AbstractsBiology & Animal Science

About 15 million people worldwide are chronically infected with the hepatitis D virus (HDV). A chronic HDV infection shows the most severe clinical course of all hepatitis infections leading to liver cirrhosis in up to 70 % and to the development of hepatocellular carcinoma. Virus replication requires the generation of genomic and antigenomic HDV RNAs which are generated in a double rolling circle, while the envelope proteins of the hepatitis B virus (HBV) are needed for assembly and release of infectious virions. The limited availability of HDV infection models has hindered investigations of HDV pathogenesis and interactions between HDV and infected human hepatocytes. Currently an HDV specific therapy does not exist. Our group recently developed an HDV in vivo infection model using humanized uPA/SCID mice, which after transplantation of primary human hepatocytes into mice livers can stably be infected with HBV and HDV. Aims of this study were to characterize interactions of HDV and the innate immune system, to investigate the persistence and cell toxicity of an HDV mono-infection and to determine effects of different antiviral drugs on HDV productivity by establishing and using a novel assay to quantify genomic and antigenomic HDV RNA. By using the uPA/SCID mouse model it could be shown that the development of HDV viremia was accompanied by a clear induction of human-specific interferon stimulated genes (ISGs), which play an important role in the defense of viruses. While an HBV mono-infection only showed moderate inductions of classic ISGs (e.g. hMxA, hOAS1, hHLA-E, hIP10) in human hepatocytes, the expression of these ISGs was significantly stronger in an HBV/HDV co-infection. Also levels of human specific cytokines (hTGF-ß, hIFN-ß, hIFN-λ) were clearly increased in HBV/HDV co-infected mice, while their expression was lower or even below the lower limit of detection in HBV mono- and uninfected mice. This strong activation of the innate immune system might directly lead to liver damage and inflammation providing a rationale for the more severe course of HDV-associated liver disease. Another investigation within this thesis showed that an HDV mono-infection in humanized mice can persist for at least 6 weeks in the absence of HBV. Moreover persistent HDV particles could be rescued upon HBV super-infection and serially passaged into naïve human chimeric mice proofing the maintenance of HDV infectivity after a 6-weeks-phase of intracellular latency. These results explain observations in patients showing detectable intrahepatic HDV markers despite very low HBV activity or even after liver transplantation and emphasize the risk for these patients to develop a productive HBV/HDV infection after re-infection with HBV. Furthermore, a novel, quantitative RT-PCR assay was established, which specifically detects genomic and antigenomic HDV RNA in human chimeric mice livers and human liver patient biopsies. This assay now provides new possibilities to investigate the intrahepatic life cycle of HDV and the impact of different…