Control of herpes simplex virus type 1 specific replication and transmission mechanisms in human dendritic cells

树突状细胞(DC)是唯一能够诱导幼稚T细胞的抗原提呈细胞，因此在诱导有效的抗病毒免疫反应中起着至关重要的作用。本研究的目的是探索DC和HSV-1之间的相互作用，以(I)表征病毒的免疫逃逸机制和(Ii)宿主免疫系统干扰病毒复制和传播的策略。从长远来看，这将有助于开发新的抗病毒策略。在宿主反应方面，我们报道了HSV-1以相似的效率感染未成熟DC(IDC)和成熟DC(MDC)，然而，病毒衣壳的核出口在MDC中受到严重阻碍，从而阻止了病毒在MDC中的完全复制和传播。此外，我们观察到HSV-1感染导致IDC中层粘连蛋白A/C的下调，而在MDC中则没有。由于层蛋白A/C层对于核膜的完整结构是重要的，因此HSV-1对这一层的破坏在IDC和MDC中受到不同的调节。因此，在本项目的目标1中，我们将研究IDC中层蛋白A/C崩溃的潜在机制，并探讨为什么HSV-1不能在感染的mDC中诱导层蛋白A/C降解。关于逃避免疫反应的病毒策略，我们证明了CD83分子从mDC表面的降解是HSV-1和HCMV的主要免疫逃避机制。我们研究了更多的细节，并报告了CD83的降解发生在一种蛋白酶体依赖但泛素不依赖的机制中。这是一种不寻常的途径，然而最近的研究报告了泛素独立的降解机制的证据，表明有其他信号针对蛋白酶体的蛋白质。例如由MDC表达的FAT10，以及描述使泛素化在特定情况下变得不必要的内在降解信号的研究。这些因素将在该项目的目标2中进行调查，以确定HSV-1感染后CD83降解的作用模式。如上所述，本课题组报道了HSV-1和HCMV在免疫原性MDC感染后降解CD83分子。CD83的降解最终导致有效的抗病毒免疫反应的抑制。然而，关于CD83的结构性质，目前还没有数据。因此，在Sticht教授和Muller教授的合作下，我们建立了CD83胞外区的三维结构。由于这一独特的知识，我们现在有可能进一步表征CD83分子，并确定对其生物学功能和与其潜在配体结合的重要区域。因此，由于病毒以CD83分子为靶标，在本项目的目标#3中，我们的目标是识别CD83的配体。这不仅可以进一步了解CD83的一般生物学功能，而且还可以深入了解病毒介导的CD83调节如何影响抗病毒免疫反应的机制。

Dendritic cells (DC) are crucial players to elicit potent antiviral immune responses since they are the only antigen-presenting cell type able to induce also naïve T-cells. The aim of this study is to explore the interplay between DC and HSV-1 to (i) characterize viral immune escape mechanisms and (ii) strategies of the host immune system to interfere with viral replication and spread. In the long run this will help to the development new antiviral strategies. Regarding host responses, we reported that HSV-1 infects immature DC (iDC) as well as mature DC (mDC) at similar efficiencies, however, the nuclear egress of viral capsids is heavily hampered in mDC, and thus full viral replication and spread is blocked in mDC. Furthermore, we observed that HSV-1 infection leads to a down-modulation of lamin A/C in iDC but not in mDC. Since lamin A/C layers are important for the intact architecture of nuclear membranes, breakdown of this layer by HSV-1 is regulated differently in iDC versus mDC. Therefore, within aim #1 of this project we will investigate the underlying mechanism of lamin A/C breakdown in iDC and in addition investigate, why HSV-1 is not able to induce lamin A/C degradation in infected mDC.Regarding viral strategies to evade immune responses, we demonstrated that degradation of the CD83 molecule from the surface of mDC is a major immune evasion mechanism for HSV-1 as well as HCMV. We investigated further details and reported that CD83 degradation occurs in a proteasome-dependent but ubiquitin-independent mechanism. This is an unusual pathway however recent studies reported evidence for ubiquitin-independent degradation mechanisms, suggesting alternative signals targeting proteins to the proteasome. Examples are FAT10, which is expressed by mDC, as well as studies describing intrinsic degradation signals making ubiquitination dispensable in specific cases. These factors will be investigated within aim #2 of this project, to identify the mode of action underlying CD83 degradation after HSV-1 infection. As mentioned above our group reported that HSV-1 as well as HCMV degrade CD83 molecules upon infection of immunogenic mDC. Degradation of CD83 finally leads to the inhibition of potent antiviral immune responses. However, regarding the structural properties of CD83 no data were available. Thus, in collaboration with Prof. Sticht and Prof. Muller, we established the 3-D structure of the extracellular domain of CD83. Due to this unique knowledge we have now the possibility to further characterize the CD83 molecule and identify the regions which are important for its biological function and for binding to its potential ligand. Therefore, since viruses target CD83 molecules, in aim #3 of this project we aim to identify the ligand for CD83. This not only allows to gain further insights into the biological function of CD83 in general, but also into the mechanism how viral mediated CD83 modulation influences antiviral immune responses.