Hepatitis C virus core protein inhibits human T lymphocyte responses by a complement-dependent regulatory pathway

Potential roles of core and core+1 proteins during the chronic phase of hepatitis C virus infection

The HCV Core protein is a multifunctional protein that interacts with many viral and cellular proteins. In addition to the encapsidation of the viral genome, it can disturb various cellular pathways and impede antiviral cellular responses such as interferon (IFN) production. The Core protein can also disrupt the functions of immune cells against HCV. The Core protein helps viral infection persistency by interfering with apoptosis. The Core+1 protein plays a significant role in inducing chronic HCV infection through diverse mechanisms. We review some of the mechanisms by which Core and Core+1 proteins facilitate HCV infection to chronic infection. These proteins could be considered for designing more sufficient treatments and effective vaccines against HCV.

A tick C1q protein alters infectivity of the Lyme disease agent by modulating interferon γ

In North America, the Lyme disease agent, Borrelia burgdorferi, is commonly transmitted by the black-legged tick, Ixodes scapularis. Tick saliva facilitates blood feeding and enhances pathogen survival and transmission. Here, we demonstrate that I. scapularis complement C1q-like protein 3 (IsC1ql3), a tick salivary protein, directly interacts with B. burgdorferi and is important during the initial stage of spirochetal infection of mice. Mice fed upon by B. burgdorferi-infected IsC1ql3-silenced ticks, or IsC1ql3-immunized mice fed upon by B. burgdorferi-infected ticks, have a lower spirochete burden during the early phase of infection compared with control animals. Mechanically, IsC1ql3 interacts with the globular C1q receptor present on the surface of CD4+ and CD8+ T cells, resulting in decreased production of interferon γ. IsC1ql3 is a C1q-domain-containing protein identified in arthropod vectors and has an important role in B. burgdorferi infectivity as the spirochete transitions from the tick to vertebrate host.

Hepatitis C Virus-Related Central and Peripheral Nervous System Disorders

Hepatitis C Virus (HCV), despite being a hepatotropic virus, is the causative agent of many systemic disorders, such as vasculitis, autoimmune diseases, lymphoproliferative disorders, and a broad spectrum of neurological and psychiatric manifestations. Although symptoms have been misdiagnosed or underdiagnosed, only recently, evidence of direct (inflammatory) or indirect (immune-mediated) HCV-dependent cerebral effects has been established. HCV infection can promote acute inflammatory response, pro-coagulative status and ischemic disorders, and neurodegeneration. These effects rely on cerebral HCV replication, possibly mediated by blood-brain barrier alterations. Further study is needed to better understand the HCV-related mechanisms of brain damage.

SARS-CoV-2 Exacerbates COVID-19 Pathology Through Activation of the Complement and Kinin Systems

Infection with SARS-CoV-2 triggers the simultaneous activation of innate inflammatory pathways including the complement system and the kallikrein-kinin system (KKS) generating in the process potent vasoactive peptides that contribute to severe acute respiratory syndrome (SARS) and multi-organ failure. The genome of SARS-CoV-2 encodes four major structural proteins - the spike (S) protein, nucleocapsid (N) protein, membrane (M) protein, and the envelope (E) protein. However, the role of these proteins in either binding to or activation of the complement system and/or the KKS is still incompletely understood. In these studies, we used: solid phase ELISA, hemolytic assay and surface plasmon resonance (SPR) techniques to examine if recombinant proteins corresponding to S1, N, M and E: (a) bind to C1q, gC1qR, FXII and high molecular weight kininogen (HK), and (b) activate complement and/or the KKS. Our data show that the viral proteins: (a) bind C1q and activate the classical pathway of complement, (b) bind FXII and HK, and activate the KKS in normal human plasma to generate bradykinin and (c) bind to gC1qR, the receptor for the globular heads of C1q (gC1q) which in turn could serve as a platform for the activation of both the complement system and KKS. Collectively, our data indicate that the SARS-CoV-2 viral particle can independently activate major innate inflammatory pathways for maximal damage and efficiency. Therefore, if efficient therapeutic modalities for the treatment of COVID-19 are to be designed, a strategy that includes blockade of the four major structural proteins may provide the best option.

HCV Core Protein Induces Chemokine CCL2 and CXCL10 Expression Through NF-κB Signaling Pathway in Macrophages

HCV core protein is the first structural protein synthesized during hepatitis C virus (HCV) infection and replication. It is released from virus infected liver cells and mediates multiple functions to affect host cell response. The innate immune response is the first line of defense against viral infection. After HCV infection, Kupffer cells (KCs) which are liver macrophages play an important role in host innate immune response. Kupffer cells act as phagocytes and release different cytokines and chemokines to counter viral infection and regulate inflammation and fibrosis in liver. Earlier, we have demonstrated that HCV core protein interacts with gC1qR and activates MAPK, NF-κB and PI3K/AKT pathways in macrophages. In this study, we explored the effect of HCV core protein on CCL2 and CXCL10 expression in macrophages and the signaling pathways involved. Upon silencing of gC1qR, we observed a significant decrease expression of CCL2 and CXCL10 in macrophages in the presence of HCV core protein. Inhibiting NF-κB pathway, but not P38, JNK, ERK and AKT pathways greatly reduced the expression of CCL2 and CXCL10. Therefore, our results indicate that interaction of HCV core protein with gC1qR could induce CCL2 and CXCL10 secretion in macrophages via NF-κB signaling pathway. These findings may shed light on the understanding of how leukocytes migrate into the liver and exaggerate host-derived immune responses and may provide novel therapeutic targets in HCV chronic inflammation.

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.

