Mutations in surface and polymerase gene of chronic hepatitis B patients with coexisting HBsAg and anti-HBs

Abstract

Aim: To investigate the clinical significance and presence of mutations in the surface (S) and overlapping polymerase gene of hepatitis B patients with coexisting HBsAg and anti-HBs.

Methods: Twenty-three patients with chronic hepatitis B were studied. Of the 23 patients, 11 were both positive for hepatitis B virus (HBV) surface antigen (HBsAg) and antibody to HBV surface antigen (anti-HBs), 12 were negative for anti-HBs while positive for HBsAg. DNA was extracted from 200 muL serum of the patients. Nucleotide of the surface and overlapping polymerase gene from HBV-infected patients was amplified by PCR, and the PCR products were sequenced.

Results: Forty-one mutations were found within the surface gene protein of HBV in 15 patients (10 with coexisting HBsAg and anti-HBs). Six (14.6%) out of 41 mutations were located at "alpha " determinant region in 5 patients (4 positive for HBsAg and anti-HBs). Eleven mutations (26.8%) occurred in the downstream or upstream of "alpha " determinant region. Lamivudine (LMV)-selected mutations were found in three patients who developed anti-HBs, which occurred in amino acid positions (196, 198, 199) of the surface protein and in YMDD motif (M204I/V) of the polymerase protein simultaneously. Presence of these mutations did not relate to changes in ALT and HBV DNA levels.

Conclusion: Besides mutations in the "alpha " deter-minant region, mutations at downstream or upstream of the "alpha " determinant region may contribute to the development of anti-HBs. These mutations do not block the replicating competency of HBV in the presence of high titer of anti-HBs.

Figure 1

Amino acid mutations in the surface gene of HBV. Positions of mutation in deduced amino acid residues are indicated by vertical line bellow the surface protein of HBV. The consensus sequences of A, B and D different from those of genotype C are listed in parentheses. Dashes mean residues identical to these reference residues. Patients 1 to 11 were positive for HBsAg and anti-HBs, the others were negative for anti-HBs.