Detection of hepatitis C virus infection by enzyme-linked immunosorbent assay system using core protein expressed in Escherichia coli

Hepatitis C virus structural proteins induce liver cell injury in transgenic mice

To develop an animal model of hepatitis C virus (HCV) infection, transgenic mice carrying part of the HCV cDNA (C980) encoding HCV-core and envelope proteins under control of the mouse class I major histocompatibility complex gene (H-2K) regulatory region were produced. HCV-C980 RNA and HCV-core protein were present in livers from line H36 as determined by RNase protection assay and immunostaining, respectively. More than 40 animals from line H36 were examined histologically. Most of these H36 mice after 10 months of age developed spontaneous focal infiltration of lymphocytes, hepatocyte necrosis, degeneration, and altered foci with mitotic hepatocytes. These pathological lesions were absent in livers from the age-matched control littermates. Liver cells from these H36 mice were sensitive to damage induced by intravenous administration of an anti-Fas antibody. It is suggested that HCV-C980 proteins by themselves may be one causative agent of liver cell injury in subjects with HCV infection.

Expression in E. coli and purification of a chimeric p22-NS3 recombinant antigen of hepatitis C virus (HCV)

A recombinant antigen (p22-NS3), possessing putative HCV nucleocapsid protein (p22) and non-structural protein 3 (NS3) epitopes, was heavily expressed in E. coli and purified. The p22-NS3 purified recombinant antigen strongly reacts with sera containing human antibodies directed against p22 and NS3 providing a starting point for the design of an HCV single all-encompassing antigen for a blood screening assay.

Synthetic gene for the hepatitis C virus nucleocapsid protein

A synthetic gene encoding the hepatitis C virus (HCV) nucleocapsid protein was constructed and expressed in E. coli. To synthesize this gene, we developed a new method that results in the enzymatic synthesis of long polydeoxyribonucleotides from oligodeoxyribonucleotides. The method, designated as the 'Exchangeable Template Reaction' (ETR), uses oligonucleotides as templates for DNA polymerase. A special mechanism was designed to exchange the templates during the polymerase reaction. The mechanism relies on the formation of a single-stranded 3'-protrusion at the 'growing point' of the elongating DNA such that it can be subsequently annealed, in a sequence-specific manner, with the next synthetic oligonucleotide. When annealed to the 3'-protrusion, the added oligonucleotide becomes a template for DNA polymerase, and the protruding 3'-end of the double-stranded DNA is used as the primer. The HCV nucleocapsid gene was assembled with DNA ligase from three fragments synthesized by ETR. The data verify that this method is efficient. The main advantage of ETR is the ability to combine more than two oligonucleotides in one tube together with polymerase and an enzymatic activity that produces a 3'-protrusion (e.g., BstXI) rather than the sequential addition of each component. The data demonstrate that as many as five oligonucleotides can be used simultaneously, resulting in a synthesized DNA fragment of designed sequence. The synthetic gene expressed in E. coli produced a 27 kDa protein that specifically interacted with antibodies from sera obtained from HCV-infected individuals.

Clinical evaluation of the antibody against core protein of hepatitis C virus

The authors measured antibody against the core protein of hepatitis C virus (HCV) in patients with acute or chronic hepatitis and healthy blood donors, and compared the results with the one obtained from anti-C100-3 assay. To characterize this antibody (anti-core), we also examined the patients with past posttransfusional acute non-A, non-B hepatitis and investigated how frequently viraemia of HCV persisted after the acute phase of hepatitis detecting HCV RNA by polymerase chain reaction. Anti-core was detected in 109/128 (85.2%) of patients with chronic hepatitis and the detection rate of anti-C100-3 was 95/128 (74.2%), respectively. Twenty seven of 33 (82%) patients with past postransfusional acute hepatitis were still positive for anti-core concomitant with the presence of anti-C100-3, having accompanied the presence of HCV RNA in 24/33 (73%). Eight of 2,020 (0.4%) healthy blood donors who were negative for anti-C100-3 were anti-core-positive, and all 5 patients transfused with this anti-core positive blood suffered from posttransfusion hepatitis C. Thus, anti-core antibody was closely associated with the presence of HCV RNA and considered to be a reliable marker of the virus replication.