SLE: Novel Postulates for Therapeutic Options

Genetic deficiency in C1q is a strong susceptibility factor for systemic lupus erythematosus (SLE). There are two major hypotheses that potentially explain the role of C1q in SLE. The first postulates that C1q deficiency abrogates apoptotic cell clearance, leading to persistently high loads of potentially immunogenic self-antigens that trigger autoimmune responses. While C1q undoubtedly plays an important role in apoptotic clearance, an essential biological process such as removal of self- waste is so critical for host survival that multiple ligand-receptor combinations do fortunately exist to ensure that proper disposal of apoptotic debris is accomplished even in the absence of C1q. The second hypothesis is based on the observation that locally synthesized C1q plays a critical role in regulating the earliest stages of monocyte to dendritic cell (DC) differentiation and function. Indeed, circulating C1q has been shown to keep monocytes in a pre-dendritic state by silencing key molecular players and ensuring that unwarranted DC-driven immune responses do not occur. Monocytes are also able to display macromolecular C1 on their surface, representing a novel mechanism for the recognition of circulating "danger." Translation of this danger signal in turn, provides the requisite "license" to trigger a differentiation pathway that leads to adaptive immune response. Based on this evidence, the second hypothesis proposes that deficiency in C1q dysregulates monocyte-to-DC differentiation and causes inefficient or defective maintenance of self-tolerance. The fact that C1q receptors (cC1qR and gC1qR) are also expressed on the surface of both monocytes and DCs, suggests that C1q/C1qR may regulate DC differentiation and function through specific cell-signaling pathways. While their primary ligand is C1q, C1qRs can also independently recognize a vast array of plasma proteins as well as pathogen-associated molecular ligands, indicating that these molecules may collaborate in antigen recognition and processing, and thus regulate DC-differentiation. This review will therefore focus on the role of C1q and C1qRs in SLE and explore the gC1qR/C1q axis as a potential target for therapy.

The Complement System and C1q in Chronic Hepatitis C Virus Infection and Mixed Cryoglobulinemia

The complement system bridges innate and adaptive immunity against microbial infections, with viral infection being a major trigger. Activation of the classical, alternative, and lectin pathways have been reported in chronic hepatitis C virus (HCV) infection and/or cryoglobulinemia. HCV infection leads to dysregulation of complement-mediated immune responses. Clinical and experimental evidence support involvement of complement in intra- and extrahepatic manifestations of HCV infection, such as liver fibrosis and type II cryoglobulinemia. In this review, we summarize studies that have investigated the interplay between HCV and the complement system to establish chronic infection and autoimmunity, as well as the association between HCV pathogenesis and abnormal complement profiles. Several unanswered questions are highlighted which suggest additional informative lines of investigation.

Hepatitis C virus core protein reduces CD8+ T-cell proliferation, perforin production and degranulation but increases STAT5 activation

Clearance of hepatitis C virus (HCV) is dependent on an effective virus-specific CD8+ T-cell response, which is dysfunctional in chronic HCV infection. Dysfunction in bulk or non-HCV-specific CD8+ T-cells in HCV infection has also been observed. This may contribute to observed reductions in immunity to other diseases (e.g. cancer, viral co-infections) in HCV-infected individuals. Evidence suggests that the HCV core protein (found in blood as free protein) may contribute to this impairment. To determine if HCV core contributes to the impairment of effector functions and survival potential of CD8+ T-cells, isolated human CD8+ T-cells from healthy donors were pre-incubated with recombinant HCV core protein for 72 hr and then stimulated in vitro to evaluate proliferation, survival potential and effector functions. Pre-incubation of stimulated CD8+ T-cells with HCV core significantly reduced their proliferation. Perforin production and degranulation were also decreased, but interferon-γ production was unchanged. Additionally, when CD8+ T-cells were treated with serum from HCV+ individuals, they produced less perforin than cells treated with healthy serum. Up-regulation of anti-apoptotic Bcl-2 was slightly lower in cells treated with HCV core, but signal transducer and activator of transcription 5 (STAT5) activation was increased, suggesting dysregulation downstream of STAT activation. Our study reveals that HCV core reduces the activity and target lysis-associated functions of CD8+ T-cells. This may contribute to the generalized impairment of CD8+ T-cells observed in HCV infection. These findings provide insight for the design of novel counteractive immune-mediated strategies including the design of effective therapeutic vaccines for use in HCV+ individuals.

The complement and contact activation systems: partnership in pathogenesis beyond angioedema

The blood plasma contains four biologically important proteolytic cascades, which probably evolved from the same ancestral gene. This in part may explain why each cascade has very similar "initiating trigger" followed by sequential and cascade-like downstream enzymatic activation pattern. The four cascades are: the complement system, the blood clotting cascade, the fibrinolytic system, and the kallikrein-kinin system. Although much has been written about the interplay between all these enzymatic cascades, the cross-talk between the complement and the kinin generating systems has become particularly relevant as this interaction results in the generation of nascent molecules that have significant impact in various inflammatory diseases including angioedema and cancer. In this review, we will focus on the consequences of the interplay between the two systems by highlighting the role of a novel molecular link called gC1qR. Although this protein was first identified as a receptor for C1q, it is now recognized as a multiligand binding cellular protein, which serves not only as C1q receptor, but also as high affinity (K_D  ≤ 0.8 nM) binding site for both high molecular weight kininogen (HK) and factor XII (FXII). At inflammatory sites, where atherogenic factors such as immune complexes and/or pathogens can activate the endothelial cell into a procoagulant and proinflammatory surface, the two pathways are activated to generate vasoactive peptides that contribute in various ways to the inflammatory processes associated with numerous diseases. More importantly, since recent observations strongly suggest an important role for both pathways in cancer, we will focus on how a growing tumor cluster can employ the byproducts derived from the two activation systems to ensure not only its survival and growth, but also its escape into distal sites of colonization.

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.

