Adaptive Immune Response to Symbiotic Bacteria as a Mediator of Gut Homeostasis

描述(由申请人提供)：我们每个人都藏匿着数万亿个不同的微生物集合，导致了一个“超有机体”，其中微生物细胞的数量比人类细胞的数量多出一个估计的数量级。我们的肠道中含有绝大多数这样的微生物。微生物群落稳定的来源，以及个人免疫系统和微生物区系的共同进化有助于共生关系的机制尚不清楚：答案应提供重要线索，说明微生物区系如何有助于我们的健康，微生物生态如何产生扰动，这种扰动如何产生某些病理状态(例如，感染性腹泻；炎症性肠道疾病)，以及如何开发新的策略来故意操纵微生物区系的组成部分的代表以获得治疗效益。我已经在诺生菌Rag1-/-小鼠身上开发了一个简化的人类肠道微生物区系模型，其中肠道微生物区系的多样性被减少到一个物种(类杆菌，正常人类肠道微生物区系中的一个重要的测序成员)，以及对一种免疫球蛋白的适应性免疫系统的全套。我已经对这种独特的免疫球蛋白A(IgA)的特异性进行了表征，这种免疫球蛋白A自然地以这种细菌在无菌小鼠中的定居为基础。该单抗(225.4)与苏云金芽胞杆菌衣壳多糖4(CPS4)位点的产物反应。无菌Rag1-/-小鼠的定植，无论有没有产生这种抗体的杂交瘤细胞，都表明对这种被膜表位的工程IgA反应随后减少了促炎信号，抑制了表位的表达，并影响了细菌的竞争力。这些发现表明，尽管肠道微生物区系的成员有免疫识别，但肠道中的“耐受性”未能发展为病理性炎症。在目标1中，我建议使用GnotoBiotic小鼠来表征表位特异性不同于225.4的额外抗体以及不同同种类型的抗体，并使用微生物和宿主的功能基因组分析来定义每种抗体以及各种抗体组合如何影响宿主-共生体的动态平衡。在目标2中，我将开发一种抗共生B细胞受体基因敲入小鼠，以评估特定抗体反应对宿主-共生体动态平衡的发展和长期影响。 相关性：了解我们如何与居住在我们的消化道中的数万亿细菌共存并从中受益，对于了解我们的健康以及各种疾病的起源非常重要，包括感染性腹泻和结肠炎。我将评估免疫反应的一部分，即免疫球蛋白A，是如何预防炎症的。了解这种反应是如何正常进行的，以及它是如何发挥作用的，将使未来能够开发炎症介导性疾病的诊断测试和治疗。

DESCRIPTION (provided by applicant): Each of us harbors a distinct collection of trillions of microbes resulting in a 'supraorganism' where the number of microbial cells exceeds the number of human cells by an estimated order of magnitude. Our gut contains the vast majority of these microbes. The sources of microbial community stability, and the mechanisms by which co-evolution of an individual's immune system and microbiota contributes to the symbiotic relationship are poorly understand: the answers should provide important clues about how the microbiota contributes to our health, how perturbations in microbial ecology arise, how such perturbations produce certain pathologic states (e.g., infectious diarrheas; inflammatory bowel diseases) and how new strategies can be developed for intentionally manipulating the representation of components of the microbiota for therapeutic benefit. I have developed a simplified model of the human gut microbiota in gnotobiotic Rag1-/- mice, where the diversity of the gut microbiota is reduced to one species (Bacteroides thetaiotaomicron, a prominent sequenced member of the normal human gut microbiota), and the repertoire of the adaptive immune system to one immunoglobulin. I have characterized the specificity of this unique immunoglobulin A (IgA), which was naturally primed by colonization of germfree mice with this bacterium. The monoclonal antibody (225.4) reacts with the product of capsular polysaccharide 4 (CPS4) locus of B. thetaiotaomicron. Colonization of germfree Rag1-/- mice, with and without hydridoma cells that produce this antibody revealed that an engineered IgA response to this capsular epitope subsequently reduces pro-inflammatory signaling, suppresses epitope expression and impacts bacterial competitiveness. These finding indicate that 'tolerance' in the gut is a failure to develop pathological inflammation despite immune recognition of members of its microbiota. In Aim 1, I propose to use gnotobiotic mice to characterize additional antibodies with different epitope specificities than 225.4, as well as antibodies of different isotypes, and define, using functional genomic analyses of both the microbe and host, how each antibody, and various combinations of antibodies impact host-symbiont homeostasis. In Aim 2, I will develop an anti-symbiotic B cell receptor gnotobiotic transgenic-knock-in mouse to evaluate the development and long-term impact of a defined antibody response on host-symbiont homeostasis. Relevance: Understanding how we can co-exist with and benefit from the trillions of bacteria that reside in our digestive tract is important for understanding our health, and the origins of various diseases, including infectious diarrheas and colitis. I will evaluate how a part of the immune response, called immunoglobulin A, prevents inflammation. Understanding how this response is normally mounted and how it functions will allow the development of diagnostic test and treatments of inflammation mediated diseases in the future.