Altered innate immunity in chronic hepatitis C infection: cause or effect?

Successful DAA therapy for chronic hepatitis C reduces HLA-DR on monocytes and circulating immune mediators: A long-term follow-up study

INTRODUCTION

After DAA treatment for chronic hepatitis C infection, peripheral monocyte subsets from patients who achieved sustained virological response (SVR) reduced compared to healthy control. Improvement in inflammatory parameters and liver stiffness has been observed. However, little is known about the long-term impact of DAA treatment on peripheral monocyte subsets and immune mediators levels.

OBJECTIVES

We aimed to examine peripheral monocyte subsets and immune mediators levels in Brazilian chronic HCV patients after long-term successful IFN-free SOF-based treatment.

MATERIAL AND METHODS

We analyzed CD14++CD16-, CD14++CD16+ and CD14+CD16++ monocytes and 27 immune mediators by flow cytometry and analysis of multiple secreted proteins assay, respectively, in monoinfected chronic HCV patients receiving IFN-free sofosbuvir-based regimens followed before treatment, at SVR and one year after the end of treatment (1y).

RESULTS

Twenty-one biomarkers decreased significantly at 1y and 55-80 % of patients this reduction at 1y. Experimented patients presented a greater modulation of immune mediators at 1y. HLA-DR expression significantly decreased on CD14++CD16- and CD14++CD16+ monocytes at 1y when compared to SVR.

CONCLUSIONS

Successful DAA therapy did not modify monocyte subsets frequency but reduced monocyte activation at 1y and sustained the downregulation and restoration of circulating immune mediators, indicating that long-term reversal of inflammation status could occur after HCV eradication.

Impact of IFN-Free and IFN-Based Treatment on Blood Myeloid Dendritic Cell, Monocyte, Slan-DC, and Activated T Lymphocyte Dynamics during HCV Infection

Chronic hepatitis C virus infection leads to the activation of innate immunity, a key component in HCV fibrosis. In the past, the use of IFN-based treatment regimens did not permit an adequate evaluation of the impact of HCV clearance on immune cells, because of their antiviral and immunomodulatory properties. The recent development of direct-acting antiviral (DAA) therapy, which is associated with high rates of sustained virological response, enables a more accurate analysis of the immunological modifications following HCV eradication. We studied the dynamics of blood myeloid dendritic cells, monocytes, slan-DCs, and T lymphocytes during IFN-free and IFN-based regimens in hepatitis C virus infection.

Daclatasvir and Sofosbuvir Therapy Enhance Monocyte Phenotypic Changes in Naive Chronic Hepatitis C Patients: A Prospective Cohort Study

Background

Liver inflammation influences monocyte function, recruitment, and consequently inflammatory and fibrogenic responses. We aimed to investigate changes in the circulating monocyte phenotypes in response to Daclatasvir-Sofosbuvir (SOF/DCV) therapy in chronic hepatitis C (CHC) and relate findings to the viral kinetics and the fibrosis score.

Methods

A longitudinal study involving 100 treatment-naïve patients and 30 healthy controls, tested for liver function, fibrosis scores (AST to platelet ratio index, FIB-4), and blood monocyte subsets based on CD14/CD16 expression by flow cytometer.

Results

CHC patients had significantly lower albumin, higher ALT, AST, alkaline phosphatase, and increased fibrosis scores [Fib-4 (1.85±0.98) and AST to platelet ratio index (APRI) (0.6±0.35)], higher monocyte and eosinophil counts and lowered neutrophil to monocyte ratio (NMR), and lymphocyte to monocyte ratio (LMR) compared to week 12 and control. CHC patients had significantly increased median [classical (52.2% versus 25.8%, P=0.004) and inflammatory CD16⁺ monocytes (23.1% versus 13.58%, P=0.035)]. Therapy results in achievement of sustained virological response in 92% of cases, liver function improvement, and normalization of the inflammatory monocytes subsets. Monocyte counts showed positive correlation with viral load, calculated fibrosis scores (APRI and FIB-4 score), AST, ALT, ANC, and inverse correlations with serum albumin, leukocyte, eosinophil, NMR, and LMR. Multivariate regression found eosinophil count as predictors of CD16+ monocyte count in CHC patients.

Conclusion

CHC infection promotes a proinflammatory and profibrotic monocytes profile. SOF/DCV therapy efficiently decreases viral load, reduces fibrosis potentials, attenuates monocyte activation, normalizes monocytes phenotypic abnormalities, and modulates monocyte subsets recruitment and differentiation later in the liver.