Intracellular complement - the complosome - in immune cell regulation

The complement system was defined over a century ago based on its ability to "complement" the antibody-mediated and cell-mediated immune responses against pathogens. Today our understanding of this ancient part of innate immunity has changed substantially and we know now that complement plays an undisputed pivotal role in the regulation of both innate and adaptive immunity. The complement system consists of over 50 blood-circulating, cell-surface expressed and intracellular proteins. It is key in the recognition and elimination of invading pathogens, also in the removal of self-derived danger such as apoptotic cells, and it supports innate immune responses and the initiation of the general inflammatory reactions. The long prevailing classic view of complement was that of a serum-operative danger sensor and first line of defence system, however, recent experimental and clinical evidences have demonstrated that "local" tissue and surprisingly intracellular complement (the complosome) activation impacts on normal cell physiology. This review will focus on novel aspects of intracellular complement activation and its unexpected roles in basic cell processes such as metabolism. We also discuss what the existence of the complosome potentially means for how the host handles intracellular pathogens such as viruses.

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.

Protection of CD4+ T cells from hepatitis C virus infection-associated senescence via ΔNp63-miR-181a-Sirt1 pathway

T cell dysfunction has a crucial role in establishing and maintaining viral persistence. We have previously shown a decline in miR-181a, which regulates CD4⁺ T cell responses via DUSP6 overexpression, in individuals with hepatitis C virus (HCV) infection. Here, we describe accelerated T cell senescence in HCV-infected individuals compared with age- and sex-matched healthy subjects. Mechanistic studies revealed that up-regulation of transcription factor ΔNp63 led to the decline of miR-181a expression, resulting in an overexpression of the antiaging protein Sirt1, in CD4⁺ T cells from HCV-infected individuals. Either reconstituting miR-181a or silencing ΔNp63 or Sirt1 expression in CD4⁺ T cells led to accelerated T cell senescence, as evidenced by an increased senescence-associated β-galactosidase (SA-β-gal) expression, shortened telomere length, and decreased EdU incorporation; this suggests that HCV-induced T cell senescence is counterregulated by the ΔNp63-miR-181a-Sirt1 pathway. An increase of IL-2 production was observed in these senescent CD4⁺ T cells and was driven by a markedly reduced frequency of Foxp3⁺ regulatory T (T_reg) cells and increased number of Foxp3^- effector T (T_eff) cells upon manipulating the ΔNp63-miR-181a-Sirt1 pathway. In conclusion, these findings provide novel mechanistic insights into how HCV uses cellular senescent pathways to regulate T cell functions, revealing new targets for rejuvenating impaired T cell responses during chronic viral infection.

Hepatitis C virus-induced myeloid-derived suppressor cells regulate T-cell differentiation and function via the signal transducer and activator of transcription 3 pathway

T cells play a pivotal role in controlling viral infection; however, the precise mechanisms responsible for regulating T-cell differentiation and function during infections are incompletely understood. In this study, we demonstrated an expansion of myeloid-derived suppressor cells (MDSCs), in particular the monocytic MDSCs (M-MDSCs; CD14(+) CD33(+) CD11b(+) HLA-DR(-/low) ), in patients with chronic hepatitis C virus (HCV) infection. Notably, HCV-induced M-MDSCs express high levels of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) and interleukin-10 (IL-10) compared with healthy subjects. Blocking STAT3 signalling reduced HCV-mediated M-MDSC expansion and decreased IL-10 expression. Importantly, we observed a significant increase in the numbers of CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells following incubation of healthy peripheral blood mononuclear cells (PBMCs) with MDSCs derived from HCV-infected patients or treated with HCV core protein. In addition, depletion of MDSCs from PBMCs led to a significant reduction of Foxp3(+) Treg cells developed during chronic HCV infection. Moreover, depletion of MDSCs from PBMCs significantly increased interferon-γ production by CD4(+) T effector (Teff) cells derived from HCV patients. These results suggest that HCV-induced MDSCs promote Treg cell development and inhibit Teff cell function, suggesting a novel mechanism for T-cell regulation and a new strategy for immunotherapy against human viral diseases.

HCV core protein binds to gC1qR to induce A20 expression and inhibit cytokine production through MAPKs and NF-κB signaling pathways

Hepatitis C virus (HCV) infection is characterized by a strong propensity toward chronicity. During chronic HCV infection, HCV core protein is implicated in deregulating cytokine expression that associates with chronic inflammation. A20 is known as a powerful suppressor in cytokine signaling, in this study, we explored the A20 expression in macrophages induced by HCV core protein and the involved signaling pathways. Results demonstrated that HCV core protein induced A20 expression in macrophages. Silencing A20 significantly enhanced the secretion of IL-6, IL-1β and TGF-β1, but not IL-8 and TNF. Additionally, HCV core protein interacted with gC1qR, but not TLR2, TLR3 and TLR4 in pull-down assay. Silencing gC1qR abrogated core-induced A20 expression. Furthermore, HCV core protein activated MAPK, NF-κB and PI3K/AKT pathways in macrophages. Inhibition of P38, JNK and NF-κB but not ERK and AKT activities greatly reduced the A20 expression. In conclusion, the study suggests that HCV core protein ligates gC1qR to induce A20 expression in macrophages via P38, JNK and NF-κB signaling pathways, which leads to a low-grade chronic inflammation during HCV infection. It represents a novel mechanism by which HCV usurps the host for persistence.

