Antibody-directed complement-mediated cytotoxicity to hepatocytes from patients with chronic hepatitis B

The Origin of Capsid-Derived Immune Complexes and Their Impact on HBV-Induced Liver Diseases

Over 240 million people worldwide are chronically infected with Hepatitis B Virus (HBV), a hepatotropic DNA virus with an evolutionary root of over 400 million years. Persistent HBV infection exhibits distinct and diverse phases of disease, from minimal liver pathology to fulminant Hepatitis, that vary in duration and severity among individuals. Although huge progress has been made in HBV research which has yielded an effective prophylactic vaccine and potent antiviral therapy, our understanding of its virology and immunobiology is still far from complete. For example, the recent re-discovery of serum HBV RNA in chronic Hepatitis B (CHB) patients has led to the proposal of noncanonical viral particles such as RNA virion and capsid-derived immune complex (Capsid-Antibody-Complexes, CACs) that contradict long-established basic theory. Furthermore, the existence of capsid-derived immune complex may hint at novel mechanism of HBV-induced liver disease. Here, we summarize the past and recent literature on HBV-induced immune complex. We propose that the release of capsid-derived particles by HBV has its deep evolutionary origin, and the associated complement activation serves as an indispensable trigger for intrahepatic damage and a catalyst for further cell-mediated immunopathology.

Natural antibody IgG levels are associated with HBeAg-positivity and seroconversion in chronic hepatitis B patients treated with entecavir

B1 cell-derived natural antibodies are non-specific polyreactive antibodies and can activate the complement pathway leading to lysis of enveloped virus particles before activation of the adaptive immune response. We investigated the relationship between natural antibody levels and treatment outcomes of 126 treatment-naïve chronic hepatitis B (CHB) patients, who underwent entecavir (ETV) treatment. Serum IgG1-3 and complement C3 levels were significantly higher in HBeAg-positive patients. In pre-treatment, IgG1 (odd ratios [OR] 2.3, p < 0.0001), IgG2 (OR 9.8, p < 0.0001), IgG3 (OR 7.4, p < 0.0001), and C3 (OR 7.2, p < 0.0001) were associated with HBeAg-positive patients. At baseline, IgG2 (OR 10.2, p = 0.025), IgG4, (OR 3.4, p = 0.026), and complement C1q (OR 5.0, p = 0.0068) were associated with seroconverters. Post-treatment levels of IgG1-4 and C3/C1q were also associated with HBeAg-positive patients and seroconverters. High levels of IgG2-4 and C1q were observed in seroconverters but not in virological responders. Thus, high pretreatment and post-treatment levels of natural antibody IgG1-4, complement C3, and/or C1q were significantly associated with HBeAg-positivity and HBeAg seroconverters in CHB patients with ETV treatment. These results suggest that the presence of preexisting host immunity against chronic hepatitis B is closely related to outcome of ETV treatment.

Humoral immunity in hepatitis B virus infection: Rehabilitating the B in HBV

Insights into the immunopathogenesis of chronic HBV infections are fundamental in the quest for novel treatment approaches aimed at a functional cure. While much is known about the ineffective HBV-specific T-cell responses that characterise persistent HBV replication, B cells have been left largely understudied. However, an important role for humoral immunity during the natural history of HBV infections, as well as after functional cure, has been inadvertently revealed by the occurrence of HBV flares following B cell-depleting treatments. Herein, we review our current understanding of the role of the humoral immune response in chronic HBV, both at the level of HBV-specific antibody production and at the phenotypic and broader functional level of B cells. The recent development of fluorescently labelled HBV proteins has given us unprecedented insights into the phenotype and function of HBsAg- and HBcAg-specific B cells. This should fuel novel research into the mechanisms behind dysfunctional HBsAg-specific and fluctuating, possibly pathogenic, HBcAg-specific B-cell responses in chronic HBV. Finally, novel immunomodulatory treatments that partly target B cells are currently in clinical development, but a detailed assessment of their impact on HBV-specific B-cell responses is lacking. We plead for a rehabilitation of B-cell studies related to both the natural history of HBV and treatment development programmes.

Pathogenicity and virulence of Hepatitis B virus

Hepatitis B virus (HBV) is a hepatotropic virus and an important human pathogen. There are an estimated 296 million people in the world that are chronically infected by this virus, and many of them will develop severe liver diseases including hepatitis, cirrhosis and hepatocellular carcinoma (HCC). HBV is a small DNA virus that replicates via the reverse transcription pathway. In this review, we summarize the molecular pathways that govern the replication of HBV and its interactions with host cells. We also discuss viral and non-viral factors that are associated with HBV-induced carcinogenesis and pathogenesis, as well as the role of host immune responses in HBV persistence and liver pathogenesis.

