| Summary: | 博士 === 國立陽明大學 === 微生物及免疫學研究所 === 102 === Hepatitis B virus (HBV) is a hepatotropic non-cytopathic DNA virus that causes a wide spectrum of human liver diseases. Although HBV vaccine has been available for decades, the immune response to HBV remains elusive. In the first part of the thesis, we investigated the innate immunity to HBV focusing on the study of RIG-I-like receptor family (RLRs) of pattern recognition receptors, including MDA5 (melanoma differentiation-associated gene 5) and RIG-I (retinoic acid-inducible gene-I). We demonstrated that the expression of MDA5, but not RIG-I, was increased in Huh7 cells transfected with the HBV replicative plasmid and in the livers of mice hydrodynamically injected with the HBV replicative plasmid. To further determine the effect of RLRs on HBV replication, we co-transfected the HBV replicative plasmid with RIG-I or MDA5 expression plasmid into Huh7 cells and found that MDA5, but not RIG-I at a similar protein level, significantly inhibited HBV replication. Knockdown of endogenous MDA5, but not RIG-I, in Huh7 cells transfected with the HBV replicative plasmid significantly increased HBV replication. Of particular interest, we found that MDA5, but not RIG-I, was able to associate with HBV specific nucleic acids and activated downstream innate signaling, suggesting that MDA5 may sense HBV and induce anti-viral signaling pathways. Importantly, we performed in vivo experiments by hydrodynamic injection of the HBV replicative plasmid into wild-type, MDA5–/–, MDA5+/–, or RIG-I+/– mice, and found that MDA5–/– and MDA5+/– mice exhibited an increase of HBV replication as compared with wild-type mice, but there was no effect on RIG-I+/– mice. Collectively, our in vitro and in vivo studies both support a critical role for MDA5 in the innate immune response against HBV infection.
HBV core antigen-specific immunity is critical for HBV clearance during acute infection, and the mutation of HBV core antigen (F97L) is frequently found in patients with chronic hepatitis B. We hypothesized that HBV F97L may induce innate immunity less efficiently and subsequently impair the dictation of adaptive immunity to HBV. In the second part of the thesis, we compared the innate immunity to HBV wild-type with HBV F97L. The HBV replication was increased in mice transfected with the HBV F97L replicative plasmid as compared with mice transfected with HBV wild-type replicative plasmid. Furthermore, the induction of viral sensors-MDA5 and DAI/ZBP1 was reduced in mice transfected with HBV F97L replicative plasmid as compared with mice transfected with the HBV wild-type replicative plasmid. These results suggest that HBV F97L may affect the expression of viral sensors, leading to the impairment of the innate immunity to HBV F97L. The detailed mechanism on the modulation of innate immunity by HBV F97L requires further investigation.
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