Extra-hepatic infection of hepatitis C virus in the colon tissue and its relationship with hepatitis C virus pathogenesis

Extra-hepatic compartments might contribute to hepatitis C virus (HCV) persistence and extra-hepatic manifestations. Therefore, we investigated HCV infection in colonic tissue in patients with chronic hepatitis C (CHC) and its relationship with HCV pathogenesis. Colonic biopsies were collected from three groups with CHC infection: treatment naïve (TN; n=12), non-responders (NR; n=10) to anti-HCV therapy (pegylated interferon-α and ribavirin) and sustained virologic response (SVR; n=10) and from a fourth healthy control group (n=10). Liver biopsies were examined to assess inflammation and fibrosis. HCV infection and colonic T regulatory (Treg) frequency were detected by immunohistochemistry. HCV core and NS3 proteins were detected in B cells and macrophage/monocytes of 42 % and 25 % of TN and 50 % and 30 % of NR, respectively, but not in SVR or control group. The numbers of cells expressing HCV proteins were positively correlated with both HCV viral load and colonic Treg frequency. A significant negative correlation between HCV-expressing cells with both liver inflammation and fibrosis was identified. Our study provides evidence that HCV can infect B cells and macrophages of the colon. The correlations between HCV infection in colonic tissue and HCV viral load and liver pathology underline the significance of this extra-hepatic infection in HCV pathogenesis and response to therapy.

Immunopathogenesis of Hepatitis C Virus Infection

Despite advances in therapy, hepatitis C virus infection remains a major global health issue with 3 to 4 million incident cases and 170 million prevalent chronic infections. Complex, partially understood, host-virus interactions determine whether an acute infection with hepatitis C resolves, as occurs in approximately 30% of cases, or generates a persistent hepatic infection, as occurs in the remainder. Once chronic infection is established, the velocity of hepatocyte injury and resultant fibrosis is significantly modulated by immunologic as well as environmental factors. Immunomodulation has been the backbone of antiviral therapy despite poor understanding of its mechanism of action.

Hepatitis C virus-induced reduction in miR-181a impairs CD4(+) T-cell responses through overexpression of DUSP6

T cells play a crucial role in viral clearance or persistence; however, the precise mechanisms that control their responses during viral infection remain incompletely understood. MicroRNA (miR) has been implicated as a key regulator controlling diverse biological processes through posttranscriptional repression. Here, we demonstrate that hepatitis C virus (HCV)-mediated decline of miR-181a expression impairs CD4(+) T-cell responses through overexpression of dual specific phosphatase 6 (DUSP6). Specifically, a significant decline of miR-181a expression along with overexpression of DUSP6 was observed in CD4(+) T cells from chronically HCV-infected individuals compared to healthy subjects, and the levels of miR-181a loss were found to be negatively associated with the levels of DUSP6 overexpression in these cells. Importantly, reconstitution of miR-181a or blockade of DUSP6 expression in CD4(+) T cells led to improved T-cell responses including enhanced CD25 and CD69 expression, increased interleukin-2 expression, and improved proliferation of CD4(+) T cells derived from chronically HCV-infected individuals.

CONCLUSION

Since a decline of miR-181a concomitant with DUSP6 overexpression is the signature marker for age-associated T-cell senescence, these findings provide novel mechanistic insights into HCV-mediated premature T-cell aging through miR-181a-regulated DUSP6 signaling and reveal new targets for therapeutic rejuvenation of impaired T-cell responses during chronic viral infection.

Effect of the infectious dose and the presence of hepatitis C virus core gene on mouse intrahepatic CD8 T cells

AIM

Chronic hepatitis C viral (HCV) infections often result in ineffective CD8 T-cell responses due to functional exhaustion of HCV-specific T cells. However, how persisting HCV impacts CD8 T-cell effector functions remains largely unknown. The aim of this study is to examine the effect of the infectious dose and the presence of HCV core gene.

METHODS

We compared responses of intrahepatic CD8 T cells during infection of wild-type or HCV core transgenic (Tg) mice with various infectious doses of HCV-NS3-expressing recombinant adenovirus (Ad-HCV-NS3).

RESULTS

Using major histocompatibility complex class I tetramer and intracellular interferon (IFN)-γ staining method to track HCV-NS3-specific CD8 T cells, we found that a significant expansion of HCV-NS3-specific CD8 T cells was restricted to a very narrow dosage range. IFN-γ production by intrahepatic CD8 T cells in HCV core Tg mice was suppressed as compared with wild-type mice. Higher levels of expression of regulatory molecules, Tim-3 and PD-1, by intrahepatic CD8 T cells and PD-L1 by intrahepatic antigen-presenting cells were observed in HCV core Tg mice following Ad-HCV-NS3 infection, and the expression increased dependent on infectious dose. Furthermore, we found a significant inverse correlation between the percentages of IFN-γ-producing cells and expression of regulatory molecules in antigen-specific intrahepatic CD8 T cells.

CONCLUSION

High infectious dose and the presence of HCV core gene were strongly involved in ineffective CD8 T-cell responses. We consider that HCV core Tg mouse infected with high infectious dose of Ad-HCV-NS3 is useful as a chronic infection model in the development of immunotherapy for chronic hepatitis C.

Functional polymorphisms in interleukin-23 receptor and susceptibility to esophageal squamous cell carcinoma in Chinese population

BACKGROUND

As a key element in the T-helper 17 (Th17) cell-mediated inflammatory process, interleukin-23 receptor (IL-23R) plays a crucial role in the pathogenesis of cancer. Single nucleotide polymorphisms (SNPs) in IL-23R have been frequently studied in several previous case-control cancer studies, but its association with esophageal squamous cell carcinoma (ESCC) in Chinese population has not been investigated. This study examined whether genetic polymorphisms in IL-23R were associated with ESCC susceptibility.

METHODS

A hospital-based case-control study of 684 ESCC patients and 1064 healthy controls was performed to assess the association between four previous reported IL-23R genotypes (rs6682925, rs6683039, rs1884444 and rs10889677) and ESCC risk. The results revealed that the C allele of the rs10889677A>C polymorphism in the 3'UTR of IL-23R gene was inversely associated with the risk of ESCC.

