the blockage of FcgammaRII was responsible for this effect. No binding of IC with either MOLT-4 or Jurkat cell lines was detected, which correlated with a very low Fc receptor expression. HCV RNA sequences were identified in the cells up to 120 h of post incubation with IC. These results suggest that IC can mediate entry of HCV to both U-937 and Monomac-6 cell lines mainly through the FcgammaRII.

Hepatitis C virus and hepatitis B virus bind to heparin: purification of largely IgG-free virions from infected plasma by heparin chromatography

Binding to heparin of hepatitis C virus (HCV) and hepatitis B virus (HBV) from chronic carriers was investigated. Eighty per cent of HCV RNA from an agammaglobulinaemic patient (IgG-free virus) was retained on immobilized heparin and eluted with > or =0.4 M NaCl, in contrast to approximately 20 % from immunocompetent chronic carriers (with < or =8 % IgG-free virus). Increased binding to heparin of the HCV fraction that was not retained by a protein G column suggested that antibodies complexed to the virions partially inhibited the interaction. A higher proportion (15-80 %) of HBV from chronic carriers bound to heparin and eluted with > or =0.4 M NaCl. After washing of the heparin columns with 0.3 M NaCl, <1 % of total plasma proteins co-eluted with HCV or HBV. By this one-step heparin chromatography, without ultracentrifugation, IgG-free HCV and IgG-free HBV were preferentially purified from human plasma by 1000-fold and greater than 500-fold, respectively. Following assessment with an anti-E2 envelope protein antibody, the amount of immunoprecipitated HCV particles after heparin purification was similar to that in the original plasma, suggesting that undamaged virions were purified. This was further supported by heparin-purified HCV binding to lymphocyte cell lines in a dose-dependent manner. Intact HBV particles were detected by electron microscopy. It was concluded that HCV and HBV from chronically infected patients bind to heparin, the closest homologue of liver heparan sulfate, and that heparin chromatography is an efficient and gentle method for purifying these viruses from human plasma. In the absence of cell-culture systems or alternative robust purification methods, heparin chromatography may help greatly in binding and infectivity studies.

Hepatitis C virus core selectively suppresses interleukin-12 synthesis in human macrophages by interfering with AP-1 activation

Hepatitis C virus (HCV) is remarkably efficient at establishing persistent infection, suggesting that it has evolved one or more strategies aimed at evading the host immune response. T cell responses, including interferon-gamma production, are severely suppressed in chronic HCV patients. The HCV core protein has been previously shown to circulate in the bloodstream of HCV-infected patients and inhibit host immunity through an interaction with gC1qR. To determine the role of the HCV core-gC1qR interaction in modulation of inflammatory cytokine production, we examined interleukin (IL)-12 production, which is critical for the induction of interferon-gamma synthesis, in lipopolysaccharide-stimulated human monocyte/macrophages. We found that core protein binds the gC1qR displayed on the cell surface of monocyte/macrophages and inhibits the production of IL-12p70 upon lipopolysaccharide stimulation. This inhibition was found to be selective in that HCV core failed to affect the production of IL-6, IL-8, IL-1beta, and tumor necrosis factor alpha. In addition, suppression of IL-12 production by core protein occurred at the transcriptional level by inhibition of IL-12p40 mRNA synthesis. Importantly, core-induced inhibition of IL-12p40 mRNA synthesis resulted from impaired activation of AP-1 rather than enhanced IL-10 production. These results suggest that the HCV core-gC1qR interaction may play a pivotal role in establishing persistent infection by dampening TH1 responses.

The molecular basis of HCV-mediated immune dysregulation

Chronic hepatitis C virus (HCV) infection, which occurs in over 85% of patients and causes mild to severe liver disease, is a growing burden to health systems worldwide. The propensity of HCV to establish persistent infection suggests that the virus, which is non-cytopathic, has evolved one or more mechanisms aimed at evading host immunity. In addition to the appearance of quasispecies, which may arise under selective pressure during B and T cell responses, HCV gene products interact with host proteins in order to subvert immune surveillance. Gaining insight into these interactions may provide the basis for novel therapies aimed at preventing chronic HCV infection.

