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AIM: To investigate the change of immunological characteristics of HBsAg caused by the mutation at codon 145 of HBsAg using DNA-based immunization.METHODS: Plasmids expressing mutant and wild type envelope antigens were transfected into human hepatocellular carcinoma cells via electrotransformation. The antigenicity of HBsAg was studied with EIA and immunocytochemical staining.Then plasmids were used to immunize 5 C57BL/6 mice.Sera of mice were detected for anti-HBs and anti-preS2with ELISA.RESULTS: The mutant HBsAg could be detected by native antibody in EIA and immunocytochemical study. But the A(450 nm) value of the mutant HBsAg in the supatant was apparently lower than that of the wild-type. Both mutant and native HBsAg expression plasmid could stimulate a strong humoral immune response to HBsAg and preS2antigen in mice. Protective antibodies against HBsAg elicited by the native HBsAg occurred earlier than that elicited by the mutant HBsAg about one to two weeks. The occurrence of protective antibodies against preS2 antigen was one to two weeks earlier than that of anti-HBs.CONCLUSION: The amino acid substitution causes changes of the antigenicity and immunogenicity of HBsAg, but mutant HBsAg can still induce a protective humoral immune response in mice.