New Insights into the Role of the Complement System in Human Viral Diseases

The complement system (CS) is part of the human immune system, consisting of more than 30 proteins that play a vital role in the protection against various pathogens and diseases, including viral diseases. Activated via three pathways, the classical pathway (CP), the lectin pathway (LP), and the alternative pathway (AP), the complement system leads to the formation of a membrane attack complex (MAC) that disrupts the membrane of target cells, leading to cell lysis and death. Due to the increasing number of reports on its role in viral diseases, which may have implications for research on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), this review aims to highlight significant progress in understanding and defining the role of the complement system in four groups of diseases of viral etiology: (1) respiratory diseases; (2) acute liver failure (ALF); (3) disseminated intravascular coagulation (DIC); and (4) vector-borne diseases (VBDs). Some of these diseases already present a serious global health problem, while others are a matter of concern and require the collaboration of relevant national services and scientists with the World Health Organization (WHO) to avoid their spread.

Diverse Virus and Host-Dependent Mechanisms Influence the Systemic and Intrahepatic Immune Responses in the Woodchuck Model of Hepatitis B

Woodchuck infected with woodchuck hepatitis virus (WHV) represents the pathogenically nearest model of hepatitis B and associated hepatocellular carcinoma (HCC). This naturally occurring animal model also is highly valuable for development and preclinical evaluation of new anti-HBV agents and immunotherapies against chronic hepatitis (CH) B and HCC. Studies in this system uncovered a number of molecular and immunological processes which contribute or likely contribute to the immunopathogenesis of liver disease and modulation of the systemic and intrahepatic innate and adaptive immune responses during hepadnaviral infection. Among them, inhibition of presentation of the class I major histocompatibility complex on chronically infected hepatocytes and a role of WHV envelope proteins in this process, as well as augmented hepatocyte cytotoxicity mediated by constitutively expressed components of CD95 (Fas) ligand- and perforin-dependent pathways, capable of eliminating cells brought to contact with hepatocyte surface, including activated T lymphocytes, were uncovered. Other findings pointed to a role of autoimmune response against hepatocyte asialoglycoprotein receptor in augmenting severity of liver damage in hepadnaviral CH. It was also documented that WHV in the first few hours activates intrahepatic innate immunity that transiently decreases hepatic virus load. However, this activation is not translated in a timely manner to induction of virus-specific T cell response which appears to be hindered by defective activation of antigen presenting cells and presentation of viral epitopes to T cells. The early WHV infection also induces generalized polyclonal activation of T cells that precedes emergence of virus-specific T lymphocyte reactivity. The combination of these mechanisms hinder recognition of virus allowing its dissemination in the initial, asymptomatic stages of infection before adaptive cellular response became apparent. This review will highlight a range of diverse mechanisms uncovered in the woodchuck model which affect effectiveness of the anti-viral systemic and intrahepatic immune responses, and modify liver disease outcomes. Further exploration of these and other mechanisms, either already discovered or yet unknown, and their interactions should bring more comprehensive understanding of HBV pathogenesis and help to identify novel targets for therapeutic and preventive interventions. The woodchuck model is uniquely positioned to further contribute to these advances.

The role of hepatitis B surface antibodies in HBV infection, disease and clearance

The clinical sequelae associated with chronic HBV infection is generally regarded as a consequence of an inadequate and inappropriate immune response to active viral replication, predominantly at the T-cell level. However, recent studies on hepatitis B surface antigen (HBsAg)-specific B cells and hepatitis B surface antibody (anti-HB) responses have identified their previously unrecognized role in the pathogenesis of chronic hepatitis B (CHB). These studies have also uncovered novel therapeutic approaches to more effectively target HBsAg loss and seroconversion, an important end point and regarded as a functional cure. Anti-HBs IgG has also been shown to have multiple direct acting antiviral roles with the Fab component directly blocking viral entry, and release while the Fc component has been linked to antibody dependent cellular cytotoxicity. Likewise, the HBsAg-specific B-cell dysfunctionality can be reversed providing new therapeutic opportunities to achieve functional cure in CHB.

Development of anti-hepatitis B surface (HBs) antibodies after HBs antigen loss in HIV-hepatitis B virus co-infected patients

BACKGROUND

Hepatitis B surface antigen (HBsAg)-seroconversion, or loss of HBsAg and acquisition of anti-hepatitis B surface (HBs) antibodies, defines functional cure of chronic hepatitis B virus (HBV) infection. After HBsAg-loss, little is known regarding the development of anti-HBs antibodies and even less so in individuals co-infected with HIV.

OBJECTIVES

To determine anti-HBs antibody kinetics after HBsAg-loss and explore determinants of HBsAg-seroconversion in HIV-HBV co-infected patients.

STUDY DESIGN

Patients enrolled in the French HIV-HBV cohort were included if they had >1 study visit after HBsAg-loss. Individual patient kinetics of anti-HBs antibody levels were modeled over time using mixed-effect non-linear regression, whereby maximum specific growth rate and maximal level of antibody production were estimated from a Gompertz growth equation.