RESULTS

The rs10889677AC genotype had significantly decreased cancer risk (odds ratio [OR]  = 0.85, 95% confidence interval [CI]  = 0.69-1.01) compared to subjects homozygous carriers of rs10889677AA, the risk decreased even further in those carrying rs10889677CC genotype (OR = 0.64, 95% CI = 0.44-0.93). No significant association was found between the other three polymorphisms and the risk of ESCC.

CONCLUSION

These findings indicated that rs10889677A>C polymorphism in IL-23R may play a protective role in mediating the risk of ESCC.

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.

HIV-1 infection is blocked at an early stage in cells devoid of mitochondrial DNA

Human immunodeficiency virus type I (HIV-1) exploits various host cellular pathways for efficient infection. Here we report that the absence of mitochondrial DNA (mtDNA) in ρ(0) cells markedly attenuates HIV-1 infection. Importantly, reduced infection efficiency in ρ(0) cells is not simply the result of impaired oxidative phosphorylation (OXPHOS) because pharmacological OXPHOS inhibition did not inhibit HIV-1 infection. Analysis of the early steps of virus infection by real-time PCR quantification of stage-specific HIV-1 DNA products in the infected ρ(0) and parental cell line have allowed us to conclude that HIV-1 infection in ρ(0) cells is blocked at the steps that occur after reverse transcription and prior to nuclear import. Additionally, confocal fluorescence microscope analysis showed that the majority of viral complexes containing HIV-1 p24 co-localize with mitochondria in target cells, suggesting an interaction between the two. Collectively, our data strongly indicate that mitochondria play an important role during early stages of HIV-1 infection, probably through direct association with HIV-1 intracellular complexes.

Hemoglobin subunit beta interacts with the capsid protein and antagonizes the growth of classical swine fever virus

The capsid (C) protein of the Flaviviridae family members is involved in nucleocapsid formation and virion assembly. However, the influence of C protein-interacting partners on the outcome of pestivirus infections is poorly defined. In this study, hemoglobin subunit beta (HB) was identified as a C protein-binding protein by glutathione S-transferase pulldown and subsequent mass spectrometry analysis of PK-15 cells, which are permissive cells for classical swine fever virus (CSFV). Coimmunoprecipitation and confocal microscopy confirmed that HB interacts and colocalizes with the C protein in the cytoplasm. Silencing of HB with small interfering RNAs promoted CSFV growth and replication, whereas overexpression of HB suppressed CSFV replication and growth. Interestingly, HB was found to interact with retinoic acid-inducible gene I and increase its expression, resulting in increased production of type I interferon (IFN). However, HB was unable to suppress CSFV growth when the RIG-I pathway was blocked. Overall, our results suggest that cellular HB antagonizes CSFV growth and replication by triggering IFN signaling, and might represent a novel antiviral restriction factor. This study reports for the first time the novel role of HB in innate immunity.

Molecular signatures of hepatitis C virus (HCV)-induced type II mixed cryoglobulinemia (MCII)

The role of hepatitis C virus (HCV) infection in the induction of type II mixed cryoglobulinemia (MCII) and the possible establishment of related lymphoproliferative disorders, such as B-cell non-Hodgkin lymphoma (B-NHL), is well ascertained. However, the molecular pathways involved and the factors predisposing to the development of these HCV-related extrahepatic complications deserve further consideration and clarification. To date, several host- and virus-related factors have been implicated in the progression to MCII, such as the virus-induced expansion of selected subsets of B-cell clones expressing discrete immunoglobulin variable (IgV) gene subfamilies, the involvement of complement factors and the specific role of some HCV proteins. In this review, we will analyze the host and viral factors taking part in the development of MCII in order to give a general outlook of the molecular mechanisms implicated.

Functional genetic variations in the IL-23 receptor gene are associated with risk of breast, lung and nasopharyngeal cancer in Chinese populations

Interleukin-23 receptor (IL-23R) is a key element in the T-helper 17 cell-mediated inflammatory process, which plays an important role in the pathogenesis of cancer. In this study, we examined whether genetic polymorphisms in IL-23R are associated with cancer risk in 4936 cancer patients and 5664 control subjects from eastern and southern Chinese populations. We found that the C allele of the rs10889677A>C polymorphism in the 3'-untranslated region of IL-23R was inversely associated with risk of multiple types of cancer, including breast cancer, lung cancer and nasopharyngeal carcinoma. Healthy controls who harbored the rs10889677C allele had significantly decreased cancer risk (odds ratio = 0.74, 95% confidence interval = 0.71-0.78) compared with those who harbored the rs10889677A allele. Biochemical analysis demonstrated that the rs10889677A allele disrupted the binding site for the microRNA miR-let-7f, thereby increasing the transcription of the IL-23R in vitro and in vivo. Furthermore, cancer-free individuals carrying the rs10889677CC homozygous genotype had a lower proportion of regulatory T cells (Tregs) and a higher T-cell proliferation rate upon stimulation with concanavalin A than individuals carrying the rs10889677AA homozygous genotype. Our findings indicate that the IL-23R rs10889677A>C polymorphism may influence T-cell proliferation, resulting in changes in the levels of Tregs in vivo and modifying cancer susceptibility.

Hepatitis C virus-mediated modulation of cellular immunity

The hepatitis C virus (HCV) is a major cause of chronic liver disease globally. A chronic infection can result in liver fibrosis, liver cirrhosis, hepatocellular carcinoma and liver failure in a significant ratio of the patients. About 170 million people are currently infected with HCV. Since 80 % of the infected patients develop a chronic infection, HCV has evolved sophisticated escape strategies to evade both the innate and the adaptive immune system. Thus, chronic hepatitis C is characterized by perturbations in the number, subset composition and/or functionality of natural killer cells, natural killer T cells, dendritic cells, macrophages and T cells. The balance between HCV-induced immune evasion and the antiviral immune response results in chronic liver inflammation and consequent immune-mediated liver injury. This review summarizes our current understanding of the HCV-mediated interference with cellular immunity and of the factors resulting in HCV persistence. A profound knowledge about the intrinsic properties of HCV and its effects on intrahepatic immunity is essential to be able to design effective immunotherapies against HCV such as therapeutic HCV vaccines.

