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

Antigenic heterogeneity of the hepatitis C virus NS4 protein as modeled with synthetic peptides

The effect of sequence heterogeneity on the immunologic properties of two strong antigenic regions of the hepatitis C virus (HCV) NS4 protein was studied by using a set of 443 overlapping 20-mer synthetic peptides. One antigenic region comprising the cleavage site between NS4a and NS4b (region 5-1-1) was modeled with peptides derived from 73 different known sequences, representing HCV genotypes 1-6. The other antigenic region, designated region 59 and located at the C-terminus of the NS4b protein, was modeled with peptides from 7 known sequences representing genotypes 1-3. All peptides were tested for antigenic reactivity by enzyme immunoassay with a panel of anti-HCV-positive serum specimens representing genotypes 1-5. The data demonstrated that immunoreactive peptides fell into two groups. One group, represented by N-terminal peptides, demonstrated genotype-independent immunoreactivity; the other group, from the central part of region 5-1-1, showed strict genotype specificity. Nineteen peptides from the genotype-independent group strongly immunoreacted with a wide range of serum samples containing antibodies to all 5 HCV genotypes. Twenty-five peptides from the genotype-specific group were found to strongly react with serum containing antibodies only to the genotype from which the peptides were derived. Similar to the N-terminal part of region 5-1-1, peptides derived from region 59 did not show genotype-specific immunoreactivity. Some peptides derived from the central part of region 59 showed very strong and broad antigenic reactivity. Thus, after examining two antigenic regions of the NS4 protein, we identified short sequences that can be used for the efficient detection of either genotype-independent or genotype-specific HCV antibodies.

Effective production of the hepatitis C virus core antigen having high purity in Escherichia coli

The amino-terminal half of putative nucleocapsid (core) protein (amino acids 1-115) of hepatitis C virus (HCV) was directly overproduced in Escherichia coli under the control of the tac promoter. Overproduction of core antigen was achieved by inserting several target genes and by optimizing the culture conditions, whereas a large amount of directly expressed and purified core antigen has not yet been reported. Although the level of expression was comparable to that of the conventional E. coli fused expression system, our recombinant proteins contain only HCV amino acid sequence. Using recombinant E. coli, overproduced large-scale culture system was achieved in jar-fermenter. A highly purified sample of the expressed protein was obtained by ion-exchange and gel permeation column chromatography in the presence of 8 M urea. From a 3.5 l culture, approximately 440 mg of recombinant core protein was obtained after a two-step purification procedure. An enzyme-linked immunosorbent assay developed using the highly purified antigen satisfactorily diagnosed hepatitis C.

Linear B-cell epitopes of the NS3-NS4-NS5 proteins of the hepatitis C virus as modeled with synthetic peptides

A set of 150 synthetic peptides spanning the proteins NS3-NS4-NS5 of the hepatitis C virus (HCV) was synthesized and tested with a panel of 20 sera obtained from HCV-infected patients. Of 62 peptides prepared from the NS3 region, none exhibited strong antigenic reactivity. Rather, five peptides from this region demonstrated specific reactivity with only 5-10% of anti-HVC-positive sera. Nonetheless, it is well known that the NS3 region contains strong antigenic epitopes. These epitopes appear to be modeled in a functionally active manner with recombinant proteins and cannot be mimicked properly with short synthetic peptides. This finding suggests that the major NS3 antigenic epitopes are conformationally dependent. Seven of 20 peptides prepared from the NS4 region were immunoreactive. Five peptides from this region demonstrated very strong HCV-specific antigenic reactivity. Four of the five peptides belong to the recognized immunoreactive 5-1-1 region located inside the C100-3 antigen. One peptide demonstrating immunoreactivity with approximately 90% of anti-HCV-positive sera was found outside the C100-3 region at the C-terminal part of the NS4 protein. Of 68 peptides synthesized from the NS5 protein, 30 were immunoreactive. Six of the 30 demonstrated immunoreactivity with 35-50% of anti-HCV-positive sera. Thus, the NS4 and NS5 regions of the HCV polyprotein contain a large number of specific, broadly reactive, linear antigenic epitopes. The highly antigenic reactivity of the NS5 region suggests that this protein may have significant diagnostic potential.

Antibodies and viremia in acute post-transfusion hepatitis C: a prospective study

Fourteen patients who developed acute post-transfusion hepatitis C after open-heart surgery were studied for seroconversion, viremia, and aminotransferase. Anti-HCV antibodies were measured by first and second generation ELISA and became positive between one week and more than 6 months after infection. Seroconversion in four patients and passively transfused antibodies were only found by the second generation assay, indicating its significantly higher sensitivity. Viremia was detected by reverse transcription and the polymerase chain reaction within the first 4 weeks of infection in 13 patients and persisted for more than 2 years in all of them. One patient died of cardiac cause. Viral strains were heterogeneous between the different patients, but showed no significant variation within one patient during the course of hepatitis deduced from the results with different sets of oligonucleotides. Viremia preceded hepatitis by 4 weeks, seroconversion determined by ELISA II followed after an 8 week interval, and anti-C-100 antibodies appeared 26 weeks later. Aminotransferase activities returned to normal values in 10 patients.

