动物造模,药效评价,乙肝病毒 z-bio 2024-08-06 510

　　Duck hepatitis B virus (DHBV) was discovered by William et al in 1980, and then it was found in ducks, grey herons and wild geese from different sources. The host range of avian hepatitis B virus is very narrow. For example, DHBV only infects birds such as ducks and swans, but does not infect American ducks or chickens.

　　There are many similarities between human HBV virus and avian hepatitis virus: both viruses have partially double helix DNA genomes; The replication of the genome relies on the presence of RNA intermediates; There is a significant overlap between the coding frames of genes. In addition, there are many similarities between the two viruses in terms of genome and viral structure, replication, and viral life cycle. Both viruses have hepatotropism, and many of the infectious characteristics of hepatotropic viruses have been discovered in the DHBV model, such as viral genome replication through reverse transcription of RNA intermediates; Formation and amplification of covalently closed circular cccDNA; The detailed process of reverse transcription; And the determinants of host tropism by the virus, etc., all have important reference significance for the study of the biological characteristics of HBV.

　　Meanwhile, there are also certain differences between DHBV and HBV: the genome of DHBV is slightly smaller than that of animal hepatitis viruses, and the nucleotide sequence homology between the two is about 40%; The DHBV genome lacks the coding frame of X gene, and there are only two envelope proteins of avian hepatitis B virus, rather than three; When DHBV is transmitted from mother ducks to eggs, its infection generally leads to chronic infection, while viral infection usually does not cause liver damage, liver disease, or liver cancer. Infected ducks will maintain a lifelong healthy state; After adult ducks are infected with DHBV, the virus will be cleared; When DHBV is transmitted from mother ducks to young ducks, it can lead to chronic infection, and this infection can cause liver damage and lead to liver cancer or cirrhosis in a large proportion. When adult ducks are infected with DHBV and the virus cannot be cleared, it may lead to an outbreak of acute hepatitis.

　　Except for the HepaRG (human liver cell line, isolated from non tumor tissue of liver cancer patients infected with chronic hepatitis C virus) cell line, only primary duck liver cells are sensitive to DHBV. Therefore, the in vitro replication of DHBV depends on primary cultured liver cells. DHBV can replicate in both primary cultured fetal and adult duck liver cells. Fetal duck liver cells are easily obtained from hatched duck embryos. After digesting the liver tissue with collagenase, wash and culture it. Of course, this cell line includes other cells in the liver besides the liver parenchyma, such as macrophages and fibroblasts. In addition, primary liver cell lines of adult ducks can be obtained by perfusion of their liver, and the liver cell lines obtained by this method are relatively pure (with a liver cell count of over 90%).

　　Primary liver cell lines can be cultured in standard media containing hydrocortisone, insulin, and DMSO, among which DMSO is crucial for maintaining liver cell differentiation and sensitivity to viruses. Researchers have discovered many detailed stages in the replication cycle of hepatitis virus using an in vitro model of DHBV infection.

　　The advantage of establishing an animal model of duck hepatitis B virus is that ducks are easy to become experimental animals. Moreover, primary liver cells susceptible to DHBV can be easily isolated from suckling ducks or embryos. The DHBV infected duck model is mainly used to study the role of the virus's cccDNA as an RNA transcription template in virus replication. Although ducks infected with DHBV do not develop liver cancer, some scholars have integrated the virus genome into the chromosomes of cells in cell tumor models and subsequently studied the role of virus replication in cancer development.

　　Similar to the development of HBV infection in humans, the course of disease in ducks infected with DHBV is age-related. Generally speaking, hepatitis virus infection has the potential to develop into acute or chronic infection. The outcome of infection is related to the dose of virus used at the time of infection. High dose viral infection increases the probability of newborn ducks developing into persistent infections. The production of neutralizing antibodies during infection also determines the different course of disease development between newborn and adult ducks after viral infection. Adult ducks can quickly generate neutralizing antibodies, which can effectively inhibit the spread of the virus in the liver.

　　In general, DHBV can spread vertically from mother ducks to duck eggs, leading to chronic infection in newborn ducks. However, due to the immune system's tolerance to the virus, animals do not exhibit symptoms. Therefore, the offspring of DHBV positive female ducks all show DHBV positivity. In chronically infected ducks, DHBV mainly replicates in liver cells. Normally, the replication level of the virus is very high, and almost all liver cells are infected and express viral antigens. A large amount of viral antigens can be detected in peripheral blood, sometimes up to 10 copies per milliliter of virus particles to the power of 10.

　　At the same time, DHBV model is also used to study the cell receptors of hepatitis B virus, the growth curve of virus mutants, and the evaluation of antiviral drugs in vivo and in vitro. However, it has been found that ducks are different from groundhogs in that they are not sensitive to the toxicity of antiviral drugs, and the metabolic system in ducks is compatible with the metabolic processes of antiviral drugs. Therefore, due to the difference between the virus and host hepatocytes, the clinical application value of drugs evaluated by duck hepatitis B virus model is still limited.