8 Abstract Human Herpes Virus 6 (HHV-6) consists of two closely related DNA viruses: HHV-6A and HHV-6B. The primoinfection proceeds at an early childhood usually as sixth exanthem disease or without any clinical symptoms. Both HHV-6 viruses are able to integrate to human genome using recombinant mechanisms which is unique compared to other human herpesviruses. The aim of the thesis is to study Ci-HHV-6 in a group of patients with malign disease and in the healthy population. We analysed 812 patients with malign disease and 420 healthy subjects from general population. The Ci-HHV-6 was assessed by real-time PCR, the specific localization of Ci-HHV-6 was determined using fluorescent in situ hybridization (FISH). Using comparative study, we did not identify significant difference between frequency of Ci-HHV-6 in patients with malign disease (1.11%) and healthy subjects (0.95%) (P-value 0.8). Consequently, we proved the heritability of Ci-HHV-6 in affected families. We determined the localization of Ci-HHV-6 to telomeric regions of chromosomes 2 and 18. We studied the production of viral proteins in the subjects with Ci-HHV-6. In this work, we conducted the first epidemiological study of Ci-HHV-6 in the Czech Republic. We also introduced novel methods which contribute to better characterization of this phenomenom.

Human herpesvirus 6A (HHV-6A) has yet to be definitively linked to a specific disease. This is due in part to the ubiquitous nature of the virus. Humanized Rag2-/-γc-/- (Rag-hu) mice were tested to determine if these were a suitable animal model to study the virus. Both cell-free and cell-associated virus was used for infection and both were found to be efficient at infecting the mice. Viral DNA was found in the plasma and cellular blood fractions, bone marrow, lymph node, and thymus, indicating successful infection and propagation of the virus in vivo. The CD3+CD4- population was depleted, while the CD3-CD4+ was increased in infected animals. The CD3-CD4+CD8- and CD3+CD4+CD8- populations were depleted and the CD3+CD4+CD8+ population increased when analysis was gated upon CD4+ cells. The CD3-CD4+CD8+ population expanded and the CD3-CD4+CD8- population was reduced when analysis was gated on the CD3- population. Additional flow cytometry analysis revealed increases in CD4+CD8+ double positive cells in the peripheral blood of cell-free infected mice, which could indicate improper T cell selection and a premature departure of these cells from the thymus, possibly contributing to autoimmunity. Previous research has shown that HIV and HHV-6A may have a synergistic effect on one another and that HHV-6A may act as a cofactor in the progression to AIDS. After determining the Rag-hu mouse model was suitable for studying HHV-6A infection, a coinfection of HHV-6A and HIV-1 was performed. Coinfected mice had fewer thymocytes when compared with the HIV-1 only, mock-infected, and to a lesser extent HHV-6A only groups which could indicate increased cell death in the coinfected group as well as possible disruptions in migration of cells, either causing cells to be sequestered in the bone marrow and unable to migrate to the thymus, or causing premature egress of the cells in the thymus due in part to premature upregulation of CCR7, both of which would explain the smaller cellular populations found in the coinfected mouse thymi. Additional studies were performed to determine if a preferential targeting existed between HHV-6A and HIV-1 as these viruses are found simultaneously coinfecting the same cell. Preferential targeting was not observed by cell-associated migration assay, but increased migration of HHV-6A-infected cells was observed in a CCL21 dependent manner. These studies have provided useful information about HHV-6A and its relevance to HIV/AIDS as well as a possible mechanism of the involvement of HHV-6A in multiple sclerosis (MS) and other autoimmune diseases.