Selection of the B cell repertoire in senescence

B淋巴细胞生成在小鼠衰老中严重受损。衰老中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，这是一个关键依赖于通过前B细胞受体（ix/5/VpreB; preBCR）和生长细胞因子IL-7的信号传导的阶段。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。这主要是由于preBCR表达下降、对IL-7的应答差和对凋亡的易感性增加。而不是随机损失的前B细胞在老年，我们建议收缩的前B细胞池在克隆特异性的方式。优先选择的是那些少数的前B细胞，它们保持着 经历preBCR/IL-7介导的生长和存活。这导致衰老中前B和未成熟B细胞特异性库的“重塑”。为了解决这个问题，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异性的？".在这一特定目标中，将讨论Vh家族的使用、CDR 3多样性、表达功能性前BCR的能力以及微环境在改变B谱系发育和抗体库“读出”中的作用。具体目标2提出“前B阶段的”库重塑“是否影响老年时B细胞库的读出？".这里，将在来自老年小鼠的未成熟B细胞中评估Vh使用和CDR 3多样性，并与前B细胞进行比较。此外，将评估老年小鼠中未成熟B细胞的抗体特异性，并确定外周中这些未成熟B细胞的命运。 具体目标3提出“凋亡应激是否导致衰老中前B细胞和未成熟B细胞库的变化？".将测定老化B细胞中对凋亡的敏感性和凋亡/存活分子的表达。将评估环境对老化B谱系细胞中凋亡易感性的影响。最后，将测试细胞凋亡在调节衰老中的前B/未成熟B细胞库中的作用。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。

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.