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

描述（由申请人提供）：我们每个人都拥有数万亿微生物的独特集合，导致“超生物体”，其中微生物细胞的数量超过人类细胞的数量，估计数量级。我们的肠道含有绝大多数这些微生物。微生物群落稳定性的来源，以及个体免疫系统和微生物群的共同进化有助于共生关系的机制知之甚少：答案应该提供关于微生物群如何有助于我们的健康，微生物生态学中的扰动如何产生，这种扰动如何产生某些病理状态（例如，传染性支气管炎;炎症性肠病）以及如何开发新的策略来有意地操纵微生物群组分的代表以获得治疗益处。我已经开发了一个简化的模型，在gnotobiotic Rag 1-/-小鼠中的人类肠道微生物群，其中肠道微生物群的多样性减少到一个物种（多形拟杆菌，正常人类肠道微生物群的一个突出的测序成员），适应性免疫系统的剧目到一个免疫球蛋白。我的特点是这种独特的免疫球蛋白A（伊加），这是自然引发的无菌小鼠与这种细菌的殖民化的特异性。单克隆抗体（225.4）与B的荚膜多糖4（CPS 4）位点的产物反应。太多了。无菌Rag 1-/-小鼠的定殖，具有和不具有产生该抗体的荚膜细胞，揭示了对该荚膜表位的工程化伊加应答随后减少促炎信号传导，抑制表位表达并影响细菌竞争力。这些发现表明，肠道中的“耐受性”是尽管其微生物群成员的免疫识别，但未能发生病理性炎症。在目标1中，我建议使用gnotobiotic小鼠来表征具有不同于225.4的表位特异性的其他抗体，以及不同同种型的抗体，并使用微生物和宿主的功能基因组分析来定义每个抗体以及抗体的各种组合如何影响宿主共生体内平衡。在目标2中，我将开发一种抗共生B细胞受体非共生转基因敲入小鼠，以评估确定的抗体应答对宿主-共生体稳态的发展和长期影响。 相关性：了解我们如何与居住在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（包括传染性肠炎和结肠炎）的起源非常重要。我将评估免疫反应的一部分，称为免疫球蛋白A，如何预防炎症。了解这种反应通常是如何安装的，以及它是如何发挥作用的，将有助于在未来开发炎症介导的疾病的诊断测试和治疗方法。

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.