Use of overlapping synthetic peptides to characterize samples from blood donors with indeterminate results to hepatitis C virus core antigen.

BACKGROUND AND OBJECTIVES: Despite recent improvements in supplemental assays, isolated reactivity to the hepatitis C virus (HCV) core antigen continues as one of the main problems in the confirmation of anti-HCV in blood donors. Reactivity against individual peptides from the c22-3 HCV recombinant antigen has been described as a useful tool for anti-HCV confirmation and donor counseling in such cases. MATERIALS AND METHODS: We used a previously described set of overlapping peptides spanning the entire sequence of the c22-3 antigen to study 87 single serum samples from blood donors with reactivity for c22-3 antigen alone in second generation recombinant immunoblot assay (RIBA-2). All of them had been previously studied by RIBA-3, anti-HCV E2 EIA and HCV PCR. RESULTS: 66 of the 87 samples studied could be classified as positive or negative for anti-HCV core using the multipeptide assay and such classification correlated well with the results obtained with RIBA-3 and the anti-E2 EIA. However, some discrepancies were found. The epitopes located along the N-terminal half of the molecule were mainly responsible for the specific antibody recognition but those enclosed within amino acids 1-15 were frequently involved in nonspecific reactivity. Some 38% of samples were considered to have specific antibody to the c22-3 antigen and a further 9% reacted for both anti-E2 and single core peptides that were often involved in specific antibody recognition. CONCLUSION: Testing of blood donor samples indeterminate to the HCV c22-3 antigen for reactivity against individual core peptides can confirm the presence of specific antibody and recognize nonspecific reactivity with certain cross-reacting epitopes. Third generation supplemental tests have reduced such false reactivity, but confirmation of samples with anticore alone is still necessary. Single reactivity to the HCV core antigen is likely to reflect prior exposure to the virus, but rarely active infection, either acute or chronic.

Detection of antibody to hepatitis C virus E2 recombinant antigen among samples indeterminate for anti-HCV after wide serological testing and correlation with viremia. The Spanish Study Group for Blood Donors at Risk of Transmission of HCV.

The detection of antibody to the second envelope protein (E2) of the hepatitis C virus (HCV) has been hampered by the lack of suitable antigens. A previously described E2 recombinant antigen (CHO-E2) expressed as a non-fused, highly glycosylated protein in mammalian cells was used to detect specific antibody (anti-E2) in samples from blood donors and viraemic patients showing positive or indeterminate results for anti-HCV after a wide serological study. Anti-E2 was detected in 50-75% of the donors positive for anti-HCV, 80% of viraemic immunocompetent patients with anti-NS3 alone and 28% of non-viraemic donors with anticore alone. In donors with anti-NS3 (15 samples) or anti-NS4 (51 samples) alone, anti-E2 was found occasionally (3 cases). Moreover, two anti-E2-positive samples from viraemic patients were misidentified by some commercial assays for screening anti-HCV. These results suggest that testing for anti-E2 may be useful for improving the performance of the current assays for anti-HCV screening and confirmation.