Hepatitis C virus: immunosuppression by complement regulatory pathway

Role of Cellular Receptors in the Innate Immune System of Crustaceans in Response to White Spot Syndrome Virus

Innate immunity is the only defense system for resistance against infections in crustaceans. In crustaceans, white spot diseases caused by white spot syndrome virus (WSSV) are a serious viral disease with high accumulative mortality after infection. Attachment and entry into cells have been known to be two initial and important steps in viral infection. However, systematic information about the mechanisms related to WSSV infection in crustaceans is still limited. Previous studies have reported that cellular receptors are important in the innate immune system and are responsible for the recognition of foreign microorganisms and in the stimulation of the immune responses during infections. In this review, we summarize the current understanding of the functions of cellular receptors, including Toll, C-type lectin, scavenger receptor, β-integrin, polymeric immunoglobulin receptor, laminin receptor, globular C1q receptor, lipopolysaccharide-and β-1,3-glucan-binding protein, chitin-binding protein, Ras-associated binding, and Down syndrome cell adhesion molecule in the innate immune defense of crustaceans, especially shrimp and crabs, in response to WSSV infection. The results of this study provide information on the interaction between viruses and hosts during infections, which is important in the development of preventative strategies and antiviral targets in cultured aquatic animals.

"Complimenting the Complement": Mechanistic Insights and Opportunities for Therapeutics in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver and a leading cause of death in the US and worldwide. HCC remains a global health problem and is highly aggressive with unfavorable prognosis. Even with surgical interventions and newer medical treatment regimens, patients with HCC have poor survival rates. These limited therapeutic strategies and mechanistic understandings of HCC immunopathogenesis urgently warrant non-palliative treatment measures. Irrespective of the multitude etiologies, the liver microenvironment in HCC is intricately associated with chronic necroinflammation, progressive fibrosis, and cirrhosis as precedent events along with dysregulated innate and adaptive immune responses. Central to these immunological networks is the complement cascade (CC), a fundamental defense system inherent to the liver which tightly regulates humoral and cellular responses to noxious stimuli. Importantly, the liver is the primary source for biosynthesis of >80% of complement components and expresses a variety of complement receptors. Recent studies implicate the complement system in liver inflammation, abnormal regenerative responses, fibrosis, carcinogenesis, and development of HCC. Although complement activation differentially promotes immunosuppressive, stimulant, and angiogenic microenvironments conducive to HCC development, it remains under-investigated. Here, we review derangement of specific complement proteins in HCC in the context of altered complement regulatory factors, immune-activating components, and their implications in disease pathogenesis. We also summarize how complement molecules regulate cancer stem cells (CSCs), interact with complement-coagulation cascades, and provide therapeutic opportunities for targeted intervention in HCC.

Virus-Encoded Complement Regulators: Current Status

Viruses require a host for replication and survival and hence are subjected to host immunological pressures. The complement system, a crucial first response of the host immune system, is effective in targeting viruses and virus-infected cells, and boosting the antiviral innate and acquired immune responses. Thus, the system imposes a strong selection pressure on viruses. Consequently, viruses have evolved multiple countermeasures against host complement. A major mechanism employed by viruses to subvert the complement system is encoding proteins that target complement. Since viruses have limited genome size, most of these proteins are multifunctional in nature. In this review, we provide up to date information on the structure and complement regulatory functions of various viral proteins.

In the Crosshairs: RNA Viruses OR Complement?

Complement, a part of the innate arm of the immune system, is integral to the frontline defense of the host against innumerable pathogens, which includes RNA viruses. Among the major groups of viruses, RNA viruses contribute significantly to the global mortality and morbidity index associated with viral infection. Despite multiple routes of entry adopted by these viruses, facing complement is inevitable. The initial interaction with complement and the nature of this interaction play an important role in determining host resistance versus susceptibility to the viral infection. Many RNA viruses are potent activators of complement, often resulting in virus neutralization. Yet, another facet of virus-induced activation is the exacerbation in pathogenesis contributing to the overall morbidity. The severity in disease and death associated with RNA virus infections shows a tip in the scale favoring viruses. Growing evidence suggest that like their DNA counterparts, RNA viruses have co-evolved to master ingenious strategies to remarkably restrict complement. Modulation of host genes involved in antiviral responses contributed prominently to the adoption of unique strategies to keep complement at bay, which included either down regulation of activation components (C3, C4) or up regulation of complement regulatory proteins. All this hints at a possible “hijacking” of the cross-talk mechanism of the host immune system. Enveloped RNA viruses have a selective advantage of not only modulating the host responses but also recruiting membrane-associated regulators of complement activation (RCAs). This review aims to highlight the significant progress in the understanding of RNA virus–complement interactions.

A Downside to Hepatitis C Virus Cure? Vigilance Is Needed Regarding Hepatitis B Virus Reactivation, Organ Rejection, or Hepatocellular Carcinoma Progression

Cure of hepatitis C virus has become feasible in almost all patients. However, vigilance is needed in 3 scenarios: previous exposure to hepatitis B virus (HBV), history of organ transplantation, and history of cured hepatocellular carcinoma (HCC). The current data suggest that HBV reactivation occurs in about 10% of hepatitis B surface antigen (HBsAg)-positive patients and approximately 1% of hepatitis B core antibody-positive but HBsAg-negative patients. The risk of organ rejection is also around 1%, but can be fatal if not acted on immediately. Finally, the risk of early HCC recurrence may be increased but should not delay initiation of antiviral therapy in the setting of cured HCC; however, increased surveillance may be warranted.

Intracellular Pathogens: Host Immunity and Microbial Persistence Strategies

Infectious diseases caused by pathogens including viruses, bacteria, fungi, and parasites are ranked as the second leading cause of death worldwide by the World Health Organization. Despite tremendous improvements in global public health since 1950, a number of challenges remain to either prevent or eradicate infectious diseases. Many pathogens can cause acute infections that are effectively cleared by the host immunity, but a subcategory of these pathogens called "intracellular pathogens" can establish persistent and sometimes lifelong infections. Several of these intracellular pathogens manage to evade the host immune monitoring and cause disease by replicating inside the host cells. These pathogens have evolved diverse immune escape strategies and overcome immune responses by residing and multiplying inside host immune cells, primarily macrophages. While these intracellular pathogens that cause persistent infections are phylogenetically diverse and engage in diverse immune evasion and persistence strategies, they share common pathogen type-specific mechanisms during host-pathogen interaction inside host cells. Likewise, the host immune system is also equipped with a diverse range of effector functions to fight against the establishment of pathogen persistence and subsequent host damage. This article provides an overview of the immune effector functions used by the host to counter pathogens and various persistence strategies used by intracellular pathogens to counter host immunity, which enables their extended period of colonization in the host. The improved understanding of persistent intracellular pathogen-derived infections will contribute to develop improved disease diagnostics, therapeutics, and prophylactics.