Interaction and Mutual Activation of Different Innate Immune Cells Is Necessary to Kill and Clear Hepatitis C Virus-Infected Cells

Innate immune cells can sense hepatitis C virus (HCV)-infected cells and respond with anti-viral actions including secretion of interferons (IFNs). In previous studies, the response of individual innate immune cells against HCV was analyzed in detail. We hypothesized that interaction of multiple innate immune cells increases the magnitude of the immune response and eventually leads to clearance of HCV-infected cells. To investigate this, we co-cultured Huh-7 HCV subgenomic replicon (SGR) cells with peripheral blood mononuclear cells (PBMCs). We confirm secretion of IFNα by plasmacytoid dendritic cells (pDCs) and IFNγ by natural killer (NK) cells in the co-culture setup. Moreover, we observed that also monocytes contribute to the anti-viral response. Flow cytometry and ImageStream analysis demonstrated that monocytes take up material from HCV SGR cells in co-culture with PBMCs. Preceding the uptake, PBMCs caused apoptosis of HCV SGR cells by tumor necrosis factor-related apoptosis inducing ligand (TRAIL) expression on NK cells. We observed that only the interplay of monocytes, pDCs, and NK cells resulted in efficient clearance of HCV SGR cells, while these cell populations alone did not kill HCV SGR cells. Despite similar TRAIL receptor expression on Huh-7 control cells and HCV SGR cells, HCV activated PBMCs specifically killed HCV SGR cells and did not target Huh-7 control cells. Finally, we showed that HCV replicating cells per se are sensitive toward TRAIL-induced apoptosis. Our results highlight the importance of the interplay of different innate immune cells to initiate an efficient, rapid, and specific response against HCV-infected cells.

Dynamic Changes of the Frequency of Classic and Inflammatory Monocytes Subsets and Natural Killer Cells in Chronic Hepatitis C Patients Treated by Direct-Acting Antiviral Agents

OBJECTIVE

Up to now, little was known about the immunological changes of chronic hepatitis C (CHC) patients treated with direct-acting antiviral agents (DAAs); we try to explore the effect of DAAs on the frequency of monocytes, NK cells, and cytokines that promote their activation.

METHODS

15 treatment-naive CHC patients and 10 healthy controls were recruited. Patients were examined before DAAs therapy (0 w) and at week 4 (4 w) and week 12 (12 w) of therapy. Percentage of monocytes and NK cells of the peripheral blood was analyzed by flow cytometry. Serum cytokines IL-12, IL-18, CXCL10, CXCL11, sCD14, and sCD163 were measured by enzyme linked immunosorbent assay.

RESULTS

The frequency of CD3-CD16+CD56+ NK cells and classic CD14++CD16- monocytes decreased, while CD14+CD16+ monocytes and cytokines IL-12, IL-18, CXCL10, CXCL11, sCD14, and sCD163 increased at 0 w compared to healthy controls. During DAAs treatment, the decreased NK cells and classic monocytes gradually increased to normal levels; the increased inflammatory monocytes and cytokines IL-12 and CXCL11 decreased to normal levels, but the increased cytokines IL-18, CXCL10, sCD14, and sCD163 still remained at high levels at 12 w though they decreased rapidly from 0 w.

CONCLUSION

Our results showed that DAAs treatment attenuated the activation of monocytes and NK cells in CHC patients. Trial registration number is NCT03063723.

Genotype-Associated Differential NKG2D Expression on CD56+CD3+ Lymphocytes Predicts Response to Pegylated-Interferon/Ribavirin Therapy in Chronic Hepatitis C

Hepatitis C virus (HCV) genotype 1 infections are significantly more difficult to eradicate with PEG-IFN/ribavirin therapy, compared to HCV genotype 2. The aim of this work is to investigate the difference of immunological impairments underlying this phenomenon. Pre-treatment NKG2D expression on peripheral CD56+CD3+ lymphocytes and CD56+CD3- NK cells from cases of chronic hepatitis C were analyzed and assessed by treatment effect. Two strains of HCV were used to co-incubate with immune cells in vitro. NKG2D expression on peripheral CD56+CD3+ lymphocytes, but not NK cells, was significantly impaired in genotype 1 infection, compared to genotype 2. When peripheral blood mononuclear cells from healthy donors were co-incubated with TNS2J1, a genotype 1b/2a chimera strain, or with JFH1, a genotype 2a strain, genotype-specific decrease of NKG2D on CD56+CD3+ lymphocytes, but not NK cells, was observed.　Pre-treatment NKG2D expression on peripheral CD56+CD3+ lymphocytes significantly correlated with reduction in serum HCV RNA levels from week 0 to week 4, and predicted treatment response. Ex vivo stimulation of peripheral CD56+CD3+ lymphocytes showed NKG2D expression-correlated IFN-γ production. In conclusion, Decreased NKG2D expression on CD56+CD3+ lymphocytes in chronic HCV genotype 1 infection predicts inferior treatment response to PEG-IFN/ribavirin therapy compared to genotype 2.