RESULTS

Fourteen (4.6%) of 308 co-infected patients followed in the cohort exhibited HBsAg-loss, all of whom were undergoing antiretroviral therapy. Nine (64.3%) of these patients achieved HBsAg-seroconversion during a median 3.0 years (IQR=1.1-5.1) after HBsAg-loss. Across individuals with HBsAg-seroconversion, the fastest rates of antibody growth ranged between 0.57-1.93year^-1 (population maximum growth rate=1.02) and antibody production plateaued between 2.09-3.66 log₁₀ mIU/mL at the end of follow-up (population maximal antibody levels=2.66). Patients with HBsAg-seroconversion had substantial decreases in HBV DNA viral loads (P=0.03) and proportion with elevated ALT levels (P=0.02) and HBeAg-positive serology (P=0.08). No such differences were observed in those without HBsAg-seroconversion.

CONCLUSIONS

Most co-infected patients with HBsAg-seroconversion produced and maintained stable antibody levels, yet kinetics of anti-HBs production were much slower compared to those observed post-vaccination or after clearance of acute HBV-infection.

Favorable Response to Long-term Nucleos(t)ide Analogue Therapy in HBeAg-positive Patients with High Serum Fucosyl-Agalactosyl IgG

Aberrant IgG glycosylation is a feature of hepatitis B virus (HBV) infection but its effect on a long-term efficacy of antiviral therapy has never been addressed. After a screening of 1,085 patients, 132 eligible HBV e antigen (HBeAg)-positive and 101 HBeAg-negative patients with anti-HBV nucleos(t)ide analogue monotherapy were enrolled with on-treatment follow-ups for at least one year. IgG1 N-glycome was profiled using mass spectrometry and evaluated for its relevance in treatment responses. The results indicated that a high level of serum fucosyl-agalactosyl IgG1 (IgG1-G0F) at baseline was associated with the severity of liver inflammation and damage but advanced treatment responses, including HBV DNA loss, HBeAg seroconversion, a reduced drug resistance rate, and a liver histological improvement at year 1, thereby improving the long-term treatment efficacy and the probability of treatment discontinuation in HBeAg-positive patients. Stepwise Cox regression analyses revealed that baseline IgG1-G0F >30% was an independent factor that links to virological response (HR 3.071, 95% CI 1.835–5.141, P < 0.001) or HBeAg seroconversion (HR 2.034, 95% CI 1.011–4.093, P = 0.046). Furthermore, a high IgG1-G0F level at the treatment endpoint was associated with an off-treatment sustained virological response. In conclusion, IgG1-G0F favors the medication outcome for HBeAg-positive chronic hepatitis B.

IFN-adjuvanted DNA vaccine against infectious salmon anemia virus: Antibody kinetics and longevity of IFN expression

Plasmids expressing interferon (IFN) have recently been shown to function as adjuvants in Atlantic salmon when co-injected with a DNA vaccine encoding hemagglutinin-esterase (HE) from infectious salmon anemia virus (ISAV). In this work we have compared the antibody kinetics and the systemic Mx/ISG15 response of fish vaccinated with HE-plasmid using either IFNa plasmid (pIFNa) or pIFNc as adjuvants over a longer time period, i.e. 22 weeks post vaccination (pv). The results showed that the antibody response against ISAV with pIFNa as adjuvant arose earlier (7 weeks pv) than with pIFNc as adjuvant (10 weeks pv), peaked at week 10 and declined at week 22. The antibody response with pIFNc as adjuvant peaked at 16 weeks and kept at this level 22 weeks pv. Fish injected with pIFNc alone expressed high levels of Mx and ISG15 in liver throughout the 22 week period. In contrast, fish injected with pIFNc together with HE-plasmid expressed high levels of Mx and ISG15 in liver for the first 10 weeks, but at week 16 this response was absent in two of three fish at week 16 and was absent in all tested fish at week 22 pv. This suggests that cells expressing HE and IFNc are intact at week 10 pv, but are eliminated by adaptive immune responses after week 10 due to recognition of HE. The longevity of the Mx/ISG15 response in pIFNc treated fish is likely due to the fact that IFNc is a self-antigen of salmon and is not attacked by the adaptive immune system.

Sustained Changes of Treg and Th17 Cells During Interferon-α Therapy in Patients with Chronic Hepatitis B

Chronic hepatitis B (CHB) is a worldwide infectious disease caused by hepatitis B virus (HBV). HBV mainly damages liver cells through immune response. The purpose of this study was to determine whether there were dynamic changes of Treg and Th17 cells and to judge the value of these indicators to antiviral treatment. Twenty-two CHB patients and selected 30 healthy adults were enrolled. Results showed that the expression of Treg (5.72±0.46 vs. 4.42±0.17, p=0.0019) and Th17 (3.94±0.64 vs. 2.66±3.12, p=0.0436) cells was significantly increased in CHB patients, as well as the level of interleukin-17 (IL-17) (16.88±5.37 vs. 8.59±3.31; p=0.004). Then, we monitored longitudinally the impact of the treatment with interferon-α and found that the suppression of viral replication induced by interferon-α resulted in a decrease in Treg, Th17 cells, and IL-17; we also found that the percentage of Treg and Th17 cells went up without clear evidence of clinical autoimmune disease at the end of treatment. Thus, Treg and Th17 cells might play an important role in interferon-α treatment to eliminate HBV. The level of changes may be served to determine the antiviral efficacy of interferon-α therapy.