Antigenic regions within the hepatitis C virus envelope 1 and non-structural proteins: identification of an IgG3-restricted recognition site with the envelope 1 protein

Antibody binding to antigenic regions of hepatitis C virus (HCV) envelope 1 (E1; residues 183-380, E2/non-structural (NS) 1 (residues 380-437), NS1 (residues 643-690), and NS4 (1684-1751) proteins were assayed for 50 sera with antibodies to HCV (anti-HCV) and for 46 sera without anti-HCV. Thirty-four peptides, 18 residues long with an eight-amino acid overlap within each HCV region, were synthesized and tested with all 96 sera. Within the E region 183-380, the major binding site was located to residues 203-220, and was recognized by eight sera. Within the E2/NS1 region 380-437, the peptide covering residues 410-427 was recognized by two sera, and within the NS1 region 643-690, peptides covering residues 663-690 were recognized by four sera. Within the NS4 region 1684-1751, 27 sera were reactive to one or more of the NS4 peptides, and 21 out of these were reactive with peptide 1694-1711. One part of the major binding site could be located to residues 1701-1704, with the sequence Leu-Tyr-Arg-Glu. The IgG1, IgG3 and IgG4 subclasses were reactive with the five antigenic regions of HCV core, residues 1-18, 11-28, 21-38, 51-68 and 101-118. Reactivity to the major envelope site consisted almost exclusively of IgG3, and reactivity to the major site of NS4 consisted only of IgG1. Thus, a non-restricted IgG response to linear HCV-encoded binding sites was found to the core protein, whereas IgG subclass-restricted linear binding sites were found within the E1 protein, and within the NS4 protein.

Serodiagnostic assay of hepatitis C virus infection using viral proteins expressed in Escherichia coli

Infection with hepatitis C virus (HCV) was analyzed by an enzyme-linked immunosorbent assay based on recombinant viral proteins encoded by regions of the putative viral core, NS3, NS4 and NS5, which were expressed in E. coli. Results showed that 106 of 124 cases (85.5%) of non-A, non-B chronic hepatitis and 43 of 45 cases (95.5%) of hepatocellular carcinoma, negative for HBV marker, were positive for antibodies against at least one of these viral proteins. One of 87 healthy individuals with normal alanine aminotransferase activity was positive for antibody against only the viral core, but was negative for HCV RNA. The serum of one patient with chronic hepatitis was positive for one of these proteins, but negative for HCV RNA. These findings in combination with results on detection of HCV RNA in the sera of patients with non-A, non-B chronic hepatitis indicated that 105 of 124 cases (84.6%) were positive for HCV infection. Sera that were negative for HCV antibodies against all these proteins were also negative for HCV RNA assayed by reverse transcription followed by the polymerase chain reaction. Screening of HCV infection by detecting viral antibodies in circulating blood using all these viral proteins is useful for reducing the number of ambiguous results in screening for viral infection. Thus, this assay system may be useful diagnostic purposes.

Marked sequence diversity in the putative envelope proteins of hepatitis C viruses

The nucleotide sequences of cDNAs (414 base pairs) encoding parts of putative envelope proteins (gp35 and gp70) of 40 isolates of hepatitis C virus (HCV-J) derived from 30 independent plasma or liver specimens from Japanese patients (13 with chronic hepatitis, 14 with hepatocellular carcinoma and 3 hemophiliacs who had received imported clotting factors), were analyzed using the polymerase chain reaction. Approximately 29-38% of the nucleotide sequences of the HCV-J isolates examined differed from those of isolates from the United States (HCV-US). Furthermore, 12-24% and 8-17% sequence diversities were found within the isolates of HCV-J and HCV-US, respectively. The diversities of the amino acid sequences were the same or greater than those of the nucleotide sequences. We confirmed that two hypervariable regions (HVR1 and HVR2) were present in this amplified region, as described in our previous report (Hijikata et al., 1991a) and we found that the HVR1 regions of HCV-J and HCV-US were 27 and 21 amino acids in length, respectively, and began from the N-terminal amino acid of gp70. HVR2 was found in HCV-J, but not in HCV-US isolates, in which the corresponding region of the genome was conserved. During the analysis, plural HCV genomes were found in 6 of 30 specimens. These plural HCV genomes in a single specimen were concluded to be derived from the same HCV ancestor, because of their relative low sequence diversities (about 10% in their nucleotide sequences).(ABSTRACT TRUNCATED AT 250 WORDS)