ACTIVATION OF CELL SUICIDE IN THE IMMUNE SYSTEM

细胞死亡是机体发育和体内平衡的一个重要生理过程。特别是，它在形成和维持非自身反应性和自我限制的免疫库中起着关键作用。我们已经解决了是否一个共同的细胞自主效应机制适用于淋巴细胞死亡的不同情况的基本问题。我们研究了不同淋巴细胞系中不同细胞死亡反应中的死亡相关事件，并利用死亡抑制基因产物来绘制相关活动的作用顺序。这项工作导致了一个主题上保守的，有序的途径的识别。我们通过区分必要但非致命的[调节]步骤与那些不能与实际死亡分离的[效应]步骤，在操作上定义了死亡承诺点。值得注意的是，半胱天冬酶（死亡相关半胱氨酸蛋白酶家族）的必要活性，在由Bcl-2间断的级联中发挥作用，映射到该过程的调节阶段，而周期蛋白依赖性激酶（Cdk）活性，通常与细胞分裂相关，在细胞死亡的效应阶段起关键作用。半胱天冬酶的作用是激活Cdk成分。对caspase依赖性Cdk复合物的遗传干扰不会改变caspase活性或其他上游事件，包括线粒体去极化，但它使细胞免于死亡。该实验旨在通过分子、生化和细胞分析来完善Cdk功能的操作特性，并确定致命Cdk作用的关键靶点。垂死细胞触发吞噬而不引起炎症反应的能力可能是生理细胞死亡过程最重要的生物学目的。我们将扩展我们对caspase和cdk依赖性细胞死亡途径的表征，涉及诱导死亡细胞非炎症吞噬的事件顺序。正如我们使用抑制基因产物来区分导致细胞完整性丧失的过程的调节和效应步骤一样，我们将剖析导致吞噬细胞适当识别和清除的事件。对生理细胞死亡过程的调控、机制和结果的理解将为正常细胞和组织发育提供新的见解，并可能为衰老和病理疾病（包括自身免疫性疾病和癌症）的治疗提供新的观点。

Cell death serves a critical physiological process in organismal development and in homeostasis. In particular, it plays a pivotal role in shaping and maintaining a non-autoreactive and self-limiting immune repertoire. We have addressed the fundamental question of whether a common cell-autonomous effector mechanism pertains in distinct cases of lymphocyte cell death. We have examined death-associated events in different cell death responses in different lymphocyte cell lines, and we have exploited death-inhibitory gene products to map the order of action of the associated activities. This work has led to the identification of a thematically conserved, ordered pathway. We have defined operationally a point of death commitment by distinguishing necessary but non-lethal [modulatory] steps from those [effector] steps which cannot be dissociated from actual death. Remarkably, the requisite activities of caspases (the family of death-associated cysteine proteases), functioning in a cascade punctuated by Bcl-2, map to the modulatory phase of the process, while cyclin dependent kinase (Cdk) activity, normally associated with cell division, plays a critical role in the effector phase of cell death. Caspases serve to activate resident Cdk components. Genetic interference with caspase- dependent Cdk complexes does not alter caspase activity or other upstream events, including mitochondrial depolarization, yet it spares cells from death. The experiments proposed seek to refine this operational characterization of Cdk function through molecular, biochemical, and cellular analyses, and to identify the critical targets of lethal Cdk action. The ability of a dying cell to trigger phagocytosis without eliciting an inflammatory response likely is the overriding biological purpose of the physiological cell death process. We will extend our characterization of the caspase- and Cdk-dependent pathway of cell death with respect to the order of events involved in inducing non-inflammatory engulfment of dying cells. Just as we employed inhibitory gene products to distinguish modulatory and effector steps of the process leading to the loss of cellular integrity, we will dissect events that lead to appropriate recognition and clearance by phagocytic cells. An understanding of the regulation, mechanism, and outcome of the physiological cell death process will offer insights to normal cell and tissue development, and may provide new views of aging and treatments for pathological conditions, including autoimmune diseases and cancers.