Studies on a new human herpesvirus, Kaposi's sarcoma-associated herpesvirus
Kaposi's sarcoma (KS)-associated herpesvirus (KSHV), also called human herpesvirus 8 (HHV8), has been been identified in all epidemiological forms of KS as well as in tissue obtained from primary effusion lymphoma (PEL) and Multicentric Castleman's disease (MCD). The KSHV genome contains several putative oncogenes, suggesting that viral infection may induce cellular transformation and tumorgenesis. Herpesviruses encode a number of different surface glycoproteins, which are involved in virus-host interactions. Studies have shown that the viral glycoproteins H and L form a complex that plays an essential role in viral attachment and cell to cell fusion. Both glycoproteins have been identified in KSHV and were expressed in mammalian cells. Expression studies revealed that KSHV gH and gL exhibit similar features to those seen in other herpesviruses. However, KSI-IV gL appears to traffic independently and may function in cell to cell fusion processes even when expressed alone. KSI-IV de novo infections are rare and the lack of a reliable cell culture system has delayed pathogenesis studies. As part of this thesis the hepatoma cell line HepG2 has been shown to allow limited KSHV infection, as judged by nested PCR. Studies have shown that infection leads to increased apoptosis, although viral replication could not be detected. Furthermore, Epstein Barr Virus (EBV) appeared to modulate the ability of KSHV to infect HepG2 cells. Finally, a microtitre plate assay has been established for the quantification of the KSHV genome. A comparison of plasma and serum samples obtained at the same time point showed that plasma is more reliable in testing for KSHV, the DNA copy number in serum samples being reduced up to 10 fold. In conclusion, this new assay is a potentially useful tool for both diagnostic proposes and research studies.