Non-enveloped HCV core protein as constitutive antigen of cold-precipitable immune complexes in type II mixed cryoglobulinaemia

Hepatitis C virus (HCV) infection has been detected in a large proportion of patients with mixed cryoglobulinaemia (MC). Circulating 'free' non-enveloped HCV core protein has been demonstrated in HCV-infected patients, and this suggests its possible involvement in the formation of cryoprecipitable immune complexes (ICs). Thirty-two anti-HCV, HCV RNA-positive patients with type II MC were evaluated. Non-enveloped HCV core protein, HCV RNA sequences, total IgM, rheumatoid factor (RF) activity, IgG and IgG subclasses, C3 and C4 fractions, C1q protein and C1q binding activity were assessed in both cryoprecipitates and supernatants. Non-enveloped HCV core protein was demonstrated in 30 of 32 (93.7%) type II MC patients. After separation of cold-precipitable material, the protein was removed completely from supernatant in 12 patients (40%), whereas it was enriched in the cryoprecipitates of the remaining 18. In addition, HCV RNA and IgM molecules with RF activity were concentrated selectively in the cryoprecipitates. Differential precipitation was found for both total IgG and IgG subclasses, as they were less represented in the cryoglobulins and no selective enrichment was noted. Immunological characterization of HCV core protein-containing cryoprecipitating ICs after chromatographic fractionation showed that the IgM monoclonal component had RF activity, whereas anti-HCV core reactivity was confined to the IgG fraction. C1q enrichment in addition to high avidity of ICs for C1q binding in the cryoprecipitates suggest that complement activation may occur through the C1q protein pathway. The present data demonstrate that non-enveloped HCV core protein is a constitutive component of cryoprecipitable ICs in type II MC patients.

CD81 engineered with endocytotic signals mediates HCV cell entry: implications for receptor usage by HCV in vivo

Although CD81 has been shown to bind HCV E2 protein, its role as a receptor for HCV remains controversial. In this study, we constructed two CD81 chimeras by linking the cytoplasmic domains of recycling surface receptors, low-density lipoprotein receptor (LDLR), and transferrin receptor (TfR), respectively, to CD81 and compared their internalization properties to wild-type CD81. Binding experiments with anti-hCD81 antibody showed that cell-surface CD81 chimeric receptors were internalized much more efficiently than wild-type CD81. In addition, CD81 chimeras, but not wild-type CD81, could internalize recombinant E2 protein and E2-enveloped viral particles from the serum of HCV-infected patients into Huh7 liver cells. The latter resulted in persistent positive-strand viral RNA and accumulation of replication intermediates, negative-strand viral RNA, in the infected cells, suggesting that the internalized viruses have undergone replication. Therefore, it appeared that CD81, possibly in association with a liver-specific endocytotic protein(s), represents one of the pathways by which HCV can infect hepatocytes.

Nonimmune complexed HCV RNA titer in serum as a predictor of interferon response in patients with chronic hepatitis C

OBJECTIVE

Hepatitis C virus (HCV) has been reported to exist in the circulation of patients in various forms such as free virions, immune complexes, and nucleocapsids. To clarify the clinical significance of serum HCV titers according to the forms of virus particles, we evaluated the immune complexed (IC) and nonimmune complexed (NIC) HCV RNA titers in 77 chronic hepatitis patients treated with interferon (IFN).

METHODS

IC and NIC forms in pretreatment serum were separated by immunoprecipitation using antihuman immunoglobulin antibody, and quantified by reverse transcription polymerase chain reaction.

RESULTS

Serum titers of NIC HCV RNA were correlated with those of whole serum HCV RNA (r = 0.96, p < 0.01) and IC HCV RNA (r = 0.98, p < 0.01), but they were not with the aminotransferase levels, gamma-globulin concentration, and grading or staging of liver histology. Nonresponders to IFN had significantly high NIC HCV RNA titers compared with sustained responders (10(4.93 +/- 0.81) copies/ml vs 10(4.06 +/- 0.69) copies/ml, p < 0.01). It is noteworthy that the relative amount of NIC HCV RNA to whole serum HCV RNA was also significantly higher in nonresponders than in sustained responders (0.66 +/- 0.10 vs 0.50 +/- 0.11, p < 0.0001). Multivariate analysis showed that low NIC HCV RNA titer (p < 0.01) and genotype 2 (p = 0.02) were independent variables contributing to sustained response to IFN, but the whole serum HCV RNA titer was not.

CONCLUSIONS

Pretreatment NIC HCV RNA titer is a more reliable predictive marker than genotype or whole serum HCV RNA of a sustained response to IFN monotherapy. This finding suggests that humoral immunity may affect the response to IFN.

