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The biological significance of amino acid substitutions in hepatitis B surface antigen (HBsAg) for glycosylation, secretion, antigenicity and immunogenicity of HBsAg and hepatitis B virus replication

¹ State Key Lab of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China;
² Institute of Virology, University Hospital of Essen, Essen, Germany;
³ Division of Clinical Immunology, Tongji Hospital, Huazhong University of Science and Technology,

⁴ E-mail: mengji.lu{at}uni-due.de

Amino acid (aa) substitutions of hepatitis B surface antigen (HBsAg) may affect the antigenicity and immunogenicity of HBsAg, leading to immune escape and diagnostic failure. The aa positions 122 and 160 are known as determinants for HBsAg subtypes d/y and w/r, respectively. The substitution K122I has been shown to strongly affect HBsAg antigenicity. In this study, we investigated the significance of naturally occurring aa substitutions K122I, T123N, A159G, and K160N. Both T123N and K160N substitutions resulted in additional N-glycosylated forms of HBsAg, while the other mutations produced more glycosylated HBsAg as compared to the wild type (wt). Detection of HBsAg by ELISA and immunofluorescence staining indicated that variant HBsAg (vtHBsAg) with K122I was not recognized by HBsAg immunoassays while vtHBsAg with T123N, A159G, K160N and A159G/K160N had reduced antigenicity. DNA immunization in BALB/c mice revealed that wtHBsAg and vtHBsAg with T123N and K160N are able to induce antibodies to HBsAg (anti-HBs), whereas K122I and A159G greatly impair the ability of HBsAg to trigger anti-HBs responses. The cellular immune response to the HBsAg aa 29-38 epitope was enhanced by K160N substitution. Using replication competent clones of hepatitis B virus, T123N and A159G substitutions were shown to strongly reduce virion assembly. The aa substitution K160N appeared to compensate for the negative effect of A159G on virion production. These results reveal complex effects of aa substitutions on biochemical properties of HBsAg, on antigenicity and immunogenicity, and on the replication of the hepatitis B virus.

Received 20 April 2009; accepted 7 October 2009.