Adaptive immune response during hepatitis C virus infection

Hepatitis C virus(HCV)infection affects about 170 million people worldwide and it is a major cause of liver cirrhosis and hepatocellular carcinoma.HCV is a hepatotropic non-cytopathic virus able to persist in a great percentage of infected hosts due to its ability to escape from the immune control.Liver damage and disease progression during HCV infection are driven by both viral and host factors.Specifically,adaptive immune response carries out an essential task in controllingnon-cytopathic viruses because of its ability to recognize infected cells and to destroy them by cytopathic mechanisms and to eliminate the virus by non-cytolytic machinery.HCV is able to impair this response by several means such as developing escape mutations in neutralizing antibodies and in T cell receptor viral epitope recognition sites and inducing HCV-specific cytotoxic T cell anergy and deletion.To impair HCV-specific T cell reactivity,HCV affects effector T cell regulation by modulating T helper and Treg response and by impairing the balance between positive and negative co-stimulatory molecules and between pro-and antiapoptotic proteins.In this review,the role of adaptive immune response in controlling HCV infection and the HCV mechanisms to evade this response are reviewed.     

Humoral immune response in Japanese acute hepatitis patients with hepatitis C virus infection.

The humoral immune response to acute infection by hepatitis C virus (HCV) is not yet perfectly clear in terms of immunoglobulin (Ig) response, diversity of HCV antigen, and the relation with hepatitis severity and antibody response. Serum IgM and IgG anti-HCV levels in patients with HCV and either acute hepatitis (AH) or fulminant hepatitis (FH) were investigated; the diversity of HCV antigen was investigated by RIBA test III. Of 22 AH patients, 12 (54.5%) were positive for IgM anti-HCV, mainly reacting to HCV core protein. The mean interval until the appearance of IgM anti-HCV after onset was 24.1+/-26.2 days. IgG anti-HCV mainly reacted to both core and NS-3 antigen, appearing 42.6+/-42.1 days after onset. From a serial study of 15 AH patients, it was considered that in seven AH patients (46. 7%), the IgM response would precede the IgG response. In another two AH patients, IgM anti-HCV was not detected during the acute disease phase. Of 48 chronic hepatitis patients with HCV-RNA, 40 patients were positive for IgM anti-HCV. Therefore, IgM anti-HCV was useful for diagnosis in some of the AH patients, but it was difficult to use for distinguishing between acute and chronic infection. All four FH patients with HCV-RNA were positive for both IgM and IgG antibody to HCV at onset. Their antibody titres were higher than those of AH patients. These results suggested that, as in FH due to HBV, FH due to HCV could induce strong and rapid humoral immunity.     

High resolution analysis of cellular immune responses in resolved and persistent hepatitis C virus infection

BACKGROUND & AIMS: Cellular immune responses are thought to play a key role in the resolution of primary HCV infection. Although it has been consistently shown that CD4+ T-cell responses are maintained in those with spontaneous resolution but lost in those with persistent infection, the role of CD8+ T-cell responses remains controversial. Previous studies have largely focused on limited HLA alleles and predefined CD8+ T-cell epitopes, and, thus, comprehensive studies remain to be performed. METHODS: To understand the composition of the immune response associated with spontaneous resolution, we comprehensively mapped CD8+ T-cell responses in 20 HLA-diverse persons with resolved HCV infection, using HCV peptides spanning the entire genome. We analyzed the magnitude, breadth, function, and phenotype using ELISpot, class-I tetramers, intracellular cytokine staining, and cytolytic assays. We studied in parallel HCV-specific responses and viral sequence variation in persistent infection. RESULTS: Responses in individuals with resolved infection were strong and broad with robust proliferation in response to antigen. Responses in those persistently infected were rarely detected ex vivo and, when present, were narrowly directed and weak. However, they also proliferated in vitro. Dominant target epitopes differed among individuals in both cohorts, despite frequently shared HLA-alleles. CONCLUSIONS: These data indicate that persisting, strong CD8+ T-cell responses are observed in the majority of persons with resolved HCV infection and provide support for strategies to boost CD8+ T-cell responses for the prevention or treatment of HCV infection but also highlight the diversity of responses that may need to be elicited to provide protection.     

