Visualization and analysis of human herpesvirus 6 and 7 using their recombinant viruses

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1. Visualization of viral latency and reactivationTo visualize the viral reactivation of human herpesvirus (HHV)-6 and HHV-7, we planned to identify the viral early gene promoters that were activated during viral reactivation and viral replication. Then, we have analyzed the character of early gene promoters, such as p41, DNA pol, U41 and U79/80. As a result, these viral early gene promoters were activated mainly by immediate early (IE) 2, and IE2 strongly activate the early gene promoters with IE1 synergistically. In the U79/80 gene promoter region, we identified the cis repression sequence (CRS) like motif that was reported in human cytomegalovirus immediate early and very early gene promoter region. These findings suggest that U79/80 gene promoter is a suitable promoter that can respond to the early stage of HHV-6 reactivation or replication.2. Establishment of HHV-6 latency/reactivation system using SCID-hu mouseTo investigate the molecular mechanism of HHV-6 and HHV-7 latency, we have established their latent infection system by using non-obese diabetic-severe combined immunodeficiency (NOD-SCID)-hu mouse. We have transplanted umbilical cord blood cells into NOD-SCID mouse, and infected wild type HHV-6 or recombinant HHV-6 expressing enhanced green fluorescent protein (EGFP). In this latency system, we have observed that approximately 100 fold number of cells had HHV-6 DNA than in the human samples. Then we have studied the form of HHV-6 DNA in this latent system, and found that it showed the circular form. These findings suggest that the HHV-6 latent system using NOD-SCID-hu mouse is useful tool for investigating HHV-6 latency and reactivation.