Viral (hepatitis C virus, hepatitis B virus, HIV) persistence and immune homeostasis

Immune homeostasis is a host characteristic that maintains biological balance within a host. Humans have evolved many host defence mechanisms that ensure the survival of individuals upon encountering a pathogenic infection, with recovery or persistence from a viral infection being determined by both viral factors and host immunity. Chronic viral infections, such as hepatitis B virus, hepatitis C virus and HIV, often result in chronic fluctuating viraemia in the face of host cellular and humoral immune responses, which are dysregulated by multi-faceted mechanisms that are incompletely understood. This review attempts to illuminate the mechanisms involved in this process, focusing on immune homeostasis in the setting of persistent viral infection from the aspects of host defence mechanism, including interferon-stimulated genes, apolipoprotein B mRNA editing enzyme catalytic polypeptide 3 (APOBEC3), autophagy and interactions of various immune cells, cytokines and regulatory molecules.

Innate immune cell networking in hepatitis C virus infection

Persistent viral infection, such as HCV infection, is the result of the inability of the host immune system to mount a successful antiviral response, as well as the escape strategies devised by the virus. Although each individual component of the host immune system plays important roles in antiviral immunity, the interactive network of immune cells as a whole acts against the virus. The innate immune system forms the first line of host defense against viral infection, and thus, virus elimination or chronic HCV infection is linked to the direct outcome of the interactions between the various innate immune cells and HCV. By understanding how the distinct components of the innate immune system function both individually and collectively during HCV infection, potential therapeutic targets can be identified to overcome immune dysfunction and control chronic viral infection.

TGF-β signal shifting between tumor suppression and fibro-carcinogenesis in human chronic liver diseases

Perturbation of transforming growth factor (TGF)-β signaling in hepatocytes persistently infected with hepatitis viruses promotes both fibrogenesis and carcinogenesis (fibro-carcinogenesis). Insights into hepatocytic fibro-carcinogenesis have emerged from recent detailed analyses of context-dependent and cell type-specific TGF-β signaling processes directed by multiple phosphorylated forms (phospho-isoforms) of Smad mediators. In the course of hepatitis virus-related chronic liver diseases, chronic inflammation, ongoing viral infection, and host genetic/epigenetic alterations additively shift hepatocytic Smad phospho-isoform signaling from tumor suppression to fibro-carcinogenesis, accelerating liver fibrosis and increasing risk of hepatocellular carcinoma (HCC). After successful antiviral therapy, patients with chronic hepatitis can experience less risk of HCC occurrence by reversing Smad phospho-isoform signaling from fibro-carcinogenesis to tumor suppression. However, patients with cirrhosis can still develop HCC owing to sustained, intense fibro-carcinogenic signaling. Recent progress in understanding Smad phospho-isoform signaling should permit use of Smad phosphorylation as a tool predicting the likelihood of liver disease progression, and as a biomarker for assessing the effectiveness of interventions aimed at reducing fibrosis and cancer risk.

Dendritic cell co-stimulatory and co-inhibitory markers in chronic HCV: an Egyptian study

AIM

To assess co-stimulatory and co-inhibitory markers of dendritic cells (DCs) in hepatitis C virus (HCV) infected subjects with and without uremia.

METHODS

Three subject groups were included in the study: group 1 involved 50 control subjects, group 2 involved 50 patients with chronic HCV infection and group 3 involved 50 HCV uremic subjects undergoing hemodialysis. CD83, CD86 and CD40 as co-stimulatory markers and PD-L1 as a co-inhibitory marker were assessed in peripheral blood mononuclear cells by real-time polymerase chain reaction. Interleukin-10 (IL-10) and hyaluronic acid (HA) levels were also assessed. All findings were correlated with disease activity, viral load and fibrogenesis.

RESULTS

There was a significant decrease in co-stimulatory markers; CD83, CD86 and CD40 in groups 2 and 3 vs the control group. Co-stimulatory markers were significantly higher in group 3 vs group 2. There was a significant elevation in PD-L1 in both HCV groups vs the control group. PD-L1 was significantly lower in group 3 vs group 2. There was a significant elevation in IL-10 and HA levels in groups 2 and 3, where IL-10 was higher in group 3 and HA was lower in group 3 vs group 2. HA level was significantly correlated with disease activity and fibrosis grade in group 2. IL-10 was significantly correlated with fibrosis grade in group 2. There were significant negative correlations between co-stimulatory markers and viral load in groups 2 and 3, except CD83 in dialysis patients. There was a significant positive correlation between PD-L1 and viral load in both HCV groups.

CONCLUSION

A significant decrease in DC co-stimulatory markers and a significant increase in a DC co-inhibitory marker were observed in HCV subjects and to a lesser extent in dialysis patients.

