Selection of B cell repertoire in senescence

描述（由申请方提供）：B淋巴细胞生成在小鼠衰老中严重受损。虽然在老年时B淋巴细胞生成途径的几个不同阶段存在缺陷，但前B细胞向前B细胞转变的下调可能在改变B细胞抗体库的组成中具有主要作用。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是与替代轻链15和VpreB相关的免疫球蛋白5重链的复合物。老年小鼠替代轻链的表达显著降低，preBCR功能较差。这导致老年小鼠中新形成的B细胞中5种重链库的进行性改变。然而，我们提出，即使在替代轻链高度减少时，老化的前B区室也会偏向于那些经历阳性选择的前B细胞，而不是老年时前B细胞的随机损失。此外，我们提出，自身反应性的增加以及对病原体的保护性抗体应答的可用性的有害变化，例如，S.肺炎，部分是由于受损的preBCR检查点。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“老年前BCR检查点的妥协是否会'重塑' Vh库并促进自身反应性”？在此，将确定preBCR功能减弱对5重链使用的影响，以及替代轻链低时发出信号的能力，以及对自身反应性的影响。特定目的2阐述了老年小鼠骨髓中自身反应性未成熟B细胞的命运及其对外周B细胞池的贡献。老年小鼠中未成熟B细胞的耐受性，它们归巢脾脏的能力，以及重要的是，对S.将评估肺炎抗原磷酸胆碱。具体目标3关注促炎细胞因子（TNF α）和效应细胞（NK）在触发前BCR下调、改变老年小鼠B淋巴细胞生成和抗体库中的重要性。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。 公共卫生相关性：产生新抗体的B细胞的发育在老年受到损害。这可能导致对疾病中的病原体以及对疫苗接种的抗体保护性应答较差。我们的研究集中在影响老年人产生抗体的B细胞产生的机制上，主要是前B细胞受体复合物的作用。深入了解老年人B细胞产生的缺陷可能会揭示它们对发展和维持有效的免疫屏障对感染性疾病的影响。

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.