Lymphocyte CD64 increased in patients with chronic HBV infection

CD64 was up-regulated in infection diseases, but there was no report about the change of CD64 in chronic hepatitis B virus (HBV) infection. The purpose of this study was to determine whether there was a dynamic change of CD 64 index and to judge the value to antiviral treatment. 96 CHB patients were enrolled and selected 33 healthy adults as control. We detected the level of CD64, found the level of CD64 were significantly increased in chronic HBV infection patients, especially the lymphocyte CD64 (8.12 ± 0.23 vs. 6.25 ± 0.27; P < 0.001). Further, we proved CD64 index was increased in various stages of chronic HBV infection. ROC curve analysis showed the level of lymphocyte CD64 had higher AUC value than neutrophil or monocyte. Then we monitor longitudinally the impact of the treatment with interferon-α and found that the suppression of viral replication induced by interferon-α resulted in a decrease in CD64 index. In conclusion, this study showed that CD64 index was increased in chronic HBV infection patients and changed with the course of disease, the therapy of interferon-α would correct it, and analysis prompted that the level of lymphocyte CD64 would be more suitable for as a biomarker to judge the condition of chronic HBV infection and the curative effect of interferon-α treatment.

Regulatory T cells and IL-17(+) T helper cells enhanced in patients with chronic hepatitis B virus infection

Hepatitis B is a worldwide infectious disease caused by hepatitis B virus (HBV), it leaded to millions of deaths every year, HBV mainly through immune response to damage liver cells. The purpose of this study was to judge the value of Regulatory T cells (Treg) and IL-17(+) T helper cells (Th17) in different chronic HBV infection stages. 96 patients with chronic HBV infection were enrolled and selected 33 healthy adults as control. Detected the expression of Treg and Th17 cells in peripheral blood by flow cytometry and assayed liver function simultaneously. Compared to the control group, the expression of Treg (6.80±1.92 vs. 4.42±0.97; P<0.0001) and Th17 (6.15±4.20 vs. 2.66±1.79; P<0.0001) cells were both increased and the ratio of Treg/Th17 was significantly decreased (1.48±0.89 vs. 2.29±1.31; P=0.0001) in patients with HBV infection. Spearman correlation analysis demonstrated that the level of Treg and Th17 cells were associated with liver function. ROC curve analysis found that Treg and Th17 cells were suitable for as a screening test for early detection of the disease. In conclusion, the expression of Treg and Th17 cells were increased in chronic hepatitis B patients and these indicators were independent risk factors to hepatitis.

Direct role of antibody-secreting B cells in the severity of chronic hepatitis B

Chronic hepatitis B involves different immune cells. The direct role of antibody-secreting B cells in the severity of chronic hepatitis B unclear. In this study, the number of plaque forming cells [PFC-(IgG, IgM, anti-HBc IgG, and anti-HBc IgM)], liver function tests (LFT) [alkaline phosphatase (ALP), alanine aminotransferase (ALT), and total serum bilirubin (TSB)], the levels of IL-10 in sera and in lymphocyte cultures, the number of CD4(+) and CD8(+) cells were measured in the peripheral blood of patients and in the controls. In addition, the hepatocytotoxic effect of anti-HBc and anti-HBe in vitro was studied. The largest number of PFCs was observed in the peripheral blood of patients with chronic hepatitis B. This was concomitant with a decrease in CD4(+) /CD8(+) ratio versus this ratio in asymptomatic HBV carriers and in healthy volunteers (P < 0.05). An increase in immunoglobulin (IgG and IgM) levels, anti-HBc IgG, and anti-HBc IgM levels and LFTs in peripheral blood of patients with chronic hepatitis B was seen. Anti-HBc induced hepatocytotoxicity in vitro. The expression of mRNA and protein for IL-10 production was observed at a significant level in culture of lymphocytes isolated from patients with chronic hepatitis B. In addition, a high level of IL-10 was found only in the sera of patients with chronic hepatitis B. It is concluded that the antibody-secreting B cells and the antibodies, which are produced, play an important role in the severity of chronic hepatitis B, which was related negatively with CD4(+) /CD8(+) ratio and positively with IL-10 expression.

