Study of Herpes Simplex Virus Infection and Reactivation in Mouse Brain and the Reactivation Regulation of Drug-resistant Virus

• Main Authors: Shih-Heng Chen, 陳士恆
• Other Authors: Shun-Hua Chen
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/73934097100403947238

博士 === 國立成功大學 === 基礎醫學研究所 === 95 === Herpes simplex virus (HSV) induced encephalitis during acute infection is the most common sporadic and life-threatening encephalitis. Current studies investigating the factors which regulate herpetic encephalitis focus on immune factors or the expression of a transgene in mice. There are very few studies investigating endogenous factors which regulate herpetic encephalitis. Therefore, we performed a microarray analysis to determine the alteration of host genes in human neuronal cells during HSV-1 infection. Early growth response 1 (Egr-1), a transcription factor, is found to be up-regulated in HSV-1-infected neuronal cells. Our results show that Egr-1 functions to enhance HSV-1 replication in neuronal cells and consequently increases the mortality rate of infected mice. These results indicate a crucial role of Egr-1 in regulating HSV-1 infection. Following acute infection, HSV establishes latency in the neurons of both peripheral sensory ganglia and central nervous system (CNS) of latently infected hosts. However, several ex vivo studies have documented that latent HSV reactivates rarely from the CNS of mice when assayed by mincing tissues before explant culture, despite the presence of viral genomes in brain tissues. Therefore, in this study, we modified the reactivation protocol originally used for trigeminal ganglia and observed as high as 88% of viral reactivation from brain stems of latently infected mice. The high reactivation frequency of brain stem correlated with higher levels of acute viral replication and latent viral genomes, and the dissociation method greatly enhanced the cell viability and viral infectivity of brain stem cultures when compared to the conventional mincing method. Lastly, the efficient reactivation of HSV from mouse CNS was observed in more than one viral strain, viral serotype, or mouse strain, further indicating that the CNS can be an authentic latency site for HSV. This model also can serve as a good tool to investigate the potential of HSV to cause recurrent diseases in the CNS. Acyclovir (ACV) is the most common drug in clinical treatment of HSV infection; however, the emergence of ACV-resistant viruses can hinder therapy and pose a significant problem, particularly, in immunocompromised patients. Many drug-resistant mutants have been reported as thymidine kinase (TK) mutants. Laboratory strains of HSV lacking TK cannot replicate to detectable levels acutely in mouse trigeminal ganglia and do not reactivate from latency. However, many pathogenic clinical isolates that are resistant to the antiviral drug ACV are heterogeneous populations of TK-negative (TK-) and TK-positive (TK+) viruses. In this study, we investigated the reactivation mechanism of TK- HSV. The results showed that TK+ virus permits TK- virus reactivation through enzymatic complementation of TK. The requirement for the amount of TK during acute replication, latency establishment, and reactivation is different.