Role of the asialoglycoprotein receptor in binding and entry of hepatitis C virus structural proteins in cultured human hepatocytes

We used a baculovirus-based system to prepare structural proteins of hepatitis C virus (HCV) genotype 1a. Binding of this preparation to cultured human hepatic cells was both dose dependent and saturable. This binding was decreased by calcium depletion and was partially prevented by ligands of the asialoglycoprotein receptor (ASGP-R), thyroglobulin, asialothyroglobulin, and antibody against a peptide in the carbohydrate recognition domain of ASGP-R but not preimmune antibody. Uptake by hepatocytes was observed with both radiolabeled and dye-labeled HCV structural proteins. With hepatocytes expressing the hH1 subunit of the ASGP-R fused to green fluorescent protein, we could show by confocal microscopy that dye stain cointernalized with the fusion protein in an area surrounding the nucleus. Internalization was more efficient with a preparation containing p7 than with one that did not. The two preparations bound to transfected 3T3-L1 cells expressing either both (hH1 and hH2) subunits of the ASGP-R (3T3-22Z cells) or both hH1 and a functionally defective variant of hH2 (3T3-24X cells) but not to parental cells. Additionally, uptake of dye-labeled preparation containing p7 was observed with 3T3-22Z cells but not with 3T3-L1 or 3T3-24X cells or with the preparation lacking p7, suggesting that p7 regulates the internalization properties of HCV structural proteins. Our observations suggest that HCV structural proteins bind to and cointernalize with the ASGP-R in cultured human hepatocytes.

Hepatitis C virus particles of different density in the blood of chronically infected immunocompetent and immunodeficient patients: Implications for virus clearance by antibody

The purpose of this study was to analyse the influence of the humoral immune response on the generation and clearance of hepatitis C virus (HCV) RNA containing particles in the blood of chronically infected patients. Blood samples were fractionated by sequential flotation ultracentrifugation and HCV RNA was recovered in three fractions: low density of < 1.063 g/ml, intermediate density of 1.063-1.21 g/ml, and high density of > 1.21 g/ml. Serum low-density lipoproteins co-fractionated with the low-density particles, and high-density lipoproteins co-fractionated with the intermediate-density particles. Immunoglobulins were found exclusively in the high-density fractions. In patients with congenital immunodeficiencies, with no or low serum antibodies to the virus, mean HCV RNA titres were equal in each fraction, at approximately 10(5) IU/ml. In antibody-positive, immunocompetent patients, however, virus titres in the low-density fraction and those in the high-density fraction were reduced or absent in most patients, suggesting that virus particles in these fractions are subject to antibody-mediated clearance. Particles of intermediate density were approximately equal in titre in both patient groups, suggesting that these particles are neither generated by, nor cleared, as a result of the humoral immune response. Immunoprecipitation experiments indicated that particles of intermediate density were not complexed with either high-density lipoprotein or immunoglobulins. Elucidation of the mechanisms by which these particles are generated and maintained in the blood may provide valuable insight into the mechanism of virus persistence.

Characterization of low- and very-low-density hepatitis C virus RNA-containing particles

The presence of hepatitis C virus (HCV) RNA-containing particles in the low-density fractions of plasma has been associated with high infectivity. However, the nature of circulating HCV particles and their association with immunoglobulins or lipoproteins as well as the characterization of cell entry have all been subject to conflicting reports. For a better analysis of HCV RNA-containing particles, we quantified HCV RNA in the low-density fractions of plasma corresponding to the very-low-density lipoprotein (VLDL), intermediate-density lipoprotein, and low-density lipoprotein (LDL) fractions from untreated chronically HCV-infected patients. HCV RNA was always found in at least one of these fractions and represented 8 to 95% of the total plasma HCV RNA. Surprisingly, immunoglobulins G and M were also found in the low-density fractions and could be used to purify the HCV RNA-containing particles (lipo-viro-particles [LVP]). Purified LVP were rich in triglycerides; contained at least apolipoprotein B, HCV RNA, and core protein; and appeared as large spherical particles with a diameter of more than 100 nm and with internal structures. Delipidation of these particles resulted in capsid-like structures recognized by anti-HCV core protein antibody. Purified LVP efficiently bind and enter hepatocyte cell lines, while serum or whole-density fractions do not. Binding of these particles was competed out by VLDL and LDL from noninfected donors and was blocked by anti-apolipoprotein B and E antibodies, whereas upregulation of the LDL receptor increased their internalization. These results suggest that the infectivity of LVP is mediated by endogenous proteins rather than by viral components providing a mechanism of escape from the humoral immune response.

