Therapeutic control of hepatitis C virus: the role of neutralizing monoclonal antibodies.

Liver failure associated with hepatitis C virus (HCV) accounts for a substantial portion of liver transplantation. Although current therapy helps some patients with chronic HCV infection, adverse side effects and a high relapse rate are major problems. These problems are compounded in liver transplant recipients as reinfection occurs shortly after transplantation. One approach to control reinfection is the combined use of specific antivirals together with HCV-specific antibodies. Indeed, a number of human and mouse monoclonal antibodies to conformational and linear epitopes on HCV envelope proteins are potential candidates, since they have high virus neutralization potency and are directed to epitopes conserved across diverse HCV genotypes. However, a greater understanding of the factors contributing to virus escape and the role of lipoproteins in masking virion surface domains involved in virus entry will be required to help define those protective determinants most likely to give broad protection. An approach to immune escape is potentially caused by viral infection of immune cells leading to the induction hypermutation of the immunoglobulin gene in B cells. These effects may contribute to HCV persistence and B cell lymphoproliferative diseases.

Intrahepatic lymphocyte phenotypes in hepatitis C virus infection: a comparison between cirrhotic and non-cirrhotic livers.

AIM: The pathogenesis of viral hepatitis involves the activation of cellular immunity, including intrahepatic lymphocytes (IHL). Lym-phocyte phenotypes play a fundamental role in the pathogenesis of chronic hepatitis C virus (HCV) infection, the progression of liver fibrosis and subsequent hepatocellular carcinoma. The aim of this study was to evaluate the frequency of intrahepatic mononuclear cell phenotypes in patients with chronic HCV. Another aim was to assess the relationship of nonparenchymal cells with liver fibrosis. METHODS: Liver fibrosis was evaluated with the Histologic Activity Index. Fourteen liver biopsies showed mild fibrosis (group 1), and 11 bridging fibrosis (group 2). Fourteen samples were explants from HCV patients who underwent liver transplantation (group 3). CD4 and CD8 T-lymphocytes, CD20 (B lymphocytes), CD16 (macrophage), and CD57 (NK) cells were detected using monoclonal antibodies on paraffin-embedded tissue. RESULTS: A minority of lobular cells stained for T- or B-lymphocytes. Most lobular cells stained with macrophage antibodies, and were more common in bridging fibrosis, compared to mild fibrosis. The percentages of lobular CD4 and CD8 cells were significantly lower in regenerative nodules of cirrhotic livers. There was a strong negative correlation between lobular CD8 and fibrosis score (R= -0.65), and a strong positive correlation between CD16-stained mononuclear cells (macrophages) and fibrosis score (R=0.66). In portal and periportal areas, CD4 but not CD8 lymphocytes decreased in parallel with fibrosis. B-lymphocytes were more commonly found in the portal areas than in the lobule. CD57-positive cells were rare in both lobule and portal areas, and their frequency was not different in the three groups studied. CONCLUSIONS: In hepatitis C, lobular mononuclear cells are mostly macrophages and appear associated with bridging fibrosis. Cirrhotic livers display significantly lower numbers of lobular CD4 and CD8 lymphocytes. This finding could help explain a decrease in immune surveillance and the promotion of neoplastic growth in HCV-associated cirrhosis.

HDV RNA replication: ancient relic or primer?

HDV replicates its circular RNA genome using a double rolling-circle mechanism and transcribes a hepatitis delta antigen-encodeing mRNA from the same RNA template during its life cycle. Both processes are carried out by RNA-dependent RNA synthesis despite the fact that HDV does not encode an RNA-dependent RNA polymerase (RdRP). Cellular RNA polymerase II has long been implicated in these processes. Recent findings, however, have shown that the syntheses of genomic and antigenomic RNA strands have different metabolic requirements, including sensitives to alpha-amanitin and the site of synthesis. Evidence is summarized here for the involvement of other cellular polymerases, probably pol I, in the synthesis of antigenomic RNA strand. The ability of mammalian cells to replicate HDV RNA implies that RNA-dependent RNA synthesis was preserved throughout evolution.

Viral and cellular proteins involved in coronavirus replication.

As the largest RNA virus, coronavirus replication employs complex mechanisms and involves various viral and cellular proteins. The first open reading frame of the coronavirus genome encodes a large polyprotein, which is processed into a number of viral proteins required for viral replication directly or indirectly. These proteins include the RNA-dependent RNA polymerase (RdRp), RNA helicase, proteases, metal-binding proteins, and a number of other proteins of unknown function. Genetic studies suggest that most of these proteins are involved in viral RNA replication. In addition to viral proteins, several cellular proteins, such as heterogeneous nuclear ribonucleoprotein (hnRNP) A1, polypyrimidine-tract-binding (PTB) protein, poly(A)-binding protein (PABP), and mitochondrial aconitase (m-aconitase), have been identified to interact with the critical cis-acting elements of coronavirus replication. Like many other RNA viruses, coronavirus may subvert these cellular proteins from cellular RNA processing or translation machineries to play a role in viral replication.

Detection of Cellular Proteins and Viral Core Protein Interacting with the 5' Untranslated Region of Hepatitis C Virus RNA.

Hepatitis C virus (HCV) is a pesti- and flavi-like virus, which contains a highly conserved 5'-untranslated region (UTR). This region is implicated in the regulation of both translation and RNA replication. To examine the possible cellular factors involved in HCV replication, we performed UV cross-linking experiments to detect cellular protein binding to 5'-UTR of HCV RNA. No cytoplasmic proteins were found to cross-link to 5'-UTR. Surprisingly, when nuclear extracts were used for UV cross-linking, a major protein of 110 kD and several other minor proteins were detected. Competition assays confirmed that the binding of the 110-kD protein was specific to the 5'-UTR. The protein-binding site was mapped within the 78-nt region between nucleotides 199 and 277 from the 5' end of the viral RNA. This protein was present in several different cell lines tested. No cellular proteins specifically bound to the complementary strands of the 5'-UTR. We have also shown by an RNA-protein blotting assay that 5'-UTR bound to the HCV core protein, which can be translocated to the nuclei. These findings suggest that HCV RNA may enter nuclei by complexing with the viral core protein and interact with nuclear proteins that are involved in the regulation of RNA replication or translation. It is thus possible that HCV employs a replication strategy distinct from its related pestiviruses or flaviviruses. Copyright 1995 S. Karger AG, Basel