| Summary: | 碩士 === 國立陽明大學 === 微生物及免疫學研究所 === 105 === Abstract
Hepatitis B virus (HBV) is one of the most prevalent viruses in the world. The infection of HBV is common in human and can lead to both acute and chronic liver diseases. More than 95% of acutely infected adults recover from the infection, whereas most of the neonatal transmitted infections become persistent. Chronic hepatitis B patients will have a higher risk of cirrhosis and liver cancer, which then lead to death. HBV infection has become a major research focus of global infectious diseases. Studying HBV persistence has long been hampered by the lacking of an immunocompetent animal model. Thus, the mechanism underlying the HBV chronicity has remained unclear. Our lab has established a HBV-persistent animal model in the FVB/N mice by hydrodynamic injection of an HBV replicon, B6.2, into the livers. Using this animal model, we have found that a single amino acid change at Asn-214 of clone B6.2 to become Ser-214, generating a new clone called B.2S, lead to a complete clearance of this new clone. This study aims to investigate the mechanism accounting for the difference between clones B6.2 and B6.2S. We first examined the expression of hepatitis B virus surface protein(HBsAg) of clones B6.2 and B6.2S in two hepatoma cell lines (Huh7 and HepG2) and in FVB/N mouse hepatocytes. Both in vitro and in vivo results demonstrated that, clone B6.2S expressed higher levels of intracellular HBsAg, whereas it secreted much lower levels of extracellular HBsAg, than clone B6.2. Previous studies have showed that the surface antigen of HBV can impair the activation of Toll-like Receptors (TLRs) pathways and inhibit the production of inflammatory cytokines, leading to suppression of host innate immunity. Hence, we speculate that the lower levels of extracellular HBsAg of clone B6.2S may cause less inhibition on host innate immunity, thus resulting in viral clearance. On the other hand, we were also curious about whether the surface antigens of B6.2 and B6.2S, differing only by one amino acid, might antagonize innate immunity differently. Therefore, we examined the cytokines gene (IL-6 and TNF-α) expression in the nonparachymal cells (NPC), which were isolated from FVB/N mice, in response to the treatment of TLR2, TLR4, and TLR9 ligands, in the presence or absence of B6.2-HBsAg or B6.2S-HBsAg. The results of RT-qPCR analysis showed that both B6.2-HBsAg and B6.2S-HBsAg exhibited inhibitory effects on the three TLR signaling pathways. Although B6.2S-HBsAg seemed to inhibit TLR signaling slightly more than B6.2-HBsAg, the difference was not statistically significant. Collectively, these results suggest that both B6.2-HBsAg and B6.2S-HBsAg have comparable inhibitory effects on host innate immunity, which thus cannot be the reason explaining the different persistent rates of both HBV clones.
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