Improvement in the specificity of assays for detection of antibody to hepatitis B core antigen

Neopterin and soluble CD14 (sCD14) levels as immunoactivation markers in aHBc-only cases

Aim: Isolated hepatitis B core antibodies (aHBc)-only pattern complicates the diagnosis of HBV infections. We evaluated neopterin and sCD14 levels in HBV infections. Methods: aHBc-only (n: 102), healthy control (healthy control group [HCG], n: 100), and chronic hepatitis (CHB) groups (n: 70) were investigated. Competitive and sandwich ELISA were used. Results: The mean neopterin levels were significantly lower in the aHBc-only group than those in the CHB group (p = 0.0001). No significant difference was found between the aHBc-only group and the HCG (p = 0.854). The mean sCD14 levels were lower in the aHBc-only group than those in the CHB group (p = 0.0001), but no significant difference was found between the aHBc-only group and HCG (p = 0.402). No significant difference was detected between aHBc-only and HCG for mean sCD14 (p = 0.402) and neopterin levels (p = 0.854). Conclusion: These two biomarkers are not useful for diagnosing the aHBc only pattern.

Novel double-antigen sandwich immunoassay for human hepatitis B core antibody

A novel diagnostic immunoassay testing procedure for hepatitis B virus core antibody (anti-HBc) using homogeneous purified full-length hepatitis B virus core antigen (HBcAg) capsids obtained from Escherichia coli was compared with Abbott Architect anti-HBc chemiluminescent microparticle immunoassay (CMIA; indirect method) against a library of specimens. A monoclonal anti-HBc neutralization confirmatory assay was then used to determine the degree of discordance between specimens. The new assay was found to be superior in both sensitivity and specificity.

The underlying mechanisms for the 'anti-HBc alone' serological profile

The serological pattern, "anti-HBc alone", characterized by the presence of antibodies against the core antigen of hepatitis B virus (anti-HBc) as the only marker of hepatitis B, is not rare in a diagnostic setting. Depending on the prevalence of HBV infection and the patient group investigated, 1-31% of positive anti-HBc results are isolated positive findings. Anti-HBc alone is frequently observed in intravenous drug addicts, HIV-infected individuals, patients who are coinfected with HBV and hepatitis C virus, and pregnant women. However, it is not clear how this profile should be interpreted. Several studies have shown that anti-HBc alone is not only compatible with acute and resolved HBV infection but also with chronic infection. The reasons for the lack of HBsAg and anti-HBs in anti-HBc-alone individuals are not clear, but several mechanisms and possibilities have been suggested that could explain this phenomenon, some of which are delineated in this article.

Evaluation of surrogate markers for human immunodeficiency virus infection among blood donors at the blood bank of "Hospital Universitário Regional Norte do Paraná", Londrina, PR, Brazil

This study evaluated the usefulness of the anti-HBc, hepatitis C virus antibodies (anti-HCV), human T cell lymphotropic virus I and II antibodies (anti-HTLV I/II), serologic tests for syphilis, and surface antigen of hepatitis B virus (HBsAg) as surrogate markers for the risk for HIV infection in 80,284 serum samples from blood donors from the Blood Bank of "Hospital Universitário Regional Norte do Paraná", Londrina, Paraná State, Brazil, analyzed from July 1994 to April 2001. Among 39 blood donors with positive serology for HIV, 12 (30.8%) were anti-HBc positive, 10 (25.6%) for anti-HCV, 1 (2.6%) for anti-HTLV I/I, 1 (2.6%) was positive for syphilis, and 1 (2.6%) for HBsAg. Among the donors with negative serology for HIV, these markers were detected in 8,407 (10.5%), 441 (0.5%), 189 (0.2%), 464 (0.6%), and 473 (0.6%) samples, respectively. The difference was statistically significant (p < 0.001) for anti-HBc and anti-HCV. Although the predictive positive values for these surrogate markers were low for HIV infection, the results confirmed the anti-HBc and anti-HCV as useful surrogate markers for HIV infection thus reinforcing the maintenance of them in the screening for blood donors contributing to the prevention of the small number of cases in which HIV is still transmitted by transfusion.

Erratum to "characterization and diagnostic potential of hepatitis B virus nucleocapsid expressed in E. coli and P. pastoris"

The hepatitis B core antigen (HBcAg) was expressed in Escherichia coli and in Pichia pastoris. A hexa-histidine tag was introduced at the C terminus of the E. coli expressed protein allowing its purification by Ni2+-chelate affinity chromatography. The P. pastoris expressed HBcAg was isolated following heat treatment. The two recombinant HBcAgs were purified further on a sucrose gradient. Mass spectrometry analysis suggested that HBcAg was N-acetylated only in P. pastoris and reaction with Ellman's reagent allowed the measurement, respectively, of 0.37 and 0.23 mole of free sulfydryl groups per mole of HBcAg monomer expressed in E. coli or P. pastoris. Electron microscopy indicated that the E. coli and the P. pastoris proteins formed capsid-like particles with, respectively, a diameter of 34 and 28 nm. Nucleic acid components were found entrapped in both particles but protected from enzymatic treatment only in the P. pastoris derived particles suggesting structural discrepancies between the two recombinant molecules. The high purity of these recombinant antigens allowed the development of a sandwich immunoassay to detect antibodies to HBcAg (anti-HBc) in human serum. The preliminary results indicate that the P. pastoris HBcAg produced intracellularly is more suitable than the renatured E. coli HBcAg for detection of anti-HBc in this diagnostic assay.

