Evolution of Diversification Mechanisms for Lymphocyte Antigen Receptors

脊椎动物共享一种适应性免疫系统，能够对致病威胁做出极大的特异性反应，并对以前的挑战具有非凡的记忆力。淋巴细胞是调节适应性免疫的血细胞，有两种类型：分泌抗体的B细胞和指挥其他免疫效应器并杀死感染或癌细胞的T细胞。B和T淋巴细胞都以庞大的群体存在，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，鲨鱼代表了具有适应性淋巴细胞系统的最古老的生物，B和T淋巴细胞之间的界限要模糊得多。鲨鱼B和T细胞具有更大的可塑性，可以使用人类严格意义上的B或T血统特有的基因、受体模块和受体多样化方法。在这个项目中，将详细研究鲨鱼体内T细胞的发育，包括在这些细胞中产生突变的机制所起的作用。这些结果将使人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，在这个过程中，为疫苗设计和免疫疗法产生新的思维和工具。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细胞受体在鲨鱼中保留了显著的祖先功能可塑性，从抗原受体基因的组织、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中可以明显看出这一点。这种功能可塑性在更多的脊椎动物抗原受体多样化系统中应该是明显的，在基底鲨鱼中也是如此。中心假说将通过追求两个目标来检验：1)确定利用免疫球蛋白可变基因的T细胞如何在初级淋巴组织中发育、多样化、转录调控，以及它们的功能更像B细胞还是T细胞；2)确定鲨鱼T细胞受体基因座上体细胞高突变(SHM)的程度、调节和生理作用，并探索激活诱导的胞苷脱氨酶(AID)功能的界限。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固有地可互换，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，细胞的转录图谱是否更像B细胞或T细胞，以及它们对免疫的贡献。第二个目标将确定T细胞受体的胸腺和外周SHM是否作用于曲线谱多样化、胸腺选择的通过或α和ã位点的亲和力成熟，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.