The role of chemokines in acute and chronic hepatitis C infection

Hepatitis C imposes a significant burden on global healthcare. Chronic infection is associated with progressive inflammation of the liver which typically manifests in cirrhosis, organ failure and cancer. By virtue of elaborate evasion strategies, hepatitis C virus (HCV) succeeds as a persistent human virus. It has an extraordinary capacity to subvert the immune response enabling it to establish chronic infections and associated liver disease. Chemokines are low molecular weight chemotactic peptides that mediate the recruitment of inflammatory cells into tissues and back into the lymphatics and peripheral blood. Thus, they are central to the temporal and spatial distribution of effector and regulatory immune cells. The interactions between chemokines and their cognate receptors help shape the immune response and therefore, have a major influence on the outcome of infection. However, chemokines represent a target for modulation by viruses including the HCV. HCV is known to modulate chemokine expression in vitro and may therefore enable its survival by subverting the immune response in vivo through altered leukocyte chemotaxis resulting in impaired viral clearance and the establishment of chronic low-grade inflammation. In this review, the roles of chemokines in acute and chronic HCV infection are described with a particular emphasis placed on chemokine modulation as a means of immune subversion. We provide an in depth discussion of the part played by chemokines in mediating hepatic fibrosis while addressing the potential applications for these chemoattractants in prognostic medicine.

The role of natural killer cells in hepatitis C infection

HCV infection is an exponentially growing health burden worldwide, with an estimated 170 million people infected. Although therapies for HCV are continually improving, there remain a considerable proportion of patients who do not achieve viral eradication and develop liver disease. Natural killer (NK) cells are crucial for T-cell activation and are one of the first-line sentinel cell responders to viral infection. A recent explosion in studies exploring the role of NK cells in HCV infection has yielded important mechanistic information and intriguing potential therapeutic options for HCV infection. This review provides a general overview of normal NK cell function and outlines some of the important mechanisms characterizing the immune interplay between NK cells and HCV infection.

Granulocyte-macrophage colony-stimulating factor genetic adjuvant enhances the immune stimulatory effects of plasmid DNA encoding the hepatitis C virus core protein

AIM: To study the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) genetic adjuvant on immune response induced by plasmid DNA encoding the hepatitis C virus (HCV) core (C) protein.

METHODS: The gene encoding the HCV C protein was amplified by PCR from HCV 1b genotype and inserted into the pUC119 vector. The HCV C gene was then subcloned into the pCMH6K eukaryotic vector, and the resulting plasmid was named pCMH6K/HCV-C. The recombinant vector was confirmed by restriction enzyme analysis and DNA sequencing, and transfected into China hamster ovary (CHO) cells with Lipofectamine 2000. Distribution of the HCV C protein in transfected CHO cells was detected by immunofluorescence. Balb/c mice were vaccinated with the recombinant plasmid with or without the GM-CSF gene. HCV C-specific antibody in serum was measured by ELISA. The changes in T lymphocyte subsets and levels of Th cell intracellular cytokines interferon-γ (IFN-γ) and interleukin-4 (IL-4) in splenic cell suspension from immunized mice were evaluated by flow cytometric analysis. CTL activity was assessed by LDH assay.

RESULTS: Restrict enzyme digestion and DNA sequencing indicated that the recombinant pCMH6K/HCV-C was successfully constructed. The expression of plasmid-encoded protein was mainly distributed in membrane and scarcely in cytoplasm of transfected CHO cells. The percentage of CD4⁺ T cells in spleen cells in the pCMH6K/HCV-C+pGM-CSF co-vaccination group was significantly higher than those in other groups (all P < 0.05). The percentage of CD8⁺ T cells showed no significant differences among each group (P > 0.05). CTL activity induced by GM-CSF DNA co-vaccination was significantly higher than that immunized with the same amount of other naked DNA (P < 0.05). The ratio of IFN-γ to IL-4 in spleen cells from GM-CSF DNA co-vaccination group was significantly higher than those in other groups (all P < 0.05).

CONCLUSION: GM-CSF DNA could enhance the immune stimulatory effects of HCV DNA vaccine and induce Th1-type immune response.

Inhibition of the HCV core protein on the immune response to HBV surface antigen and on HBV gene expression and replication in vivo

