Influence of RCMV-encoded vXCL1 on XCR1+ DC

巨细胞病毒（CMV）使用多种策略来调节免疫反应。其中一种策略是病毒编码的趋化因子的表达，这些趋化因子干扰宿主趋化因子网络，而宿主趋化因子网络在启动和组织白细胞运输中起着重要作用。英国和柏林分离的大鼠巨细胞病毒（MuHV-8）编码迄今为止唯一已知的病毒γ趋化因子。其序列与内源性大鼠、小鼠和人γ趋化因子XCL1相似，因此被命名为病毒XCL1 （vXCL1）。为了更好地了解vXCL1的功能并研究其与宿主趋化因子的竞争，我们对宿主XCL1的表达以及这两种趋化因子与XCR1的结合进行了表征。大鼠的XCL1主要由CD8+ T细胞、NKT细胞和NK细胞分泌，人类和小鼠的XCL1已被证实。宿主大鼠XCL1和vXCL1均具有趋化因子样特性，与相应的受体XCR1结合，并只吸引表达XCR1的CD4-大鼠DC。因此，它们的功能相似。受体XCR1在约80%的脾CD4- XCR1+大鼠DC上表达。病毒XCL1和人类XCL1都是选择性激动剂，分别只激活其物种特异性受体rXCR1和hXCR1。相比之下，宿主大鼠XCL1是一种激活这两个受体的激动剂。病毒XCL1似乎是一种超级激动剂，与内源性rXCL1趋化因子相比，它与rXCR1具有更好的结合。为了进一步研究vXCL1与XCR1在啮齿类动物中的相互作用，我们利用XCR1基因敲除大鼠来研究病毒感染背景下vXCL1与XCR1的受体功能。在目前的提案中，我们将初步表征敲除大鼠并检查其对感染的反应。我们计划研究vXCL1是否只激活大鼠XCR1，或者是否对不同物种的XCR1有交叉反应或拮抗活性。进一步，我们打算感染XCR1+ DC，并分析它们的感染能力。然后，我们计划用野生型、vxcl1突变型和逆转型病毒感染动物并分析宿主XCL1的表达。我们推测vXCL1吸引XCR1+ CD4- DC有利于病毒传播或损害交叉呈递，以规避CD8+ T淋巴细胞施加的细胞毒性免疫反应。为了检验这一点，我们将描述IE1免疫优势表位，鉴定表达的MHC等位基因呈现病毒肽，并最终测试vXCL1是否参与阻断交叉呈现。

Cytomegaloviruses (CMV) use multiple strategies to modulate the immune response. One of these strategies is the expression of virus-encoded chemokines that interfere with the hosts chemokine network which plays an important role in initiating and organizing leukocyte trafficking. The English and Berlin isolates of rat CMV (MuHV-8) encode the so far only known viral gamma-chemokine. Its similar sequence to the endogenous rat, mouse, and human gamma-chemokine XCL1 resulted in its designation as viral XCL1 (vXCL1). To better understand vXCL1 function and investigate a putative competition with the host chemokine, expression of host XCL1 as well as binding of both chemokines to XCR1 was characterized. Rat XCL1 is mostly secreted by CD8+ T cells, NKT cells and NK cells as has been shown for human and mouse XCL1. Both host rat XCL1 and vXCL1 have chemokine-like properties, bind to the corresponding receptor XCR1 and attract exclusively CD4- rat DC that express XCR1. Hence, they function similarly. The receptor XCR1 is expressed on about 80% of splenic CD4- XCR1+ rat DC. Both viral XCL1 and human XCL1 are selective agonists that only activate their species-specific receptors rXCR1 and hXCR1, respectively. In contrast, host rat XCL1 is an agonist that activates both receptors. Viral XCL1 appears to be a super agonist that exhibits superior binding to rXCR1 than the endogenous rXCL1 chemokine. To further study the interaction between vXCL1 and XCR1 in rodents an xcr1 knockout rat was generated to study receptor function in the context of viral infection. In the current proposal, we will initially characterize the knockout rat and examine its response to infection. We plan to investigate if vXCL1 only activates rat XCR1 or if there is cross reactivity or antagonistic activity to XCR1 of different species. Further, we intend to infect XCR1+ DC and analyze their infection capacity. We then plan to infect animals and analyze host XCL1 expression upon infection using wild-type, vxcl1 mutant and revertant viruses. We speculate that vXCL1 attracts XCR1+ CD4- DC to benefit viral dissemination or to impair cross-presentation to circumvent cytotoxic immune responses exerted by CD8+ T lymphocytes. To examine this, we will characterize an IE1 immunodominant epitope, identify an expressed MHC allele presenting a viral peptide and ultimately test if vXCL1 is involved in blocking cross-presentation.