CD55 limits sensitivity to complement-dependent cytolysis triggered by heterologous expression of α-gal xenoantigen in colon tumor cells

Engineering cancer cells to express heterologous antigen α-gal and induce the destruction of tumor cells depending on the complement cascade may be a promising strategy of tumor therapy. However, the feasibility and effect of using α-gal to induce colorectal adenocarcinoma cell line cytolysis is not yet known. In this study, we evaluated α-gal expression's ability to sensitize human colorectal adenocarcinoma cell lines to complement attack in cell lines LoVo, SW620, and Ls-174T. Nearly all α-gal-expressing LoVo and SW620 cells were killed by normal human serum (NHS), but α-gal-expressing Ls-174T cells showed no significant lysis. We analyzed the expression levels of membrane-bound complement regulatory proteins (mCRPs) on the three cell lines, and their protective role in α-gal-mediated activation of the complement. LoVo showed no expression of any of the three proteins. CD59 was strongly expressed by SW620 and Ls-174T. CD46 and CD55 varied between the two cell lines. CD46 on SW620 was only half the intensity of CD46 on Ls-174T. Ls-174T showed a notable expression of CD55, while expression of CD55 on SW620 was not detected. The sensitivity of Ls-174T expressing α-gal to NHS greatly increased following the downregulation of CD46 and CD55 with short hairpin RNA (shRNA). However, there is no increase in cell killing when CD59 expression was diminished. Our findings suggest that the use of α-gal as antigen to induce tumor cell killing may be a potential therapeutic strategy in colon cancer and that CD55 plays a primary role in conferring resistance to lysis.

Complement activation and disease: protective effects of hyperbilirubinaemia

Complement, an important effector mechanism of the immune system, is an enzymatic cascade of approx. 30 serum proteins leading to the amplification of a specific humoral response. It can be activated through the classical or alternative pathways, or through the mannose-binding lectin pathway. The activation of the classical pathway is initiated by the binding of the C1 component to antigen-bound antibodies, known as immunocomplexes. C1 is a complex of one molecule of C1q, two molecules of C1r and two molecules of C1s. C1q contains three copies of a Y-shaped fundamental unit with globular heads included in its structure, which play a major role in the interaction with the Fc portion of immunoglobulins. Deficient or exacerbated activation of the complement system leads to diseases of variable severity, and pharmacological inhibition of the complement system is considered as a therapeutic strategy to ameliorate the inflammatory effects of exacerbated complement activation. Bilirubin is a product of haem degradation by the concerted action of haem oxygenase, which converts haem into biliverdin, and biliverdin reductase, which reduces biliverdin to UCB (unconjugated bilirubin). UCB exerts both cytoprotective and cytotoxic effects in a variety of tissues and cells, acting either as an antioxidant at low concentrations or as an oxidant at high concentrations. In the present review, we describe in detail the anti-complement properties of bilirubin, occurring at levels above the UCB concentrations found in normal human serum, as a beneficial effect of potential clinical relevance. We provide evidence that UCB interferes with the interaction between C1q and immunoglobulins, thus inhibiting the initial step in the activation of complement through the classical pathway. A molecular model is proposed for the interaction between UCB and C1q.

Risk Factors for Acute Liver Enzyme Abnormalities in HIV-Hepatitis B Virus-Coinfected Patients on Antiretroviral Therapy

Background

Little is known about the prognostic factors of acute liver enzyme variations in HIV-hepatitis B virus (HBV)-coinfected patients.

Objectives

To identify prognostic factors of acute liver enzyme abnormalities in HIV-HBV-coinfected patients with a focus on the putative role of antiretroviral drugs.

Design

Data from a 3-year, prospective, multicentre cohort study involving HIV-HBV patients were used.

Methods

A Markov model was used to identify prognostic factors of acute episodes of cytolysis and cholestasis in 300 HIV-HBV-coinfected patients. The effect of antiretroviral therapy was analysed according to the classes of drugs, duration of treatment and treatment modifications.

Results

The incidence rates of acute episodes of cytolysis and cholestasis were 13.4 per 100 patient-years (95% confidence interval [CI] 9.5–17.3) and 7.1 per 100 patient-years (95% CI 4.2–10.0), respectively (median follow up 34.1 months). Independent risk factors for cytolysis were a high level of HBV or HIV replication, as well as a low of CD4+ T-cell count. No antiretroviral drug was associated with cytolysis, whereas protease inhibitors seemed to be independently associated with cholestasis, along with treatment modifications and the duration of HIV infection.

Conclusion

Acute and reversible episodes of cytolysis or cholestasis were common and associated with virus- and host-related determinants. The choice of the optimal antiretroviral combination in HIV-HBV-coinfected patients must take into account the necessity of exerting an efficient control of HIV and HBV replication (associated with transient cytolysis) and the risk of inducing cholestasis (associated with the use of protease inhibitors and treatment modifications).

Protective role of unconjugated bilirubin on complement-mediated hepatocytolysis

Hyperbilirubinemia and complement-mediated immune attack on hepatocyte membrane are common features of certain hepatic diseases. To assess whether unconjugated bilirubin (UB) counteracts complement-mediated hepatocytolysis, we first generated a rabbit polyclonal antibody (Ab) against rat hepatocyte plasma membrane (RHPM). An assay performed with isolated rat hepatocytes in the presence of the polyclonal Ab and rat serum as complement donor demonstrated that UB inhibits cell lysis, as lactate dehydrogenase release into the medium was inhibited by the pigment in a dose-dependent manner. Immunofluorescence microscopy studies showed that UB significantly attenuates the binding of C3 to the hepatocyte-Ab complex. Further enzyme immunoassay studies showed that UB interferes the binding of C1q to purified anti-RHPM IgG, also in a dose-dependent manner. A dot-blot assay showed that [14C]-UB binds to C1q and human serum albumin (HSA) to a similar extent. A differential spectrum analysis of UB in the presence of C1q further confirmed that the pigment interacts with this protein. In conclusion, we demonstrated an inhibitory action of UB on complement-mediated Ab-induced hepatocytolysis, this action being evidenced at pathophysiological pigment concentrations (171 microM and higher). A direct binding of the pigment to C1q is likely involved.