The hepatitis C virus (HCV) core protein is a multifunctional protein that can interfere with the induction of an immune response. It has been reported that the HCV core protein inhibits HBV replication in vitro. In this study, we test the effect of the HCV core gene on the priming of the immune response to hepatitis B surface antigen (HBsAg) and on the replication of HBV in vivo. Our results showed that the full-length HCV core gene inhibits the induction of an immune response to the heterogeneous antigen, HBsAg, at the site of inoculation when HCV core (pC191) and HBsAg (pHBsAg) expression plasmids are co-administered as DNA vaccines into BALB/c mice. The observed interference effect of the HCV core occurs in the priming stage and is limited to the DNA form of the HBsAg antigen, but not to the protein form. The HCV core reduces the protective effect of the HBsAg when the HBsAg and the HCV core are co-administered as vaccines in an HBV hydrodynamic mouse model because the HCV core induces immune tolerance to the heterogeneous HBsAg DNA antigen. These results suggest that HCV core may play an important role in viral persistence by the attenuation of host immune responses to different antigens. We further tested whether the HCV core interfered with the priming of the immune response in hepatocytes via the hydrodynamic co-injection of an HBV replication-competent plasmid and an HCV core plasmid. The HCV core inhibited HBV replication and antigen expression in both BALB/c (H-2d) and C57BL/6 (H-2b) mice, the mouse models of acute and chronic hepatitis B virus infections. Thus, the HCV core inhibits the induction of a specific immune response to an HBsAg DNA vaccine. However, HCV C also interferes with HBV gene expression and replication in vivo, as observed in patients with coinfection.

Hepatitis C virus spontaneous clearance: immunology and genetic variance

Hepatitis C virus (HCV) infection is one of the most common chronic viral infections in the world. Approximately 80-90% of acutely infected individuals develop persistent infection, which is a major risk for liver cirrhosis and liver cancer. However, a small portion of patients (10-20%) clear the virus. Clinical outcomes of HCV infection are determined by the interplay between the host immune response, and viral and environmental factors. In regulating immune responses, cytokines play an indispensable role that controls the underlying pathogenesis and the resulting outcome of HCV infection. Cytokines themselves are manipulated by polymorphisms in their genes. In fact, the majority of genetic variants that apparently confer a significant risk for chronic HCV infection have been localized in genes involved in cytokine synthesis and the ultimate immune response. So far, treatment strategies for HCV infection have remained controversial. Genotyping of different polymorphisms will aid clinical decision making for both current standard and personalized care. Genotyping can potentially be useful for future integration of other agents, which provides an opportunity for clinicians to personalize treatment regimens for HCV patients. This review summarizes findings of different studies on host immune responses after HCV infection and the association between cytokine gene polymorphisms and the likelihood of HCV clearance.

Differential alteration of CD56(bright) and CD56 (dim) natural killer cells in frequency, phenotype, and cytokine response in chronic hepatitis C virus infection

BACKGROUND

Natural killer (NK) cells play an important role in immune responses to virus infection. The cell population consists of CD56(bright) (bright-subset) and CD56(dim) (dim-subset) subsets that possess armed functions of cytokine production and cytolysis, respectively. How these subsets are involved in chronic hepatitis C virus infection (CHC) remains obscure.

METHODS

We investigated the frequency, phenotype, and cytokine response of these subsets in blood from CHC patients and healthy subjects (HS).

RESULTS

Dim-subset, but not bright-subset, showed lower frequency in the patients than in HS. Bright-subset from the patients more frequently expressed the NKG2A/CD94 inhibitory receptor than that from HS, while both subsets from the patients expressed lower levels of the NKG2D activating receptor. Both subsets from the patients displayed a significantly higher level of the signal transducer and activator of transcription (STAT) 1, compared with the HS. Upon stimulation with interferon-α, bright-subset activated less STAT4, required for interferon-γ production, and dim-subset activated more STAT1, required for cytolysis, in the patients than in HS.

CONCLUSIONS

These results indicate alterations of NK cell subsets in frequency, phenotype, and cytokine response in CHC, which might be associated with the immune pathogenesis of CHC.

Activation of natural killer cells by hepatitis C virus particles in vitro

Little is known about the ability of hepatitis C virus (HCV) to alter early innate immune responses in infected patients. Previous studies have shown that natural killer (NK) cells are functionally impaired after interaction of recombinant HCV glycoprotein E2 with the co-stimulatory CD81 molecule in vitro; however, the functional consequences of a prolonged contact of NK cells with HCV particles have remained unclear. We have examined the phenotypes of purified, interleukin-2-activated NK cells from healthy donors and HCV genotype 1b patients after culture for 5 days with HCV pseudoparticles (HCVpp) and serum samples containing HCV genotype 1b. NK cells from healthy donors and chronic HCV patients were found to up-regulate receptors associated with activation (NKp46, NKp44, NKp30, NKG2D), while NK receptors from the killer cell immunoglobulin-like receptor family (KIR/CD158), predominantly having an inhibitory function, were significantly down-modulated after culture in the presence of HCV particles compared with control cultures of NK cells. HCV-infected sera and HCVpp elicited significantly higher secretion of the NK effector lymphokines interferon-γ and tumour necrosis factor-α. Furthermore, HCV stimulated the cytotoxic potential of NK cells from normal donors and patients. The enhanced activation of NK cells after prolonged culture with HCVpp or HCV-containing sera for 5 days suggests that these innate effector cells may play an important role in viral control during early phases of HCV infection.

