Immune response to a single peptide containing an immunodominant region of hepatitis C virus core protein: the isotypes and the recognition site

Production and characterization of monoclonal antibodies for the detection of the hepatitis C core antigen

Background: Despite highly effective treatments to cure hepatitis C, almost 80% of chronically HCV-infected people are not treated, as they are unaware of their infection. Diagnostic rates and linkage to care must be substantially improved to reverse this situation. The HCV core antigen (HCVcAg) is a highly conserved protein that can be detected in the blood of HCV-infected patients and indicates active infection. Aim: To produce murine monoclonal antibodies against HCVcAg suitable for rapid and inexpensive tests to detect HCV infection. Methods: BALB/c mice were sequentially inoculated with purified recombinant HCVcAg from Gt1a, Gt3a, Gt4a, and Gt1b genotypes. Hybridomas producing the desired monoclonal antibodies were selected, and the reactivity of antibodies against HCVcAg from various genotypes was tested by Western blotting and dot blotting. The binding kinetics of the antibodies to purified HCVcAg was analyzed by surface plasmon resonance (SPR), and their ability to detect HCVcAg was tested by double antibody sandwich ELISA (DAS-ELISA). Results: Four specific monoclonal antibodies (1C, 2C, 4C, and 8C) were obtained. 1C, 2C, and 4C recognized HCVcAg of all genotypes tested (Gt1a, Gt1b, Gt2a, Gt3a, and Gt4a), while 8C did not recognize the Gt2a and Gt3a genotypes. Based on SPR data, the antibody-HCVcAg complexes formed are stable, with 2C having the strongest binding properties. DAS-ELISA with different antibody combinations easily detected HCVcAg in culture supernatants from HCV-infected cells. Conclusion: Specific and cross-reactive anti-HCVcAg monoclonal antibodies with strong binding properties were obtained that may be useful for detecting HCVcAg in HCV-infected samples.

IgG1 and IgG4 antibodies against Core and NS3 antigens of hepatitis C virus

INTRODUCTION

IgG subclasses involved in the immune response to hepatitis C virus (HCV) antigens have been rarely studied. We investigated the immune response mediated by IgG1 and IgG4 antibodies against the recombinant core and NS3 antigens in patients with chronic hepatitis C.

METHODS

Sixty patients infected with HCV genotype 1 without antiviral treatment and 60 healthy subjects participated in the study. Serum levels of alanine aminotransferase, HCV viremia, and the presence of cryoglobulinemia and liver fibrosis were determined. We investigated the serum IgG1 and IgG4 antibodies against recombinant HCV core and NS3 non-structural protein antigens using amplified indirect ELISA.

RESULTS

Anti-core and anti-NS3 IgG1 antibodies were detected in 33/60 (55%) and 46/60 (77%) patients, respectively, whereas only two healthy control samples reacted with an antigen (NS3). Anti-core IgG4 antibodies were not detected in either group, while 30/60 (50%) patients had anti-NS3 IgG4 antibodies. Even though there were higher levels of anti-NS3 IgG4 antibodies in patients with low viremia (< 8 × 105 IU/mL), IgG1 and IgG4 antibody levels did not correlate with ALT levels, the presence of cryoglobulinemia, or degree of hepatic fibrosis. High production of anti-core and anti-NS3 IgG1 antibodies was observed in chronic hepatitis C patients. In contrast, IgG4 antibodies seemed to only be produced against the NS3 non-structural antigen and appeared to be involved in viremia control.

CONCLUSIONS

IgG1 antibodies against structural and non-structural antigens can be detected in chronic hepatitis C, while IgG4 antibodies seem to be selectively stimulated by non-structural HCV proteins, such as the NS3 antigen.