Characterization and functional analysis of a novel gC1qR in the swimming crab Portunus trituberculatus

The receptor for the globular head of complement component C1q, gC1qR, is a multifunctional and multiligand binding protein with a crucial role in host defense. In the present study, a full-length cDNA sequence of a gC1qR homolog (PtgC1qR) in Portunus trituberculatus was identified. PtgC1qR was a 268-amino-acid polypeptide with a conserved MAM33 domain and a mitochondrial targeting sequence in the first 56 amino acids. The transcripts of PtgC1qR were detected in all examined tissues with the highest level detected in the hepatopancreas. Compared with other early embryonic stages, PtgC1qR was highly expressed in the fertilized eggs and embryos at the cleavage stage, which suggest PtgC1qR may be a maternal gene. The transcripts of PtgC1qR in hemocytes exhibited time-dependent response expression pattern after challenged with bacteria (Vibrio alginolyticus, Micrococcus luteus) and fungi (Pichia pastoris). Moreover, the recombinant PtgC1qR (rPtgC1qR) exhibited strong antibacterial activity and microbial-binding activity, suggesting its crucial role in immune defense and recognition. Further phenoloxidase (PO) assay showed that rPtgC1qR could suppress the crab PO activity in vitro in a dose-dependent manner, and it could result in nearly 100% inhibition of PO activity under the concentration of 11.65 μM. Knockdown of PtgC1qR could significantly enhance the expression of serine protease related genes (PtSP1-3 and PtSPH), proPO-associated genes (PtproPO and PtPPAF) and C3-like genes (Ptα2M1 and PtTEP). However, the phagocytosis related genes (PtMyosin, PtRab5 and PtArp) and Ptα2M2 were significantly down-regulated in the PtgC1qR silenced crabs. These findings together demonstrate that PtgC1qR might function in crab immune response via its antibacterial activity, immune recognition or regulating the proPO system, complement pathway and phagocytosis.

Complement Evasion Strategies of Viruses: An Overview

Being a major first line of immune defense, the complement system keeps a constant vigil against viruses. Its ability to recognize large panoply of viruses and virus-infected cells, and trigger the effector pathways, results in neutralization of viruses and killing of the infected cells. This selection pressure exerted by complement on viruses has made them evolve a multitude of countermeasures. These include targeting the recognition molecules for the avoidance of detection, targeting key enzymes and complexes of the complement pathways like C3 convertases and C5b-9 formation - either by encoding complement regulators or by recruiting membrane-bound and soluble host complement regulators, cleaving complement proteins by encoding protease, and inhibiting the synthesis of complement proteins. Additionally, viruses also exploit the complement system for their own benefit. For example, they use complement receptors as well as membrane regulators for cellular entry as well as their spread. Here, we provide an overview on the complement subversion mechanisms adopted by the members of various viral families including Poxviridae, Herpesviridae, Adenoviridae, Flaviviridae, Retroviridae, Picornaviridae, Astroviridae, Togaviridae, Orthomyxoviridae and Paramyxoviridae.

Let's Tie the Knot: Marriage of Complement and Adaptive Immunity in Pathogen Evasion, for Better or Worse

The complement system is typically regarded as an effector arm of innate immunity, leading to recognition and killing of microbial invaders in body fluids. Consequently, pathogens have engaged in an arms race, evolving molecules that can interfere with proper complement responses. However, complement is no longer viewed as an isolated system, and links with other immune mechanisms are continually being discovered. Complement forms an important bridge between innate and adaptive immunity. While its roles in innate immunity are well-documented, its function in adaptive immunity is less characterized. Therefore, it is no surprise that the field of pathogenic complement evasion has focused on blockade of innate effector functions, while potential inhibition of adaptive immune responses (via complement) has been overlooked to a certain extent. In this review, we highlight past and recent developments on the involvement of complement in the adaptive immune response. We discuss the mechanisms by which complement aids in lymphocyte stimulation and regulation, as well as in antigen presentation. In addition, we discuss microbial complement evasion strategies, and highlight specific examples in the context of adaptive immune responses. These emerging ties between complement and adaptive immunity provide a catalyst for future discovery in not only the field of adaptive immune evasion but in elucidating new roles of complement.

Single injection of CD8+ T lymphocytes derived from hematopoietic stem cells - Mathematical and numerical insights

Recently, hematopoietic stem cell (HSC) based therapy is being discussed as a possible treatment for HIV infection. The main advantage of this approach is that it limits the immune impairing effect of infection by introducing an independent influx of antigen-specific cytotoxic T lymphocytes (CTL). In this paper, we present a mathematical approach to predict the dynamics of HSC based therapy. We use a modification of a basic mathematical model for virus induced impairment of help to study how virus - immune system dynamics can be influenced by a single injection of CD8+ T lymphocytes derived from hematopoietic stem cells. Our mathematical and numerical results indicate that a single, large enough dose of genetically derived CTL may lead to restoration of the cellular immune response and result in long-term control of infection.

Assessment of total hepatitis C virus (HCV) core protein in HCV-related mixed cryoglobulinemia

Introduction

In hepatitis C virus (HCV)-related mixed cryoglobulinemia (MCG), the nonenveloped HCV core protein (HCV-Cp) is a constituent of the characteristic cold-precipitating immune complexes (ICs). A possible correlation between HCV-Cp, virologic, laboratory, and clinical parameters in both untreated MCG patients and those undergoing specific treatment was explored.

Methods

HCV-Cp was quantified by a fully automated immune assay. Correlations between HCV-Cp and HCV RNA, cryocrit, and virus genotype (gt) were investigated in 102 chronically HCV-infected MCG patients.

Results

HCV-Cp concentrations strongly correlated with HCV RNA levels in baseline samples. An average ratio of 1,425 IU and 12,850 IU HCV RNA per picogram HCV-Cp was estimated in HCV gt-1 and gt-2 patients, respectively. This equation allowed us to estimate that, on average, HCV-Cp was associated with the viral genome in only 3.4% of the former and in 35% of the latter group of patients. The direct relation between HCV-Cp and the cryocrit level suggests that the protein directly influences the amount of cryoprecipitate. Although the therapy with rituximab (RTX) as a single agent resulted in the enhancement of HCV-Cp levels, in patients treated with RTX in combination with a specific antiviral therapy (pegylated interferon-α plus ribavirin), the prompt and effective clearance of HCV-Cp was documented.

Conclusions

Our data provide evidence that HCV-Cp has a direct effect on the cold-precipitation process in a virus genotype-dependence in HCV-related MCG patients.

Complement activation correlates with liver necrosis and fibrosis in chronic hepatitis C

Chronic hepatitis C viral infection modulates complement. The aim of this study was to determine whether complement analysis predicts liver inflammation and fibrosis in patients with chronic hepatitis C. 50 chronic hepatitis C patients who underwent a liver biopsy were compared to 50 healthy controls and 35 patients with various liver diseases. Total plasma complement activity (CH50) in plasma was diminished in hepatitis C patients suggesting complement activation. This decrease correlated with increased necrosis (r = -0.24, p < 0.05), and patients with levels below the normal range had a higher METAVIR activity score reflecting enhanced inflammation. SC5b-9, a marker of complement activation, correlated with inflammation (r = 0.40, p < 0.05), activity (r = 0.42, p < 0.05), and fibrosis scores (r = 0.49, p < 0.05). Finally, the prevalence of C1q auto-antibodies was higher in hepatitis C patients, and their presence was associated with increased inflammation and seemed to affect fibrosis. We conclude that complement-induced liver inflammation contributes to fibrosis in patients with chronic hepatitis C.

