The human herpesvirus Epstein-Barr virus (EBV) is a large DNA virus that infects over 90% of the adult world population. EBV is the causative agent of infectious mononucleosis and EBV infection is... Show moreThe human herpesvirus Epstein-Barr virus (EBV) is a large DNA virus that infects over 90% of the adult world population. EBV is the causative agent of infectious mononucleosis and EBV infection is associated with various malignancies. EBV establishes lifelong infections in immunocompetent hosts. To counteract the host’s immune defence, EBV acquired numerous immune evasion mechanisms. During latency of EBV, viral protein synthesis is limited or absent, making the virus-infected cells virtually invisible to the immune system. Evasion mechanisms of EBV active during primary infection as well as in reactivation are necessary for establishment of latent infection and prolonged replication. Studying viral evasion not only helps to understand EBV, but also the human immune system. Viral molecules interfering with antigen presentation by HLA I and HLA II have been identified previously, but so far, it was unclear how EBV interferes with the lipid antigen-presenting molecule CD1d. The work described in this thesis shows EBV’s mechanism to interfere with cell surface expression of CD1d. Further, a novel immune evasion molecule that obstructs antigen-presentation during the late lytic phase of EBV infection was identified and its working mechanism was unravelled. Understanding viral immune evasion mechanisms may aid in developing therapies for EBV-associated diseases. Show less
Persistent infections with high-risk type human papillomaviruses (hrHPVs) can progress to cancer. HrHPVs infect keratinocytes (KCs) and successfully suppress host immunity for up to two years... Show morePersistent infections with high-risk type human papillomaviruses (hrHPVs) can progress to cancer. HrHPVs infect keratinocytes (KCs) and successfully suppress host immunity for up to two years despite the fact that KCs are well equipped to detect and initiate immune responses to invading pathogens. HrHPV interferes with the innate immune response by affecting several signaling pathways that otherwise would prompt anti-viral mechanisms in the host cell. Furthermore, hrHPV interferes with the production of cytokines that are involved in the attraction of immune cells to the infected epithelium. In addition, hrHPV hides itself from the immune system by suppressing the antigen presentation machinery and employs means to hamper the response of KC__s to signals from adaptive immune cells. In this thesis we show that hrHPV attenuates innate immune signaling (Chapter 2) and CD40-mediated (Chapter 3) and IFN_ and/or TNF_-induced (Chapter 4) adaptive immune signaling. HrHPV exploits the cellular proteins UCHL1 (Chapter 2) and IFRD1 (Chapter 4) that act on multiple points in the IRF and NF_B signaling pathways. Moreover, hrHPV downregulates cellular IFITM1 to resist the growth inhibitory effects of IFN_ and/or TNF_ (Chapter 5). Our data provide important new insights on how hrHPV can persist in the face of host immunity. Show less
From the earliest times of their evolution, multi-cellular organisms have been defending themselves against infectious agents like nucleic acids, viruses, bacteria, fungi and parasites. Continuous... Show moreFrom the earliest times of their evolution, multi-cellular organisms have been defending themselves against infectious agents like nucleic acids, viruses, bacteria, fungi and parasites. Continuous selection pressure resulted in the development of sophisticated immune systems, which in their adaptive forms have exquisite specificity as well as memory for pathogen antigens. On the other hand, infectious agents developed elaborate strategies to escape from, or counteract, host defense mechanisms. Viruses are totally dependent upon host cells for replication and have developed an impressive variety of mechanisms to shield themselves from being detected by the host immune system. The subject of this thesis concerns a particular example of how viruses, specifically some members of genus Varicellovirus, counteract an important step in one of the acquired immunity pathways: the presentation of antigen by Major Histocompatibility Complex (MHC) class I molecules to cytotoxic T-cells. This thesis describes the discovery of a new family of proteins that inhibit the Transporter associated with Antigen Processing (TAP), and sets the first steps towards the explanation of how these inhibitors interfere with antigen transport by the MHC class I loading complex. Show less
In gene therapy, expression of a corrected gene leads to synthesis of proteins foreign to the immune system. Cells expressing these will therefore be recognized as aberrant and destructed. We used... Show moreIn gene therapy, expression of a corrected gene leads to synthesis of proteins foreign to the immune system. Cells expressing these will therefore be recognized as aberrant and destructed. We used a known immune evasion mechanism to "stealth" transgene products. We fused the coding sequence of the Gly-Ala repeats (GAr) of the Epstein-Barr Virus (EBV) nuclear antigen 1 (EBNA-1) with three different transgenes, i.e. E.coli LacZ, firefly Luciferase and herpes simplex virus 1 thymidine kinase (TK). We show that the EBV GAr system could well be used to prevent the immune system of reacting on transgenes. We could also show, that GAr-TK might be a good candidate to use in bone marrow transplantation protocols. In addition to the GAr, we used an alternative open reading frame found within the ENBA-1 sequence (GZr). We made a fusion of the GZr with the LacZ gene and show that, in contrast to a repeat deleted construct, the construct bearing repeats was protected for recognition by LacZ specific CTLs. This shows that the GZ repeats might be another candidate to shield transgenes for the immune system. The human herpes virus 8 (HHV-8) has a protein like EBNA-1, involved in establishing latency, latency-associated nuclear antigen-1 (LANA-1). We show that LANA-1, like EBNA-1, possesses an immune evasion effect. Show less