Dysregulation of IFN system can lead to poor response to pegylated interferon and ribavirin therapy in chronic hepatitis C

BACKGROUND

Despite being expensive, the standard combination of pegylated interferon (Peg-IFN)-α and ribavirin used to treat chronic hepatitis C (CH) results in a moderate clearance rate and a plethora of side effects. This makes it necessary to predict patient outcome so as to improve the accuracy of treatment. Although the antiviral mechanism of genetically altered IL28B is unknown, IL28B polymorphism is considered a good predictor of IFN combination treatment outcome.

METHODOLOGY

Using microarray, we quantified the expression profile of 237 IFN related genes in 87 CH liver biopsy specimens to clarify the relationship between IFN pathway and viral elimination, and to predict patients' clinical outcome. In 72 out of 87 patients we also analyzed IL28B polymorphism (rs8099917).

PRINCIPAL FINDINGS

Five IFN related-genes (IFI27, IFI 44, ISG15, MX1, and OAS1) had expression levels significantly higher in nonresponders (NR) than in normal liver (NL) and sustained virological responders (SVR); this high expression was also frequently seen in cases with the minor (TG or GG) IL28B genotype. The expression pattern of 31 IFN related-genes also differed significantly between NR and NL. We predicted drug response in NR with 86.1% accuracy by diagonal linear discriminant analysis (DLDA).

CONCLUSION

IFN system dysregulation before treatment was associated with poor IFN therapy response. Determining IFN related-gene expression pattern based on patients' response to combination therapy, allowed us to predict drug response with high accuracy. This method can be applied to establishing novel antiviral therapies and strategies for patients using a more individual approach.

Hepatitis C Virus Evasion from RIG-I-Dependent Hepatic Innate Immunity

Exposure to hepatitis C virus (HCV) usually results in persistent infection that often develops into chronic liver disease. Interferon-alpha (IFN) treatment comprises the foundation of current approved therapy for chronic HCV infection but is limited in overall efficacy. IFN is a major effector of innate antiviral immunity and is naturally produced in response to viral infection when viral pathogen-associated molecular patterns (PAMPs) are recognized as nonself and are bound by cellular pathogen recognition receptors (PRRs), including Toll-like receptors (TLRs) and the RIG-I-like receptors (RLRs). Within hepatocytes, RIG-I is a major PRR of HCV infection wherein PAMP interactions serve to trigger intracellular signaling cascades in the infected hepatocyte to drive IFN production and the expression of interferon-stimulated genes (ISGs). ISGs function to limit virus replication, modulate the immune system, and to suppress virus spread. However, studies of HCV-host interactions have revealed several mechanisms of innate immune regulation and evasion that feature virus control of PRR signaling and regulation of hepatic innate immune programs that may provide a molecular basis for viral persistence.

Altered interferon-alpha-signaling in natural killer cells from patients with chronic hepatitis C virus infection

BACKGROUND & AIMS

Natural killer (NK) cells play an important role in the immune response against virus infection. Interferon (IFN)-alpha, an essential component in therapy against hepatitis C virus (HCV) infection, regulates NK cell function. However, it remains obscure how chronic HCV infection (CHC) modifies intracellular IFN-alpha signaling in NK cells. We investigated IFN-alpha signaling in NK cells in patients with CHC.

METHODS

Peripheral blood mononuclear cells were obtained from patients with CHC and healthy subjects (HS) as controls.

RESULTS

The expression level of signal transducer and activator of transcription (STAT) 1, a key molecule of IFN-alpha signaling, was clearly higher in NK cells from the CHC patients than in those from HS. The phosphorylation level of STAT1 with IFN-alpha stimulation was significantly greater in NK cells from the CHC patients than in those from the HS, while that of STAT4 was significantly less. These phosphorylation levels of STAT1 and STAT4 positively and negatively correlated with the STAT1 level in NK cells, respectively. The IFN-alpha induced messenger RNA level of the suppressor of cytokine signaling 1, which is a downstream gene of phosphorylated-STAT1, was clearly greater in NK cells from the CHC patients than in those from the HS, while that of IFN-gamma, which is a downstream gene of phosphorylated-STAT4, was clearly lower.

CONCLUSIONS

These results indicate altered IFN-alpha signaling in NK cells in CHC patients, suggesting that this alteration is associated with the persistence of HCV infection and resistance to IFN-alpha therapy.