Comparative Immunogenicity in Rabbits of the Polypeptides Encoded by the 5' Terminus of Hepatitis C Virus RNA

Recent studies on the primate protection from HCV infection stressed the importance of immune response against structural viral proteins. Strong immune response against nucleocapsid (core) protein was difficult to achieve, requesting further experimentation in large animals. Here, we analyzed the immunogenicity of core aa 1–173, 1–152, and 147–191 and of its main alternative reading frame product F-protein in rabbits. Core aa 147–191 was synthesized; other polypeptides were obtained by expression in E. coli. Rabbits were immunized by polypeptide primes followed by multiple boosts and screened for specific anti-protein and anti-peptide antibodies. Antibody titers to core aa 147–191 reached 10⁵; core aa 1–152, 5 × 10⁵; core aa 1–173 and F-protein, 10⁶. Strong immunogenicity of the last two proteins indicated that they may compete for the induction of immune response. The C-terminally truncated core was also weakly immunogenic on the T-cell level. To enhance core-specific cellular response, we immunized rabbits with the core aa 1–152 gene forbidding F-protein formation. Repeated DNA immunization induced a weak antibody and sustained proliferative response of broad specificity confirming a gain of cellular immunogenicity. Epitopes recognized in rabbits overlapped those in HCV infection. Our data promotes the use of rabbits for the immunogenicity tests of prototype HCV vaccines.

The use of epitope arrays in immunodiagnosis of infectious disease: hepatitis C virus, a case study

Serodiagnosis of infectious disease is often based on the detection of pathogen-specific antibodies in a patient's blood. For this, mixtures of pathogen-related antigens are used as bait to capture corresponding antibodies in solid phase immunoassays such as enzyme immunoassay (EIA). Western blots provide improved diagnostic power as compared with EIA due to the fact that the mixture of markers in the EIA well is resolved and tested as individual antigens on the Western blot. Hence, confirmation of EIA results is accomplished using the antigen arrays of Western blots. Here we took this approach one step further and tested the attributes of using epitope arrays in a diagnostic platform coined "combinatorial diagnostics." As a case in point, we tested a panel of phage-displayed epitope-based markers in the serodiagnosis of hepatitis C virus (HCV). The repertoire of HCV antigens was deconvoluted into panels of distinct linear and conformational epitopes and tested individually by quantitative EIA. Combinatorial diagnostics proved to be effective for the discrimination between positive and negative sera as well as serotyping of HCV.

Identification of serologically silent occult hepatitis C virus infection by detecting immunoglobulin G antibody to a dominant HCV core peptide epitope

BACKGROUND/AIMS

Occult HCV infection has been described among anti-HCV-HCV RNA-negative individuals with abnormal transaminase values in whom HCV RNA is detected in liver.

METHODS

IgG antibody to an HCVcore-derived peptide (anti-HCVcore) was investigated in 145 patients with serologically silent occult HCV infection.

RESULTS

At the time of the diagnostic biopsy 45/145 (31%) occult HCV-infected patients tested IgG anti-HCVcore-positive but none of the 140 patients with HCV-unrelated liver disease (P<0.001). Among 23 IgG anti-HCVcore-positive patients at baseline, 22 remained antibody-reactive (one became antibody-negative). Similarly, 17/31 baseline anti-HCVcore-negative patients remained non-reactive whereas 14 seroconverted to IgG anti-HCVcore (although transiently in 10 patients). Thus, a total of 59/145 (40.7%) patients with occult HCV infection showed IgG anti-HCVcore reactivity at any time point analyzed, including 14 initially non-reactive patients. By supplemental immunoblot assay 16 sera reacted weakly with an HCVcore-peptide band (indeterminate result) of which 10 (62.5%) reacted in the IgG anti-HCVcore assay. Occult HCV-infected patients who tested anti-HCVcore-positive showed more frequently signs of necro-inflammation (P=0.035) and greater percentages of HCV RNA-positive hepatocytes (P=0.004) compared with those anti-HCVcore-negative.

CONCLUSIONS

This work documents that IgG anti-HCVcore testing identifies occult HCV infection among seronegative, non-viremic patients using screening tests and may be useful in tracking anti-HCV-negative infections.

A novel recombinant multiepitope protein as a hepatitis C diagnostic intermediate of high sensitivity and specificity

