Mechanisms of pyknotic cell death in vivo and their biological significance

大多数发育过程中的程序性细胞死亡被认为是伴随着DNA片段化的细胞凋亡。我们精确地检测了生发中心的胸腺细胞死亡和B细胞死亡，即原位的细胞死亡，发现它们是固缩的，细胞核大量凝聚，没有DNA片段化；它们与典型的以DNA片段化和边际染色质凝集为特征的细胞凋亡完全不同。我们重新评估了体内各种细胞死亡，并在新观点的基础上对原位细胞死亡进行了重新分类，以分析这种新型细胞死亡的机制，并阐明其生物学意义。我们对发育过程中体内细胞死亡，特别是指间组织中观察到的细胞死亡进行了形态分析，发现该组织中的细胞死亡不伴随DNA片段化，因此，我们得出结论，它们不是细胞凋亡。由抗CD3抗体治疗引发的大量细胞死亡被发现是典型的细胞凋亡，因为它们在可以观察到形态变化的更早阶段就使DNA片段化。我们开展了一个项目来开发一种单抗来检测最早的固缩迹象，这是死亡胸腺细胞的一种表面抗原，可以被巨噬细胞识别来摄取。该项目一直在进行中，并将一直进行到抗原的开发。

Most of programmed cell deaths during the developmental processes have been considered to be apoptosis accompanying DNA fragmentation. We have precisely examined thymocyte deaths and B cell deaths in the germinal centers, i.e., "cell deaths" in situ, and found that they are pyknosis with heavy nuclear condensation without DNA fragmentation ; they are totally distinct from typical apoptosis, which is characterized by DNA fragmentation and marginal chromatin condensation. We re-evaluated various cell deaths in vivo, and rectategorize those in situ cell deaths on the basis of the novel point of view, in order to analyze the mechanisms of the new type of cell deaths, pyknosis, and to delineate their biological significance.We analyzed morphologically cell deaths in vivo during the development, especially the cell deaths observed in the interdigital tissues and found that the cell deaths in this tissue did not accompany DNA fragmentation, and accordingly, we concluded that they are not apoptosis. Massive cell deaths triggered by anti-CD3 antibody treatment have been found typical apoptosis, because they fragmented DNA at much earlier stages when morphological changes could be observed.We have undertaken a project to develop a monoclonal antibody to detect the earliest sign of pyknosis, a surface antigen of dying thymocytes to be recognized by macrophages for ingestion. This project has been underway, and will be pursued until the development of the antigen.