Selection of the B cell repertoire in senescence

B淋巴细胞的生成在小鼠的衰老过程中受到严重损害。衰老时B淋巴细胞生成的缺陷主要“映射”到前B细胞到前B细胞的转变，这一阶段严重依赖于通过前B细胞受体(ix/_5/VpreB；preBCR)和生长细胞因子IL-7传递的信号。我们认为，在衰老过程中，前B细胞的发育受到越来越严格的负选择的影响。这主要是由于前BCR的表达下降，对IL-7的反应不佳，以及对凋亡的敏感性增加所致。我们建议以克隆特异性的方式收缩前B细胞池，而不是在老年时随机丧失前B细胞。优先选择的将是那些维持容量的少数前B细胞 接受前BCR/IL-7介导的生长和存活。这导致了衰老过程中前B细胞和未成熟B细胞特异性谱系的“重塑”。为了解决这一假设，我们提出了三个具体目标。具体目标1问“老年前B细胞的丧失是随机的还是克隆特有的？”在这个特定的目标中，VH家族的使用，CDR3的多样性，表达功能前BCRs的能力，以及微环境在改变B谱系发育和抗体谱“读出”中的作用将被讨论。具体目标2问“在B前阶段的‘谱系重塑’是否会影响老年B细胞谱系的读出？”在这里，VH的使用和CDR3的多样性将在老年小鼠未成熟的B细胞中进行评估，并与前B细胞进行比较。此外，还将评估衰老小鼠中未成熟B细胞的抗体特异性，并将确定这些未成熟B细胞在外周的命运。 特定目标3问：“在衰老过程中，凋亡应激是否会导致前B细胞和未成熟B细胞谱系的改变？”老年B细胞对凋亡的敏感性和凋亡/存活分子的表达将被确定。将评估环境对老年B系细胞凋亡易感性的影响。最后，将测试细胞凋亡在调节前B/未成熟B细胞在衰老过程中的作用。这些研究将促进对伴随衰老而来的免疫缺陷及其细胞和分子机制的了解。

B lymphopoiesis is severely compromised in murine senescence. The defect in B lymphopoiesis in senescence predominantly "maps" to the pro-B to pre-B cell transition, a stage critically dependent upon signaling via the pre-B cell receptor (ix/_.5/VpreB; preBCR) and the growth cytokine IL-7. We propose that in senescence the development ofpre-B cells is subject to increasingly stringent negative selection. This results primarily from decline in expression of the preBCR, poor responses to IL-7, and increased susceptibility to apoptosis. Rather than random loss of pre-B cells in old age, we propose contraction of the pre-B cell pool in a clone-specific manner. Preferentially selected would be those few pre-B ceils which maintain the capacity to undergo preBCR/IL-7 mediated growth and survival. This results in a "reshaping" of the pre-B and immature B cell specificity repertoires in senescence. To address this hypothesis, we propose 3 Specific Aims. Specific Aim 1 asks "Is the loss of pre-B cells in old age random or clone-specific?". In this Specific Aim, Vh family use, CDR3 diversity, capacity to express functional preBCRs, and the role of the microenvironment in altering B lineage development and "read-out" of the antibody repertoire will be addressed. Specific Aim 2 asks "Does 'repertoire reshaping' at the pre-B stage affect the read-out of the B cell repertoire in old age?". Here, Vh use and CDR3 diversity will be assessed in immature B cells from aged mice and compared with that of pre-B cells. Furthermore, the antibody specificity of immature B cells in aged mice will be assessed and the fate of these immature B cells in the periphery will be determined. Specific Aim 3 asks "Does apoptotic stress result in changes in the pre-B and immature B cell repertoires in senescence?". Sensitivity to apoptosis and the expression of apoptotic/survival molecules in aged B cells will be determined. The effects of the environment on apoptotic susceptibility among aged B lineage cells will be assessed. Finally, the role of apoptosis in modulating the pre-B/immature B cell repertoires in senescence will be tested. These studies will advance understanding of the immune defects which accompany old age and their cellular and molecular mechanisms.