Antibodies to a novel antigen in acute hepatitis C virus infections

Background Conformational viral proteins potentially play an important role in the immunobiology of acute hepatitis C virus (HCV) infection and may enable earlier antibody detection. Materials and Methods HCV RNA was detected using nucleic acid testing. Early antibody production was evaluated using three enzyme immunoassays (EIAs) containing antigenic proteins not present in licensed EIAs. Respectively, these contained: 1 multiple-epitope fusion antigen (MEFA) 7·1-NS3/4a, 2 F and Core, and 3 E1/E2 proteins. NS3/4a is a conformational antigen retaining protease and helicase enzymatic activities. MEFA 7·1 contains the linear epitopes used in licenced EIAs, including the latest EIA-3·0, in combination with genotype 1–3 specific epitopes. Forty-two RNA positive, EIA-3·0 negative samples, including two persistently serosilent cases, were used to evaluate these research EIAs. As controls, 54 EIA-3·0 negative/RNA negative and three HCV RNA+/antibody positive specimens were included. Results Only the MEFA 7·1-NS3/4a EIA was positive in seven (17%) of the 42 HCV RNA + specimens, in all three EIA-3·0 positive controls but in none of 54 EIA-3·0 negative/HCV RNA negative controls. Notably, six of the seven (86%) specimens had evidence of active hepatitis (ALT > 210 IU/l). The two serosilent cases were research EIA negative. Conclusion A novel EIA with conformational and linear epitopes detected HCV antibodies in 17% of viraemic specimens missed by the standard reference EIA-3·0. Our research EIA appears to detect HCV antibodies closer to the initiation of acute hepatitis. Given that the average RNA-positive, antibody-negative window period is ∼56·4 days, this 17% yield would translate into a ∼10-day earlier detection of antibodies.