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.

HCV proteins and immunoglobulin variable gene (IgV) subfamilies in HCV-induced type II mixed cryoglobulinemia: a concurrent pathogenetic role

The association between hepatitis C virus (HCV) infection and type II mixed cryoglobulinemia (MCII) is well established, but the role played by distinct HCV proteins and by specific components of the anti-HCV humoral immune response remains to be clearly defined. It is widely accepted that HCV drives the expansion of few B-cell clones expressing a restricted pool of selected immunoglobulin variable (IgV) gene subfamilies frequently endowed with rheumatoid factor (RF) activity. Moreover, the same IgV subfamilies are frequently observed in HCV-transformed malignant B-cell clones occasionally complicating MCII. In this paper, we analyze both the humoral and viral counterparts at the basis of cryoglobulins production in HCV-induced MCII, with particular attention reserved to the single IgV subfamilies most frequently involved.

Th17 cells are increased with severity of liver inflammation in patients with chronic hepatitis C

BACKGROUND AND AIM

As a newly identified subset of T helper cells, T-helper 17 cells (Th17) are major mediators of inflammation-associated disease. Some reports have revealed significantly increased Th17 cells in hepatitis B virus-infected patients, and a recent study has demonstrated that hepatitis C virus (HCV)-specific Th17 cells can be induced in vitro and regulated by transforming growth factor-β. This study attempted to characterize the role of Th17 cells in the disease progression of chronic hepatitis C (CHC).

METHODS

The current study enrolled 53 patients with CHC and 23 healthy controls, in which the circulating and liver-infiltrating Th17 cells were monitored.

RESULTS

We found that CHC patients had increased proportions of both circulating and liver-infiltrating Th17 cells compared to healthy individuals, and both measures of Th17 cells were correlated with severity of liver inflammation. We further demonstrated that the HCV-specific Th17 cells were correlated with liver damage but not HCV viral replication.

CONCLUSIONS

Such a correlation between the severity of liver damage of CHC and Th17 cells illustrated in this study sheds some light on the understanding of the pathogenesis of CHC.

Hepatitis C virus proteins inhibit C3 complement production

The third component of human complement (C3) plays a central role in innate immune function as its activation is required to trigger classical as well as alternative complement pathways. In this study, we have observed that sera from patients chronically infected with hepatitis C virus (HCV) displayed significantly lower C3 levels than sera from healthy individuals. Liver biopsy specimens from the same patients also exhibited lower C3 mRNA expression than liver tissues from healthy donors. C3 mRNA level was reduced in hepatocytes upon infection with cell culture-grown HCV genotype 1a or 2a in vitro. Further analysis suggested that HCV core protein displayed a weak repression of C3 promoter activity by downregulating the transcription factor farnesoid X receptor (FXR). On the other hand, HCV NS5A protein strongly downregulated C3 promoter activity at the basal level or in the presence of interleukin-1β (IL-1β) as an inducer. In addition, the expression of the transcription factor CAAT/enhancer binding protein beta (C/EBP-β), which binds to the IL-1/IL-6 response element in the C3 promoter, was inhibited in liver biopsy specimens. Furthermore, expression of C/EBP-β was reduced in hepatocytes infected with cell culture-grown HCV, as well as in hepatocytes transfected with the NS5A genomic region of HCV. Together, these results underscore the role of HCV NS5A protein in impairing innate immune function.

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.

Complement and viral pathogenesis

The complement system functions as an immune surveillance system that rapidly responds to infection. Activation of the complement system by specific recognition pathways triggers a protease cascade, generating cleavage products that function to eliminate pathogens, regulate inflammatory responses, and shape adaptive immune responses. However, when dysregulated, these powerful functions can become destructive and the complement system has been implicated as a pathogenic effector in numerous diseases, including infectious diseases. This review highlights recent discoveries that have identified critical roles for the complement system in the pathogenesis of viral infection.

Modulation of IL-2 expression after uptake of hepatitis C virus non-enveloped capsid-like particles: the role of p38 kinase

Hepatitis C virus (HCV) has been shown to actively replicate in cells of the immune system, altering both their function and cytokine expression. Naked nucleocapsids have been reported in the serum of infected patients. We investigated interference of recombinant non-enveloped capsid-like particles with signaling pathways in T cells. HCV non-enveloped particles (HCVne) internalization was verified in Jurkat and Hut 78 T cells, as well as primary human peripheral blood and intrahepatic mononuclear cells. HCVne uptake leads to activation of the MAPKs-p38 signaling pathway. Using specific phosphoantibodies, signaling pathways inhibitors, and chemical agents, it was demonstrated that p38 activation in T cells correlated with IL-2 transcriptional activation and was accompanied by a parallel increase of IL-2 cytokine secretion. c-fos and egr-1, two transcription factors, essential for IL-2 promoter activity, were also found to be elevated. We propose that HCVne uptake by T lymphocytes results in increased MAPKs-p38 activity and IL-2 expression, thus altering the host immune response.

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.

