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 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.