Hepatitis C virus and the immune system: a concise review

Hepatitis C Virus (HCV) induces a chronic infection in 50%-80% of infected individuals, which can lead to cirrhosis and hepatocellular carcinoma. The inefficiency of the immune system in eliminating the virus is not well understood as humoral and cellular immune responses are induced. While a persistent infection is generally associated with a weak CD4+ and CD8+ T cell response during the acute phase, there is no good explanation as to why this response is strong enough in 20% of acutely infected people such that they spontaneously resolve the infection. However, the immune system partially controls the viral infection but due to a long-lasting inflammatory milieu, hepatic damage occurs. During the chronic phase of the infection, HCV does not seem to be cytopathic. This aspect is still controversial as the virus was linked to the development of cholestatic syndrome or acute lobular hepatitis after liver transplant in HCV infected patients. The development of new experimental systems such as HCV pseudoparticles, genomic replicon and transfected cell lines have improved our vision of the virus cycle as well as the understanding of the mechanism of persistence. However, a convincing explanation for the chronicity of the infection in the presence of a functional immune response is still missing and is an important area of research to understand HCV immune pathogenesis. Future research should dissect mechanisms that lead to quantitatively or qualitatively inadequate immune responses, the role of the high variability of the virus, the relevance of host's genetic factors and mechanisms of immunosuppression induced by the virus.

Modulation of the outcome and severity of hepadnaviral hepatitis in woodchucks by antibodies to hepatic asialoglycoprotein receptor

Viral hepatitis is frequently accompanied by humoral autoimmune responses toward both organ-nonspecific and liver-specific antigens, but contribution of these reactivities to liver injury remains unrecognized. Infection with woodchuck hepatitis virus (WHV) has been identified as a potent inducer of autoantibodies against asialoglycoprotein receptor (anti-ASGPR), a molecule essentially unique to hepatocytes that mediates clearance of desialylated serum proteins. In this study, we applied the WHV-woodchuck model of hepatitis B to examine the effect of experimentally elicited anti-ASGPR on the progression and the severity of WHV hepatitis in initially healthy animals immunized with the receptor and then infected with WHV and in woodchucks with ongoing chronic WHV hepatitis. The results implied that the induction of anti-ASGPR prior to WHV infection tends to modulate acute viral hepatitis toward chronic outcome and, in animals with established chronic WHV infection, exacerbates histologic severity of liver lesions. The findings also suggest that the liver compromised by chronic hepadnavirus infection might be prone to anti-ASGPR-directed complement-mediated hepatocellular injury and that this is associated with formation of the ASGPR-anti-ASGPR immune complexes on hepatocyte surface. In conclusion, the host's immune response mounted against a hepatocyte-specific autoantigen may modulate both the outcome and the severity of liver injury in viral hepatitis.

Immune-mediated destruction of transfected myocytes following DNA vaccination occurs via multiple mechanisms

The delivery of antigenic proteins in the context of a DNA vaccine leads to the intracellular synthesis of antigen and the induction of both humoral and cellular immune responses. Subsequent to immune activation, any transfected cell expressing the immunogenic protein should, by the rules of immunology, become a legitimate target for removal by immune-mediated mechanisms. Herein, we have used an indirect assay of myocyte integrity following intra-muscular (i.m.) delivery of a DNA vaccine, in mice with various immune deficiencies, to determine which immunological mechanisms may be involved in destruction of antigen-expressing cells. We demonstrate that destruction of antigen- expressing myocytes following i.m. injection of a DNA vaccine is dependent on major histocompatibility complex (MHC) class II restricted CD4+ T cell activation, but is not mediated solely by MHC I-restricted or perforin-mediated lysis and appears to have a component that is antibody-mediated. Although we studied myocytes, the results likely represent what happens to any transfected cell expressing a foreign antigen. This study underscores the ability of DNA vaccines at inducing antigen-specific immune responses that include a number of effector mechanisms. From the perspective of gene therapy, this study highlights the significance of immune activation when considering strategies where maintenance of therapeutic gene expression is desired.

