ACTIVATION OF CELL SUICIDE IN THE IMMUNE SYSTEM

细胞死亡在生物体发育和动态平衡中起着关键的生理作用。特别是，它在形成和维持一种非自身反应和自我限制的免疫谱系方面发挥着关键作用。我们已经解决了一个基本的问题，即共同的细胞自主效应机制是否与不同的淋巴细胞死亡病例有关。我们已经检测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。这项工作导致了一条主题保守、有序的途径的确定。我们通过将必要但非致命的[调节]步骤与那些不能从实际死亡中分离出来的[效应器]步骤区分开来，在操作上定义了死亡承诺。值得注意的是，caspase(死亡相关半胱氨酸蛋白酶家族)的必需活性在细胞死亡的效应阶段起着关键作用，而细胞周期蛋白依赖性激酶(CDK)的活性通常与细胞分裂有关，它在细胞死亡的级联反应中发挥作用。半胱氨酸天冬氨酸酶用于激活驻留的CDK组分。对caspase依赖的CDK复合体的遗传干扰不会改变caspase的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。这些实验试图通过分子、生化和细胞分析来完善CDK功能的可操作性特征，并确定CDK致死作用的关键靶点。濒临死亡的细胞能够在不引发炎症反应的情况下触发吞噬作用，这可能是生理性细胞死亡过程的最重要的生物学目的。我们将根据诱导死亡细胞非炎症性吞噬的事件顺序，扩展我们对caspase和CDK依赖的细胞死亡途径的表征。正如我们使用抑制性基因产物来区分导致细胞完整性丧失的过程的调制步骤和效应步骤一样，我们将剖析导致吞噬细胞适当识别和清除的事件。对生理性细胞死亡过程的调节、机制和结果的了解将为正常的细胞和组织发育提供洞察力，并可能为衰老和包括自身免疫性疾病和癌症在内的病理条件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.