Role of T cells during central nervous system (CNS) bacterial infection

描述(申请人提供)：脑脓肿的形成是化脓性细菌感染的结果，可引起炎症、水肿、神经元毒性，通常还会导致长期的健康问题，如癫痫发作。脑脓肿的诊断和治疗是复杂的，未经治疗的病变可能会破裂到脑室间隙，从而导致80%的死亡率。尽管接受了治疗，但由于细菌的无处不在的性质以及金黄色葡萄球菌(S.aureus)等耐多药细菌菌株的数量不断增加，脑脓肿的发病率可能会持续存在。拟议的培训计划与NINDS的使命相关，因为其广泛的目标是减少细菌引起的脑脓肿带来的神经疾病的负担。金黄色葡萄球菌在脑脓肿形成过程中所引起的先天免疫反应是相对明确的；然而，关于获得性免疫在感染过程中的重要性的信息却很少。初步研究表明，脑脓肿中存在CD4+、CD8+、34T细胞和NKT细胞，提示先天免疫反应和获得性免疫反应是解决中枢神经系统细菌感染所必需的。基于携带12T细胞受体(TCR)的T细胞群渗入脑脓肿的频率，后续研究在缺乏CD4+、CD8+和NKT细胞的TCR12KO小鼠中进行。与能够有效清除金黄色葡萄球菌的WT小鼠相比，TCR12KO小鼠在感染后期的细菌负荷显著增加。TCR12+细胞的丧失也影响了先天免疫细胞渗入中枢神经系统的情况，主要是在感染的后期(即细菌暴露后7-14天)。脑内的主要细胞类型为CD4+和NKT细胞，可产生IL-17和干扰素-3，参与天然免疫细胞的激活和细菌的清除。这一假设认为，在脑脓肿形成过程中，CD4+Th1/Th17细胞和NKT细胞影响天然免疫群体的流入和激活状态，从而调节细菌清除和组织损伤。为了评估Th1和Th17细胞在脑脓肿发病机制中的功能作用，该研究计划将检测特定的CD4+T辅助(Th)细胞群过继转移到TCR12KO小鼠后的感染参数(即细菌负荷、促炎介质表达、先天免疫渗透和组织损伤)。此外，NKT细胞在感染期间的重要性将使用缺乏NKT细胞的商业可获得的CD1d缺陷小鼠进行评估。这些研究的目的是明确Th1/Th17和NKT细胞在脑脓肿发病机制中的功能作用，并首次建立脓肿形成过程中天然免疫和获得性免疫之间的直接联系。可以预见，这些研究可以确定新的治疗靶点，以限制伴随脑脓肿而来的过度神经元损伤，同时还可以获得不影响有效细菌清除的额外好处。 与公共卫生相关：脑脓肿是一种毁灭性的感染，特别是由于最近出现了多药耐药菌株，并可导致包括癫痫发作和认知丧失在内的长期缺陷。在这项建议中，我将评估各种T细胞亚群在脑脓肿发展过程中影响抗细菌免疫的能力的功能重要性。更好地了解T细胞反应如何调节炎症可能会揭示新的治疗靶点，以限制脑脓肿伴随的过度神经元损伤，同时不影响有效的细菌清除。

DESCRIPTION (provided by applicant): Brain abscess formation is consequent of pyogenic bacterial infection, and can elicit inflammation, edema, neuronal toxicity, and often long-term health problems such as seizures. Diagnosing and treating brain abscesses is complicated, and untreated lesions can rupture into the ventricular space which engenders an 80% mortality rate. The incidence of brain abscesses is likely to persist, in spite of therapy, due to the ubiquitous nature of bacteria and the ever increasing number of multi-drug resistant bacterial strains such as Staphylococcus aureus (S. aureus). The proposed training plan is relevant to the mission of NINDS in that its broad objective is to reduce the burden of neurological disease brought on by bacterial-induced brain abscesses. The innate immune responses elicited during brain abscess development due to S. aureus are relatively well-defined; however, little information is available regarding the importance of adaptive immunity during infection. Preliminary studies have demonstrated CD4+, CD8+, 34 T cell, and NKT cell infiltrates in brain abscesses, suggesting both innate and adaptive immune responses are required to resolve bacterial infections in the CNS. Based on the frequency of T cell populations infiltrating brain abscesses bearing the 12 T cell receptor (TCR), subsequent studies were performed in TCR 12 KO mice, deficient in CD4+, CD8+, and NKT cells. Bacterial burdens were significantly elevated in TCR 12 KO mice at later stages of infection compared to WT animals, which were able to effectively clear S. aureus. The loss of TCR 12+ cells also affected the profiles of infiltrating innate immune cells into the CNS, primarily during the late phase of infection (i.e. days 7-14 following bacterial exposure). The predominant cell types infiltrating the brain, CD4+ and NKT cells, were found to produce IL-17 and IFN-3, which are involved in the activation of innate immune cells and bacterial clearance. The hypothesis of this proposal is that CD4+ Th1/Th17 cells and NKT cells impact the influx and activation status of innate immune populations to regulate bacterial clearance and tissue injury during brain abscess development. To assess the functional effects of Th1 and Th17 cells in brain abscess pathogenesis, the research plan will examine parameters of infection (i.e. bacterial burdens, pro-inflammatory mediator expression, innate immune infiltrates, and tissue injury) after specific CD4+ T helper (Th) cell populations are adoptively transferred into TCR 12 KO mice. In addition, the importance of NKT cells during infection will be evaluated using commercially available CD1d-deficient mice that lack NKT cells. The objective of these studies is to define the functional contributions of Th1/Th17 and NKT cells in brain abscess pathogenesis and establish for the first time a direct link between innate and adaptive immunity during abscess formation. It is envisioned that these studies may identify novel therapeutic targets to limit the excessive neuronal damage that accompanies brain abscesses with the added benefit of not compromising effective bacterial clearance. PUBLIC HEALTH RELEVANCE: Brain abscesses represent a devastating infection, especially due the recent emergence of multi-drug resistant strains of bacteria, and can cause long-term deficits including seizures and cognitive loss. In this proposal, I will assess the functional importance of various T cell subsets for their ability to influence anti-bacterial immunity during brain abscess development. A better understanding of how T cell responses regulate inflammation may reveal novel therapeutic targets to limit the excessive neuronal damage that accompanies brain abscesses with the added benefit of not compromising effective bacterial clearance.