Serodiagnosis of hepatitis C virus infection by ELISA for antibodies against the putative core protein (p20c) expressed in Escherichia coli

Prevalence of the hepatitis C virus among University employees in São Paulo, Southeastern Brazil: predictive factors and geoprocessing spatial analysis

BACKGROUND

There are limited studies on the prevalence and risk factors associated with hepatitis C virus (HCV) infection. Objective Identify the prevalence and risk factors for HCV infection in university employees of the state of São Paulo, Brazil.

METHODS

Digital serological tests for anti-HCV have been performed in 3153 volunteers. For the application of digital testing was necessary to withdraw a drop of blood through a needlestick. The positive cases were performed for genotyping and RNA. Chi-square and Fisher's exact test were used, with P-value <0.05 indicating statistical significance. Univariate and multivariate logistic regression were also used.

RESULTS

Prevalence of anti-HCV was 0.7%. The risk factors associated with HCV infection were: age >40 years, blood transfusion, injectable drugs, inhalable drugs (InDU), injectable Gluconergam®, glass syringes, tattoos, hemodialysis and sexual promiscuity. Age (P=0.01, OR 5.6, CI 1.4 to 22.8), InDU (P<0.0001, OR=96.8, CI 24.1 to 388.2), Gluconergam® (P=0.0009, OR=44.4, CI 4.7 to 412.7) and hemodialysis (P=0.0004, OR=90.1, CI 7.5 - 407.1) were independent predictors. Spatial analysis of the prevalence with socioeconomic indices, Gross Domestic Product and Human Development Index by the geoprocessing technique showed no positive correlation.

CONCLUSIONS

The prevalence of HCV infection was 0.7%. The independent risk factors for HCV infection were age, InDU, Gluconergan® and hemodialysis. There was no spatial correlation of HCV prevalence with local economic factors.

Identification of a human epitope in hepatitis C virus (HCV) core protein using a molecularly cloned antibody repertoire from a non-symptomatic, anti-HCV-positive patient

Healthy carriers of hepatitis C virus (HCV) infection exhibit a specific antibody response against all HCV antigens, which could play a role in disease control. Generation of panels of human antibodies may permit a thorough characterization of this response and further identify particular antibodies with potential clinical value. To this effect, we have established a human phage-display antibody library from a patient exhibiting a high antibody response against HCV antigens and no clinical symptoms of disease. This library was screened against a recombinant core antigen [amino acids (aa) 1-119] produced in E. coli. Two recombinant Fab-carrying phages (rFabCs) were isolated and characterized. Both rFabC3 and rFabC14 recognize aa 1-48 on core antigen, but rFabC14 is competed out by a synthetic peptide, C(2-20) (aa 1-20), at much lower concentrations than rFabC3. In order to identify more precisely the recognition sites of these antibodies, we produced soluble forms of the rFabs (sFabs), and used them to pan a random phage-display peptide library. A single peptide sequence, QLITKPL, was identified with sFabC3, while two equally represented sequences, HAFPHLH and SAPSSKN, were isolated using sFabC14. The QLITKPL sequence was partially localized between aa 8 and 14 of core protein, but no clear homology was found for the two sFabC14 peptides. However, we confirmed the specificity of these peptides by competition experiments with sFabC14.

An ELISA for the detection of antibody to the core antigen of hepatitis C virus: use in diagnosis and analysis of indeterminate samples

AIMS

In order to examine more carefully the natural history of hepatitis C virus infection and to determine a role for anti-core in the discrimination of indeterminate samples, a solid phase ELISA to detect antibody of the immunoglobulin G class to the hepatitis C virus core antigen was developed using purified protein expressed in Escherichia coli from a major portion of the core antigen coding region.

METHODS/RESULTS

In a study which examined 651 samples submitted for routine testing by a commercial ELISA (Ortho), only 11 samples showed discrepant results; of these, 10 were Ortho ELISA positive, anti-core negative and one was Ortho ELISA negative anticore positive. Supplemental tests showed that 5/10 of these samples were anti-HCV negative by RIBA and the reciprocal 5 were negative for anti-C22 but positive for anti-C100 and anti-C33. The Ortho ELISA negative, anticore positive sample was weakly positive for anti-C22. The anti-core ELISA was then used to examine 67 indeterminate samples from the blood bank; 11/11 samples which were HCV-RNA positive were anti-core positive and 7/56 samples which were HCV-RNA negative were anti-core positive. The anti-core titre was then examined in two groups of indeterminate samples; group 1, polymerase chain reaction-positive, anti-core positive and group 2, polymerase chain reaction-negative, anti-core positive. The geometric mean anti-core titres in these groups were 1 x 10(-3.6) and 1 x 10(-2.3), respectively. Thus in this group of indeterminate samples, all samples (except one) with an anti-core titre > or = 1/200 were polymerase chain reaction-positive, confirming a close correlation between anti-core levels and hepatitis C viraemia. Anti-core was detected with equal efficiency in patients infected with genotypes which differed to that used to express the recombinant core antigen.