Immunoprophylaxis of hepatitis C virus infection

Because hepatitis C virus is etiologically involved in about half the cases of the world's most common cancer, hepatocellular carcinoma, and because this virus is likely to continue to spread in most of the developing world for many years, the authors believe that development of a prophylactic vaccine is imperative. Numerous approaches are available to overcome the many impediments which make the development of an HCV vaccine difficult. Such impediments include the many viral genotypes and quasispecies of HCV and the association of virions with host lipids. It is likely that overcoming these impediments will require a vaccine which induces a strong cell-mediated response. The most promising approach seems to be DNA-based immunization or a prime-boost regimen with DNA priming and boosting with a viral vector. Potentiation of responses with adjuvant strategies will probably be necessary. Hepatitis C virus immunization is in an early stage of development. Given the explosive growth in the understanding of immunology, progress should be rapid.

The dynamics of hepatitis C virus binding to platelets and 2 mononuclear cell lines

Hepatitis C virus (HCV) binds to platelets in chronically infected patients where free HCV constitutes only about 5% of total circulating virus. Free HCV preferentially binds to human mononuclear cell lines but free and complexed virus binds equally to platelets. The extent of free HCV binding to human Molt-4 T cells (which express CD81) and to human promonocytic U937 cells or to platelets (which do not express CD81) was similar. The binding of free HCV to the cell lines was saturated at a virus dose of 1 IU HCV RNA per cell but binding to platelets was not saturable. Human anti-HCV IgG, but not anti-CD81, markedly inhibited HCV binding to target cells in a dose-dependent manner. Human antibodies to HCV hypervariable region 1 of E2 glycoprotein partially inhibited viral binding to target cells. Recombinant E2 also inhibited viral binding to target cells in a dose-dependent manner, with the efficacy of this decreasing in the rank order of Molt-4 cells more than U937 cells more than platelets. In contrast to HCV, recombinant E2 bound to Molt-4 cells to an extent markedly greater than that apparent with U937 cells or platelets. These results suggest that the binding of HCV to blood cells is mediated by multiple cell surface receptors and that recombinant E2 binding may not be representative of the interaction of the intact virus with target cells.

The dynamics of hepatitis C virus binding to platelets and 2 mononuclear cell lines

Hepatitis C virus (HCV) binds to platelets in chronically infected patients where free HCV constitutes only about 5% of total circulating virus. Free HCV preferentially binds to human mononuclear cell lines but free and complexed virus binds equally to platelets. The extent of free HCV binding to human Molt-4 T cells (which express CD81) and to human promonocytic U937 cells or to platelets (which do not express CD81) was similar. The binding of free HCV to the cell lines was saturated at a virus dose of 1 IU HCV RNA per cell but binding to platelets was not saturable. Human anti-HCV IgG, but not anti-CD81, markedly inhibited HCV binding to target cells in a dose-dependent manner. Human antibodies to HCV hypervariable region 1 of E2 glycoprotein partially inhibited viral binding to target cells. Recombinant E2 also inhibited viral binding to target cells in a dose-dependent manner, with the efficacy of this decreasing in the rank order of Molt-4 cells more than U937 cells more than platelets. In contrast to HCV, recombinant E2 bound to Molt-4 cells to an extent markedly greater than that apparent with U937 cells or platelets. These results suggest that the binding of HCV to blood cells is mediated by multiple cell surface receptors and that recombinant E2 binding may not be representative of the interaction of the intact virus with target cells.

Nonenveloped nucleocapsids of hepatitis C virus in the serum of infected patients

One of the characteristics of hepatitis C virus (HCV) is the high incidence of persistent infection. HCV core protein, in addition to forming the viral nucleocapsid, has multiple regulatory functions in host-cell transcription, apoptosis, cell transformation, and lipid metabolism and may play a role in suppressing host immune response. This protein is thought to be present in the bloodstream of the infected host as the nucleocapsid of infectious, enveloped virions. This study provides evidence that viral particles with the physicochemical, morphological, and antigenic properties of nonenveloped HCV nucleocapsids are present in the plasma of HCV-infected individuals. These particles have a buoyant density of 1.32 to 1.34 g/ml in CsCl, are heterogeneous in size (with predominance of particles 38 to 43 or 54 to 62 nm in diameter on electron microscopy), and express on their surface epitopes located in amino acids 24 to 68 of the core protein. Similar nucleocapsid-like particles are also produced in insect cells infected with recombinant baculovirus bearing cDNA for structural HCV proteins. HCV core particles isolated from plasma were used to generate anti-core monoclonal antibodies (MAbs). These MAbs stained HCV core in the cytoplasm of hepatocytes from experimentally infected chimpanzees in the acute phase of the infection. These chimpanzees had concomitantly HCV core antigen in serum. These findings suggest that overproduction of nonenveloped nucleocapsids and their release into the bloodstream are properties of HCV morphogenesis. The presence of circulating cores in serum and accumulation of the core protein in liver cells during the early phase of infection may contribute to the persistence of HCV and its many immunopathological effects in the infected host.

