Genotype dependence of peptide-based immunoassays for the detection of HCV core antibodies

A rainbow of acridinium chemiluminescence

Multicolor chemiluminescent acridinium derivatives were synthesized by attaching various common fluorophores to the N¹⁰ -acridinium position through a piperazine linker. Triggering of each acridinium derivative using alkaline hydrogen peroxide resulted in a chemiluminescence spectrum dominated by a strong emission (>95%) from the attached fluorophore. The highly quenched emission from the triggered acridinium, acting as a donor, points to a highly efficient intramolecular energy transfer in acridinium-based chemiluminophore-fluorophore tandems. A variable, and in many cases minimal, spectral overlap between the donor emission and the acceptor absorption may indicate that in such tandems the energy transfer follows the Dexter electron exchange mechanism. Moreover, fluorophores affixed through the acridinium 9-position produce a typical acridinium emission profile, demonstrating the need for close distances and favorable intramolecular orientation of the donor and acceptor moieties for the energy transfer to occur. A family of red-shifted chemiluminescent labels, all sharing a uniform triggering method, will find immediate application in multicolor ligand-receptor assays. Along with the multiplexing capabilities, the red-shifted chemiluminescent detection offers a higher tolerance to green-colored biological interferences and will therefore benefit many screening and diagnostic clinical tests.

Characterization of differential antibody production against hepatitis C virus in different HCV infection status

BACKGROUND

The Centers for Disease Control and Prevention (CDC) issued an update on hepatitis C virus (HCV) testing approach, in which it omitted the use of recombinant immunoblot assay (RIBA) in the diagnostic algorithm and recommended that future studies are needed to evaluate the performance of HCV testing without RIBA. As Egypt has the highest prevalence of HCV worldwide, we aimed to evaluate the value of RIBA in HCV testing in a high prevalence population. Our objective was to clarify whether enzyme linked immunosorbent assay (ELISA) anti-HCV signal-to-cutoff (S/CO) ratios were able to discriminate true positive from false positive anti-HCV antibody status and to evaluate the role of RIBA in solving this problem which may lead to a redefined strategy for diagnosis of HCV infection. Our second objective was to elucidate the effects of different HCV peptides of both structural and non-structural proteins on the humoral immune response to HCV infection.

METHODS

The current study drew results from 167 individuals divided into three groups: Group I: included 77 HCV antibody positive (ELISA) high risk health care workers (HCW), Group II: included 56 presumably uninfected individuals who showed normal liver enzymes, negative HCV RNA and were asymptomatic. Their ELISA HCV antibody S/C ratio ranged from 0.9 to <5. Group III: included 34 patients enrolled from outpatient clinics of Ain Shams Hospital with persistent viral replication, elevated liver enzymes, and chronic HCV related liver disease. All study participants were assessed for the presence of anti-HCV antibodies by 3(rd) generation ELISA which was confirmed by RIBA.

RESULTS

Interpreting the results of both ELISA and RIBA together, false positive results were highly significantly increased in HCW when compared with the other two groups. Indeterminate and false negative results were only found in the presumably uninfected group. For differentiated antibody responses by RIBA, chronic HCV cases had the highest frequency of positive antibody response to core peptides while the presumably uninfected group had the lowest. Antibody response to E2 was found less frequently in chronic cases than Core 1, Core 2 and NS3. The specific antibody response to the different HCV peptides showed the same distribution of frequencies in both chronic HCV cases and the presumably uninfected individuals with the chronic cases having the highest frequencies. This distribution was different from the HCW. The most evident difference was the reaction towards NS3 which was the highest antibody producing peptide in chronic HCV and presumably uninfected individuals whereas in HCW Core1 was the highest.

CONCLUSION

The HCV antibody immunoblot assay (RIBA) is still necessary for the detection of false positive cases which can occur quite frequently in countries of high prevalence as Egypt. Indeterminate RIBA results indicate a waning antibody response in elderly individuals who recovered from previous or distant HCV infection.

Hepatitis C virus-specific cell-mediated immune responses in children born to mothers infected with hepatitis C virus

OBJECTIVE

To investigate the association between hepatitis C virus (HCV)-specific cell-mediated immunity (CMI) responses and viral clearance in children born to mothers infected with HCV.

