Determining the role of CXCR5-expressing dendritic cells in immune function and TSE agent neuroinvasion from the intestine

传染性海绵状脑病（tse）是一种导致大脑广泛变性的长期性疾病。在没有治疗方法的情况下，这些疾病总是致命的。这些疾病影响动物和人类，包括人类的克雅氏病（CJD）、牛的牛海绵状脑病（“疯牛病”）、骡子鹿和麋鹿的慢性消耗性疾病以及绵羊和山羊的痒病。一些动物物种和人类在食用了被TSE物质污染的食物后，或通过移植被TSE物质污染的组织或组织产品（例如：输入感染了变型cjd的供者的血液）感染了这些疾病。关于传染性TSE病原体从暴露部位（如肠道）到大脑的途径，它对神经细胞造成损害，仍然存在许多问题。我们已经证明，在接种后不久，TSE制剂首先靶向并在淋巴组织（肠、淋巴结和脾脏的Peyer's斑块）内积累，然后扩散到大脑。许多TSE因子必须在这些淋巴组织中积累，然后才能进入大脑（这一过程称为神经侵袭），最终导致神经变性和死亡。TSE药物如何从肠道传递到淋巴组织，并在神经浸润前积聚尚不清楚。鉴定参与TSE制剂运输的细胞或机制可能确定一个重要的过程，可以针对该过程进行治疗以阻止神经侵袭。因此，本提案的研究目的是研究这一重要的缺失环节，并确定TSE药物初始递送到淋巴组织的机制。迁移的树突状细胞（dc）不断地在全身循环。这些前哨细胞采集外来颗粒和微生物，并将它们传递到淋巴组织，以启动适当的免疫反应。我们最近的数据表明，迁移dc在TSE因子从肠道到淋巴组织的运输中也起着关键作用。然而，树突状细胞是否将TSE药物直接转移到淋巴组织内的细胞中，随后发生神经侵袭尚不清楚。DC的状态受肠道内微生物含量和炎症状况的强烈影响，表明这些因素可能显著影响口服获得性TSE药物的易感性。因此，需要进一步的实验来确定dc在TSE发病早期的确切作用。趋化因子通过趋化因子受体的刺激在将dc等细胞吸引到淋巴组织并确定其在淋巴组织中的位置方面起着重要作用。例如，趋化因子CXCL13在B细胞滤泡内表达，并吸引表达CXCR5趋化因子受体的细胞进入其中。B细胞滤泡内的滤泡树突状细胞产生高水平的CXCL13，是淋巴组织内TSE剂积累的关键位点。因此，本研究的主要目的是评估表达cxcr5的dc在免疫功能和肠内TSE因子神经侵袭中的作用。具体来说，在缺乏表达cxcr5的dc的情况下，这些dc无法将TSE药物传递到淋巴组织B细胞滤泡内的fdc，因此，TSE药物的神经侵袭被阻断。深入了解TSE发病机制的早期事件将有助于确定风险和开发临床前诊断和治疗方法。

Transmissible spongiform encephalophathies (TSEs) are prolonged diseases which cause extensive degeneration in the brain. In the absence of a cure these diseases are invariably fatal. These diseases affect both animals and humans, and include Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy ('mad cow disease') in cattle, chronic wasting disease in mule deer and elk, and scrapie in sheep and goats. Some animal species and humans have become infected with these diseases after eating TSE agent-contaminated food, or through transplantation of TSE agent-contaminated tissues or tissue products (eg: transfusion of blood from a variant CJD-infected donor). Many questions remain concerning the route the infectious TSE agent takes from the site of exposure (eg: intestine) to the brain where it causes damage to nerve cells. We have shown that soon after inoculation TSE agents first target and accumulate within lymphoid tissues (Peyer's patches in the intestine, lymph nodes and spleen) before they spread to the brain. Many TSE agents must accumulate in these lymphoid tissues before they can subsequently gain access to the brain (a process termed neuroinvasion) where they ultimately cause neurodegeneration and death. How TSE agents are delivered from the intestine to the lymphoid tissues where they accumulate before neuroinvasion is not known. The identification of the cells or mechanisms involved in TSE agent transport may identify an important process to which treatments can be directed to block neuroinvasion. Therefore, the aim of the research in this proposal is to study this important missing link and determine the mechanism/s involved in the initial delivery of TSE agents to lymphoid tissues. Migratory dendritic cells (DCs) continually circulate throughout the body. These sentinel cells sample foreign particles and microbes and deliver them to the lymphoid tissues to initiate an appropriate immune response. Our recent data suggest that migratory DCs also play a key role in the transportation of the TSE agents from intestine to the lymphoid tissues. However, whether DCs transfer TSE agents directly to the cells within the lymphoid tissues from which neuroinvasion subsequently occurs is not known. The status of DC is strongly influenced by the microbial contents and inflammatory conditions in the intestine, suggesting that these factors are likely to dramatically affect susceptibility to orally-acquired TSE agents. Therefore, further experiments are necessary to determine the precise role that DCs play in the early stages of TSE pathogenesis. Stimulation from chemokines through chemokine receptors play important roles in attracting cells such as DCs to lymphoid tissues and determining their location within them. For example, the chemokine CXCL13 is expressed within in B cell follicles and attracts cells that express the CXCR5 chemokine receptor into them. The follicular dendritic cells that reside within B cell follicles produce high levels of CXCL13 are critical sites of TSE agent accumulation within lymphoid tissues. Therefore, the major aim of the research in this proposal is to assess the role of CXCR5-expressing DCs in immune function and TSE agent neuroinvasion from the intestine. Specifically, the hypothesis will be tested that in the absence of CXCR5-expressing DCs, these DCs are unable to deliver the TSE agent to the FDCs within the B cell follicles of lymphoid tissues, and as a consequence, TSE agent neuroinvasion is blocked. A thorough understanding of the early events in TSE pathogenesis will aid the determination of risk and the development pre-clinical diagnostics and therapeutics.