Characterization and diagnostic potential of hepatitis B virus nucleocapsid expressed in E. coli and P. pastoris

The hepatitis B core antigen (HBcAg) was expressed in Escherichia coli and in Pichia pastoris. A hexahistidine tag was introduced at the C terminus of the E. coli expressed protein allowing its purification by Ni(2+)-chelate affinity chromatography. The P. pastoris expressed HBcAg was isolated following heat treatment. The two recombinant HBcAgs were purified further on a sucrose gradient. Mass spectrometry analysis suggested that HBcAg was N-acetylated only in P. pastoris and reaction with Ellman's reagent allowed the measurement respectively, of 0.37 and 0.23 mole of free sulfydryl groups per mole of HBcAg monomer expressed in E. coli or P. pastoris. Electron microscopy indicated that the E. coli and the P. pastoris proteins formed capsid-like particles with respectively, a diameter of 34 and 28-nm. Nucleic acid components were found entrapped in both particles but protected from enzymatic treatment only in the P. pastoris derived particles suggesting structural discrepancies between the two recombinant molecules. The high purity of these recombinant antigens allowed the development of a sandwich immunoassay to detect anti-HBc antibodies in human serum. The preliminary results indicate that the P. pastoris HBcAg produced intracellularly is more suitable than the renatured E. coli HBcAg for detection of anti-HBc in this diagnostic assay.

Presence of low levels of anti-HBs antibody in so-called 'anti-HBc alone' subjects

BACKGROUND/AIMS

The 'anti-Hbc alone' pattern could sometimes be that of subjects who produced anti-HBs after recovery, but at a lower level than that detectable using commercial assays. This study aimed to test this hypothesis.

METHODS

A total of 104 'anti-HBc alone' serum samples, i.e.positive for the anti-HBc antibody but not for HBsAg nor for anti-HBs antibody, were recruited when routine testing a broad population of employees, patients and pregnant women from a university hospital. A possible subliminal anti-HBs production, that would have escaped detection by commercial EIAs, was investigated by comparing the optical densities (ODs) obtained in vaccinees (commercial anti-HBs EIA) to those of a control group of 100 nonimmunised and nonvaccinated subjects.

RESULTS

The median OD was significantly higher (p<0.0001) in the 'anti-HBc alone' subjects (OD=0.035) than in the controls (OD=0.023). Thirty-six percent of the 'anti-HBc alone' subjects had an anti-HBs OD higher than the median OD of the controls+2SD. 'Anti-HBc alone' subjects with anti-HBe antibody had higher anti-HBs ODs (0.041) than had those without anti-HBe (0.029). In 'anti-HBc alone' subjects, the anti-HBs ODs, although under the cut-off value of the EIA, were found to be higher than in the controls.

CONCLUSION

Our results show low anti-HBs production in some of the subjects studied.

Detection of IgM to hepatitis B core antigen in a reductant containing, chemiluminescence assay

The Abbott PRISM(R) hepatitis B core (HBc) antigen assay is an automatic in vitro competitive chemiluminescence immunoassay for the detection of total antibody to HBc (anti-HBc) antigen in human serum or plasma. The assay utilizes cysteine solution as a reducing reagent in order to maximize specificity. To help understand the effect of cysteine on detection of anti-HBc antigen, we separated and purified anti-HBc IgM and IgG from human plasma using size exclusion, protein A/G, and affinity chromatography techniques. We showed that cysteine affected the reactivity of anti-HBc IgM with recombinant HBc (rHBc) antigen but not the reactivity of anti-HBc IgG. Anti-HBc IgM treated with cysteine yielded byproducts which were reactive in the PRISM HBcore assay. Reduction-sensitive factor (RSF) - IgM fraction from serum known to be non-specific for anti-HBc activity, similarly treated with cysteine, was no longer reactive in the PRISM HBcore assay. We showed that cysteine treatment is effective against non-specific IgM in human blood. Also, the inclusion of cysteine in the PRISM HBcore assay does not compromise the detection of HBc specific antibodies.

Hepatitis B core antibody screening in a high prevalence group: comparison of three enzyme immunoassays using receiver operating characteristic analysis

Selected sera from 296 homosexual men were screened by 3 commercially available anti-HBc enzyme immunoassays (EIA). All patients could be classified either as non-immune to hepatitis B, or with current or previous hepatitis B infection. Using the cut-off optical density values (O.D. values) recommended by the respective manufacturers, the results from these three assays were identical for 83% of the serum samples. For anti-HBc reactivity, the ratio (percentage) was calculated using O.D. sample x 100 divided by the O.D. cut-off value. Employing these ratios, sensitivities and specificities for the three assays were compared. All assays performed well when analyzed by receiver operating characteristic curves with area under the curves of 96-97%. A higher specificity, with only a marginal loss of sensitivity could be achieved by lowering the cut-off to 55% for the Enzygost EIA, to 85% for the Enzygost-monoclonal EIA and to 60% for the Corzyme EIA. Using the modified cut-off values, the results with the three assays agreed for 93% of the serum samples.

