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）是一种长期的疾病，导致广泛的变性，在大脑中。这些疾病如无治疗方法，无一例外都是致命的.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），黑尾鹿和麋鹿的慢性消耗病，以及绵羊和山羊的瘙痒症。一些动物物种和人类在食用TSE病原体污染的食物后感染了这些疾病，或者通过移植TSE病原体污染的组织或组织产品（例如：从感染CJD的变异供体输血）。关于传染性TSE因子从暴露部位（例如：肠）到大脑的途径，仍存在许多问题，在大脑中它会对神经细胞造成损伤。我们已经证明，接种后不久，TSE因子首先靶向淋巴组织（肠、淋巴结和脾脏中的派尔集合淋巴结）并在淋巴组织中积累，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（称为神经侵入的过程），最终导致神经变性和死亡。目前尚不清楚TSE因子如何从肠递送至淋巴组织，在神经侵袭前在淋巴组织中积聚。鉴定参与TSE试剂转运的细胞或机制可以鉴定治疗可以针对其阻断神经侵袭的重要过程。因此，本提案中研究的目的是研究这一重要的缺失环节，并确定TSE药物初始递送至淋巴组织的机制。迁移性树突状细胞（DC）在全身持续循环。这些哨兵细胞对外来颗粒和微生物进行采样，并将它们递送到淋巴组织以启动适当的免疫应答。我们最近的数据表明，迁移性DC也在运输TSE试剂从肠道到淋巴组织中发挥关键作用。然而，DC是否将TSE试剂直接转移到随后发生神经侵袭的淋巴组织内的细胞尚不清楚。DC的状态受到肠道中微生物含量和炎症状况的强烈影响，这表明这些因素可能会显著影响对口服获得性TSE试剂的敏感性。因此，需要进一步的实验来确定DC在TSE发病的早期阶段中发挥的确切作用。趋化因子通过趋化因子受体的刺激在将细胞如DC吸引到淋巴组织并确定它们在其中的位置中起重要作用。例如，趋化因子CXCL 13在B细胞滤泡内表达，并吸引表达CXCR 5趋化因子受体的细胞进入其中。位于B细胞滤泡内的滤泡树突状细胞产生高水平的CXCL 13，是淋巴组织内TSE因子蓄积的关键部位。因此，本研究的主要目的是评估表达CXCR5的DC在免疫功能和TSE因子从肠道神经侵袭中的作用。具体而言，将检验以下假设：在不存在表达CXCR 5的DC的情况下，这些DC不能将TSE试剂递送至淋巴组织的B细胞滤泡内的FDC，因此，TSE试剂神经侵袭被阻断。全面了解TSE发病机制中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.