A novel recombinant multiepitope protein has been designed that consists of six linear, immunodominant, and phylogenetically conserved epitopes from hepatitis C virus. Five of these antigens (core, NS3, NS4I, NS4II, and NS5) are being used in many of the third-generation kits while sixth epitope (core3g) is an additional sequence from a newly identified Indian isolate. The genes for these epitopes have been joined together to code for a single multiepitope protein that has been evaluated for its diagnostic potential for the detection of anti-HCV antibodies in human plasma. Two separate synthetic genes have been designed, both encoding the same six epitopes in a single open reading frame along with spacers having additional amino acids to function as flexible (r-HCV-F-MEP) or rigid (r-HCV-R-MEP) linkers. High-level expression of hepatitis C multiepitope protein in Escherichia coli has been achieved. The protein has been purified using a single affinity step yielding >25 mg pure protein/liter culture and used as the coating antigen in anti-HCV EIA. The use of this multiepitope protein eliminates the requirement for multiple diagnostic intermediates for the development of anti-HCV diagnostic kit. The sensitivity and specificity of the HCV multiepitope protein was evaluated by Boston Biomedica Worldwide Performance Panels, HCV Seroconversion Panels and Viral Co-infection Panels, and was found to be comparable with commercially available anti-HCV EIA kits. This analysis indicated its unequivocal performance as capture antigen in anti-HCV EIA. The high epitope density, careful choice of epitopes and use of E. coli system for expression, coupled with simple purification protocol provides the potential for the development of an inexpensive diagnostic test with high degree of sensitivity and specificity.

Restricted isotypic antibody reactivity to hepatitis C virus synthetic peptides in immunocompromised patients

An enzyme immunoassay based on three synthetic peptides from the core, NS4, and NS5 regions of hepatitis C virus allowed the detection of antibodies in 100% of immunocompetent infected patients and in 91% of immunocompromised patients (hemodialysis and hemophiliac patients). Immune impairment seemed to restrict the spectrum of antibody isotypes reacting to the core peptide.

HCV core immunodominant region analysis using mouse monoclonal antibodies and human sera: characterization of major epitopes useful for antigen detection

Monoclonal antibodies (MAbs) were generated by immunizing mice with a truncated recombinant protein corresponding to the immunodominant region (residues 1-120) of hepatitis C virus (HCV) nucleocapsid protein. The specific recognition by either human sera or mouse monoclonal antibodies of overlapping peptides spanning the core region 1-120 as well as the comparison with epitopes described earlier allowed the fine mapping of HCV core. Within the region 1-120, the major antigenic domain could be restricted to the first 45 amino acids. Indeed, the peptide S42G (residues 2-45) allowed the detection of an anti-HCV core response by all anticore-positive human sera examined. According to their epitope localization, three groups of mouse MABs could be evidenced that were directed against different regions of core. Group II MAbs recognized a strictly linear epitope (QDVKF, residues 20-24), whereas group I MABs were directed against a conformational epitope mainly located at the amino acid residues (QIVGG, 29-33). The epitope of group III MABs was also conformational (PRGRRQPI, residues 58-65). These three epitopes appeared close but different from the three major human epitopes RKTKRNTN, VYLLPR, and GRTWAQPGYPWPLY (residues 7-17, 34-39, and 73-86, respectively). Group II MAB 7G12A8 and group I MAB 19D9D6 were used in a sandwich ELISA for the capture and the detection, respectively, of viral core antigen in sera of patients with chronic HCV infection. After treatment of sera with triton x 100 in acidic conditions, amounts of viral antigen as low as 20 pg/ml of sera could be detected.

Antibody production against hepatitis C virus core and nonstructural 3 proteins is highly sensitive to deficits in T-cell function

The influence of suppression of CD4+ and CD8+ T cells on the humoral responses to hepatitis C virus (HCV) core and nonstructural 3 proteins was studied. An increasing viral burden cannot substitute for the lack of functional T cells in maintaining humoral HCV-specific responses.

Comparison of prevalence of anti-hepatitis C virus antibodies in differing South American populations

Very little is known about the distribution of hepatitis C virus (HCV) within South America. To assess the exposure of the general population to this virus, a number of sera obtained from three distinct geographical and racial groups were screened using a combination of immunoassays. Initial screening was undertaken with an inhouse immunoassay (core-ELISA) using synthetic peptides based on the N-terminus of the HCV core protein. Sera which were repeatedly positive by core-ELISA were also assessed using a commercial third-generation assay. The highest prevalence rate (2.3%) was seen in sera taken from the Tumaco region of Colombia. Lower rates were found in sera taken from La T, Ecuador (0.7%) and Las Majadas, Venezuela (0.7%). This indicates significantly different prevalence in different racial and geographical groups within the region.