Assembly of truncated HCV core antigen into virus-like particles in Escherichia coli

Core protein is one of the most conserved and immunogenic of the hepatitis C virus proteins. Several pieces of experimental evidence suggest its ability for formation of virus like particles alone or in association with other viral proteins in mammalian or yeast cells with great similarity to those detected in patient sera and liver extract. In this work we report an Escherichia coli-derived truncated hepatitis C core protein that is able to aggregate. SDS-PAGE and size exclusion chromatography patterns bring to mind the aggregation of monomers of recombinant protein Co.120. The Co.120 protein migrated with buoyant density of 1.28 g/cm(3) when analyzed using CsCl density gradient centrifugation. Spherical structures with an average diameter of 30 nm were observed using electron microscopy. We report here that VLPs are generated when the first 120 aa of HCV core protein are expressed in E. coli.

Evolution in the hypervariable region of hepatitis C virus in infants after vertical transmission

To elucidate the clonal evolution of hepatitis C virus (HCV) during mother-to-infant transmission, we prospectively analyzed HCV clones of the hypervariable region in four HCV RNA-positive infants and compared them with those of the mother. Cord blood samples from three of the four infants were positive for the HCV RNA (< or =10(3) copies/mL), and all of the four infants had the HCV RNA titer of >10(6) copies/mL within 2 mo after birth. The hypervariable region clones detected in the infants were closely related to those in the respective mothers. The results suggest the perinatal transmission of HCV. The hypervariable region clones transmitted to infants were not a single selected clone or minor clones in the mother. None of the clones specific to the low-density fraction in the mother was transmitted to the infants. Moreover, the proportion of HCV in the low-density fraction was minimal in the first few months of life, but increased several months after birth in association with the elevation of alanine aminotransferase. These results suggest that the increase of HCV in the low-density fraction reflect the evolution of immune response in infants. We also demonstrated that the emergence of quasispecies in infants precedes the infantile antibody response.

Dominant role of host selective pressure in driving hepatitis C virus evolution in perinatal infection

The dynamics of the genetic diversification of hepatitis C virus (HCV) populations was addressed in perinatal infection. Clonal sequences of hypervariable region 1 of the putative E2 envelope protein of HCV were obtained from four HCV-infected newborns (sequential samples spanning a period of 6 to 13 months after birth) and from their mothers (all samples collected at delivery). The data show that the variants detected between birth and the third month of life in samples from the four newborns were present in the HCV populations of their mothers at delivery. In the newborns, a unique viral variant (or a small group of closely related variants) remained stable for weeks despite active viral replication. Diversification of the intrahost HCV population was observed 6 to 13 months after birth and was substantially higher in two of the four subjects, as documented by the intersample genetic distance (GD) (P = 0.007). Importantly, a significant correlation between increasing GD and high values for the intersample K(a)/K(s) ratio (the ratio between anoffymous and synonymous substitutions; an index of the action of selective forces) was observed, as documented by the increase of both parameters over time (P = 0.01). These data argue for a dominant role of positive selection for amino acid changes in driving the pattern of genetic diversification of HCV populations, indicate that the intrahost evolution of HCV populations is compatible with a Darwinian model system, and may have implications in the designing of future antiviral strategies.

Nonrandom distribution of hepatitis C virus quasispecies in plasma and peripheral blood mononuclear cell subsets

The existence of an extrahepatic reservoir of hepatitis C virus (HCV) is suggested by differences in quasispecies composition between the liver, peripheral blood mononuclear cells, and serum. We studied HCV RNA compartmentalization in the plasma of nine patients, in CD19(+), CD8(+), and CD4(+) positively selected cells, and also in the negatively selected cell fraction (NF). HCV RNA was detected in all plasma samples, in seven of nine CD19(+), three of eight CD8(+), and one of nine CD4(+) cell samples, and in seven of eight NF cells. Cloning and sequencing of HVR1 in two patients showed a sequence grouping: quasispecies from a given compartment (all studied compartments for one patient and CD8(+) and NF for the other) were statistically more genetically like each other than like quasispecies from any other compartment. The characteristics of amino acid and nucleotide substitutions suggested the same structural constraints on HVR1, even in very divergent strains from the cellular compartments, and homogeneous selection pressure on the different compartments. These findings demonstrate the compartmental distribution of HCV quasispecies within peripheral blood cell subsets and have important implications for the study of extrahepatic HCV replication and interaction with the immune system.