Early detection of anti-HCc antibody in acute hepatitis C virus (HCV) by western blot (immunoblot) using a recombinant HCV core protein fragment

Crude extract from Escherichia coli which expressed a recombinant protein containing amino acids 2 to 127 of the hepatitis C virus (HCV) core protein was used to detect the antibody against HCV core protein (anti-HCc). After electrophoretic separation of proteins from the extract, Western blot (immunoblot) analysis was performed with the serum samples. This method was compared with a commercially available second-generation enzyme immunoassay (EIA) which employed synthetic peptides corresponding to highly antigenic segments of both structural and nonstructural portions of HCV. Also, reverse transcription PCR for HCV RNA was used for comparison. Seventy-two serum samples from three groups of patients were tested. Groups I and II represented healthy subjects and subjects with acute hepatitis A or B, respectively. Group III included patients with newly acquired acute hepatitis C. By Western blot analysis, 31 of 31 (100%) samples from group I were negative for anti-HCc antibody, whereas 4 of 22 (18%) samples from group II were positive for anti-HCc. One of these four samples was also positive for anti-HCV antibody by the second-generation EIA (1 of 22 [4.5%]). Among 19 patients diagnosed with newly acquired acute hepatitis C, 4 (21%) were positive for anti-HCV by the second-generation EIA, whereas 12 of 19 (63%) were positive for anti-HCc by Western blot analysis. Of EIA-positive subjects, 4 of 4 (100%) were also positive for anti-HCc by Western blot analysis, whereas among EIA-negative subjects, 8 of 15 (53%) were positive. For HCV RNA detected by reverse transcription PCR, 15 of 19 (80%) of this group of samples were positive. Strikingly, the peak bilirubin level for patients with EIA-negative and Western blot-positive results is significantly higher than that for patients with consistent EIA and Western blot results (22.7 versus 7.2 mg/dl). A series of serum samples from a patient with concurrent hepatitis B and C viral infection was also studied by both tests. Although anti-HCc persisted throughout the course of infection, anti-HCV by EIA converted from negative to positive 20 days after admission and then converted back to negative 30 days later.

Isotype-specific immune response to a single hepatitis C virus core epitope defined by a human monoclonal antibody: diagnostic value and correlation to PCR

In this study we tested the seroreactivity of 223 selected anti-HCV-reactive blood donors to the human B-cell epitope N-VYLLPR-C (C34-39) of the hepatitis C virus core antigen. The epitope was recently identified and characterized by the human monoclonal IgG antibody Ul/F10 and is located within the amino acid residues 34-39 of the aminoterminal core region. The blood donor sera were selected from anti-HCV ELISA (Ortho, 2nd generation)-reactive samples. Sixty-seven of these sera were further reactive in RIBA (Ortho, 2nd generation). According to their RIBA pattern, these samples were divided into four groups. Samples in the first group (n = 18) reacted to all four recombinant HCV antigens. The samples of the second (n = 9) and third group (n = 8) reacted to c22-3/c33c and c22-3/c100-3, respectively. Sera from group 4 (n = 32) showed a RIBA indeterminate pattern with reactivity only to c22-3. All 223 samples were analyzed for anti-C34-39 antibodies by ELISA, and the 67 RIBA-reactive samples were additionally tested for the presence of HCV RNA by RT/PCR. In groups 1 and 2, over 80% of the samples showed anti-C34-39 reactivity which was restricted to the IgG1 isotype. In contrast, in groups 3 and 4, antibodies to the epitope C34-39 were detected in less than 10% of the samples. Interestingly, the anti-C34-39 response correlates with the presence of HCV RNA; 95.5% of the samples had coincident results in all subgroups. None of the RIBA-negative sera showed a specific seroreaction to the C34-39 peptide.