Characterization of a dominant antigenic determinant of Par o I encoded by recombinant DNA

BACKGROUND

The pollens from Parietaria judaica and Parietaria officinalis are a major cause of pollinosis in Europe. Par o I (13.5 kDa) and Par j I (12 kDa), the major allergens from these species, are highly crossreactive.

METHODS

We have immunoscreened a P. judaica pollen cDNA expression library with a rabbit antiserum specific for Par j I and with a serum pool from allergic patients. An immunopositive clone containing a 26 bp insert was further characterized. The insert sequence was determined and the beta-galactosidase fusion protein was partially purified by electroelution from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels.

RESULTS

This fusion protein specifically and extensively inhibited Par o I and Par j I binding of a rabbit antiserum and of a serum pool obtained from allergic patients. The antifusion-protein antiserum obtained in a rabbit (anti 6a) specifically precipitated radioiodinated purified Par o I in the double antibody radioimmunoassay (DARIA) and competed with antibodies of sera from allergic patients for the binding to Parietaria pollen extract allergens by enzyme linked immunosorbent assay (ELISA). We investigated the prevalence of antibody response towards the 6a epitope in patients naturally sensitized to Parietaria. The presence of 6a specific IgE antibodies was assessed in the sera of 33 patients using inhibition assays. All sera had antibodies with this specificity: the extensive percentage of inhibition reached suggested that they dominated individual ab response.

CONCLUSION

In conclusion, the antibody response induced by natural exposure to the pollen of Parietaria appears to be higly focused on a single linear antigenic determinant of the major allergens which may play a relevant role in the development of clinical allergy. This report is, to our knowledge, the first description of a dominant linear epitope of a major allergen.

Passive adsorption of immunologically active and inactive synthetic peptides to polystyrene is influenced by the proportion of non-polar residues in the peptide

A well-known drawback in the use of synthetic peptides as solid-phase antigens in immunoassays is that positive controls confirming the presence of the peptide on the solid phase are not always present. We therefore evaluated the applicability of a recently described enzyme immunoassay (EIA) method by which the presence of peptides is detected by biotinylation (BioEIA) of alpha- and/or epsilon-amino groups after passive adsorption. This approach allows the rapid screening of a large number of proteins and peptides in respect to passive adsorption to plastic surfaces. When using irradiated polystyrene microplates we found that 240 (94%) of 256 synthetic peptides, covering 85% of the complete hepatitis C virus (HCV) sequence, passively adsorbed to polystyrene. When comparing the results from the BioEIA to the peptide reactivity of human sera it was obvious that the absence of serum reactivities was not due to lack of peptide adsorption to the plates. Using 192 peptides the relation between the signal-to-cutoff ratio (S/CO) in the BioEIA and the amino acid content of the individual peptides was further analyzed. The S/CO ratio was related to the number of epsilon NH2 groups (Lys residues) present in the peptide (P < 0.001, Kruskal-Wallis). We separately related the amino acid content of 68 peptides with Lys and 124 peptides lacking Lys to the S/CO ratio in the BioEIA. In both cases it was found that an increasing amount of nonpolar residues such as Ala, Phe, Ile, Met, and Val (P < 0.05, respectively) in the peptides was related to a lower S/CO ratio in the BioEIA.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigenic structure of the hepatitis C virus envelope 2 protein

The antigenic structure of the envelope 2 (e2) protein of the hepatitis C virus (HCV) was characterized by the use of 70 synthetic peptides and 131 human sera from persons with antibodies to HCV. Among 34 overlapping peptides spanning the e2 protein of HCV, two major antigenic regions were located to residues 484-499 and residues 554-569. The sequence of the two major antigenic regions of the e2 protein are partly well conserved within the described types of HCV. Both regions contain two Cys residues in close proximity, and the region at residues 554-569 contains a putative N-glycosylation site, which are factors that previously have been suggested to affect the immune recognition of the e2 protein. Using substitution peptide analogues where each position within residues 484-499 and 554-569 were sequentially substituted by Ala or Gly, the most essential residues for antibody binding were found to be the Pro-498, Ala-499, Ala-566, Pro-567, and Pro-568. All of these, except for the Pro-498 and Ala-566, are conserved among different HCV strains. Also, according to previous studies, position 496 often shows variations, which could be explained by position 496 being contained within the antigenic region at residues 484-499. Interestingly, none of the Cys residues at positions 486, 494, 564 and 569 were found to be essential for antibody binding, indicating that these are not essential in maintaining the e2 antigenicity of the peptides. In a material of 114 confirmed anti-HCV positive sera, derived from patients during the acute or the chronic phase of HCV infection, the prevalence of antibodies to the two major linear antigenic regions of the e2 protein was found to be 55% among HCV RNA-positive sera, and 53% among HCV RNA-negative sera. In conclusion, we have identified and characterized two major linear antigenic regions outside the two hypervariable regions of the e2 protein. Since these regions are accessible to the B cells of the infected host, these two regions are likely to be surface exposed either on the precursor polyprotein or the native e2 protein. Also, we could confirm that antibodies to the e2 protein co-exist with HCV viraemia.