Cellular immune response to the hepatitis C virus

Hepatitis C virus (HCV) infection is most often clinically inapparent and rarely associated with symptoms of acute hepatitis. Most patients, however, fail to resolve the acute infection and proceed to develop chronic hepatitis with the risk of liver cirrhosis and hepatocellular carcinoma later in life. Since the kinetics of the earliest events of virus–host interaction are likely to determine the outcome of infection, research has focused on the characterization of the strength and kinetics of the antiviral immune response in different stages of disease. The identification of the immunological correlates of viral clearance is pivotal for the development of vaccines and efficient therapies.     

Assessment of humoral immune response in patients with chronic hepatitis C virus infection

Hepatitis C infection is a major public health problem worldwide. Hepatitis C virus (HCV) infection has been identified as a major causative agent of post-transfusion hepatitis. The host immune response to HCV infection is composed of both non- specific immune response, including interferon (IFN) production and natural killer (NK) cell activity and a virus-specific immune response, including humoral and cellular components. Susceptibility to infection has been related to immunological disturbances. Several studies have provided experimental evidence of disorders of both cellular and humoral immunity. Humoral Immunity is dependent mainly on immunoglobulins and little data are available about serum immunoglobulin values in chronic hepatitis C. The present study aimed to evaluate humoral immune response by measuring the concentration of serum immunoglobulin isotypes (IgG, IgM, IgA) and IgG-subclasses level (IgG1-4) in chronic hepatitis C patients and healthy controls. This study included 50 patients with chronic hepatitis C. All of them had positive serum anti-HCV antibodies, positive serum HCV-RNA by PCR, and histologically-proven chronic hepatitis. The results were compared with 25 healthy controls. Total IgG, IgA and IgM were assayed by nephelometry. IgG subclasses were assayed using human IgG subclasses enzyme immunoassay. Serum protein electrophoresis was performed in agarose gel. The results showed that no significant difference in serum immunoglobulin levels were found among patients with chronic hepatitis C of minimal liver damage( Knodell index < or =3) and patients with mild liver disease (Knodell index > 3). A significant increase in total serum IgG, IgG1 and IgG2 levels were found in patients with chronic hepatitis than in healthy controls but no difference was found in IgG3 and IgG4 in both patients and controls. Mean serum IgM was increased in patients with HCV infection compared with healthy controls. No significant difference was found in IgA level in both the patients and healthy controls. Our data revealed an increase of humoral immune response in chronic hepatitis C infection. This is evidenced by an elevation in serum immunoglobulin isotypes; IgG and its subclasses IgG1 and IgG2 and IgM. These findings may provide some new insights into the antibody response to HCV.     

Influence of hepatitis C virus infection on soluble cellular adhesion molecules in hemodialysis patients

BACKGROUND/AIMS: Higher levels of soluble cellular adhesion molecules have been found to be a strong indicator of endothelial dysfunction and atherosclerosis in the general population. In hemodialysis patients, soluble cellular adhesion molecules have been found at higher levels as well. Such an increase has been considered as a sign of chronic inflammation. Chronic viral hepatitis C (HCV) infection, highly prevalent in hemodialysis patients, is also a disease that can induce chronic inflammation. We conducted a cross-sectional association study of soluble cellular adhesion molecules and hepatitis C in maintenance hemodialysis patients. METHODS: A total of 87 stable hemodialysis patients were included in this study, mean age was 60.0 +/- 13.7 years. Anti-HCV antibody and HCV RNA assay were done. Patients were divided into anti-HCV-positive and anti-HCV-negative groups. Predialytic serum soluble intercellular adhesion molecules-1 (sICAM-1), soluble vascular cellular adhesion molecules-1 (sVCAM-1), and soluble E-selectin were assayed by commercially available enzyme-linked immunosorbent assay (ELISA) kits. The results were correlated with other hematological and biochemical results. RESULTS: In the anti-HCV-positive group, the time on hemodialysis was longer (105.5 +/- 65.7 vs. 49.2 +/- 44.0 months, p = 0.001). The sICAM-1, sVCAM-1 and E-selectin levels were higher in the anti-HCV-positive group. HCV infection was determined as an independent determinant of sICAM-1 and sVCAM-1 by multiple linear regression analysis. CONCLUSION: Elevated serum soluble cellular adhesion molecules are multifactorial in hemodialysis patients. The role of HCV infection must be considered. The clinical significance and implications of soluble cellular adhesion molecules remains to be elucidated.     