Tim-3 pathway controls regulatory and effector T cell balance during hepatitis C virus infection

Hepatitis C virus (HCV) is remarkable at disrupting human immunity to establish chronic infection. Upregulation of inhibitory signaling pathways (such as T cell Ig and mucin domain protein-3 [Tim-3]) and accumulation of regulatory T cells (Tregs) play pivotal roles in suppressing antiviral effector T cell (Teff) responses that are essential for viral clearance. Although the Tim-3 pathway has been shown to negatively regulate Teffs, its role in regulating Foxp3(+) Tregs is poorly explored. In this study, we investigated whether and how the Tim-3 pathway alters Foxp3(+) Treg development and function in patients with chronic HCV infection. We found that Tim-3 was upregulated, not only on IL-2-producing CD4(+)CD25(+)Foxp3(-) Teffs, but also on CD4(+)CD25(+)Foxp3(+) Tregs, which accumulate in the peripheral blood of chronically HCV-infected individuals when compared with healthy subjects. Tim-3 expression on Foxp3(+) Tregs positively correlated with expression of the proliferation marker Ki67 on Tregs, but it was inversely associated with proliferation of IL-2-producing Teffs. Moreover, Foxp3(+) Tregs were found to be more resistant to, and Foxp3(-) Teffs more sensitive to, TCR activation-induced cell apoptosis, which was reversible by blocking Tim-3 signaling. Consistent with its role in T cell proliferation and apoptosis, blockade of Tim-3 on CD4(+)CD25(+) T cells promoted expansion of Teffs more substantially than Tregs through improving STAT-5 signaling, thus correcting the imbalance of Foxp3(+) Tregs/Foxp3(-) Teffs that was induced by HCV infection. Taken together, the Tim-3 pathway appears to control Treg and Teff balance through altering cell proliferation and apoptosis during HCV infection.

Hepatitis C virus infection and mixed cryoglobulinemia

Hepatitis C virus (HCV) chronic infection is recognized as the major cause of mixed cryoglobulinemia (MC). Its persistence represents a continuous stimulus for host immune system with production of circulating immune complexes (ICs), one-third of them with cryoprecipitate property. Several factors contribute to the biological activities of ICs, many of which are not completely known. Among them, complement factors play a crucial role in the cold-insoluble ICs-mediated vasculitis, involving primarily small blood vessels in different tissues including skin, kidney, peripheral, and central nervous system. Liver represents the major target of HCV infection with inflammatory infiltrates, resembling secondary lymphoid follicles. Cytokine like CXCL13 contribute to B-cell homing in intraportal lymphoid aggregates, in which B-cell clonal selection may arise. B-cell clonal expansion starts as an antigen-driven event and expands towards indolent and malignant B-cell proliferation. Occurrence of intrahepatic B-cell clonalities correlates with extrahepatic clinical manifestations of HCV infection. In this context, cryoglobulinemic patients should be considered a peculiar HCV-infected population that needs a clinical multidisciplinary approach and more articulated therapeutic measures.

A novel pathogen-binding gC1qR homolog, FcgC1qR, in the Chinese white shrimp, Fenneropenaeus chinensis

In vertebrates, the globular "head" of complement component C1q receptor (gC1qR) is a versatile, multiligand binding protein. However, research on its function in invertebrates is limited. In the present study, a full-length cDNA sequence of a novel gC1qR homolog, FcgC1qR, from the Chinese white shrimp Fenneropenaeus chinensis was cloned. Semi-quantitative polymerase chain reaction (PCR) detected FcgC1qR in all examined tissues, with the highest level detected in the intestine. Western blot assay further revealed that the FcgC1qR protein was distributed in all tested tissues except the cell-free hemolymph of normal Chinese white shrimp. In the expression pattern study, quantitative real-time PCR demonstrated that the transcripts of FcgC1qR were up-regulated when challenged with bacteria (Vibrio anguillarum or Staphylococcus aureus) and white spot syndrome virus. Subsequently, FcgC1qR was over-expressed in Escherichia coli, and the polyclonal antibody was prepared with the purified recombinant protein. Microorganism binding was examined using Western blot assay, and revealed that FcgC1qR could bind to Bacillus cereus, Bacillus thuringiensis, S. aureus, V. anguillarum, Vibrioharveyi, and Candida albicans. FcgC1qR was also proven able to bind to S. aureus in a concentration-dependent manner, and this binding activity was partly inhibited by the polyclonal antibody. These results suggest that FcgC1qR may be involved in defending against bacterial infections in the Chinese white shrimp.

Tim-3 negatively regulates IL-12 expression by monocytes in HCV infection

T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) is a newly identified negative immunomodulator that is up-regulated on dysfunctional T cells during viral infections. The expression and function of Tim-3 on human innate immune responses during HCV infection, however, remains poorly characterized. In this study, we report that Tim-3 is constitutively expressed on human resting CD14⁺ monocyte/macrophages (M/M_Ø) and functions as a cap to block IL-12, a key pro-inflammatory cytokine linking innate and adaptive immune responses. Tim-3 expression is significantly reduced and IL-12 expression increased upon stimulation with Toll-like receptor 4 (TLR4) ligand - lipopolysaccharide (LPS) and TLR7/8 ligand - R848. Notably, Tim-3 is over-expressed on un-stimulated as well as TLR-stimulated M/M_Ø, which is inversely associated with the diminished IL-12 expression in chronically HCV-infected individuals when compared to healthy subjects. Up-regulation of Tim-3 and inhibition of IL-12 are also observed in M/M_Ø incubated with HCV-expressing hepatocytes, as well as in primary M/M_Ø or monocytic THP-1 cells incubated with HCV core protein, an effect that mimics the function of complement C1q and is reversible by blocking the HCV core/gC1qR interaction. Importantly, blockade of Tim-3 signaling significantly rescues HCV-mediated inhibition of IL-12, which is primarily expressed by Tim-3 negative M/M_Ø. Tim-3 blockade reduces HCV core-mediated expression of the negative immunoregulators PD-1 and SOCS-1 and increases STAT-1 phosphorylation. Conversely, blocking PD-1 or silencing SOCS-1 gene expression also decreases Tim-3 expression and enhances IL-12 secretion and STAT-1 phosphorylation. These findings suggest that Tim-3 plays a crucial role in negative regulation of innate immune responses, through crosstalk with PD-1 and SOCS-1 and limiting STAT-1 phosphorylation, and may be a novel target for immunotherapy to HCV infection.