Reduced hepatitis B virus surface antigen-specific Th1 helper cell frequency of chronic HBV carriers is associated with a failure to produce antigen-specific antibodies in the trimera mouse

In chronic hepatitis B virus (HBV) infection weak antiviral immune responses are associated with viral persistence. We studied possible immune deficits underlying the lack of serum antibodies of such patients against the HBV surface antigen (HBsAg) in a novel human/mouse chimeric model. A hepatitis B surface antigen (HBs) vaccination of Balb/c mice engrafted with peripheral blood mononuclear cells (PBMC) of naturally HBV-immunized donors induced high frequencies of human HBsAg-specific B and T helper 1 (Th1) cells. These responses were associated with high serum anti-HBs antibody levels of the subclasses immunoglobulin G1 (IgG1) and IgG2 that are driven by interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). In contrast, PBMC of chronic HBV carriers transplanted into the chimera failed to produce anti-HBs antibodies after vaccination with HBsAg and exhibited a deficit of antigen-specific Th1 cells. A possible influence of HBsAg or viremia was excluded by the lack of viral replication in such chimera. The observed T-cell defect was specific for HBsAg, as the B- and T-cell responses to tetanus toxoid (TT) were fully retained. Thus, our study shows that viral persistence in chronic HBV carriers is associated with an HBsAg-specific Th1 cell defect, which likely is responsible for the insufficient neutralizing anti-HBs-antibody response and is not reversed by HBs vaccination. Alternative approaches to induce HBs-specific Th1 cell responses might represent a future therapeutic option.

Pathogenesis of autoimmune hepatitis

Autoimmune hepatitis (AIH) is an idiopathic disorder affecting the hepatic parenchyma. There are no morphological features that are pathognomonic of the condition but the characteristic histological picture is that of an interface hepatitis without other changes that are more typical of other liver diseases. It is associated with hypergammaglobulinaemia, high titres of a wide range of circulating auto-antibodies, often a family history of other disorders that are thought to have an autoimmune basis, and a striking response to immunosuppressive therapy. The pathogenetic mechanisms are not yet fully understood but there is now considerable circumstantial evidence suggesting that: (a) there is an underlying genetic predisposition to the disease; (b) this may relate to several defects in immunological control of autoreactivity, with consequent loss of self-tolerance to liver auto-antigens; (c) it is likely that an initiating factor, such as a hepatotropic viral infection or an idiosyncratic reaction to a drug or other hepatotoxin, is required to induce the disease in susceptible individuals; and, (d) the final effector mechanism of tissue damage probably involves auto-antibodies reacting with liver-specific antigens expressed on hepatocyte surfaces, rather than direct T-cell cytotoxicity against hepatocytes.

Kinetics of hepatitis B surface antigen-specific immune responses in acute and chronic hepatitis B or after HBs vaccination: stimulation of the in vitro antibody response by interferon gamma

Because cellular and humoral immune responses against the hepatitis B virus (HBV) surface antigen (HBs) might be crucial to overcome HBV infection, HBs-specific B- and T-cell responses of HBV patients and HBs vaccine recipients were analyzed quantitatively and functionally. In patients with acute hepatitis B (AHB), transient high anti-HBs-secreting B-cell frequencies were observed early after clinical onset, whereas 1 patient who probably developed chronic infection and chronic HBV carriers had absent or weak B- and T-cell responses. In HBs vaccine recipients, maximal HBs-specific B- and T-cell responses were detected after the first injection that decreased gradually before anti-HBs antibodies appeared in serum. Years after vaccination, anti-HBs-secreting B cells were enriched in the bone marrow. After in vitro stimulation with HBsAg, peripheral blood mononuclear cells (PBMC) of only 1 of 5 acute and 1 of 6 chronic HBV patients, but of all 6 vaccine recipients, secreted varying amounts of interferon gamma (IFN-gamma), but no interleukin-4 (IL-4) or IL-5. Furthermore, the addition of IFN-gamma, but not of IL-2, -4, -12, or IFN-alpha, resulted in strong increases of anti-HBs-secreting B cells in vaccine recipients and chronic carriers. In conclusion, circulating anti-HBs-secreting B cells were significantly higher in early acute hepatitis B or early after HBs vaccination than in chronic hepatitis B and decreased in the follow-up as a result of compartmentalization to lymphoid tissues. Release of IFN-gamma by antigen-stimulated T cells might be critical for anti-HBs formation.

Complement-mediated cytotoxicity and inhibition of ligand binding to hepatocytes by woodchuck hepatitis virus-induced autoantibodies to asialoglycoprotein receptor

