Induction mechanisms of B cell self-toleranace

本研究利用转基因技术，探讨了在生殖中心培养的自身反应性B细胞的诱导凋亡机制。我们显示1. Bcl 6基因已从B细胞淋巴瘤中的染色体易位断裂点鉴定，编码序列特异性转录抑制因子，并且在生殖中心B和T细胞中强烈表达。Bcl 6-/-小鼠骨髓细胞连续性移植实验表明，Bcl 6对生殖中心B细胞的分化是必需的。bcl 6在正常小鼠睾丸生殖细胞中也有表达，主要是精母细胞。我们发现在成年Bcl-6-/-睾丸中，Bax蛋白诱导的中期I期精母细胞大量凋亡。杂合子Bcl 6 +/-小鼠的凋亡发生率也高于Bcl 6 +/+小鼠。结论：1.成年Bcl 6-/-小鼠精母细胞中存在p38 MAP激酶的激活形式，Bcl 6可能在应激诱导的精母细胞凋亡中起稳定剂的作用. Bcl 6-/-小鼠显示大量嗜酸性粒细胞炎症。我们最近建立了携带Ig-Bcl 6或lck-Bcl 6基因的转基因小鼠，并分析了这些Bcl 6转基因小鼠的淋巴细胞功能。转基因小鼠的生发中心形成和记忆反应增强，提示Bcl 6可能在生发中心B细胞存活中起作用.我们描述了一种新定义的小鼠细胞凋亡抑制剂（TIAP），它与Caspase-3的加工形式相互作用并抑制Caspase-3诱导的细胞死亡。TIAP在同步化的NIH3T3细胞中的表达在细胞周期的S至G2/M期上调。我们提出在细胞增殖过程中，细胞保护活性可能会增加诱导型IAP，如TIAP。我们正在研究TIAP在生发中心B细胞中的作用。

We investigated the induction mechanisms of apoptosisi of self-reactive B cells developed in germinal centers using transgenic system. We show that1. The Bcl6 gene has been identified from the chromosomal translocation breakpoint in B cell lymphomas, encodes a sequence-specific transcriptional repressor, and is strongly expressed in germinal center B and T cells. Adoptive transfer experiments with bone marrow cells from Bcl6-deficient (Bcl6-/-) mice revealed that Bcl6 is essential for the differentiation of germinal center B cells. Bcl6 was also detected in testicular germ cells, mainly spermatocytes, of normal mice. We found numerous apoptotic spermatocytes at the metaphase I stage with induction of Bax protein in adult Bcl6-/-testes. The incidence of apoptosis in heterozygous Bcl6+/-mice was also higher than that of Bcl6+/+mice. Since the activated form of p38 MAP kinase was detected in spermatocytes of adult Bcl6-/-mice, Bcl6 may play a role as a stabilizer in protecting spermatocytes from apoptosis induced by stresses.2. Bcl6-/-mice displayed massive eosinophilic inflammation. We have recently established transgenic mice carrying the Ig-Bcl6 or the lck-Bcl6 gene, and analyzed functions of lymphocytes of these Bcl6 transgenic mice. The germinal center fromation and memory responses were augmented in transgenic mice, suggesting that Bcl6 may play a role in survival of germinal center B cells.3. we describe a newly defined murine inhibitor of apoptosis (LAP), designated TIAP.TIAP interacted with the processed form of Caspase-3 and inhibited caspase-induced cell death. The expression of TIAP was upregulated in synchronized NIH3T3 cells at S to G2/M phase of the cell cycle. We propose that during cell proliferation, cellular protective activity may be augmented with inducible IAPs such as TIAP.We are investigating the role of TIAP in germinal center B cells.