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.

Sequence variability of hepatitis C virus and its clinical relevance

Chronic type C hepatitis is a potentially serious disease that can lead to cirrhosis and hepatocellular carcinoma. This complex disease is caused by the hepatitis C virus (HCV), a positive sense, single-stranded RNA virus. HCV has been assigned to a separate genus within the Flaviviridae, and shares a close relationship to the pestiviruses. Nucleotide sequence variation has been observed in genomes amplified from serum of patients with HCV infection, and cloning of RNA amplified from patients infected with HCV has confirmed the heterogeneity of the agent responsible for post-transfusion and sporadic hepatitis C. The variability of HCV is structured in a way that immediately suggests a two tiered classification: this nomenclature comprises 'types' corresponding to the major branches in a phylogenetic tree of sequences from genomic or subgenomic regions of the genome, and 'subtypes', corresponding to the more closely related sequences within some of the major groups. This genotyping designation has provided an epidemiological tool for studying geographical differences in hepatitis C infection. Clearly discernible patterns of genotype distribution have been found in those countries that have been studied so far. In many European countries genotype distributions vary with the age of patients, reflecting rapid changes in genotype distribution with time within a single geographical area. Unfortunately we know very little about modes of transmission within different communities. There is considerable interest in the clinical significance of different HCV genotypes, and the intriguing question of whether these differences may affect the spectrum of the disease associated with hepatitis C. These data also have implications for diagnosis and treatment of acute and chronic hepatitis C. A uniform typing scheme and nomenclature will facilitate our understanding of the disease caused by this virus worldwide.

Molecular basis for antibody cross-reactivity between the hepatitis C virus core protein and the host-derived GOR protein

The presence of antibodies reactive to a recently cloned host-derived antigen GOR is highly correlated with the presence of antibodies to the hepatitis C virus (HCV). We explored the molecular basis for this observation, and address the following question: are antibodies reactive with GOR19-27 (QKAKSNPNR) a result of a cross-reactivity triggered by the antigenic region at residues 9-17 of HCV core (RKTKRNTNR)? We compared the relative antibody avidity between antibodies reactive to both regions, and determined the residues essential for antibody binding using substitution peptide analogues. Of 96 sera assayed, 60 were found positive for anti-HCV, and of these 55 were found to react with HCV core. Twenty-nine sera were found reactive to the GOR peptide, and these were all reactive to HCV core. In most cases the relative antibody avidity of antibodies reactive to GOR was higher for the HCV core peptide. In 21 of the GOR-reactive sera we were able to determine the essential residues for antibody binding. The essential residues in > 50% of all tested sera coincided with the well conserved residues Lys10, Lys12, Asn14, and Asn16. Also, reactivity to GOR was not related to any certain serotype of antibodies to HCV. Taken together, these findings explain at the molecular level the observed cross-reactivity between these two proteins, since sequence homology per se is not evidence for cross-reactivity.