Hepadnavirus invasion in woodchucks has been identified as a potent inducer of autoantibodies against asialoglycoprotein receptor (anti-ASGPR), a molecule essentially unique to hepatocytes that mediate clearance of desialylated serum proteins. We evaluated the possible pathogenetic importance of anti-ASGPR triggered by woodchuck hepatitis virus (WHV), using anti-ASGPR-reactive serum immunoglobulins (Igs) from five animals with different stages of WHV hepatitis or self-limited WHV infection and isolated woodchuck hepatocytes or HepG2 cells as targets. The results revealed that WHV-induced anti-ASGPR can specifically inhibit asialoglycoprotein recognition by both homologous and heterologous liver cells, as tested in an asialofetuin (ASFN)-binding radioassay. However, the extent of the interference significantly varied (from 85% inhibition to none) for anti-ASGPR with similar titer from different animals, indicating a high degree of heterogeneity in the ASGPR epitope specificity and in the potential biological effects of these autoantibodies. The WHV-triggered anti-ASGPR also induced complement-mediated hepatocytolysis in a microculture tetrazolium (MTT) assay, which ranged from 8.9% +/- 0.3% to 33.6% +/- 3.6% (mean +/- SD) for different animals and target cell numbers. This cytopathic effect was strictly ASGPR-specific, complement-dependent, and was not related to the anti-ASGPR ability to inhibit ligand-hepatocyte binding. Our findings indicate that among pathways by which anti-ASGPR autoimmunity could cause liver damage, hepadnavirus-induced anti-ASGPR might impair hepatocytes by both disrupting clearance of desialylated proteins and activation of the complement-mediated cytolysis. These cytopathic effects might contribute to the pathogenesis, aggravate severity, and prolong recovery from liver injury in viral hepatitis.

Analysis of hepatitis B virus populations in an interferon-alpha-treated patient reveals predominant mutations in the C-gene and changing e-antigenicity

It is largely unknown whether hepatitis B virus (HBV) sequence variation during chronic infection hampers HBV immune recognition or the antiviral effect of cytokines on HBV production. Here we have analyzed which region of the HBV genome changes most drastically during an interferon-alpha (IFNalpha)-stimulated immune response. In addition, we have investigated whether the mutations affect viral replication, gene expression, and immune recognition of the mutant viral proteins. The study was performed with full-length HBV genomes taken longitudinally from a patient who transiently cleared HBV and seroconverted to anti-HBe during a long-term IFNalpha treatment. We found a replacement of the predominant virus population during IFNalpha therapy The virus populations differed mainly by a cluster of nucleotide changes in the C-gene and a pre-S2 deletion. Most of the newly emerging mutations localized within core/HBe B-cell epitopes, changed HBe antigenicity toward mono- and polyclonal antibodies, and also influenced the reactivity of the anti-HBc/e antibodies of the patient. All genomes tested expressed less HBeAg than wild-type HBV, while replication and IFNalpha susceptibility were similar. These data indicate that IFNalpha therapy can lead to the emergence of HBV variants with mutations mainly affecting recognition of the core/HBe proteins by antibodies. Taken together, the type of core/HBe-specific B-cell immune response, the sequence of the corresponding epitopes, and the HBe expression level appear to contribute to the decision on viral clearance or persistence.

The role of immune responses in the pathogenesis of hepatitis C virus infection

Hepatitis C virus (HCV) is notable for the high rate of chronic infection, which occurs in nearly all individuals who become infected. Liver biopsies from individuals with chronic HCV infection are notable for the presence of numerous mononuclear cells, at least some of which are CD4+ and CD8+ T lymphocytes. The immune response to HCV is polyclonal and multispecific, both in terms of antibody and cellular immune responses. Individuals who recover from acute HCV infection appear to have quantitatively more vigorous CD4+ proliferative responses against one or more HCV proteins compared with those individuals who develop chronic disease. CD8+ responses are less well characterized, in part because of the technical difficulties involved in isolating and characterizing these cells. HCV-specific CTL can be readily isolated from the liver and PBMC of chronically infected individuals, and recognize multiple epitopes. Even individuals with the same HLA type do not consistently recognize the same epitope. Thus, there does not appear to be an immunodominant response on the CD8+ level in this infection. CD8+ cells do appear to play some role in limiting viral replication. These responses are insufficient to eradicate virus completely, however, and may cause liver injury once chronic infection is established. Cytokines produced by both CD4+ and CD8+ cells may play an important role in both inhibiting viral replication and causing liver injury. A better understanding of the role of cellular immunity in the pathogenesis of HCV infection may aid in the development of vaccines and immunotherapeutic intervention strategies.

Composition, antigenic properties and hepatocyte surface expression of the woodchuck asialoglycoprotein receptor

We have purified woodchuck hepatic asialoglycoprotein receptor (ASGPR) by ligand affinity chromatography and have identified it as a heterooligomeric complex comprised of two subunits with molecular masses of 40 and 47 kD, designated as woodchuck hepatic lectin 1 and 2 (WHL1 and WHL2), respectively. With the help of antisera generated against the soluble, bioactive woodchuck and rabbit ASGPRs and anti-subunit monospecific antibodies, distinct antigenic specificity of each of the ASGPR polypeptide subunits and interspecies immunologic cross-reactivity of the receptor polypeptides displaying comparable molecular masses were documented. In contrast to the purified woodchuck receptor, WHL2 antigenic reactivity was not identifiable in woodchuck hepatocyte plasma membranes unless the intact membranes were exposed to an asialylated ligand or a soluble membrane fraction was incubated with anti-receptor antibody. These findings imply that both WHL1 and WHL2 are expressed on the hepatocyte surface and contribute to ligand binding, since antibody specific to either subunit blocks ligand attachment. Our results also indicate that ligand binding modifies antigenic properties of the membrane expressed ASGPR.