Feasibility and usefulness of an efficient anti-HBc screening programme in blood donors

Post-transfusion hepatitis B remains a risk for recipients of hepatitis B surface antigen (HBsAg) screened blood. Anti-hepatitis B core antibody (anti-HBc) screening may help reduce this risk. To evaluate its usefulness, 9,238 East Anglian blood donors were screened for anti-HBc. Those with isolated anti-HBc were identified with two confirmatory anti-HBc and anti-HB surface antibody (anti-HBs) assays. The prevalence of anti-HBc reactions in screening and confirmatory assays was 1.29% and 0.35%, respectively. The level of reactivity was significantly higher when two anti-HBc assays gave concordant results or, being concordant, were anti-HBs positive. All isolated anti-HBc-positive units (0.04%) were negative for additional HBV markers including DNA tested with nested polymerase chain reaction (PCR). A 0.31% prevalence of past HBV infection was found in this population, all carrying both anti-HBc and anti-HBs antibody, most above the protective level (0.1 IU/ml). The proposed screening schemes would limit the number of deferred donors and discarded units and keep the testing time within the remit of routine blood banking practices for an additional cost of approximately 1 pound per unit. However, no evidence was found in this donor population to suggest that anti-HBc screening would significantly reduce the incidence of post-transfusion hepatitis B.

Characterization of a reduction-sensitive factor from human plasma responsible for apparent false activity in competitive assays for antibody to hepatitis B core antigen

Addition of reducing agents to competitive assays for antibody to hepatitis B core antigen (anti-HBc) eliminates apparent false reactivity of specimens obtained from individuals with no prior history of hepatitis B virus (HBV) infection and without other serological markers of HBV infection. We have purified and characterized a reduction-sensitive factor (RSF) isolated from the plasma of several volunteer blood donors. Column fractions were assayed fro anti-HBc by using a highly sensitive chemiluminescence assay with a detection of 0.15 Paul Ehrlich Institut units per ml at 50% inhibition. Gel filtration on Sephacryl S-300 indicated that reductant-sensitive samples possessed anti-HBc activity that was associated with immunoglobulin M (IgM), whereas reductant-stable activity was associated with IgG. Gel filtration followed by metal chelate affinity chromatography resulted in a 55-fold purification and demonstrated that RSF activity copurifies with IgM. RSF was recovered from a recombinant hepatitis B core antigen matrix and shown to be an IgM species by immunoblot. In addition, RSF activity coeluted with IgM protein from anti-mu-chain Sepharose. Discrepancies between enzyme immunoassay and radioimmunoassay procedures for anti-HBc (Corzyme and Corab, respectively: Abbott Laboratories, North Chicago, Ill.) appear to be due to the relative sensitivity of the enzyme immunoassay for IgM anti-HBc (sevenfold greater than the radioimmunoassay using a specific panel). The biological basis for the occurrence of low levels of nonspecific IgM anti-HBc reactivity in individuals not previously exposed to HBV remains to be elucidated.

Improvements in detection of antibody to hepatitis B core antigen by treating specimens with reducing agent in an automated microparticle enzyme immunoassay

A fully automated microparticle enzyme immunoassay (EIA), IMx Core, was developed for the detection of antibody against hepatitis B core antigen (anti-HBc). IMx Core sensitivity was less than 0.5 Paul Ehrlich Institut units per ml and was greater than that of the commercial radioimmunoassay (RIA) or EIA, Corab and Corzyme, respectively. Specimens from blood donors and diagnostic and hospital patients, which included individuals with a variety of infectious and immune diseases, were tested in parallel by the IMx Core and EIA. Overall agreement of 99.1% (4,797 of 4,841) was obtained. Prevalence of anti-HBc tested by IMx Core ranged from 1.2% in volunteer blood donors to 9.1% in hospital laboratories. Discordant specimens reactive by IMx Core but negative by Corzyme or Corab resulted from the increased sensitivity of the IMx Core assay, since other hepatitis B markers were usually present. However, most discordant specimens were positive by the EIA or RIA but negative by IMx Core. No other hepatitis B markers could be detected in these discordants, and after addition of reducing agent, these specimens also became negative by EIA or RIA. In clinical trials, 30% (14 of 47) of volunteer blood donors and 8% (9 of 119) of hospital patients testing repeatedly reactive by the EIA had reduction-sensitive (unspecific) anti-HBc reactivity. The reducing agent, dithiothreitol, was added to each specimen automatically in the IMx assay to eliminate these unspecific reactions without significantly affecting anti-HBc reactivity resulting from hepatitis B virus infection as judged by the correlation with other hepatitis B markers.