Locations of antibody binding sites within conserved regions of the hepatitis C virus core protein

The binding sites for human antibodies recognising antigenic domains within the hepatitis C virus (HCV) core protein were analyzed using synthetic peptides. Omission peptide analogues where a pair of residues was sequentially omitted were produced corresponding to the regions 1-18, 11-28, 21-38, 51-68, and 101-118. The N-terminal part of HCV core was found to contain three distinct antibody binding sites, which includes the previously reported one at residues 9-16. The other two were located at residues 19-26 and residues 29-34. Within the region 51-68 two overlapping sites were found, the first at residues 51-60 and the second at residues 59-68. Within the region 101-118, residues 107-114 were identified as the binding site, which contains two residues differing between genotypes I/II and III/VI. Thus the HCV core protein contains at least six distinct linear antibody binding sites, located at regions highly conserved between the genotypes of HCV. The human recognition of these regions show a variation with respect to the amino- and carboxy-terminal extension of each individual binding site. These findings will have implications for the prediction of the structure of the HCV core protein, since these antibody binding sequences are likely to be more or less accessible from the exterior of either, or both, of the native HCV core and its precursor polyprotein.

Antigenic structure of the complete nonstructural (NS) 2 and 5 proteins of hepatitis C virus (HCV): anti-HCV NS2 and NS5 antibody reactivities in relation to HCV serotype, presence of HCV RNA, and acute HCV infection

Antigenic regions within the nonstructural (NS) 2 and 5 proteins of hepatitis C virus (HCV) were identified and characterized by the use of 127 overlapping synthetic peptides and a serum panel consisting of 167 human serum samples from persons with antibodies to HCV. Initially, 20 anti-HCV-positive serum samples were used to screen the peptides covering the complete NS2 and NS5 proteins. Among the 27 overlapping peptides spanning the NS2 protein of HCV, only the peptide covering residues 960 to 975 was recognized by human sera. Within the 100 peptides covering the NS5 protein, major linear antigenic regions were located at residues 2284 to 2329 within the putative NS5a and at residues 2584 to 2599 and 2944 to 2959 within the putative NS5b. Additional minor linear antigenic regions were also identified within the NS5. The sequence of the antigenic region of the NS2 protein is, unlike most parts of the NS2 protein, highly conserved among the described types of HCV, whereas the sequence of the major antigenic region of NS5 shows variability among HCV types. The recognition of a peptide corresponding to a part of the major region of NS5 was found to be dependent on HCV type. In 129 anti-HCV-positive serum samples, the prevalence of antibodies to the NS2 protein was found to be 23% among HCV RNA-positive sera and 10% among HCV RNA-negative sera. In the same samples, reactivity to the major linear antigenic regions of HCV NS5 was found in 68% of the HCV RNA-positive sera and 67% of the HCV RNA-negative sera. Of 18 serum samples from five patients with acute HCV infections, and who seroconverted with respect to anti-HCV, 4 were found to be reactive to one or more of the 100 NS5 peptides and in three serum samples the NS5 reactivities were found to shorten the time for serodiagnosis of cross-reactive with a region form residues 2584 to 2599 of NS5, which has 67% homology with a six-residue sequence of NS2. In conclusion, in this study we have identified and evaluated the potential use of synthetic peptides corresponding to linear antigenic regions of the NS2 and NS5 proteins.

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.

Immune recognition of linear antigenic regions within the hepatitis B pre-C and C-gene translation products using synthetic peptides

The antibody recognition of linear regions within the amino acid (aa) sequence of hepatitis B (HB) core antigen (HBcAg), e antigen (HBeAg), and pre-C region was investigated in 46 patients infected with hepatitis B virus (HBV), and one immunized rabbit. Peptide analogues were synthesized to cover the complete product of the C-gene, including the pre-C region using various synthetic methods. Two carriers of hepatitis B surface antigen (HBsAg) with anti-HBe, recognized pin-bound decapeptides covering amino acid (aa) 76-83 of HBc/eAg, and the most essential residues were found to be Asp78, Pro79, Arg82, and Asp83. Pre-C peptides were recognized by IgG1 or IgG3 in sera from two out of ten cases with acute HB, in four out of twelve sera from HBeAg-positive carriers of HBsAg, and in two out of twelve sera from anti-HBe-positive carriers of HBsAg. Two sera from the cases of acute HB showed strong reactivity of the IgG3 isotype with HBc/eAg peptides 61-85. Five of the sera from HBeAg-positive carriers of HBsAg were weakly reactive with peptides 41-60, 61-85, 121-140, and/or 141-160. Eight of the sera from anti-HBe-positive carriers of HBsAg recognized aa 121-140 of HBc/e with IgG1, IgG3, and/or IgG4 isotypes. IgG from one immunized rabbit recognized peptides 1-20, 61-85, and 71-90, and the T-cells recognized peptides 1-20 and 71-90. Thus, human and rabbit antibodies recognize linear antigenic regions within the pre-C, and within regions 1-20, 41-60, 61-85, 121-140, and 141-160 of HBcAg.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatitis C virus (HCV)-specific cytotoxic T lymphocytes recognize epitopes in the core and envelope proteins of HCV