Isolation and epitope characterization of human monoclonal antibodies to hepatitis C virus core antigen

In this study we describe the establishment of two hybridoma cell lines secreting human monoclonal antibodies to the 22-kD nucleocapsid protein (core, p22) of the hepatitis C virus (HCV). For this purpose we isolated B lymphocytes from an anti-HCV positive blood donor and infected them with Epstein-Barr (EBV). We obtained several lymphoblastoid cell clones secreting antibodies to the recombinant HCV core protein. The B-cell cultures were oligoclonally expanded and two of them were fused with the (mouse:human) heteromyeloma cell line K6H6/B5. The resulting stable hybridomas produce antibodies of the IgG1/kappa (U1/F10) and the IgM/kappa (Ul/F11) isotype reacting specifically with the recombinant core protein p22. To identify the epitopes recognized by these antibodies we synthesized overlapping peptides (13-mer and 6-mer) from the amino terminus of the core amino acid sequence. Antibody reactivity to these peptides was analyzed in an immunoblot assay. Finally, we were able to define a linear epitope recognized by the Ul/F10 antibody on the nucleocapsid protein. The antibody shows specificity to the sequence N-VYLLPR-C, which corresponds to the amino acids 34-39 of the core sequence.

Chimeric hepatitis B virus core particles with parts or copies of the hepatitis C virus core protein

Either parts or multiple copies of the core gene of hepatitis C virus (HCV) were fused to the 3' terminus of the hepatitis B virus (HBV) core gene with 34 codons removed. As many as four copies of HCV core protein (720 amino acids) were fused to the carboxy terminus of truncated HBV core protein (149 amino acids) without preventing the assembly of HBV core particles. Chimeric core particles were sandwiched between monoclonal antibody to HBV core and that to HCV core, thereby indicating that antigenic determinants of both HBV and HCV cores were accessible on them. Proteolytic digestion deprived chimeric core particles of the antigenicity for the HCV core without affecting that of the HBV core, confirming the surface exposure of HCV core determinants. The density of HCV core determinants on chimeric core particles increased as copies of fused HCV core protein were increased. Hybrid core particles with multiple HCV core determinants would be instrumental as an antigen probe for detecting class-specific antibodies to the HCV core in patients with acute and chronic hepatitis C and for simultaneous detection of antibodies to HBV core and those to HCV core in donated blood.

Immunoglobulin M reactivity towards the immunologically active region sp75 of the core protein of hepatitis C virus (HCV) in chronic HCV infection

Serum samples from a cohort of patients with chronic hepatitis C virus (HCV) infection were assayed for IgM anti-HCV/core reactivity with a "site-specific" ELISA, in which the solid phase was charged with the synthetic polypeptide analogue corresponding to the first 75 amino acids of the HCV core antigen (sp75). Thirteen of 24 (54%) patients exhibited IgM anti-sp75 reactivity. Both high-titered (1/16,000-1/32,000) and low-titered (1/1,000-1/4,000) IgM anti-sp75 reactive sera were found. IgM anti-sp75 antibodies persisted in the circulation over a long period in patients with fluctuating abnormal ALT levels. There was a striking association between detection of specific IgM anti-sp75 reactivity and the presence of HCV RNA in serum. Thus 11 of 15 (73%) sera containing HCV RNA also contained IgM anti-sp75 antibodies, while none of the HCV RNA-negative sera were IgM anti-sp75 reactive. Five of 11 patients without detectable levels of specific IgM anti-sp75 antibodies had their ALT levels returned to normal within 8 months to 3 years. Furthermore, a significant correlation was noted between the specific IgM anti-sp75 titers and the concentration of total plasma IgM, indicating that the immunological active region sp75 within the capsid of HCV has the capacity to induce an IgM secretion, which constitutes a substantial portion of the total plasma IgM, in patients with chronic HCV infection.(ABSTRACT TRUNCATED AT 250 WORDS)

p26 protein and 33-nm particle associated with nucleocapsid of hepatitis C virus recovered from the circulation of infected hosts

Hepatitis C virus (HCV) has not yet been cultured or visualized. We attempted to recover HCV-associated particles from plasma of infected humans to assess the natural properties of the virus. Starting with 720 ml of donor plasma containing high titer of HCV core antigen ELISA activities, we identified HCV core antigen activity and viral RNA enriched in a potassium bromide density gradient fraction with a density of 1.115 g/ml. Icosahedron-shaped particles with an average diameter of 33 nm were liberated by treatment of the fraction with the detergent Tween 80. These particles were selectively visualized with an electron microscope using a grid coated with a murine monoclonal antibody directed to HCV core peptide and were also observed in aggregated forms with an immune electron microscope (IEM) with use of the anti-core antibody. An ultracentrifugation pellet of the above fraction was treated with sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2ME) and run in SDS-PAGE. A protein that bound antibodies directed to the predicted core protein of HCV was found at a molecular size estimated as about 26,000 Da, significantly greater than the 191 amino acid residues predicted from the presumed core gene of HCV. It is possible that translation initiation and/or the COOH-terminal cleavage site for HCV core protein in vivo may differ from estimates derived from the amino acid sequence of the polyprotein precursor. The nucleocapsid could also be chemically altered in the infected cell, resulting in a gel mobility different from the native protein.