Cytokines and chemokines in the immune response to hepatitis C infection

Over 170 million people are infected with the hepatitis C virus worldwide, resulting in a large disease burden and significant mortality. Hepatitis C virus is rarely cleared in the acute phase of the infection and most patients become chronically infected; a proportion of these patients develop progressive liver disease and fibrosis. The outcome of infection depends on the immune responses of both the innate and cognate immune systems, and these in turn are orchestrated by networks of cytokines and chemokines. There is evidence that a vigorous type 1 immune response to viral proteins is required for viral elimination, and the recruitment of such effector cells to the liver is dependent on the local activity of specific inducible chemokines. Multiple factors determine the ability of the hepatitis C virus to survive host immune responses, including an ability to alter the cytokine profile secreted by T cells and to cause resistance to the effects of antiviral cytokines such as interferon. In the present review, we briefly cover the important advances made in this area over the past 12 months.     

Specific cellular immune response and cytokine patterns in patients coinfected with hepatitis C virus and Schistosoma mansoni

Patients coinfected with hepatitis C virus (HCV) and Schistosoma mansoni show high incidence of viral persistence and accelerated fibrosis. To determine whether immunological mechanisms are responsible for this alteration in the natural history of HCV, the HCV-specific peripheral CD4(+) T cell responses and cytokines were analyzed in patients with chronic hepatitis C monoinfection, S. mansoni monoinfection, or HCV and S. mansoni coinfection. An HCV-specific CD4(+) proliferative response to at least 1 HCV antigen was detected in 73.3% of patients infected with HCV, compared with 8.6% of patients coinfected with HCV and S. mansoni. Stimulation with HCV antigens produced a type 1 cytokine profile in patients infected with HCV alone, compared with a type 2 predominance in patients coinfected with HCV and S. mansoni. In contrast, there was no difference in response to schistosomal antigens in patients infected with S. mansoni alone, compared with those coinfected with HCV and S. mansoni. These findings suggest that the inability to generate an HCV-specific CD4(+)/Th1 T cell response plays a role in the persistence and severity of HCV infection in patients with S. mansoni coinfection.     

Impact of human immune deficiency virus infection on hepatitis C virus infection and replication

Human immune deficiency virus (HIV) and human hepatitis C virus (HCV) infection are frequent in patients who have been exposed to blood or blood-derived products. It has been suggested that HIV infection increases HCV replication altering the course of HCV-related disease. However, it is not known if HIV directly enhances HCV replication or if its effect is the consequence of HIV infection of other cell types that control HCV replication (lymphocytes, macrophages). While the main cell targets for HIV infection are mononuclear leukocytes bearing CD4 and the chemokine receptors CCR5 and CXCR4, HCV was originally thought to be strictly hepatotropic, but it is now known that HCV can also replicate in peripheral blood mononuclear cells (PBMC). Therefore, in co-infected individuals, these two different viruses could share cell targets and interact either directly or indirectly. Some membrane receptors can be used by both HCV and HIV for entry into target cells, but the intracellular mechanisms shared by these viruses are not known. Lack of experimental systems providing suitable methods for the study of HCV replication in the presence or absence of HIV co-infection has hampered advances in this research area, but recent investigations are currently going on in order to answer these questions. This is an important issue, as knowledge of HIV/HCV interactions is required for the design of effective antiviral therapies.     

