The roles of the anaphylatoxin receptors during invasive disease as well as mucosal colonization caused by Neisseria meningitidis

脑膜炎奈瑟菌(脑膜炎球菌，NME)是暴发性败血症和脑膜炎的病原体，可导致24小时内死亡。然而，通常情况下，NME在鼻咽定植而不会引起疾病，在大约10%的总人口中被发现。补体系统是控制侵袭性脑膜炎球菌病(IMD)的先天免疫系统中最重要的分支。特别是末端膜攻击复合体在防御NME方面的贡献得到了很好的表征。然而，补体激活也释放了小的促炎分裂产物C3a和C5a，即所谓的过敏性毒素(AT)。这些高效的炎症介质激活了一组三种同源受体，即过敏性毒素受体(ATR)C3aR、C5aR和C5L2，它们可以加剧全身炎症。令人惊讶的是，关于AT和ATR在IMD病理生理学中的作用或它们在无症状的NME呼吸道粘膜定植过程中的作用的数据缺乏。在该项目的第一部分，将通过比较缺乏ATR的野生型和基因敲除小鼠的病程，在脑膜炎双球菌败血症的腹膜感染模型中描绘个体ATR的影响。获得的结果将通过特定抗体或肽拮抗剂靶向AT和ATR来证实，这也将确定它们作为IMD治疗靶点的潜力。特定的体内耗竭方案以及体外实验将确定介导ATR依赖的IMD免疫病理的细胞。在该项目的第二部分中，将描述补体在NME粘膜防御中的总体作用。特别是，ATR在局部炎症反应中的作用将从吞噬细胞的募集方面进行阐述，这有助于清除NME粘膜定植。此外，ATR对针对NME的适应性免疫反应的影响将被阐明，重点是产生保护性的NME特异性的免疫球蛋白G亚类，其靶向是补体激活(IgG2a，IgG2b)。为了考虑NME的人类限制性取向，这些研究将使用一种新型的表达人CEACAM1的转基因小鼠来进行，该转基因小鼠允许NME在小鼠中定植，并与缺乏ATR或其他补体成分的基因敲除小鼠相结合。综上所述，该项目将首次确定补体介导的炎症在感染NME过程中的作用。为此，该项目将包括NME生活方式(黏膜定植期间的共生与脓毒症期间的致病性)以及ATR介导的炎症(粘膜定植期间的生理性与脓毒症期间的放松调节)的二分法。因此，该项目将对致病奈瑟菌以及补体系统的研究领域具有新的见解。

Neisseria meningitidis (meningococcus, Nme) is the causative agent of fulminant sepsis and meningitis which can lead to death within 24 hours. Usually, however, Nme colonizes the nasopharynx without causing disease and is found in approximately 10% of the general population. The complement system represents the most important branch of the innate immune system to control invasive meningococcal disease (IMD). Especially the contribution of the terminal membrane attack complex in defence against Nme is well characterized. Yet, complement activation also liberates the small pro-inflammatory split products C3a and C5a, the so-called anaphylatoxins (AT). These highly potent mediators of inflammation activate a set of three cognate receptors, the anaphylatoxin receptors (ATR) C3aR, C5aR and C5L2, which can exacerbate systemic inflammation. There is a surprising lack of data regarding the contribution of the AT and ATR to IMD pathophysiology or their role during asymptomatic Nme colonization of the respiratory mucosa. In the first part of the project, the influence of the individual ATR will be delineated in an intraperitoneal infection model of meningococcal sepsis by comparing the course of disease in wild-type versus knockout mice lacking ATR. The obtained results will be corroborated by targeting the AT as well as ATR by specific antibodies or peptide antagonists, which will also determine their potential as therapeutic targets in IMD. Specific in vivo depletion protocols as well as in vitro experiments will identify the cells which mediate the ATR-dependent IMD immunopathology. In the second part of the project, the overall role of complement in the mucosal defence against Nme will be characterized. Especially the role of the ATR in the local inflammatory response will be elaborated in this context with respect the recruitment of phagocytes, which clear Nme mucosal colonization. Furthermore, the impact of ATR on the adaptive immune response towards Nme will be elucidated with focus on the generation of protective Nme-specific IgG subclasses, which target complement activation (IgG2a, IgG2b). In order to consider the human-restricted tropism of Nme, these studies will be conducted using a novel transgenic mouse expressing human CEACAM1, which allows for Nme colonization in mice, in conjunction with knockout mice lacking ATR or other complement components. Taken together, this project will, for the first time, define the role of complement-mediated inflammation during infection with Nme. To do so, this project will embrace the dichotomy of both, the Nme lifestyle (commensal during mucosal colonization versus pathogenic during sepsis) as well as the ATR-mediated inflammation (physiologic during mucosal colonization versus deregulated during sepsis). Therefore, this project will bear novel insights for the fields of research on pathogenic Neisseriae as well as on the complement system.