OBJECTIVETo study the mechanism of hepatitis B virus infected patients who is negative for HbsAg.

METHODSDNA sequences of 46 patients were analyzed. In these patients, HBsAg was negative but HBV DNA was positive and six new HBsAg variants were identified. Four of the six variants were combined point mutants and two were insertion variants. These S genes were subcloned into eukaryotic expression vector EBO-plpp, and the recombinant eukaryotic expression plasmids were transfected into COS7 cells. Cell lines expressing mutant type HBsAg were obtained. The supernatants were detected by ELISA and RIA.

RESULTSOnly the two-amino acid-insertion variants could be detected and the others failed to react with polyclonal and monoclonal antibodies against HbsAg.

CONCLUSIONThe results indicated that the point mutations and insertions may result in a conformational change of the S gene, which affect HBsAg antigenicity, suggesting a possible relationship between the variants and the negative conversion of HBsAg of the patients.