Interaction between Core protein of classical swine fever virus with cellular IQGAP1 protein appears essential for virulence in swine

Here we show that IQGAP1, a cellular protein that plays a pivotal role as a regulator of the cytoskeleton interacts with Classical Swine Fever Virus (CSFV) Core protein. Sequence analyses identified residues within CSFV Core protein (designated as areas I, II, III and IV) that maintain homology to regions within the matrix protein of Moloney Murine Leukemia Virus (MMLV) that mediate binding to IQGAP1 [EMBO J, 2006 25:2155]. Alanine-substitution within Core regions I, II, III and IV identified residues that specifically mediate the Core-IQGAP1 interaction. Recombinant CSFV viruses harboring alanine substitutions at residues (207)ATI(209) (I), (210)VVE(212) (II), (213)GVK(215) (III), or (232)GLYHN(236) (IV) have defective growth in primary swine macrophage cultures. In vivo, substitutions of residues in areas I and III yielded viruses that were completely attenuated in swine. These data shows that the interaction of Core with an integral component of cytoskeletal regulation plays a role in the CSFV cycle.

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.

Effects of the interactions of classical swine fever virus Core protein with proteins of the SUMOylation pathway on virulence in swine

Here we have identified host cell proteins involved with the cellular SUMOylation pathway, SUMO-1 (small ubiquitin-like modifier) and UBC9, a SUMO-1 conjugating enzyme that interact with classical swine fever virus (CSFV) Core protein. Five highly conserved lysine residues (K179, K180, K220, K221, and K246) within the CSFV Core were identified as putative SUMOylation sites. Analysis of these interactions showed that K179A, K180A, and K221A substitutions disrupt Core-SUMO-1 binding, while K220A substitution precludes Core-UBC9 binding. In vivo, Core mutant viruses (K179A, K180A, K220A, K221A) and (K220A, K221A) harboring those substitutions were attenuated in swine. These data shows a clear correlation between the disruption of Core protein binding to SUMO-1 and UBC9 and CSFV attenuation. Overall, these data suggest that the interaction of Core with the cellular SUMOylation pathway plays a significant role in the CSFV growth cycle in vivo.

Hepatitis C virus core protein induces neuroimmune activation and potentiates Human Immunodeficiency Virus-1 neurotoxicity

Background

Hepatitis C virus (HCV) genomes and proteins are present in human brain tissues although the impact of HIV/HCV co-infection on neuropathogenesis remains unclear. Herein, we investigate HCV infectivity and effects on neuronal survival and neuroinflammation in conjunction with HIV infection.

Methodology

Human microglia, astrocyte and neuron cultures were infected with cell culture-derived HCV or exposed to HCV core protein with or without HIV-1 infection or HIV-1 Viral Protein R (Vpr) exposure. Host immune gene expression and cell viability were measured. Patch-clamp studies of human neurons were performed in the presence or absence of HCV core protein. Neurobehavioral performance and neuropathology were examined in HIV-1 Vpr-transgenic mice in which stereotaxic intrastriatal implants of HCV core protein were performed.

Principal Findings

HCV-encoded RNA as well as HCV core and non-structural 3 (NS3) proteins were detectable in human microglia and astrocytes infected with HCV. HCV core protein exposure induced expression of pro-inflammatory cytokines including interleukin-1β, interleukin-6 and tumor necrosis factor-α in microglia (p<0.05) but not in astrocytes while increased chemokine (e.g. CXCL10 and interleukin-8) expression was observed in both microglia and astrocytes (p<0.05). HCV core protein modulated neuronal membrane currents and reduced both β-III-tubulin and lipidated LC3-II expression (p<0.05). Neurons exposed to supernatants from HCV core-activated microglia exhibited reduced β-III-tubulin expression (p<0.05). HCV core protein neurotoxicity and interleukin-6 induction were potentiated by HIV-1 Vpr protein (p<0.05). HIV-1 Vpr transgenic mice implanted with HCV core protein showed gliosis, reduced neuronal counts together with diminished LC3 immunoreactivity. HCV core-implanted animals displayed neurobehavioral deficits at days 7 and 14 post-implantation (p<0.05).

Conclusions

HCV core protein exposure caused neuronal injury through suppression of neuronal autophagy in addition to neuroimmune activation. The additive neurotoxic effects of HCV- and HIV-encoded proteins highlight extrahepatic mechanisms by which HCV infection worsens the disease course of HIV infection.

Adoptive transfer of splenocytes to study cell-mediated immune responses in hepatitis C infection using HCV transgenic mice

Background

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and a health problem affecting over 170 million people around the world. We previously studied transgenic mice that express HCV Core, Envelope 1 and Envelope 2 proteins predominantly in the liver, resulting in steatosis, liver and lymphoid tumors, and hepatocellular carcinoma. Herein, the immune-mediated cell response to hepatitis C antigens was evaluated by adoptive transfers of carboxyfluorescein succinimidyl ester (CFSE) labelled splenocytes from HCV immunized mice into HCV transgenic mice.

Results

In comparison to non-transgenic mice, there was a significant decrease in the percentage of CFSE-labeled CD4⁺ and CD8⁺ T cells in transgenic mouse peripheral blood receiving adoptive transfers from immunized donors. Moreover, the percentage of CFSE-labeled CD4⁺ and CD8⁺ T cells were significantly higher in the spleen of transgenic and non-transgenic mice when they received splenocytes from non-immunized than from immunized mice. On the other hand, the percentages of CD4⁺ and CD8⁺ T cells in the non-transgenic recipient mouse lymph nodes were significantly higher than the transgenic mice when they received the adoptive transfer from immunized donors. Interestingly, livers of transgenic mice that received transfers from immunized mice had a significantly higher percentage of CFSE labeled T cells than livers of non-transgenic mice receiving non-immunized transfers.

Conclusions

These results suggest that the T cells from HCV immunized mice recognize the HCV proteins in the liver of the transgenic mouse model and homed to the HCV antigen expression sites. We propose using this model system to study active T cell responses in HCV infection.