Hepatitis C virus (HCV) is a major cause of posttransfusion and community-acquired hepatitis, and a majority of individuals infected with this virus will subsequently develop chronic hepatitis. Characterization of the host immune response to this infection is an important first step that should facilitate the development of immunomodulatory agents and vaccines. Cellular immune responses, especially those mediated by cytotoxic T lymphocytes (CTL), are important in the control of many viral diseases. In this study, liver-infiltrating lymphocytes from persons with chronic HCV hepatitis were examined for evidence of HCV-specific CTL by using target cells infected with recombinant vaccinia viruses expressing the HCV core, E1, E2, and part of the NS2 proteins. Bulk expansion of liver-derived CD8+ lymphocytes resulted in the detection of HCV-specific CTL activity, whereas activity could not be found in CD8+ lymphocytes expanded from peripheral blood. Epitopes recognized by these CTL were defined by using CTL clones obtained by limiting dilution and target cells sensitized with synthetic HCV peptides. Four distinct HLA class I-restricted epitopes were identified, including two epitopes in the amino-terminal portion of the core protein. These studies provide evidence that the highly conserved core protein is a target for HCV-specific CTL and identify CTL epitopes within the more highly variable E2 envelope protein. Our studies also suggest that HCV-specific CTL are localized at the site of tissue injury in infected persons with chronic hepatitis. Identification of the epitopes recognized by HCV-specific CTL will facilitate exploration of their role in disease pathogenesis and may provide information useful in development of therapeutic interventions or vaccines.

Analysis of antibody response to the measles virus using synthetic peptides of the fusion protein. Evidence of non-random pairing of T and B cell epitopes

The measles virus induces a life-long immune response associated with antibodies specific for the fusion protein. To map the linear immunodominant recognition sites of the fusion (F) protein of the measles virus, we have reacted a complete set of 108 overlapping pentadecapeptides with purified IgG obtained from donor sera with elevated anti-measles titers. The antibodies recognized about 20% of the peptides and generated a characteristic binding pattern, defining about 6 or 7 distinctive regions (31-75; 111-145; 151-165; 191-215; 271-320; 421-440; 481-530) which include the major hydrophobic segment (111-145) of the intersubunit region and the C-terminal Cys-cluster region. The binding sites were located in close proximity of the few experimentally defined T cell epitopes. This pairing of T and B cell epitopes was corroborated by computer-assisted T cell prediction. The significance of a non-random association of T and B cell epitopes for processing and presentation is discussed. It is speculated that in long-term immunity against measles (F protein), B cells of the same sIg specificity play an important role both as antigen presenting cells and as antibody producing cells. In contrast to human sera from late convalescent donors, mouse and rabbit MV antisera with high neutralizing titers as well as neutralizing MV-F specific monoclonal antibodies did not react with the peptides.

Analysis of the neutralizing antibody response to the measles virus using synthetic peptides of the haemagglutinin protein

Infection or immunization with measles virus induces a protective immune reaction including neutralizing antibodies against the haemagglutinin and fusion protein. The reactivity of the polyclonal IgG response of sera obtained from late convalescent donors was studied, using overlapping 15mer peptides covering the complete sequence of the measles virus haemagglutinin. Most sera reacted with a similar set of peptides generating a characteristic binding pattern. The reactive peptides correspond to a region mediating cell hemolysis (aa310-325), to regions which serve as targets to neutralizing antibodies and to a putative transmembrane region (aa35-58). The latter region contains also a human T-cell epitope providing evidence of a non-random association of T- and B-cell epitopes. We also immunized different strains of mice and rabbits with measles virus. In contrast to the human sera, animal sera with strong neutralizing activities did not react with any of the H-protein peptides. The mostly weak reactivities with the linear sequences contrast with the strong neutralizing activities of the human or animal antibodies, suggesting that these primarily recognize the fusion protein or conformational epitopes of the haemagglutinin protein.

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.