| Summary: | 博士 === 國立陽明大學 === 臨床醫學研究所 === 98 === Hepatitis D virus (HDV) is a small defective RNA virus. Various domains of hepatitis B surface antigen (HBsAg) are essential for the assembly and secretion of HDV. The assembly efficiency of genotype 1 HDV is higher than that of genotype 2. This study aimed to investigate the influences of the levels and sequences of HBsAg of naturally-occurring HBV variants on the assembly and secretion of HDV. Six hepatitis B virus (HBV)-producing plasmids (3 genotype B and 3 genotype C) and 6 HBsAg-expression plasmids that expressed various HBsAg levels were constructed from sera of HDV-infected patients. These plasmids were cotransfected with 6 expression plasmids of HDV of genotypes 1, 2 or 4 into Huh-7 hepatoma cell line. Serum HBsAg and HBV DNA levels were correlated with HDV RNA levels and outcomes of chronic hepatitis D (CHD) patients. The secretion of genotype 1, 2 or 4 HDV generally correlated with HBsAg levels, but not with HBV genotypes or HBV DNA levels. Swapping and residue mutagenesis experiments of HBsAg-coding sequences revealed that the residue Pro-62 in the cytosolic domain-I affects the assembly and secretion of genotype 2 and 4 HDV, not those of genotype 1. The HDV package signal at the 19 C-terminal aa sequences of the HDAg-L is markedly divergent (73.7%) between genotype 1 and 2, while genotype 4 is more close to genotype 2 in this domain (78.9% homology). HDAg-L plasmids (wild-type or proline substituted mutants) of three different genotypes (genotypes 1, 2 and 4) were cotransfected with HBsAg plasmids with Pro-62 or Leu-62 into Huh-7 hepatoma cell line. The experiment obvious revealed that both Pro-205 of the HDAg-L and Pro-62 of the major HBsAg play a critical role in the assembly of HDV. The presence of Pro-205 in genotype 1 HDV isolates may account for its higher assembly efficiencies and wider global distribution. The pre-S2 N-terminal deletion HBV mutant adversely affects secretion of the three HDV genotypes. In patients, serum HDV RNA levels correlated with HBsAg levels, but not with HBV DNA levels. Viremia of HDV or HBV correlated with poor outcomes. In conclusion, the assembly and secretion of HDV were influenced by the amounts and sequences of HBsAg. For an effective treatment of CHD, reduction of HBsAg production in addition to the suppression of HBV and HDV replication might be crucial.
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