The wild-type hepatitis C virus core inhibits initiation of antigen-specific T- and B-cell immune responses in BALB/c mice

In this study, the effects of wild-type and deletion mutant hepatitis C virus (HCV) core proteins on the induction of immune responses in BALB/c mice were assessed. p2HA-C145-S23, encoding a core protein with the C-terminal 46 amino acids truncated, significantly produced stronger antibody and cellular responses than p2HA-C191-S23. The induction of immune responses by p2HA-C145-S23 was dose dependent. However, increasing the doses or repeated administration did not enhance immune responses by the wild-type core protein. In addition, p2HA-C191-S23 was apparently able to interfere with the priming of specific immune responses by p2HA-C145-S23 when the two were coadministered. These results demonstrated that the wild-type HCV core protein itself could inhibit the priming of immune responses in the course of a DNA vaccination, whereas the truncated HCV core protein could provide potential applications for the development of DNA- and peptide-based HCV vaccines.

Natural killer cell functional dichotomy in chronic hepatitis B and chronic hepatitis C virus infections

BACKGROUND & AIMS

The phenotypic and functional characteristics of natural killer (NK) cells in chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are incompletely defined and largely controversial.

METHODS

We studied NK cell receptor expression, cytotoxic activity, and cytokine production in peripheral blood mononuclear cells from 35 patients with chronic hepatitis C, 22 with chronic hepatitis B, and 30 healthy controls.

RESULTS

Patients with chronic HBV infection had an increased proportion of NKG2C(+) NK cells with normal inhibitory receptor expression and a lower proportion of activated NK cells compared with HCV(+) patients, which was associated with normal or reduced cytolytic activity and markedly dysfunctional tumor necrosis factor-alpha and interferon-gamma production. Patients with chronic HCV infection showed a predominantly activating phenotype, featuring a decreased percentage of cells expressing the inhibitory receptor KIR3DL1 and a concomitant increase in the proportion of NKG2D(+) NK cells. Expression of the CD69 early activation antigen on NK cells positively correlated with serum alanine aminotransferase and HCV RNA values, suggesting participation of virus-induced effector NK cells in liver necroinflammation. Phenotypic changes in HCV(+) patients were associated with enhanced cytokine-induced cytolytic activity and increased usage of natural cytotoxicity and NKG2D receptor pathways, accompanied by defective cytokine production, although to a lesser extent than patients with chronic HBV infection.

CONCLUSIONS

These findings provide evidence for a functional dichotomy in patients with chronic HBV and HCV infections, featuring conserved or enhanced cytolytic activity and dysfunctional cytokine production, which may contribute to virus persistence.

The evolution of the major hepatitis C genotypes correlates with clinical response to interferon therapy

BACKGROUND

Patients chronically infected with hepatitis C virus (HCV) require significantly different durations of therapy and achieve substantially different sustained virologic response rates to interferon-based therapies, depending on the HCV genotype with which they are infected. There currently exists no systematic framework that explains these genotype-specific response rates. Since humans are the only known natural hosts for HCV-a virus that is at least hundreds of years old-one possibility is that over the time frame of this relationship, HCV accumulated adaptive mutations that confer increasing resistance to the human immune system. Given that interferon therapy functions by triggering an immune response, we hypothesized that clinical response rates are a reflection of viral evolutionary adaptations to the immune system.

METHODS AND FINDINGS

We have performed the first phylogenetic analysis to include all available full-length HCV genomic sequences (n = 345). This resulted in a new cladogram of HCV. This tree establishes for the first time the relative evolutionary ages of the major HCV genotypes. The outcome data from prospective clinical trials that studied interferon and ribavirin therapy was then mapped onto this new tree. This mapping revealed a correlation between genotype-specific responses to therapy and respective genotype age. This correlation allows us to predict that genotypes 5 and 6, for which there currently are no published prospective trials, will likely have intermediate response rates, similar to genotype 3. Ancestral protein sequence reconstruction was also performed, which identified the HCV proteins E2 and NS5A as potential determinants of genotype-specific clinical outcome. Biochemical studies have independently identified these same two proteins as having genotype-specific abilities to inhibit the innate immune factor double-stranded RNA-dependent protein kinase (PKR).

CONCLUSION

An evolutionary analysis of all available HCV genomes supports the hypothesis that immune selection was a significant driving force in the divergence of the major HCV genotypes and that viral factors that acquired the ability to inhibit the immune response may play a role in determining genotype-specific response rates to interferon therapy.

Impaired interferon type I signalling in the liver modulates the hepatic acute phase response in hepatitis C virus transgenic mice

BACKGROUND/AIMS

The immunomodulatory active hepatitis C virus (HCV) has been shown to interfere with antiviral interferon (IFN) type I functions. The aim of the study was to determine whether further basic innate immunologic functions are influenced by HCV.

METHODS

The acute phase response (APR) was induced in HCV transgenic (tg) mice and C57BL/6J control mice using lipopolysaccharide. Activation of transcription factors, mRNA expression and production of cytokines and acute phase proteins (APP) were determined. IFN type I and tumor necrosis factor (TNF) alpha signalling were investigated after polyI:C or TNF-alpha treatment.

