Hepatitis D Virus Infection in Cell Culture for Innate Immune Response Study
Date Issued
2016
Date
2016
Author(s)
Wang, Hsin-Wei
Abstract
Hepatitis D Virus (HDV) is the simplest RNA virus with a unique circular genome. It is a defective RNA virus because it has to rely on Hepatitis B Virus (HBV) to assemble new virions and propagate infection. Without HBV, HDV would be unable to finish its life cycle; therefore, it is called the satellite virus of HBV. Approximately 350 million people worldwide are chronically infected with HBV. Although there is only about 5% of HBV carriers infected with HDV, the risk is that it could lead to the most severe forms of hepatitis— fulminant hepatitis. Also, antivirals against HBV do not ameliorate hepatitis D. It has long been unclear to what extent cellular immune responses attribute to liver disease and why immune responses fail to control viral replication in persistent HDV infection. Recently, two studies in mouse model have given some hints on the relation between innate immunity and HDV infection. One of the two studies, using hNTCP-transgenic mice to investigate how innate and adaptive immunity affect the clearance of HDV. Their data indicated that it is innate immunity but not adaptive immunity plays a role in HDV clearance. Pattern-recognition receptors (PRRs), which detect pathogens and initiate host antimicrobial responses such as producing type I interferons and proinflammatory cytokines, are important parts of innate immunity. We are interested in whether such unique circular RNA structure of HDV can be recognized by specific host PRRs. The other studies, using chimeric mice with humanized liver to analyze regulation of genes in host liver after HDV infection. Genes of PRRs in sensing viral nucleic acid are indeed up-regulated after HDV infection. According to those preliminary observation, we would like to further explore such matter in cell models; hence, a stable HDV infection system is needed. In this study, we used two specific HepG2 cell lines (HepG2-hNTCP-C4 and HepG2-hNTCP-SW1) which both stably overexpress an HBV entry receptor, human Sodium taurocholate cotransporting polypeptide (NTCP). Our results showed only NTCP-C4 cells are susceptible to HDV infection, and at 1000 genome equivalent/ cell, only 0.46% of the cells were infected at Day 6 post infection. To see a 4.3% infection rate, the genome equivalent/ cell would need to increase to 5000. In addition, with the aim of enhancing infection efficiency, we tried different conditions during HDV infection by adjusting concentration of PEG and DMSO. However, it seems that increase of PEG concentration or addition of DMSO both not improve the infection process. For our final goal is to find out possible PRRs detecting hepatitis delta virus, and evaluate how anti-viral response be initiated via this cell system in the future. HDV infection rate has to reach a certain level to induced sequential host immune responses. To see immune signaling mechanisms, a 50% infection rate might be necessary. We hope this infection model could shed light on the interactions between host immunity and HDV infected cells, and provide help in future study.
Subjects
Hepatitis D virus
Hepatitis B Virus
HDV infection
host immune response
SDGs
Type
thesis
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