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Journal of Virology, February 2004, p. 1945-1953, Vol. 78, No. 4
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.4.1945-1953.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Identification of Antigenic Regions of Duck Hepatitis B Virus Core Protein with Antibodies Elicited by DNA Immunization and Chronic Infection

INSERM U271, 69424 Lyon Cedex 03,¹ Pôle BioInformatique Lyonnais Lyon Gerland, IBCP, 69367 Lyon Cedex 7, France²

Received 6 August 2003/ Accepted 22 October 2003

The induction of humoral response in ducks by DNA-based immunization against duck hepatitis B virus (DHBV) core protein (DHBc) was investigated. In addition, the amino acid specificity of the induced response was compared by using peptide scanning to that elicited either by protein immunization or during chronic DHBV infection. Immunization of ducks with a plasmid expressing DHBc protein led to the induction of a long-lasting antibody response able to specifically recognize viral protein in chronically infected duck livers. Peptide scanning analysis of anti-DHBc response induced during chronic DHBV infection allowed us to identify six major antigenic regions (AR1 to AR6). The reactivity spectrum of duck sera elicited by protein immunization appeared narrower and was restricted to only four of these antigenic regions in spite of higher anti-DHBc antibody titers. Interestingly, anti-DHBc antibodies induced by DNA-based immunization recognized five of six antigenic regions, and the epitope pattern was broader and more closely related to that observed in chronic viral infections. To gain more insight into the location of antigenic regions, we built a three-dimensional (3-D) model of DHBc protein based on human and duck core sequence alignment data and the HBc 3-D crystal structure. The results suggest that two identified antigenic regions (AR2, amino acids [aa] ⁶⁴T-P⁸⁴, and AR5, aa ¹⁸³A-R²¹⁰) are located at positions on the protein surface equivalent to those of the two HBc major epitopes. Moreover, we identified another antigenic region (AR3, aa ⁹⁹I-I¹¹²) that was recognized by all sera from chronically infected, DNA- or protein-immunized ducks within the large 45-aa insertion in DHBc protein, suggesting that this region, which lacks HBc, is externally exposed.

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