Mouse Models for the Study of Viral Hepatitis : (intra)cellular innate immunity

Liver-residing leukocytes are essential in determining the outcome of infection with hepatitis viruses. Patient studies of liver innate immune cells during chronic viral hepatitis have been performed but are hampered by, amongst others, a lack of baseline data and unknown time of infection. Therefore, animal models are essential for the study of the innate immune response in viral hepatitis.
In the studies presented in this thesis, we aimed to better understand the cellular innate immune responses in the liver during lymphocytic choriomeningitis virus (LCMV) clone 13 induced chronic hepatitis, and to establish the human-liver chimeric mice as model for chronic Hepatitis E virus (HEV) infections in order to study the intracellular innate immune mechanisms upon HEV infection.
In chapter 2 and 3, we aimed to unravel how the cellular innate immune system deals with chronic viral infection in the liver using the LCMV infection mouse model. In chapter 2, we described that early after LCMV infection a functional dichotomy is observed for inflammatory monocytes and F4/80high-Kupffer cells with respect to endocytosis, but their activation and cytokine gene expression profiles exhibit a strong resemblance. In addition, inflammatory monocytes exhibit a huge capacity for recruitment to the liver and plasticity dependent on the nature of the inflammatory signal, either viral or sterile. This suggests that inflammatory monocytes play a crucial role in shaping the inflammatory environment in the liver early after infection. In chapter 3, we showed that LCMV induces chronic viral hepatitis with limited intrahepatic cytokine and interferon responses during the chronic infection. Furthermore, we identified KC and IM as distinct cell populations before, during, and after chronic infection, with important differences in activation status, antigen presentation, and gene expression profile correlating with the presence of viral antigens. Overall, these data suggest that intrahepatic monocytes and KC play distinctive roles during chronic virus-induced hepatitis, which is crucial knowledge in order to develop new antiviral strategies aimed at eradicating chronic viral infection.
In chapters 4, 5, and 6, we investigated Europe’s new hepatitis threat. Increasing numbers of endemic infections with genotype (gt) 3 HEV are observed in European countries. Unfortunately, no adequate in vivo model system exists to mimic this disease course, which hampers studies on HEV infectivity, transmission, and antiviral drug development. Therefore, in chapter 4, we explored and showed that human-liver chimeric mice can model chronic HEV infections. Humanized mice could productively be infected with clinical fecal, but not plasma, samples from several chronic HEV patients. In chapter 5, we described that HEV gt3 genomically adapted to in vitro culture, but that in vivo selection pressure in immune-deficient hosts was minimal. In chapter 6, we compared infection of HEV gt1 and HEV gt3 in human liver chimeric mice, and examined the intracellular innate immune responses in human hepatocytes upon infection. Despite higher viral loads for HEV gt1 in human-liver chimeric mice, neither HEV gt1 nor gt3 induced an intrahepatic innate immune response. Interestingly, treatment of infected chimeric mice with intracellular innate immune activating drugs pegIFNɑ, showed rapid clearance of HEV.
Overall, these data show that humanized mice could be productively infected with HEV isolated from feces, and that HEV does not induce intracellular innate immune responses in human hepatocytes, but is very sensitive to these immune mechanisms induced by pegIFNɑ.