Protective immune response to hepatitis C virus in chimpanzees rechallenged following clearance of primary infection

Hepatitis C virus (HCV) infections were evaluated in chimpanzees that had previously cleared HCV and were rechallenged. Animals that had previously cleared HCV infection rapidly cleared homologous and heterologous virus upon rechallenge, indicative of a strong protective immunity. In one animal, sterilizing immunity was observed with regard to viremia, although viral RNA was transiently detected in the liver. Accelerated viral clearance following rechallenge with HCV was observed in animals that had not been exposed to HCV for over 16 years, suggesting that long-lasting protective immunity may be possible. The ability of peripheral blood mononuclear cells (PBMC) to recognize HCV proteins was evaluated during the course of the rechallenge experiments. A very early and strong in vitro recall response to HCV nonstructural proteins appeared to be associated with viral clearance. In contrast, proliferative responses to HCV proteins were not observed in 4 persistently infected chimpanzees, and a weak proliferative response was observed in 1 of 2 animals during acute resolving infection. The results suggest that a strong T-cell proliferative response is induced upon rechallenge of chimpanzees with HCV and that this response is associated with rapid viral clearance. The antibody response to HCV proteins increased by over 1,000-fold in all animals following rechallenge as well. A more complete understanding of the role of the cellular immune response in the clearance of HCV and the nature of the protective immune response following viral clearance may aid in the generation of therapies and vaccines.     

Extrahepatic immune related manifestations in chronic hepatitis C virus infection

The association of chronic hepatitis C with immune related syndromes has been frequently reported. There is a great range of clinical manifestations affecting various systems and organs such as the skin, the kidneys, the central and peripheral nervous system, the musculoskeletal system and the endocrine glands. Despite the high prevalence of immune related syndromes in patients with chronic hepatitis C, the exact pathogenesis is not always clear. They have been often associated with mixed cryoglobulinemia, a common finding in chronic hepatitis C, cross reaction with viral antigens, or the direct effect of virus on the affected tissues. The aim of this review is to analyze the reported hepatitis C virus immune mediated syndromes, their prevalence and clinical manifestations and to discuss the most supported theories regarding their pathogenesis.     

Viral and host immune regulatory mechanisms in hepatitis C virus infection

Recent studies suggest that liver inflammation in chronic hepatitis C virus (HCV) infection is controlled by several mechanisms, including host regulatory immune responses and viral polypeptides interacting with cells involved in innate and adaptive immunity. This article provides an overview about current thinking on host-pathogen symbiotic relationship in HCV infection and its significance with respect to pathogenesis. Special emphasis is given to regulatory T-cell subsets which have recently received attention and which are thought to play a major role in persistent viral infections such as HCV.     

Effects of antiviral therapy on the cellular immune response in acute hepatitis C

Spontaneous recovery occurs in a minority of patients with acute hepatitis C but is associated with vigorous and long-lasting cellular immune responses. Treatment-induced recovery can be achieved in the majority of patients who are treated in the acute phase, but the kinetics and mechanisms of viral clearance and immune responsiveness are not known. Both direct antiviral effects and indirect immune-mediated effects, such as immune modulation of Th2 to Th1 responses and prevention of exhaustion of cellular responses by rapid reduction of viral titer, have been proposed. To investigate how early antiviral therapy affects hepatitis C virus (HCV)-specific T cell responses, we performed detailed prospective clinical, virological, and immunological studies on 7 patients with acute hepatitis C who received antiviral therapy and were followed at 2 to 4 week intervals for 1 to 2 years. The total CD4(+) and CD8(+) cell response was analyzed with 600 overlapping HCV peptides and 6 proteins by ex vivo enzyme-linked immunospot (ELISpot), intracellular cytokine staining, and proliferation assays. In contrast to earlier studies with selected HCV epitopes, this extended analysis detected multispecific interferon gamma(+) (IFN-gamma(+)) responses in each patient, even in the absence of T-cell proliferation. After initiation of antiviral therapy (at a mean of 20 weeks after infection), all sustained responders demonstrated gradually decreasing, then nearly absent HCV-specific T-cell responses, whereas the sole patient who developed viral breakthrough after initial HCV control maintained cellular immune responses. In conclusion, a sustained response to antiviral therapy was not associated with a lasting enhancement of HCV-specific T-cell responsiveness in the blood.     