Hepatitis C: the complications of immune dysfunction

Hepatitis C virus (HCV) infection has been linked to numerous diseases of immune dysfunction, including, but not limited to, essential mixed cryoglobulinemia and non-Hodgkin's lymphoma. Clinical studies support these associations and treatment of the underlying HCV infection has been variably successful. Recent studies, focusing on the role of HCV gene products, have discovered evidence of dysregulated responses in multiple aspects of host immunity that may be contributing to the genesis of these diseases. Novel treatments that target these areas of dysregulation offer hope for improved therapy for the diseases associated with immunodysregulation by HCV.

Immune response of cytotoxic T lymphocytes and possibility of vaccine development for hepatitis C virus infection

Immune responses of cytotoxic T lymphocytes (CTLs) are implicated in viral eradication and the pathogenesis of hepatitis C. Weak CTL response against hepatitis C virus (HCV) may lead to a persistent infection. HCV infection impairs the function of HCV-specific CTLs; HCV proteins are thought to actively suppress host immune responses, including CTLs. Induction of a strong HCV-specific CTL response in HCV-infected patients can facilitate complete HCV clearance. Thus, the development of a vaccine that can induce potent CTL response against HCV is strongly expected. We investigated HCV-specific CTL responses by enzyme-linked immuno-spot assay and/or synthetic peptides and identified over 40 novel CTL epitopes in the HCV protein. Our findings may contribute to the development of the HCV vaccine. In this paper, we describe the CTL responses in HCV infection and the attempts at vaccine development based on recent scientific articles.

Abnormal B-cell activation associated with TALL-1 over-expression and SOCS-1 suppression during chronic hepatitis C virus infection

Chronic hepatitis C virus (HCV) infection is associated with cirrhosis, autoimmunity and lymphoproliferative disorders. We have previously reported a differential regulation of T and B lymphocytes by HCV core protein in vitro. In this report, we employed a translational approach to characterize the activation status of peripheral B cells from individuals with chronic HCV infection and to explore potential mechanisms for B-cell dysregulation in the setting of HCV infection. In contrast to the T-cell suppression observed in HCV-infected individuals, B cells exhibit a non-specific polyclonal activation phenotype, characterized by significantly higher levels of (1) the early activation marker, CD69, (2) the costimulatory molecule, CD86, and (3) the CCR5 chemokine receptor, CD195, when compared with B cells from healthy donors in response to phytohaemagglutinin (PHA) stimulation. Importantly, tumour necrosis factor- and Apo-L-related leucocyte-expressed ligand-1 (TALL-1), also known as B-lymphocyte stimulator (BLYS), was found to be up-regulated on the surface of B cells from HCV patients in response to PHA as well as HCV core antigen stimulation. This up-regulation of TALL-1 was associated with vigorous memory B-cell responses to viral antigenic stimulation. Additionally, suppressor of cytokine signalling-1 (SOCS-1), a negative feedback immunoregulator that is inhibited in B lymphocytes by HCV core in vitro, was also inhibited in B cells from HCV patients when compared with healthy donors. These findings suggest that TALL-1 over-expression and SOCS-1 suppression are associated with aberrant B-cell activation, providing a plausible basis for the B-cell clonal expansion underlying the lymphoproliferative disorders and autoimmune phenomena observed during chronic HCV infection.

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).

Hepatic inflammation mediated by hepatitis C virus core protein is ameliorated by blocking complement activation

BACKGROUND

The pathogenesis of inflammation and fibrosis in chronic hepatitis C virus (HCV) infection remains unclear. Transgenic mice with constitutive HCV core over-expression display steatosis only. While the reasons for this are unclear, it may be important that core protein production in these models begins during gestation, in contrast to human hepatitis C virus infection, which occurs post-natally and typically in adults.

AIMS

To more realistically model the effect of core protein production in the adult liver, we developed a mouse with conditional expression of HCV core and examined the effect of core protein production in the adult liver.

METHODS

Liver biopsy samples from transgenic mice with tetracycline(tet)-regulated conditional core protein expression were evaluated immunohistologically. Microarray analysis of HCV core transgenic mice with steatohepatitis pointed to a role of the complement pathway. This was further explored by blocking complement activation by in vivo administration of CD55 (decay accelerating factor for complement), which inhibits activation of C3.

RESULTS

Transgenic mice exhibited low, intermediate, or high HCV core protein expression when fed a permissive diet of standard chow. Aside from hepatic steatosis, hepatic inflammation and fibrosis were seen in mice with intermediate levels of core protein. Microarray analyses of inflamed liver demonstrated activation of both the complement (C3 up-regulation) and coagulation pathways (fibrinogen B up-regulation). Administration of CD55 reduced hepatic inflammation.

CONCLUSION

Transgenic mice that conditionally express intermediate HCV core protein develop inflammation, steatosis, and fibrosis. These effects mediated by HCV core are reduced by administration of CD55, a regulator of the complement pathway. The model may be valuable in investigating the pathogenesis of liver inflammation in chronic hepatitis C.

Frequency of gC1qR+CD4+ T cells increases during acute hepatitis C virus infection and remains elevated in patients with chronic infection

CD4+ T cell responses are impaired in chronic HCV infection. To determine factor(s) involved in CD4+ T cell dysregulation, we examined the effect of extracellular core on the alteration of CD4+ T cell responses and the cell surface level of core-binding protein, gC1qR on CD4+ T cells from acute HCV patients with resolved and chronic infection. During the acute phase of infection, the frequency of gC1qR+CD4+ T cells increased in both resolved and chronic HCV infection compared to healthy controls. Notably, 6 months later, the frequency of gC1qR+CD4+ T cells maintained elevated in chronic patients compared to that in resolved patients. In addition, TCR stimulation increased the frequency of gC1qR+CD4+ T cells, resulting in core-induced inhibition of T cell responses in both resolved and chronic patients. These results suggest that HCV infection expands gC1qR+CD4+ T cells, which increase the susceptibility to core-mediated immune dysregulation and facilitate the establishment of HCV persistency.