STUDY DESIGN

A cross-sectional study of children from a mother-infant cohort in Egypt were enrolled to detect CMI responses to recombinant core and nonstructural HCV antigens (nonstructural segments NS3, NS4a/b, and NS5 of the HCV genome) using an interferon-gamma enzyme-linked immunospot assay. Children born to mothers with chronic HCV were enrolled into 3 groups: transiently viremic (n = 5), aviremic (n = 36), and positive control (n = 6), which consisted of 1 child with chronic HCV from this cohort and another 5 children with chronic HCV from a companion study. Children without HCV born to mothers without HCV (n = 27) served as a negative control group. Wilcoxon rank sum test was used to compare the magnitude of CMI responses between groups.

RESULTS

None of the 6 control children who were positive for HCV responded to any HCV antigen, and 4 (80%) of 5 children with transient viremia responded to at least one HCV antigen, compared with 5 (14%) of 36 and 3 (11%) of 27 children in the aviremic and negative control groups, respectively. Children with transient viremia elicited stronger responses than did negative controls (P = .005), positive controls (P = .011), or children without HCV viremia (P = .012), particularly to nonstructural antigens.

CONCLUSIONS

HCV-specific CMI responses were significantly higher in magnitude and frequency among transiently infected children compared with those persistently infected. This suggests CMI responses may be associated with past viral clearance and can identify children at high risk of infection, who can be targeted for health education, screening, and follow-up.

Evaluation of core and NS4B synthetic peptide-based immunoassays for the detection of hepatitis C virus antibodies in clinical samples from Cameroon, Central Africa

BACKGROUND

According to previous data, the antibodies produced during natural hepatitis C virus (HCV) infection frequently recognize amino acids 10-43 in the core protein and 1689-1740 or 1921-1940 in the non-structural 4B (NS4B) protein. The reactivity of these peptides with the corresponding antibodies has mainly been evaluated using serum samples from Western countries where HCV genotype 1 (HCV-1) is predominant, and no information is available concerning samples from sub-Saharan countries where high HCV variability has been reported. OBJECTIVE OF THIS STUDY: To evaluate the performance of HCV core and NS4B peptide-based immunoassays in the serodiagnosis of HCV infection in Cameroon subjects.

STUDY DESIGN

Three core and four NS4B-based synthetic peptides derived from HCV genotypes 1b and 2a were designed and tested against a panel of 151 serum samples from Cameroon (40 positive for HCV-1, 32 for HCV-2, 39 HCV-4, and 40 HCV-negative).

RESULTS

The three core peptides all demonstrated strong immunoreactivity, regardless of the HCV genotype from which they were derived, with greater than 90% and 92% sensitivity and specificity. In contrast, the NS4B-derived peptides exhibited lower sensitivities (24.3-65.8% depending on the HCV genotype) but higher specificities (100% for all four peptides tested).

CONCLUSIONS

Our findings indicate that an HCV core peptide could be used for the diagnosis of chronic HCV infection. Among the NS4B peptides tested, a chimeric NS4B peptide encompassing both N- and C-terminal portions of the NS4B protein gave a much better performance than the two component N- and C-terminal peptides used individually.

Hepatitis C virus core, NS3, NS4B and NS5A are the major immunogenic proteins in humoral immunity in chronic HCV infection

Background

The viral genome of hepatitis C virus constitutes a 9.6-kb single-stranded positive-sense RNA which encodes altogether 11 viral proteins. In order to study the humoral immune responses against different HCV proteins in patients suffering from chronic HCV infection, we produced three structural (core, E1 and E2) and six nonstructural proteins (NS2, NS3, NS4A, NS4B, NS5A and NS5B) in Sf9 insect cells by using the baculovirus expression system.

Results

The recombinant HCV core, E1, E2, NS2, NS3, NS4A, NS4B, NS5A and NS5B proteins were purified and used in Western blot analysis to determine antibody responses against individual HCV protein in 68 HCV RNA and antibody positive human sera that were obtained from patients suffering from genotype 1, 2, 3 or 4 infection. These sera were also analysed with INNO-LIA Score test for HCV antibodies against core, NS3, NS4AB and NS5A, and the results were similar to the ones obtained by Western blot method. Based on our Western blot analyses we found that the major immunogenic HCV antigens were the core, NS4B, NS3 and NS5A proteins which were recognized in 97%, 86%, 68% and 53% of patient sera, respectively. There were no major genotype specific differences in antibody responses to individual HCV proteins. A common feature within the studied sera was that all except two sera recognized the core protein in high titers, whereas none of the sera recognized NS2 protein and only three sera (from genotype 3) recognised NS5B.

Conclusion

The data shows significant variation in the specificity in humoral immunity in chronic HCV patients.

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.