BCR MEDIATED SIGNALING AND CYCLING B CELL BIOLOGY

抗原驱动的B细胞应答发生在次级淋巴组织内。 活跃的周期性B细胞迁移到卵泡中， (GC)反应发展。 由于循环GC B单元被编程为 当它们经历凋亡时，它们必须接受存活和/或增殖能力， 从GC环境中发出信号，以便生存。 本研究 利用体外模型系统探索循环B的生物学 细胞 为此目的，将从小鼠脾脏中分离的小的静息B细胞， 将小鼠的脾在大量培养物中活化2或4天， 脂多糖，并在3步循环中恢复活跃的B细胞 Percoll梯度。保护自行车运动所需的第一个生存信号 B细胞继续进入凋亡是通过占据 BCR抗原。 这代表了在这个过程中的第一步， 亲和力成熟，因为只有最适合的克隆可以竞争或 限制性抗原 在第一个具体目标，实验概述 为了验证CD 19/CD 21共受体在肿瘤发生中起重要作用的假设， 在向循环B细胞传递这种初始存活信号期间发挥作用。 为此，将再刺激循环HEL转基因B细胞 与可溶性或固定化的HEL或HEL-C3 d融合蛋白。 自C3 d以来 是CD 21的配体，这种融合蛋白有效地招募了 CD 19/CD 21共受体与被占据的BCR位点结合。 我们以前的研究 已经表明通过循环B表示的BCR的信号强度 细胞决定Bcl-2家族表达的模式。 循环B 细胞表达促凋亡蛋白Bax和Bcl-XS。 交联 循环B细胞上的BCR与可溶性F（ab '）2抗mu诱导了 抗血小板蛋白Bcl-XL的出现，而最佳的交叉- 通过固定化抗mu连接BCR诱导Bcl-XL和Bcl-2 抗凋亡蛋白。 在第二个具体实施例中描述的实验 aim将研究这些不同BCR的生物学后果- 诱导生存/死亡蛋白的模式。 我们以往的研究 还显示了通过由循环B表示的BCR的信号强度 细胞决定了它们对Th细胞来源的信号作出反应的能力。 第三个具体目标的实验将检验以下假设： BCR衍生的信号部分通过调节 CD 40信号传导复合物的组成。 总之，这些实验 将扩展我们对外部信号如何影响命运的理解 循环的B细胞。

Antigen driven B cell responses occur within secondary lymphoid tissues. Actively cycling B cells migrate into follicles where germinal center (GC) responses develop. Since cycling GC B cells are programmed to undergo apoptosis, they must receive viability and/or proliferative signals from the GC environment in order to survival. The present study utilizes an in vitro model system to explore the biology of cycling B cells. For this purpose, small resting B cells isolated from the spleens of mice are activated in bulk culture for 2 or 4 days with lipopolysaccharide, and the actively cycling B cells recovered on 3-step Percoll gradients. The first survival signal required to protect cycling B cells from continuing into apoptosis is delivered by occupancy of the BCR by antigen. This represents the first step in the process of affinity maturation, since only the best fit clones can compete or limiting antigen. In the first specific aim, experiments are outlined to test the hypothesis that the CD19/CD21 co-receptor plays an important role during delivery of this initial survival signal to cycling B cells. For this purpose, cycling HEL transgenic B cells will be restimulated with soluble or immobilized HEL or a HEL-C3d fusion protein. Since C3d is the ligand for CD21, this fusion protein effectively recruits the CD19/CD21 co-receptor to sites of occupied BCR. Our previous studies have shown that strength of signal through BCR expressed by cycling B cells determines the pattern of Bcl-2 family expression. Cycling B cells express the pro-apoptotic proteins Bax and Bcl-XS. Cross-linking BCR on cycling B cells with soluble F(ab')2 anti-mu induces the appearance of the anti-apoptitic protein Bcl-XL, while optimal cross- linking of BCR by immobilized anti-mu induces both Bcl-XL and Bcl-2 anti-apoptotic proteins. Experiments described in the second specific aim will examine the biological consequences of these different BCR- induced patterns of survival/death proteins. Our previous studies have also shown that strength of signal through BCR expressed by cycling B cells determines their ability to respond to Th cell-derived signals. Experiments in the third specific aim will test the hypothesis that the BCR-derived signals accomplish this, in part, by regulating the composition of the CD40 signaling complex. In sum, these experiments will expand our understanding of how external signals impact on the fate of cycling B cells.