RESULTS

HCV tg mice showed an attenuated APR: hepatic activation of nuclear factor kappa B (NFkappaB) and interferon-stimulated gene factor 3 (ISGF3), hepatic expression of interleukin (IL) 6, IL-10, and IFN-gamma mRNA, serum concentrations of IL-6 and IFN-gamma and production of type II acute phase proteins were reduced compared to wild-type mice. While no differences in NFkappaB activation could be detected after TNF-alpha injection, HCV tg mice showed reduced activation of ISGF3 and reduced transactivation of IFN target genes after polyI:C treatment.

CONCLUSIONS

Besides antiviral defence mechanisms, interruption of IFN type I signalling by HCV modulates the APR which is aimed at a variety of pathogens.

Low interleukin-10 production by monocytes of patients with a self-limiting hepatitis C virus infection

Host factors seem to be crucial for the spontaneous clearance of hepatitis C virus (HCV). Monocytes play a pivotal role in innate immunity and help regulate adaptive responses. This study assesses the characteristics of monocytes from patients with self-limiting HCV infections. We studied 35 consecutive patients [11 with a self-limiting HCV infection, 16 chronically infected with HCV and sustained virological responders (SVR) following antiviral therapy, and eight chronically infected HCV but untreated] and eight healthy donors (HD). The production of interleukin (IL)-10, tumour necrosis factor-alpha (TNF-alpha) and IL-12p40 by monocytes stimulated with lipopolysaccharides(LPS) or HCV Core protein was measured by enzyme-linked immunoassay. Monocyte surface markers were analysed by flow cytometry. LPS and Core protein triggered IL-10 and TNF-alpha production, but monocytes from self-limiting infection patients produced significantly less IL-10 and TNF-alpha than those of SVR, chronically infected or HD (P < 0.05), while IL-12p40 production was unchanged. This cytokine production profile did not appear to be due to expansion of the CD14(+) CD16(+) monocyte subset or to a classical or alternative activation monocyte profile. Monocytes from self-limiting infection patients had more CCR7 than those from SVR or chronically infected patients (P < 0.05). Monocytes of self-limiting infection patients appear to produce little IL-10 and TNF-alpha in response to viral or unspecific stimulation and to have a higher CCR7 expression. This profile seems to be independent to a particular monocyte subset or activation state. Low IL-10 production may help establish an effective immune response and spontaneous HCV clearance.

Mechanisms of HCV survival in the host

HCV infection is an important cause of liver disease worldwide-nearly 80% of infected patients develop chronic liver disease, which leads to the development of liver cirrhosis and hepatocellular carcinoma. The ability of HCV to persist within a host is believed to be related to the numerous mechanisms by which it evades the immune response of the host. These mechanisms can be divided into defensive and offensive strategies. Examples of defensive mechanisms include replication within enclosed structures, which provides protection from the host's antiviral defenses, genetic diversity created by inaccurate replication, which yields mutants resistant to the cell's antiviral strategies, and association of the virion with protective lipoproteins. Offensive mechanisms include virally encoded proteins and other factors that disrupt the ability of the host cells to detect the virus and downregulate its ability to respond to interferon, impair innate immune defense mechanisms and alter T-cell responses, and prevent the development of an effective B-cell-mediated humoral response. Greater understanding of these viral survival strategies will ultimately translate into more effective antiviral therapies and better prognosis for patients.

Prospective study of natural killer cell phenotype in recurrent hepatitis C virus infection following liver transplantation

BACKGROUND/AIMS

Graft re-infection invariably occurs after liver transplantation (OLT) for chronic hepatitis C and disease progression is unpredictable. We prospectively examined peripheral blood mononuclear cells (PBMC) subsets and natural killer (NK) cell receptors (NKRs) in patients with recurrent hepatitis C post-OLT.

METHODS

PBMC were obtained at baseline and at different time points after OLT. NKRs were identified using monoclonal antibodies by flow cytometry.

RESULTS

The proportions of NK, natural T (NT), total and gammadelta T cells were significantly reduced (p<0.01) 7 days post-transplant, probably as a result of graft repopulation. NKG2D+ NK cells were significantly higher compared with healthy controls (p<0.01), declined post-OLT and subsequently returned to baseline values. This, together with a progressive increase in the proportion of CD94/NKG2C+ NK cells over time (p< or = 0.01), appeared to be related to hepatitis C recurrence. There was a statistically significant correlation between expression of the natural cytotoxicity receptors (NCRs) and ALT (p<0.05), supporting the hypothesis that NK cells participate in the necroinflammatory process.

CONCLUSIONS

The data are compatible with homing of immune cells to the liver allograft after surgery, most of which return to pre-OLT levels. HCV recurrence may cause variations in selected NKRs expression akin to other viral infections.