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，从而形成“超有机体”，其中微生物细胞的数量超过了估计数量级的人类细胞数量。我们的肠道包含了这些微生物的绝大部分。微生物群落稳定性的来源，以及个体免疫系统和微生物群共同进化促进共生关系的机制尚不清楚：这些答案应该为以下方面提供重要线索：微生物群如何促进我们的健康，微生物生态的扰动如何产生，这种扰动如何产生某些病理状态(例如感染性腹泻；炎症性肠病)以及如何开发新的策略来有意地操纵微生物群组成部分的代表以获得治疗益处。我已经开发了一种简化的人类肠道微生物群模型，在这种模型中，肠道微生物群的多样性被减少到一个物种（拟杆菌，正常人类肠道微生物群的重要测序成员），适应性免疫系统的全部功能仅为一种免疫球蛋白。我已经描述了这种独特的免疫球蛋白A （IgA）的特异性，它是由带有这种细菌的无菌小鼠定植自然引发的。该单克隆抗体（225.4）与白螺旋藻荚膜多糖4 （CPS4）位点的产物反应。对无菌Rag1-/-小鼠，无论有无产生该抗体的水瘤细胞，定建表明，对该荚膜表位的工程IgA反应随后减少促炎信号，抑制表位表达并影响细菌竞争力。这些发现表明，尽管免疫系统对肠道菌群的成员进行了识别，但肠道中的“耐受性”未能发展为病理性炎症。在目标1中，我建议使用非生物小鼠来表征与225.4不同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种抗体以及抗体的各种组合如何影响宿主-共生体的稳态。在目标2中，我将开发一种抗共生B细胞受体转基因敲入小鼠，以评估一种特定抗体反应对宿主-共生体内平衡的发展和长期影响。

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.