慢性HBV/HCV感染人群伴随的免疫相关表现

慢性HBV/HCV感染者常常伴有自身免疫系统紊乱,在丙型肝炎中尤为常见。介绍了慢性丙型肝炎患者免疫状态紊乱的机制,出现非器官特异性自身抗体的比例,以及伴随的免疫相关疾病,如混合型冷球蛋白血症、肾小球肾炎、干燥综合征、甲状腺疾病、2型糖尿病的临床表现、诊断和治疗等。简述了慢性乙型肝炎患者免疫状态紊乱的机制、相关的免疫表现以及抗病毒治疗对其的影响。慢性乙型或丙型肝炎的抗病毒治疗可以减轻伴随的免疫系统疾病,但是不宜采用干扰素治疗,因此,乙型肝炎患者应采用核苷和核苷酸类药物治疗,丙型肝炎患者应采用直接抗病毒药物治疗。     

Long-term outcome of hepatitis C virus infection after liver transplantation

We analyzed the long-term clinical course of 71 patients with RNA-positive hepatitis C virus (HCV) infection after liver transplantation. Patients with reinfection after transplantation for HCV-related liver disease, or de novo infection at transplantation were followed for up to 12 years. Cumulative survival for patients with HCV infection at 2, 5, and 10 years after transplantation was 67%, 62%, and 62%, respectively. It was not significantly different from that in patients transplanted for other nonmalignant diseases without HCV infection. The main factor determining long-term survival was the presence or absence of hepatocellular carcinoma (HCC) at transplantation. The 5-year survival rate for HCV patients with or without HCC was 35% versus 73%, respectively (P < .05). No deaths because of viral hepatitis of the graft were observed. Deaths in the first year after transplantation were caused by infectious complications, cardiovascular problems, or rejection; deaths after more than 12 months were exclusively because of recurrence of HCC. Biochemical and histological evidence of hepatitis was found in the majority of the patients, only 16% had normal alanine aminotransferase (ALT) values throughout. Twenty-two percent of patients complained of symptoms, with hepatitis C being the cause in 82% of these. Two patients lost their HCV-RNA for prolonged, ongoing periods of time. The severity of the posttransplantation hepatitis was unrelated to age, sex, severity of liver disease before transplantation, cold ischemic time of the graft, duration of the operation, transfusions, the number of rejection episodes, or the long-term immunosuppressive regime. Only initial short-term therapy with interleukin 2 (IL2) receptor antibodies adversely influenced inflammatory activity. Viral genotype did not influence the course of the graft hepatitis in our series. Histology showed inflammation in 88% of the biopsies and signs of fibrosis in 24%. Mean ALT values correlated with inflammation but not with fibrosis in the biopsies. Porto-portal bridging was observed in six patients, one patient developed cirrhosis within 2 years after orthotopic liver transplantation (OLT). We conclude that chronic hepatitis develops in the majority of patients with HCV infection after liver transplantation. Carrier states without significant laboratory abnormalities are observed in approximately 16%, biochemical abnormalities without symptoms are seen in 60%, and symptomatic disease develops in a quarter of the patients. The disease course closely resembles that seen in nontransplanted hepatitis C patients. It is generally mild but little over 10% of patients develop signs of fibrosis of the graft during the first decade.(Hepatology 1997 Jan;25(1):203-10)