Selection of B cell repertoire in senescence

描述（由申请人提供）：B淋巴系统在小鼠衰老中严重受损。虽然在老年B淋巴生成途径的几个不同阶段存在缺陷，但在前B细胞向前B细胞转变的下调可能在改变B细胞抗体库的组成中起主要作用。这种转变特别依赖于前b细胞受体（preBCR）的表达和信号传导，preBCR是免疫球蛋白5重链与替代轻链15和VpreB相关的复合物。老龄小鼠替代轻链的表达显著降低，preBCR功能较差。这导致老年小鼠新形成的B细胞中5重链库的进行性改变。然而，我们认为，即使替代轻链高度减少，衰老的前b区室也会偏向于那些经历正选择的前b细胞，而不是在老年时随机失去前b细胞。此外，我们提出，自身反应性的增加以及对病原体（如肺炎链球菌）保护性抗体反应的可用性的有害变化，部分原因是由于preBCR检查点受损。为了解决这一假设，我们提出了3个综合的具体目标。在具体目标1中，我们提出了这样的问题：“老年期preBCR检查点的受损是否会“重塑”Vh功能并促进自身反应？”在这里，preBCR功能减少对5重链使用的影响，以及替代轻链低时的信号能力，将与对自身反应性的影响一起确定。特异性目标2解决老年小鼠骨髓内自身反应性未成熟B细胞的命运及其对外周B细胞池的贡献。将评估老年小鼠未成熟B细胞的耐受性，它们返回脾脏的能力，以及重要的是，对肺炎链球菌抗原磷酸化胆碱的保护性和非保护性克隆型的表达。特异性目的3侧重于促炎细胞因子（TNFa）和效应细胞（NK）在触发前bcr下调、改变老年小鼠B淋巴生成和抗体谱中的重要性。这些研究将促进对伴随老年的免疫缺陷及其细胞和分子机制的理解。

DESCRIPTION (provided by applicant): B lymphopoiesis is severely compromised in murine senescence. While there are defects at several distinct stages in the B lymphopoietic pathway in old age, down-regulation at the pro-B to pre-B cell transition likely has a major role in altering the composition of the B cell antibody repertoire. This transition is particularly dependent upon expression of and signaling by the pre-B cell receptor (preBCR), a complex of immunoglobulin 5 heavy chain associated with the surrogate light chains l5 and VpreB. Aged mice have significantly reduced expression of surrogate light chains and poor preBCR function. This results in progressive alteration of the 5 heavy chain repertoire in newly formed B cells in aged mice. However, rather than a random loss of pre-B cells in old age, we propose that the aged pre-B compartment will become skewed in favor of those pre-B cells that undergo positive selection even when surrogate light chain is highly reduced. Moreover, we propose that increases in autoreactivity as well as detrimental changes in the availability of protective antibody responses to pathogens, e.g., S. pneumoniae, are, in part, due to a compromised preBCR checkpoint. To address this hypothesis, we propose 3 integrated Specific Aims. In Specific Aim 1, we ask "Does compromise of the preBCR checkpoint in old age 'reshape' the Vh repertoire and promote autoreactivity"? Here, the effects of diminished preBCR function on 5 heavy chain usage, and capacity to signal when surrogate light chain is low, will be determined together with impact on autoreactivity. Specific Aim 2 addresses the fate of autoreactive immature B cells within the bone marrow of aged mice and their contribution to the peripheral B cell pools. Tolerance among immature B cells in aged mice, their capacity to home to the spleen, and, importantly, the expression of protective versus non-protective clonotypes in response to the S. pneumoniae antigen phosphorylcholine will be assessed. Specific Aim 3 focuses upon the importance of proinflammatory cytokines (TNFa) and effector cells (NK) in triggering the down-regulation of preBCR, altering both B lymphopoiesis and antibody repertoires in aged mice. These studies will advance understanding of the immune defects that accompany old age and their cellular and molecular mechanisms. PUBLIC HEALTH RELEVANCE: The development of new antibody producing B cells is compromised in old age. This may result in both poor antibody protective responses to pathogens in disease as well as to vaccination. Our studies focus on the mechanisms that affect antibody producing B cell production in old age, primarily the role of the pre-B cell receptor complex. Insight into the defects in B cell production in old age may reveal their influence on developing and maintaining effective immune barriers to infectious disease.