Abstract:

Objective To investigate the difference of hepatitis B virus（HBV） S protein mutations in patients with chronic hepatitis B （CHB） and cirrhosis,and to assess its role in clinical application. Methods A total of 114 patients with CHB were enrolled,and they were classified into 3 groups,asymptomatic HBV carriers（41 cases）,inactive hepatitis B surface antigen（HBsAg） carriers（38 cases） and cirrhosis patients（35 cases）. DNA sequencing was used to determine HBV S protein gene mutation. Results There was statistical significance in age and HBV DNA loads of asymptomatic HBV carrier,inactive HBsAg carrier and cirrhosis groups（P<0.01）,and there was no statistical significance in sex and HBV genotypes（P>0.05）. The gene mutation frequency of HBV S protein was higher in cirrhosis group than those in asymptomatic HBV carrier group（P<0.05） and inactive HBsAg carrier group（P<0.01）. The mutation rates in outside major hydrophilic region（MHR） and cytotoxic T lymphocytes（CTL） +helper T cell（Th） epitopes were increased in the 3 groups（asymptomatic HBV carrier<inactive HBsAg carrier<cirrhosis patient）（P<0.01）. There was no statistical significance among the 3 groups in MHR and a determinant,LOOP1,LOOP2 located in MHR and non-immune epitopes located outside MHR（P>0.05）. Single amino acid substitution was found in the majority of asymptomatic HBV carriers except 2 patients. Of these,one had 3 amino acid substitutions in CTL+Th epitopes and non-immune epitopes located outside MHR,and another had 2 amino acid substitutions in MHR and CTL+Th epitopes outside MHR. The mutation rates in CTL+Th epitopes and non-immune epitopes outside MHR were comparable and random for asymptomatic HBV carriers,whereas more than 2 mutation sites were determined in 5 cases of inactive HBsAg carriers（13.15%） and 9 patients with cirrhosis（25.71%）. These mutation sites preferentially concentrated at the CTL+Th epitopes outside MHR. Conclusions High prevalence of outside MHR variants especially CTL+Th epitopes is associated not only with hepatitis B e antigen（HBeAg）-negative serostatus but also with severe liver diseases,particularly cirrhosis.

Key words: Hepatitis B virus, S protein, DNA sequencing