Kidney grafts from HCV-positive donors: advantages and disadvantages

The Organ Procurement and Transplantation Network database (2001-2006) was reviewed for kidney transplant (KT) recipients, to evaluate the effects of use of grafts from donors positive for hepatitis C virus (HCV) on recipient outcome. Data for 76,787 de novo adult KT recipients were included in the analysis. Serologic tests revealed HCV positivity in 6.25% of cadaver kidneys and 2.97% of living-donor kidneys. Median follow-up in patients still alive was 36 months. At multivariable Cox regression analysis in recipients of cadaver kidney, HCV serostatus was significantly associated with overall and graft survival (both P < .001), with a hazard ratio for HCV-positive patients of 1.43 for overall survival and 1.48 for graft survival. Similar results were obtained for living-donor kidney recipients. Recipients of HCV-positive organs tended to be male and African American and to have a shorter waiting time. Infection was the most commonly reported cause of death in recipients of organs from HCV-positive donors. In patients willing to accept HCV-positive grafts (929 [25.6%]), waiting time was significantly shortened (P < .001). However, this benefit was offset by decreased patient survival (P < .001) and graft survival (P = .007).

Cross-talk between programmed death-1 and suppressor of cytokine signaling-1 in inhibition of IL-12 production by monocytes/macrophages in hepatitis C virus infection

Hepatitis C virus (HCV) dysregulates innate immune responses and induces persistent viral infection. We previously demonstrated that HCV core protein impairs IL-12 expression by monocytes/macrophages (M/M(Φ)s) through interaction with a complement receptor gC1qR. Because HCV core-mediated lymphocyte dysregulation occurs through the negative immunomodulators programmed death-1 (PD-1) and suppressor of cytokine signaling-1 (SOCS-1), the aim of this study was to examine their role in HCV core-mediated IL-12 suppression in M/M(Φ)s. We analyzed TLR-stimulated, primary CD14(+) M/M(Φ)s from chronically HCV-infected and healthy subjects or the THP-1 cell line for PD-1, SOCS-1, and IL-12 expression following HCV core treatment. M/M(Φ)s from HCV-infected subjects at baseline exhibited comparatively increased PD-1 expression that significantly correlated with the degree of IL-12 inhibition. M/M(Φ)s isolated from healthy and HCV-infected individuals and treated with HCV core protein displayed increased PD-1 and SOCS-1 expression and decreased IL-12 expression, an effect that was also observed in cells treated with gC1qR's ligand, C1q. Blocking gC1qR rescued HCV core-induced PD-1 upregulation and IL-12 suppression, whereas blocking PD-1 signaling enhanced IL-12 production and decreased the expression of SOCS-1 induced by HCV core. Conversely, silencing SOCS-1 expression using small interfering RNAs increased IL-12 expression and inhibited PD-1 upregulation. PD-1 and SOCS-1 were found to associate by coimmunoprecipitation studies, and blocking PD-1 or silencing SOCS-1 in M/M(Φ) led to activation of STAT-1 during TLR-stimulated IL-12 production. These data suggested that HCV core/gC1qR engagement on M/M(Φ)s triggers the expression of PD-1 and SOCS-1, which can associate to deliver negative signaling to TLR-mediated pathways controlling expression of IL-12, a key cytokine linking innate and adaptive immunity.

Programmed death-1 affects suppressor of cytokine signaling-1 expression in T cells during hepatitis C infection

Chronic hepatitis C virus (HCV) infection is associated with T-cell exhaustion that is mediated through upregulation of the PD-1 negative regulatory pathway. PD-1 expression is induced by HCV core protein, which also induces upregulation of SOCS-1, a key modulator that controls the Jak/STAT pathway regulating cytokine expression. To determine whether these two negative regulatory pathways are linked during T-cell signaling, SOCS-1 expression was examined by blocking the PD-1 pathway in T cells stimulated with anti-CD3/CD28 in the presence of HCV core protein. T cells isolated from healthy subjects or HCV-infected individuals were treated with anti-PD-1 or anti-PDL-1 antibodies in the presence or absence of HCV core protein, and SOCS-1 gene expression was detected by RT-PCR or immunoblotting, while T-cell functions were assayed by flow cytometric analyses. Both PD-1 and SOCS-1 gene expression were upregulated in healthy T cells exposed to HCV core protein, and blocking the PD-1 pathway downregulated SOCS-1 gene expression in these cells. Additionally, T cells isolated from chronically HCV-infected subjects exhibited increased PD-1 and SOCS-1 expression compared to healthy subjects, and SOCS-1 expression in T cells isolated from HCV-infected subjects was also inhibited by blocking PD-1 signaling; this in turn enhanced the phosphorylation of STAT-1, and improved the impaired T-cell proliferation observed in the setting of HCV infection. These data demonstrate that PD-1 and SOCS-1 are linked in dysregulating T-cell signaling during HCV infection, and their cross-talk may coordinately inhibit T-cell signaling pathways that lead to T-cell exhaustion during chronic viral infection.

PD-1 modulates regulatory T cells and suppresses T-cell responses in HCV-associated lymphoma

T regulatory (T_R) cells suppress T cell responses that are critical in the development of chronic viral infection and associated malignancies. Programmed death-1 (PD-1) also plays a pivotal role in regulation of T cell functions during chronic viral infection. To examine the role of PD-1 pathway in regulating T_R cell functions that inhibit T cell responses during virus-associated malignancy, T_R cells were investigated in the setting of hepatitis C virus-associated lymphoma (HCV-L), non-HCV-associated lymphoma (non-HCV-L), HCV infection alone, and healthy subjects (HS). Relatively high numbers of CD4⁺CD25⁺ and CD8⁺CD25⁺ T_R cells as well as high levels of PD-1 expressions on these T_R cells were found in the peripheral blood of subjects with HCV-L compared to those from non-HCV-L or HCV alone or HS. T_R cells from the HCV-L subjects were capable of suppressing the autogeneic lymphocyte response, and depletion of T_R cells in PBMC from HCV-L improved T cell proliferation. Additionally, the suppressed T cell activation and proliferation in HCV-L was partially restored by blocking the PD-1 pathway ex vivo, resulting in both a reduction in T_R cell number and the ability of T_R to suppress the activity of effector T cells. This study suggests that the PD-1 pathway is involved in regulating T_R cells that suppress T cell functions in the setting of HCV-associated B cell lymphoma.

A gC1qR prevents white spot syndrome virus replication in the freshwater crayfish Pacifastacus leniusculus

The gC1qR/p32 protein is a multiple receptor for several proteins and pathogens. We cloned a gC1qR homologue in a crustacean, Pacifastacus leniusculus, and analyzed the expression of P. leniusculus C1qR (PlgC1qR) in various tissues. The gC1qR/p32 transcript was significantly enhanced by white spot syndrome virus (WSSV) infection 6 h after viral infection both in vitro in a hematopoietic tissue cell culture (Hpt) and in vivo compared to appropriate controls. Moreover, PlgC1qR silencing in both the Hpt cell culture and live crayfish enhanced the WSSV replication. In addition, by making a recombinant PlgC1qR protein we could show that if this recombinant protein was injected in a crayfish, Pacifastacus leniusculus, followed by injection of WSSV, this significantly reduced viral replication in vivo. Furthermore, if the recombinant PlgC1qR was incubated with Hpt cells and then WSSV was added, this also reduced viral replication. These experiments clearly demonstrate that recombinant PlgC1qR reduce WSSV replication both in vivo and in vitro. The results from a far-Western overlay and glutathione S-transferase pull-down assays showed that PlgC1qR could bind to VP15, VP26, and VP28. Altogether, these results demonstrate a role for PlgC1qR in antiviral activity against WSSV.