Rapid detection of hepatitis C virus RNA by direct capture from blood

A new diagnostic assay for hepatitis C virus RNA detection is described. HCV genomic RNA is captured onto streptavidin-coated magnetic beads by solution hybridization with biotinylated complementary oligonucleotides. The specificity of the capture assay is confirmed using different capture oligonucleotides as well as sera representing different types of HCV. Sensitivity was determined by testing serial dilutions of a HCV infected plasma. A panel of 50 sera was tested for anti-HCV by a Line Immunoassay and for HCV-RNA by both a conventional guanidinium extraction method and the new capture assay. The specificity of the capture assay was 95.8% and the sensitivity was 92.3% compared to the standard protocol. This method provides a rapid and simple alternative for HCV-RNA detection in blood samples.

Two proteinase activities in HCV polypeptide expressed in insect cells using baculovirus vector

Processing of HCV viral precursor protein requires at least two viral proteinases, Cpro-1 and Cpro-2, in addition to cellular proteinases. The HCV polypeptide that covers the region for the two viral proteinase domains was expressed in insect cells using a baculovirus expression system. The two proteinase activities were demonstrated in the infected cells. The Cpro-1-dependent cleavage site was estimated from the amino acid sequence of the N-terminus of the processed product. Analyses of the susceptibilities of various mutants altered at position P1 and P1' of the putative cleavage site suggested that amino acid residues at these positions is not essential for recognition and cleavage by Cpro-1-dependent activity.

Two distinct proteinase activities required for the processing of a putative nonstructural precursor protein of hepatitis C virus

Gene products of hepatitis C virus (HCV), a possible major causative agent of posttransfusion non-A, non-B hepatitis, are considered to be produced from a precursor polyprotein via proteolytic processing mediated by either host cell or viral proteinases. The presence of HCV serine proteinase has been proposed from analyses of amino acid sequence homology. To examine the processing mechanism of the HCV precursor polyprotein, the amino-terminal region of the putative nonstructural protein region of the HCV genome, containing the serine proteinase motif, was expressed and analyzed by using an in vitro transcription/translation system and a transient expression system in cultured cells. Two distinct proteinase activities which function in the production of a 70-kDa protein (p70) from the precursor polyprotein were detected. One of these proteinase activities, which cleaved the carboxyl (C)-terminal side of p70, required the presence of the serine proteinase motif, which is located in the amino (N)-terminal region of p70. That suggested that the predicted HCV serine proteinase was functional. The other activity, which was responsible for the cleavage of the N-terminal side of p70, required the expression of the region upstream and downstream of that cleavage site, including the p70 serine proteinase domain. From the results of pulse-chase analysis, using proteinase inhibitors coupled with a point mutation analysis, the latter activity was proposed to be a novel zinc-dependent metalloproteinase.

A sensitive serodiagnosis of hepatitis C virus (HCV) infection with two non-fused peptides: comparison of antibody responses detected with a newly developed assay and a commercial second-generation test

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of anti-HCV antibody. We assayed for antibodies against either oligopeptide (S29-1) deduced from the nucleocapsid gene or the product of nonstructural region (NS3) synthesized in a recombinant Escherichia coli (S4). To reduce false-positive results induced by non-specific binding of antibodies with a carrier protein and to increase the sensitivity of an immunoassay, non-fused S4 peptide was prepared by the recombinant DNA technique and site-specific proteolysis (by factor Xa). In 71 non-A, non-B hepatitis patients with chronic liver disease, 70 (98.5%) were positive by S29-1/S4 ELISA as well as by a second-generation test (Abbott II). On the other hand, of 40 serum samples from blood donors, in which anti-N14 (core) and C100-3 antibodies were not detected but hepatitis C virus (HCV) RNA was detectable by polymerase chain reaction (PCR), 24 (60%) were positive by S29-1/S4 ELISA, whereas only 18 (45%) were diagnosed by Abbott II. In addition, based on results in a small group of 92 blood donors, detection of anti-S29-1/S4 antibody correlated well with HCV viremia as confirmed by PCR. These results indicated that the preparation of nonfused protein (S4) by recombinant DNA technique and a combination of S29-1 and S4 as immobilized antigens in an ELISA provide a sensitive and specific diagnosis for HCV infection with good correlation with the presence of viral RNA as confirmed by PCR.