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Human monoclonal antibodies for the immunological characterization of a highly conserved protein domain of the hepatitis C virus glycoprotein E1

Although both envelope glycoproteins of the hepatitis C virus, E1 and E2/NS1, show a high degree of sequence variation, the E1 protein includes a well conserved domain, which may be functionally important. We have analysed the human B cell response to a peptide fragment from amino acid residues 314–330 (EP3) covering the central conserved sequence of this domain. Anti‐hepatitis C virus‐positive blood donors were screened for anti‐EP3 antibodies with an ELISA based on immobilized peptide. Thirty out of 92 (32%) RIBA‐confirmed donors displayed a significant antibody response to EP3. From three of these blood donors we established four anti‐EP3‐producing heterohybridoma cell lines: U1/F30 and U1/F31 produced IgM‐κ, whereas U1/F32 and U1/F33 secreted the isotypes IgG1‐λ and IgG1‐κ, respectively. Epitope analysis with overlapping nonapeptides suggests the existence of different antigenic determinants within the EP3 fragment. Although both IgG antibodies U1/F32 and U1/F33 have dissociation constants to the peptide of ∼ 10−9 M, binding to recombinant E1 protein expressed in COS‐7 cells was different. Only U1/F33 detected envelope protein of ∼ 24–35 kD in Western blot. This human MoAb will be useful for further investigations on the hepatitis C virus glycoprotein E1.