Role of the receptor for the globular domain of C1q protein in the pathogenesis of hepatitis C virus-related cryoglobulin vascular damage

Mixed cryoglobulinemia (MC) is a lymphoproliferative disorder observed in approximately 10 to 15% of hepatitis C virus (HCV)-infected patients. Circulating, nonenveloped HCV core protein, which has been detected in cryoprecipitable immune complexes, interacts with immunocytes through the receptor for the globular domain of C1q protein (gC1q-R). In this study, we have evaluated circulating gC1q-R levels in chronically HCV-infected patients, with and without MC. These levels were significantly higher in MC patients than in those without MC and in healthy controls and paralleled specific mRNA expression in PBL. Soluble gC1q-R circulates as a complexed form containing both C1q and HCV core proteins. Higher serum gC1q-R levels negatively correlated with circulating concentrations of the C4d fragment. The presence of sequestered C4d in the vascular bed of skin biopsies from MC patients was indicative of in situ complement activation. In vitro studies showed that release of soluble gC1q-R is regulated by HCV core-mediated inhibition of cell proliferation. Our results indicate that up-regulation of gC1q-R expression is a distinctive feature of MC, and that dysregulated shedding of C1q-R molecules contributes to vascular cryoglobulin-induced damage via the classic complement-mediated pathway.

Evidence that a C1q/C1qR system regulates monocyte-derived dendritic cell differentiation at the interface of innate and acquired immunity

Growing evidence shows that C1q modulates the growth and function of cells committed to the monocyte-derived dendritic cell (DC) lineage. Because C1q regulates both innate and acquired immune responses, we postulated that C1q modulates the transition from monocytes to DCs, i.e. the interface between innate and acquired immunity. Human peripheral blood monocytes cultured with soluble C1q and DC growth factors (granulocyte-macrophage colony-stimulating factor + Interleukin-4) failed to down-regulate monocyte-associated (CD14, CD16) and up-regulate DC-associated (CD83, CD86) markers. Impaired DC differentiation was not due to apoptosis; further analysis revealed the development of CD14(hi)CD11c(hi)CD16 (+/-) cells that have previously been associated with both innate and acquired immunity. Monocyte-DC precursors expressed gC1qR, the receptor for globular heads of C1q, from the outset, while cC1qR, the receptor for the collagen tails of C1q, was expressed at low levels. Notably, the binding pattern of monoclonal antibodies specific to the globular heads of C1q indicated that C1q is bound to monocytes via globular heads, presumably through gC1qR. Moreover, gC1qR levels decreased, while cC1qR levels were dramatically amplified as monocytes differentiated into immature DC. Thus, specific C1q/C1q receptor (R) interactions may control the transition from the monocyte state (innate immunity) toward the professional antigen-presenting cell state (adaptive immunity).

Plasmacytoid dendritic cells move down on the list of suspects: in search of the immune pathogenesis of chronic hepatitis C

Chronic hepatitis C is a major public health problem. Despite numerous clinical studies in humans and experimental observations made in chimpanzees, hepatitis C pathogenesis remains poorly understood. Here, we review the clinical features of acute and chronic disease, and discuss the role of the immune system in the pathogenesis of disease. Many are aware of the dual role of T cells: responsibility for clearance of the virus during acute phase; and liver injury during chronic phase. Nonetheless, there is an emerging belief that failure to prime HCV-specific T cells is responsible for the failure to spontaneously clear the virus, and possibly, for the lack of response to pegylated-IFNalpha(2a)/ribavirin therapy. We have focused on the latest suspects, plasmacytoid dendritic cells (pDCs), considered to be the professional type I IFNs producing cells. We review the somewhat contradictory data regarding the functional capacity of pDCs in chronic HCV patients and argue that, while lower in relative concentration as compared to healthy individuals, they are not defective in their ability to initiate an innate inflammatory response. Thus, instead of being the culprit, pDCs may in fact represent a novel therapeutic target in order to improve upon existing therapies for treating HCV patients.

Differential regulation of SOCS-1 signalling in B and T lymphocytes by hepatitis C virus core protein

Hepatitis C virus (HCV) infection is characterized by a strong propensity toward chronicity, autoimmune phenomena and lymphomagenesis, supporting a role for lymphocyte dysregulation during persistent viral infection. We have shown that HCV core protein inhibits T-cell functions through interaction with a complement receptor, gC1qR. Here, we further report that B cells also express gC1qR that can be bound by HCV core protein. Importantly, using flow cytometry, we demonstrated differential regulation of B and T lymphocytes by the HCV core-gC1qR interaction, with down-regulation of CD69 activation in T cells but up-regulation of CD69 activation and cell proliferation in B cells. HCV core treatment led to decreased interferon-gamma production in CD8+ T cells but to increased immunoglobulin M and immunoglobulin G production as well as cell surface expression of costimulatory and chemokine receptors, including CD86 (B7-2), CD154 (CD40L) and CD195 (CCR5), in CD20+ B cells. Finally, we showed down-regulation of suppressor of cytokine signalling-1 (SOCS-1) using real-time reverse transcription-polymerase chain reaction, accompanied by up-regulation of signal transducer and activator of transcription-1 (STAT1) phosphorylation in B cells in response to HCV core protein, with the opposite pattern observed in HCV core-treated T cells. This study demonstrates differential regulation of B and T lymphocytes by HCV core and supports a mechanism by which lymphocyte dysregulation occurs in the course of persistent HCV infection.

Hepatitis C virus core protein up-regulates anergy-related genes and a new set of genes, which affects T cell homeostasis

Hepatitis C virus (HCV) infection is the main cause for chronic hepatitis, leading to cirrhosis and hepatic carcinoma. Virally induced immune dysfunction has been called as the cause for viral persistence. Previous results demonstrate that CD4 Jurkat cells stably expressing the HCV core protein show an increased activation of NFAT transcription factor and an impaired IL-2 promoter activity, affecting intracellular signaling pathways in a manner that mimics clonal anergy. We had shown previously that NFAT activates a transcriptional program, ensuing in immunological tolerance. In the present work, we have engineered lentiviral vectors expressing the HCV core to analyze the events, which unfold in the initial phase of HCV core-induced anergy. We show that genes initially described to be up-regulated by ionomycin-induced anergy in mice are also up-regulated in humans, not only by ionomycin but also by HCV core expression. We also show that HCV core is sufficient to cause NFAT nuclear translocation and a slow-down in cell-cycle progression, and using whole genome microarrays, we identify novel genes up-regulated in Jurkat cells expressing HCV core. The relevance of our results is highlighted by the presence of HCV in CD4 T cells from HCV chronically infected patients.

