Localization and reactivity of an immunodominant domain in the NS3 region of hepatitis C virus

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Abstract
Analysis of the amino acid sequences of the non-structural region 3 (NS3) of the hepatitis C virus type 1 revealed four points with a high average hydrophilicity (Ah). Two of these potential anti-genie sites were expressed in E. coli as short fragments. The first fragment of 91 residues (NS3f3: residues 1359–1449) harbors the hexapeptide K-K-K-C-D-E with an Ah of 2.33; the second fragment is 73 residues long (NS3f4: residues 1460–1532) and encompasses the hep-tapeptide R-S-N-R-R-G-R with an Ah of 1.79. Both fragments were expressed with truncated hepatitis B core (tHBc) as a carrier protein. The fusion proteins were purified from the bacterial lysates by affinity chromatography on immobilized monoclonal antibodies against HBc, and evaluated as antigens in an enzyme immunoassay for the detection of HCV antibodies. In a specificity control panel, reactivity with NS3f3 was only found in proven HCV carriers, while reactivity with NS3f4 was weak in HCV carriers but accounted for some of the nonspecific serological reactions. In a group of 48 genotyped HCV-in-fected volunteer blood donors, antibodies against NS3f3 were detected in 90% (27/30) of HCV-type 1 infections and in all HCV-type 4 infections (5/5). However, in carriers infected with HCV-types 2, 3, or 5, the response rate was on average only 23% (3/13). With NS3f4 as antigen, weak antibody titers were found in only about half of the carriers, independent of the infectious genotype. In a cohort of hemodialysis patients, all infected with HCV-type 1b, NS3f3 antibodies were detected in 80% (16/20) of the carriers, while only one patient showed a weak NS3f4 reactivity. It is concluded that NS3f3 harbors an immunodominant domain of the NS3 region showing an apparently HCV-type-dependent serological response.