ABSTRACT
Epstein-Bar virus (EBV) infection is widespread within the human population with over 95% of adults being infected. In response to primary EBV infection, the host mounts an antiviral immune response comprising both innate and adaptive immune system. In healthy populations, the immune system can control EBV infection to a large extent. However, the virus cannot be cleared. Instead, EBV establishes a persistent latent infection in B lymphocytes characterized by limited viral gene expression. To establish a persistent infection efficiently, EBV have evolved a number of strategies to avoid immune elimination. In this review, we focus on the immune evasion mechanisms of EBV encoded immune-evasion proteins, microRNA and host exosome pathway.
ABSTRACT
Aims: To understand the mechanisms of Early Growth Response Protein 1 (Egr-1) induction upon HSV-1 lytic infection and its roles in regulating viral gene expression and replication. Study Design: Rabbit corneal cell line SIRC and other cell lines were infected by HSV-1 to investigate the Egr-1 induction and its occupancy on the viral genome in different conditions. UV-inactivated HSV-1 and a recombinant virus over-expressing Egr-1 were generated to evaluate the regulatory effects on viral gene expression and replication during the infection. Methodology: Egr-1 induction triggered by viral infection was determined by Western Blot analyses and immune-fluorescent microscopy. Real-time RT-PCR and a novel Cignal™ Reporter Assay were used for quantitative measurement of Egr-1 expression. Chromatin Immuno-precipitation (ChIP) was performed to address the Egr-1 occupancy to the viral regulatory sequences and the influence on viral replication was assessed by plaque assays. Results: Our results indicated that Egr-1 expression requires viral gene expression since the UV-inactivated HSV-1 failed to produce Egr-1 protein. Blockade of viral replication did not block the Egr-1 protein synthesis, supporting the hypothesis that HSV-1 replication was not essential for Egr-1 production. Chromatin immune-precipitation (ChIP) and RT-PCR assays demonstrated that induced Egr-1 was able to interact with key regulatory elements near HSV-1 immediate-early (IE) genes and promote viral gene expression. Recombinant virus overexpressing Egr-1 revealed that Egr-1 enhanced the viral replication and the release of infectious virus. Conclusion: Together these results concluded that HSV-1 triggers the expression of an important host transcription factor Egr-1 via a unique mechanism and benefit the viral gene expression and replication.