T cell dysfunction by hepatitis C virus core protein involves PD-1/PDL-1 signaling

Reports have shown that a negative T cell costimulatory pathway mediated by PD-1 (programmed death-1) and PDL-1 (programmed death ligand-1) is associated with T cell exhaustion and persistent viral infection. Persistent hepatitis C virus (HCV) infection in humans is also characterized by impaired T lymphocyte function, but the role of the PD-1 and PDL-1 pathway in HCV infection is unknown. Here we report that T cells isolated from chronically HCV-infected patients express significantly higher levels of PD-1 when compared with healthy donors. In addition, PD-1 and PDL-1 expression is upregulated on healthy donor T cells exposed to HCV core, a nucleocapsid protein that is immunosuppressive; upregulation of PD-1 is mediated through interaction of HCV core with the complement receptor, gC1qR. Importantly, T cell functions that are dysregulated by HCV core, including T cell activation, proliferation, and apoptosis, can be restored by blocking PD-1 and PDL-1 engagement. Our results indicate that HCV core can upregulate a key negative T cell signaling pathway associated with viral persistence and highly expressed on the T cells of persistently infected individuals. This upregulation of the PD-1 and PDL-1 pathway in humans represents a novel and perhaps common mechanism by which a virus usurps host machinery to facilitate persistence.

Hepatitis C virus infection and kidney transplantation: predictors of patient and graft survival

BACKGROUND

The effect of hepatitis C virus (HCV) infection on patients undergoing kidney transplantation (KTx) is uncertain. This study aimed to evaluate the outcomes of our HCV+/end-stage renal disease (ESRD) patient population based on the therapeutic option including KTx or continuation in dialysis.

METHODS

KTx performed at Virginia Commonwealth University Hospital between January 2000 and December 2004 were tracked prospectively. Forty-three out of a total of 394 KTx patients included in the analysis were HCV+. A group of 52 contemporaneous HCV+/ESRD patients listed, but never transplanted, was also analyzed. HCV-negative transplanted patients were used as the control group.

RESULTS

Patient survival posttransplantation was 81.4% and 68.5% at 1 and 3 years in the HCV+ group, and 97.1% and 92.9% at 1 and 3 years in the HCV- group, respectively (P=0.001). Graft survival was 81.2% and 64.1% at 1 and 3 years in the HCV+ group, and 93.2% and 84.1% at 1 and 3 years posttransplantation in the HCV- group (P=0.01). Univariate analysis identified Knodell score as a predictor of mortality in HCV+ patients (P=0.04). Cox proportional hazards multivariate analysis identified deceased donor (P=0.02), previous kidney transplant (P=0.007), pretransplant diabetes (P=0.05), and Knodell Score (P=0.012) as predictors of patient mortality. Patient survival was superior in HCV+ patients undergoing KTx versus remaining on dialysis.

CONCLUSIONS

Patients with ESRD/HCV+ benefit from KTx without achieving the excellent survival of HCV-/ESRD patients. Liver biopsy is a useful tool to identify advanced liver disease at pretransplantation time.

A prospective evaluation of fibrosis progression in patients with recurrent hepatitis C virus following liver transplantation

Recurrence of hepatitis C virus (HCV) following liver transplantation (LT) is universal. A subset of these patients develop advanced fibrosis and cirrhosis and it is believed that this leads to increased posttransplantation mortality. The specific aims of this study were to determine the incidence of advanced fibrosis and those factors associated with this process, and to evaluate causes for mortality in patients with recurrent HCV. A total of 227 patients who underwent LT with chronic HCV were monitored prospectively. The mean age of this group at LT was 49.5 yr; 76% were male and 85% were Caucasian. Fibrosis progression was monitored by protocol liver biopsy, initially performed 6 months after LT and then at 6- to 24-month intervals. Advanced fibrosis, defined as the bridging fibrosis or cirrhosis, developed in 1%, 11%, 25%, and 41% of patients after 1, 3, 5, and 6-10 yr, respectively. Acute cellular rejection hepatic steatosis, a persistent elevation in serum alanine aminotransferase and donor-race were associated with the development of advanced fibrosis. In contrast, the development of advanced fibrosis was not affected by the use of interferon prior to undergoing LT, cytomegalovirus disease, or donor age. A total of 60 patients (26%) died over 15 yr of follow-up. Although graft failure accounted for 45% of deaths in patients with advanced fibrosis, this represented only 8% of all deaths in patients with recurrent HCV. Sepsis was the most common cause of death and this was observed with similar frequency in patients who developed advanced fibrosis (45%) and in those with less advanced fibrosis (47%). In conclusion, approximately 41% of patients with recurrent HCV developed advanced fibrosis 6-10 yr after LT. However, complications associated with sepsis, not recurrent cirrhosis, was the most common cause of death in patients with recurrent HCV and this was similar in patients with or without advanced fibrosis.

A case report of progressive multifocal leukoencephalopathy in a human T-cell lymphotropic virus type 1-infected hemodialytic patient

We experienced a case manifesting progressive multifocal leukoencephalopathy (PML) in a hemodialytic patient with hepatitis C virus-induced liver cirrhosis and human T-cell lymphotropic virus type-1 (HTLV-1)-associated uveitis. A 57-year-old male patient had received chronic hemodialysis therapy for 10 years, during which he received multiple blood transfusions and HTLV-1-associated uveitis developed. He complained of visual disturbance and disorientation. Brain CT scan showed diffuse and multifocal low density areas in occipital and temporal lobes, with gray matter relatively spared. MRI imaging showed high intensity lesions in the same areas. Cerebrospinal fluid culture was negative, but using nested PCR, rearranged regulatory region of JC virus DNA was detected. His consciousness level gradually deteriorated and complete paraplegia developed. Seven months after admission, he died of pneumonia. An autopsy confirmed the diagnosis of PML. Notably, mononuclear cell infiltration, gliosis and demyelinating lesions but no nuclear inclusion bodies were observed in the thoracic cord, which suggested HTLV-1-associated myelopathy. Because JC virus is activated under immunocompromised conditions, precipitating factors in this case appear multifactorial; depressed immune system induced by chronic hemodialysis as well as blood-borne hepatitis C virus/HTLV-1 infection might contribute to the activation of dormant JC virus and the development of florid clinical manifestation of PML.

Upregulation of hyaluronan binding protein 1 (HABP1/p32/gC1qR) is associated with Cisplatin induced apoptosis

We have earlier reported that overexpression of HABP1 in fibroblast cells causes perturbed cell growth, extensive vacuolation and restricted entry to the S-phase, finally leading to apoptosis (Biochem Biophys Res Commun 2003; 300: 686-693). In the present study, we investigate the regulation of HABP1 expression in cisplatin induced apoptosis in HeLa cells. Apoptosis induced in HeLa cells at 24 h of cisplatin treatment was confirmed by nuclear fragmentation, increase in subdiploid population and the enhanced activation of ERK and upregulation of p53. In association with apoptosis induction, an upregulation of HABP1 expression was observed in HeLa cells at 18 and 24 h of cisplatin treatment. Quantification of HABP1 expression by flow cytometry confirmed a two-fold increase in total intracellular HABP1 expression at 24 h of cisplatin treatment. Under the same condition the HABP1 transcript level measured by semi quantitative RT PCR showed 2.5-fold increase ascertaining transcriptional regulation of HABP1 during cisplatin induced apoptosis. Further, in normal HeLa cells though a small amount of HABP1 can be detected in nucleus, but with apoptosis induction the protein is mainly concentrating around the nuclear periphery at 18 h of cisplatin treatment and is present both in the nucleus as well as in the cytosol at 24 h of treatment, suggesting its nuclear translocation during apoptosis. To substantiate our findings prior to the cisplatin treatment, the expression of HABP1 was reduced by small interfering RNA mediated knockdown. We observed a reduction in apoptotic cell population in cisplatin treated HeLa cells with disrupted HABP1 conferring resistance to cisplatin induced apoptosis. We report here that HABP1 upregulation in the cell is important for cisplatin induced apoptosis.

