Pathogenesis of chronic hepatitis C: Immunological features of hepatic injury and viral persistence

Abstract

The immune response to viral antigens is thought to be responsible for viral clearance and disease pathogenesis during hepatitis C virus (HCV) infection. In chronically infected patients, the T-cell response to the HCV is polyclonal and multispecific, although it is not as strong as the response in acutely infected patients who display a more vigorous T-cell response. Importantly, viral clearance in acutely infected patients is associated with a strong CD4 ؉ helper T-cell response. Thus, the dominant cause of viral persistence during HCV infection may be the development of a weak antiviral immune response to the viral antigens, with corresponding inability to eradicate infected cells. The most striking feature of hepatitis C is its tendency toward chronicity. The hepatitis C virus (HCV) contains a positive-stranded RNA genome of about 10 kilobases, which contains a single uninterrupted open reading frame that encodes a protein of 3010-3011 amino acids. 1,2 The virus is classified as a Flavivirus. HCV infects an estimated 400 million people, corresponding to more than 3% of the world population. 3 Numerous partial and complete nucleotide sequences have been derived from geographically widespread HCV isolates. The data indicate substantial sequence diversity within, and especially between, each geographic area. The European and American isolates appear to be more closely related to each other than to the Japanese isolates. Based on a polymerase chain reaction-based algorithm, a classification system has been proposed by Okamoto 4 and revised by Simmonds. 5 Different viral sequences (quasispecies) have been isolated from the same patient upon sequential sampling, and multiple isolates have been reported in a single sample. 6 The degree of similarity between isolates at the amino acid level varies from genome region to region. The nucleocapsid protein (core) has the highest sequence homology among all isolates sequenced to date. In contrast, the E1 and E2/NS1 regions present the highest degree of sequence variability among different isolates; in particular, the N terminal portion of E2/NS1 contains a hypervariable region of 30 amino acids, which shows extensive variation between virtually all known isolates. 7 The major extracellular loop of CD81, a cell-surface protein widely expressed on B and T lymphocytes and other cells including hepatocytes, has been shown to bind E2. 8 The recent success of isolating a cDNA clone capable of generating infectious RNA transcripts may be an important step toward the development of a tissue culture system. 9,10 The only animal model, the chimpanzee, mirrors several features of human HCV infection. Most importantly, the frequency of persistent infection is high in both species, and virus replication occurs despite evidence of cellular and humoral immune responses. 11,12 A key difference is that necroinflammatory lesions in chronically infected chimpanzees are almost always mild, whereas in humans, the disease spectrum is very wide, ranging from mild to severe hepatitis and end-sta...

Pathogenesis of hepatitis C: HCV consensus 2007

“…In individuals infected with HCV, the persistence of the virus can be attributed the large inoculum and the high rate of viral replication, which allow the virus to evade the host immune response [4,23]. There is controversy over whether the sequence of nucleotides is directly associated with more intense hepatic lesions [6,24,25].…”

“…Similar to what occurs in auto-immune type 2 hepatitis, HCV can mimic the immune system, leading to viral escape or postinfection immunity [4,56]. Anti-HCV antibodies have been implicated in tissue damage due to the formation of immunocomplexes such as antinuclear antibodies [57], autoantibodies that act against cytochrome P450 and antibodies that act against the liver and kidney [4].…”

“…The elimination or persistence of HCV infection depends on the balance between the effectiveness, specificity and rapidity of the innate and adaptive immune responses, as well as on the HCV replication rate [3]. Persistence of HCV can also be caused by infection at privileged (extrahepatic) sites, viral inhibition of antigen presentation, selective immune suppression, negative regulation of HCV gene expression, viral mutations, immune exhaustion of T cells and the incomplete differentiation of memory T cells [4,5].Fibrosis is the principal complication of chronic hepatitis C, and it is estimated that 20% of patients develop cirrhosis over a period of 10, 20 or 30 years [2,6]. The progression of fibrosis increases morbidity and mortality in chronic hepatitis C [7], since it can lead to death due to complications caused by cirrhosis or hepatocarcinoma [2].…”

“…The production of new viruses is counterbalanced by the destruction of infected cells through tissue apoptosis or degradation in peripheral blood, since the half-life of the virus in peripheral blood is approximately 2.7 hours [7]. Experimental studies have shown that NS3 and NS5 proteins induce apoptosis in infected hepatocytes [22].In individuals infected with HCV, the persistence of the virus can be attributed the large inoculum and the high rate of viral replication, which allow the virus to evade the host immune response [4,23]. There is controversy over whether the sequence of nucleotides is directly associated with more intense hepatic lesions [6,24,25].…”

“…The elimination or persistence of HCV infection depends on the balance between the effectiveness, specificity and rapidity of the innate and adaptive immune responses, as well as on the HCV replication rate [3]. Persistence of HCV can also be caused by infection at privileged (extrahepatic) sites, viral inhibition of antigen presentation, selective immune suppression, negative regulation of HCV gene expression, viral mutations, immune exhaustion of T cells and the incomplete differentiation of memory T cells [4,5].…”