Selection of B cell repertoire in senescence

描述(由申请人提供)：B淋巴细胞生成在小鼠衰老过程中严重受损。虽然老年人在B淋巴细胞生成途径的几个不同阶段都存在缺陷，但前B细胞向前B细胞转变的下调可能在改变B细胞抗体库的组成方面起着主要作用。这种转变特别依赖于前B细胞受体(PreBCR)的表达和信号传递，preBCR是一种与替代轻链L5和VpreB相关的免疫球蛋白5重链的复合体。衰老小鼠代理轻链表达显著减少，前BCR功能低下。这导致了老年小鼠新形成的B细胞中5个重链谱系的进行性改变。然而，我们认为，即使在代理轻链高度减少的情况下，老化的前B细胞也会偏向那些经历阳性选择的前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)的保护性抗体反应的可获得性的有害变化，部分是由于BCR前检查点的受损。为了解决这一假设，我们提出了三个综合的具体目标。在具体目标1中，我们问“老年前BCR检查点的妥协是否‘重塑’了VH谱系并促进了自身反应”？在这里，前BCR功能减弱对5重链使用的影响，以及当替代轻链低时发出信号的能力，将与对自身反应的影响一起确定。特定目标2解决了老年小鼠骨髓中自身反应性未成熟B细胞的命运以及它们对外周B细胞库的贡献。将评估老年小鼠中未成熟B细胞之间的耐受性，它们归巢于脾的能力，以及重要的是，保护性和非保护性克隆型对肺炎链球菌抗原磷胆碱的反应。具体目标3集中在促炎细胞因子(TNFa)和效应细胞(NK)在触发前BCR下调中的重要性，从而改变老年小鼠的B淋巴细胞和抗体库。这些研究将促进对老年伴随的免疫缺陷及其细胞和分子机制的理解。 与公共卫生相关：产生新抗体的B细胞的发育在老年时受到影响。这可能导致在疾病和疫苗接种中对病原体的抗体保护性反应较差。我们的研究集中在影响老年人产生抗体的B细胞产生的机制，主要是前B细胞受体复合体的作用。洞察老年人B细胞产生的缺陷，可能会揭示它们对发展和维持有效的传染病免疫屏障的影响。

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.