Activation of common antiviral pathways can potentiate inflammatory responses to septic shock

Induction of the antiviral cytokine interferon alpha/beta (IFN-alpha/beta) is common in many viral infections. The impact of ongoing antiviral responses on subsequent bacterial infection is not well understood. In human disease, bacterial superinfection complicating a viral infection can result in significant morbidity and mortality. We injected mice with polyinosinic-polycytidylic (PIC) acid, a TLR3 ligand and known IFN-alpha/beta inducer as well as nuclear factor kappaB (NF-kappaB) activator to simulate very early antiviral pathways. We then challenged mice with an in vivo septic shock model characterized by slowly evolving bacterial infection to simulate bacterial superinfection early during a viral infection. Our data demonstrated robust induction of IFN-alpha in serum within 24 h of PIC injection with IFN-alpha/beta-dependent major histocompatibility antigen class II up-regulation on peritoneal macrophages. PIC pretreatment before septic shock resulted in augmented tumor necrosis factor alpha and interleukins 6 and 10 and heightened lethality compared with septic shock alone. Intact IFN-alpha/beta signaling was necessary for augmentation of the inflammatory response to in vivo septic shock and to both TLR2 and TLR4 agonists in vitro. To assess the NF-kappaB contribution to PIC-modulated inflammatory responses to septic shock, we treated with parthenolide, an NF-kappaB inhibitor before PIC and septic shock. Parthenolide did not inhibit IFN-alpha induction by PIC. Inhibition of NF-kappaB by parthenolide did reduce IFN-alpha-mediated potentiation of the cytokine response and lethality from septic shock. Our data demonstrate that pathways activated early during many viral infections can have a detrimental impact on the outcome of subsequent bacterial infection. These pathways may be critical to understanding the heightened morbidity and mortality from bacterial superinfection after viral infection in human disease.

SOCS1 and SOCS3 are targeted by hepatitis C virus core/gC1qR ligation to inhibit T-cell function

T cells play an important role in the control of hepatitis C virus (HCV) infection. We have previously demonstrated that the HCV core inhibits T-cell responses through interaction with gC1qR. We show here that core proteins from chronic and resolved HCV patients differ in sequence, gC1qR-binding ability, and T-cell inhibition. Specifically, chronic core isolates bind to gC1qR more efficiently and inhibit T-cell proliferation as well as gamma interferon (IFN-gamma) production more profoundly than resolved core isolates. This inhibition is mediated by the disruption of STAT phosphorylation through the induction of SOCS molecules. Silencing either SOCS1 or SOCS3 by small interfering RNA dramatically augments the production of IFN-gamma in T cells, thereby abrogating the inhibitory effect of core. Additionally, the ability of core proteins from patients with chronic infections to induce SOCS proteins and suppress STAT activation greatly exceeds that of core proteins from patients with resolved infections. These results suggest that the HCV core/gC1qR-induced T-cell dysfunction involves the induction of SOCS, a powerful inhibitor of cytokine signaling, which represents a novel mechanism by which a virus usurps the host machinery for persistence.

Induction of p38- and gC1qR-dependent IL-8 expression in pulmonary fibroblasts by soluble hepatitis C core protein

Background

Recent studies suggest that HCV infection is associated with progressive declines in pulmonary function in patients with underlying pulmonary diseases such as asthma and chronic obstructive pulmonary disease. Few molecular studies have addressed the inflammatory aspects of HCV-associated pulmonary disease. Because IL-8 plays a fundamental role in reactive airway diseases, we examined IL-8 signaling in normal human lung fibroblasts (NHLF) in response to the HCV nucleocapsid core protein, a viral antigen shown to modulate intracellular signaling pathways involved in cell proliferation, apoptosis and inflammation.

Methods

NHLF were treated with HCV core protein and assayed for IL-8 expression, phosphorylation of the p38 MAPK pathway, and for the effect of p38 inhibition.

Results

Our studies demonstrate that soluble HCV core protein induces significant increases in both IL-8 mRNA and protein expression in a dose- and time-dependent manner. Treatment with HCV core led to phosphorylation of p38 MAPK, and expression of IL-8 was dependent upon p38 activation. Using TNFα as a co-stimulant, we observed additive increases in IL-8 expression. HCV core-mediated expression of IL-8 was inhibited by blocking gC1qR, a known receptor for soluble HCV core linked to MAPK signaling.

Conclusion

These studies suggest that HCV core protein can lead to enhanced p38- and gC1qR-dependent IL-8 expression. Such a pro-inflammatory role may contribute to the progressive deterioration in pulmonary function recently recognized in individuals chronically infected with HCV.

Schistosoma infection inhibits cellular immune responses to core HCV peptides

Patients coinfected with hepatitis C virus (HCV) and the trematode, Schistosoma mansoni, have an increased incidence of viral persistence and accelerated fibrosis. To investigate immunological mechanisms responsible for this more aggressive natural history of HCV, the core HCV-specific T-cell responses were analysed in 44 donated blood units rejected because they had antibodies to HCV (anti-HCV). Half also had anti-S. mansoni antibodies, evidence of past or active infection. HCV-specific ELISPOT responses were examined using pools of 180 overlapping 9-mer peptides with offsets of one covering the core of HCV genotype 4a. Comparison of T-cell responses in blood units positive for both anti-HCV and anti-Schistosoma antibodies with blood units positive only for anti-HCV antibodies showed a significant decrease in core-specific T-cell IFN-gamma (505+/- 46 vs. 803 +/- 66 ISC/10(6) cells, P < 0.001), IL-4 (2 +/- 108 vs. 641 +/- 131 ISC/10(6) cells, P < 0.001), and IL-10 (159 +/- 105 vs. 466 +/- 407 ISC/10(6) cells, P < 0.002) responses. In contrast, there was no significant difference in cell-mediated immune response (CMI) to PHA mitogen between these two groups. Therefore, we concluded T cells from persons with anti-Schistosoma have reduced IFN-gamma, IL-4, and IL-10 secreting HCV-specific T-cell responses. This may explain why Schistosoma coinfection increases persistence and severity of HCV infection.

