Evolution of Diversification Mechanisms for Lymphocyte Antigen Receptors

脊椎动物都有一种适应性免疫系统，在应对致病性威胁方面具有很强的特异性，并且对以前的挑战有着惊人的记忆。淋巴细胞是介导适应性免疫的血细胞，有两种类型：分泌抗体的B细胞和引导其他免疫效应物杀死感染细胞或癌细胞的T细胞。B淋巴细胞和T淋巴细胞都是大量存在的，其中每个细胞都有一个独特的抗原受体，这是DNA重组过程的产物。人类有不同的基因、受体和多样化机制，分别由T细胞和B细胞使用。然而，在具有适应性淋巴细胞系统的最古老的生物体鲨鱼中，B淋巴细胞和T淋巴细胞之间的界限要模糊得多。鲨鱼B细胞和T细胞在使用基因、受体模块和受体多样化方法方面具有更大的可塑性，这些基因、受体模块和受体多样化方法在人类中是严格针对B或T谱系的。在这个项目中，将详细研究鲨鱼中T细胞的发育，包括在这些细胞中产生突变的机制的作用。这一结果将使我们更深入地了解脊椎动物如何协调适应性免疫的基本原理，并在此过程中为疫苗设计和免疫治疗提供新的思路和工具。该项目将通过本科生和高中生参与研究，利用迭代教学计划和与当地高中教师合作的实践研究经验，为STEM教育做出贡献。该项目的中心假设是，T细胞受体在鲨鱼体内保留了重要的、祖先的、功能的可塑性，这一点可以通过抗原受体位点的组织、作用于其中基因的免疫遗传过程、胸腺细胞的发育以及表达这些受体的细胞的转录谱来证明。这种功能可塑性应该在更多衍生的脊椎动物抗原受体多样化系统中以及在基底鲨鱼中都很明显。中心假设将通过追求两个目标来验证：1)确定使用免疫球蛋白可变基因的T细胞如何在原发性淋巴组织中发育，使库多样化，受到转录控制，以及它们是否更多地发挥B细胞或T细胞的功能；2)确定鲨鱼T细胞受体位点在áâ和ãä中体细胞超突变（SHM）的程度，调节和生理作用，并探索激活诱导胞苷脱氨酶（AID）功能的边界。预期的结果如下：第一个目标将确定B细胞和T细胞可变基因片段是否具有内在的可互换性，携带免疫球蛋白-T细胞嵌合受体的细胞是否在胸腺中发育，细胞的转录谱是否更像B细胞或T细胞，以及它们对免疫的贡献。第二个目的是确定T细胞受体的胸腺和外周SHM是否对库多样化、胸腺选择的传递或<s:1>和ã位点的亲和成熟起作用，并更好地定义AID催化的反应。

Vertebrates share an adaptive immune system that is capable of great specificity in responding to pathogenic threats and a remarkable memory for previous challenges. Lymphocytes, the blood cells that mediate adaptive immunity, come in two types: B cells that secrete antibodies, and T cells that direct other immune effectors and kill infected or cancerous cells. Both B and T lymphocytes exist as vast populations in which each cell has a unique antigen receptor that is the product of DNA recombination processes. Humans have distinct genes, receptors, and diversification mechanisms that are separately employed by T cells and B cells. However, in sharks, which represent the oldest organisms with an adaptive lymphocyte system, the line between B and T lymphocytes is much blurrier. Shark B and T cells have greater plasticity to use genes, receptor modules, and receptor diversification methods that are strictly B or T lineage-specific in humans. In this project, the development of T cells in the shark will be studied in detail, including the role of a mechanism of generating mutations in these cells. The results will yield greater insight into the fundamentals of how vertebrates orchestrate adaptive immunity, in the process yielding new thinking and tools for vaccine design and immunotherapeutics. The project will contribute to STEM education through the participation of undergraduates and high school students in the research, utilizing an iterative program of teaching and hands-on research experience in collaboration with a local high school teacher.The central hypothesis of the project is that T cell receptors retain significant, ancestral, functional plasticity in the shark, evident by the organization of the antigen receptor loci, the immunogenetic processes acting upon the genes therein, development of the cells in the thymus, and the transcription profiles of the cells that express these receptors. This functional plasticity should be evident in more derived vertebrate antigen receptor diversification systems as well as in the basal shark. The central hypothesis will be tested by pursuing two aims: 1) Determine how T cells employing immunoglobulin variable genes develop in primary lymphoid tissues, diversify repertoire, are transcriptionally controlled, and whether they function more as B or T cells and 2) Identify the extent, regulation and physiological role of somatic hypermutation (SHM) at shark T cell receptor loci in both áâ and ãä T cells, and explore the boundaries of activation- induced cytidine deaminase (AID) function. The following expected outcomes are anticipated: the first aim will determine if B and T cell variable gene segments are inherently interchangeable, if the cells bearing immunoglobulin-T cell chimeric receptors develop in the thymus, if the transcriptional profile of the cells is more B- or T-like, and what they contribute to immunity. The second aim will define if thymic and peripheral SHM of T cell receptors operates for repertoire diversification, passage of thymic selection, or affinity maturation at the á and ã loci, and better define reactions catalyzed by AID.