Cell-Mediated Immunity and the Outcome of Hepatitis C Virus Infection

The hepatitis C virus (HCV) infects approximately three percent of the world's population. Some individuals resolve the infection spontaneously, but the majority develop persistent viremia that often causes progressive liver disease. There is an emerging consensus that cellular immune responses are essential for spontaneous resolution of acute hepatitis C and long-term protection from persistent infection. This review focuses on the recent advances in understanding mechanisms of protective immunity and why they fail in most infected individuals. The distinct yet complementary role of CD4+ and CD8+ T lymphocytes in this process is highlighted.

Direct binding of hepatitis C virus core to gC1qR on CD4+ and CD8+ T cells leads to impaired activation of Lck and Akt

Complement plays a pivotal role in the regulation of innate and adaptive immunity. It has been shown that the binding of C1q, a natural ligand of gC1qR, on T cells inhibits their proliferation. Here, we demonstrate that direct binding of the hepatitis C virus (HCV) core to gC1qR on T cells leads to impaired Lck/Akt activation and T-cell function. The HCV core associates with the surface of T cells specifically via gC1qR, as this binding is inhibited by the addition of either anti-gC1qR antibody or soluble gC1qR. The binding affinity constant of core protein for gC1qR, as determined by BIAcore analysis, is 3.8 x 10(-7) M. The specificity of the HCV core-gC1qR interaction is confirmed by reduced core binding on Molt-4 T cells treated with gC1qR-silencing small interfering RNA and enhanced core binding on GPC-16 guinea pig cells transfected with human gC1qR. Interestingly, gC1qR is expressed at higher levels on CD8(+) than on CD4(+) T cells, resulting in more severe core-induced suppression of the CD8(+)-T-cell population. Importantly, T-cell receptor-mediated activation of the Src kinases Lck and ZAP-70 but not Fyn and the phosphorylation of Akt are impaired by the HCV core, suggesting that it inhibits the very early events of T-cell activation.

HCV core/gC1qR interaction arrests T cell cycle progression through stabilization of the cell cycle inhibitor p27Kip1

Hepatitis C virus (HCV) is efficient in the establishment of persistent infection. We have previously shown that HCV core protein inhibits T cell proliferation through its interaction with the complement receptor, gC1qR. Here we show that HCV core-induced inhibition of T cell proliferation involves a G(0)/G(1) cell cycle arrest, which is reversible upon addition of anti-gC1qR antibody. Correspondingly, the expression of cyclin-dependent kinases (Cdk) 2/4 and cyclin E/D, as well as subsequent phosphorylation of retinoblastoma (pRb), is reduced in core-treated T cells in response to mitogenic stimulation. Remarkably, degradation of p27(Kip1), a negative regulator of both Cdk4/cyclin D and Cdk2/cyclin E complexes, is significantly diminished in T cells treated with HCV core upon mitogenic stimulation. These data indicate that the stability of p27(Kip1) by HCV core is associated with blocking activated T cells for the G(1) to S phase transition and inhibiting T cell proliferation.

Lethiferous effects of a recombinant vector carrying thymidine kinase suicide gene on 2.2.15 cells via a self-modulating mechanism

AIM: To determine the lethiferous effects of a recombinant vector carrying thymidine kinase (TK) suicide gene on 2.2.15 cells and the possible self-modulating mechanism.

METHODS: A self-modulated expressive plasmid pcDNA3-SCITK was constructed by inserting the fragments carrying hepatitis B virus antisense-S (HBV-anti-S) gene, hepatitis C virus core (HCV-C) gene, internal ribosome entry site (IRES) element of HCV and TK gene into the eukaryotic vector pcDNA3, in which the expression of TK suicide gene was controlled by the HBV S gene transcription. 2.2.15 cells that carry the full HBV genome and stably express series of HBV antigen were transfected with pcDNA₃-SCITK or vector pcDNA₃-SCI which was used as the mock plasmid. The HepG2 cells transfected with pcDNA₃-SCITK were functioned as the negative control. All the transfected cells were incubated in DMEM medium supplemented with 10 μg/mL. of ganciclovir (GCV). The HBsAg levels in the supernatant of cell culture were detected by ELISA on the 1^st, 3^rd and 6^th day post-transfection. Meanwhile, the morphology of tranfected cells was recorded by the photograph and the survival cell ratio was assessed by the trypan blue exclusion test on the 6^th day post-transfection.

RESULTS: The structural accuracy of pcDNA₃-SCITK was confirmed by restriction endonuclease digestion, PCR with specific primers and DNA sequencing. The HBsAg levels in the supernatant of transfected 2.2.15 cell culture were significantly decreased on the 6^th day post-transfection as compared with that of the mock control (P < 0.05). The lethiferous effect of pcDNA₃-SCITK expression on 2.2.15 cells was initially noted on the 3^rd day after transfection and aggravated on the 6^th day post transfection, in which the majority of transfected 2.2.15 cells were observed shrunken, round in shape and even dead. With assessment by the trypan blue exclusion test, the survival cell ratio on the 6^th day post transfection was 95% in the negative control and only 11% in the experimental group.

CONCLUSION: The results indicate that suicide gene expression of pcDNA₃-SCITK can only respond to HBV-S gene transcription, which may be potentially useful in the treatment of HBV infection and its related liver malignancies.

Construction of the vector that harbors self-restricted system for hepatitis B virus clearance in gene therapy

AIM

To construct the vector that harbors self-restricted system for clearing hepatitis B virus, eliminating infected hepatic cells and inhibiting hepatitis B recurrence in gene therapy.

METHODS

After amplifying hepatitis C virus (HCV) internal ribosome entry sites (IRES) by reverse-transcription PCR (RT-PCR), the products were cloned into pcDNA3. A biscistronic vector was obtained. A part of sequence in HBV anti-surface gene and part of sequence in HCV core gene were cloned into the vector before IRES site in turn and thymidine kinase (TK) was also cloned into it following the IRES site. After determination by PCR and sequencing, we acquired the vector containing HBV anti-S, HCV-C gene, HCV IRES and thymidine kinase gene, which was named the vector pcDNA3-SCITK. The vectors were separately transfected into HepG2 cells and 2.2.15 cells and all the media contained ganciclovir.

RESULTS

The novel vector was transfected into 2.2.15 and hepG2 cells, the expressed protein could destroy the former, but had no effect on HepG2 cells if all the media contained ganciclovir. Apoptosis cells in the former accounted for 15 per cent of all cells by fluorescence (FACS) detection. There was obvious difference between the two types of cells (the later was only 6 per cent).

CONCLUSION

The function of genes that pcDNA3-SCITK carried with self-restricted system could be ego-controlled, and it might be used as gene therapy vector for HBV clearance if taking HBV S gene as target gene and TK gene as objective gene.

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.

Hepatitis C virus infection: when silence is deception

Hepatitis C virus (HCV) uses complex and unique mechanisms to prevent, evade or subvert innate and adaptive immune responses and to establish persistent infection and chronic hepatitis. Recently developed experimental systems have significantly facilitated the analysis of HCV replication, virus-host interaction and pathogenesis of chronic hepatitis and have provided new insights into the mechanisms of HCV clearance and persistence.