APOPTOSIS AND COMPLEMENT-STUDIES ON THE MECHANISM OF COMPKEMENT ACTIVATION AND THE BIOLOGICAL SIGNIFICANCE

我们研究了凋亡细胞活化自体补体的机制以及补体活化在巨噬细胞清除凋亡细胞中的生物学意义。凋亡细胞中自体补体通路的激活因子。补体活化不会发生在同源活细胞上。我们观察到人类凋亡细胞对自体补体通路的激活，提示一种新的补体激活剂在凋亡细胞上的出现。为了表征新的激活剂，Jurkat Y细胞系被允许凋亡，其细胞蛋白进行SDS-PAGE处理，随后用人血清作为补体来源处理。补体激活发生在一个50 KDa的蛋白上，该蛋白与C3b一起沉积，表明存在能够激活自身补体的50 KDa分子。在活细胞的膜组分中检测到相同的分子。基于这些数据，我们提出50 KDa激活蛋白可能更多地位于活细胞的膜部分，并在细胞凋亡时暴露于细胞表面。目前，新型补体激活剂的分离研究正在进行中。补体活化对巨噬细胞吞噬凋亡细胞的影响。我们发现经血清处理的凋亡细胞被ic3b标记，ic3b被称为调理素。提示凋亡细胞上的ic3b可能与巨噬细胞的CR3相互作用，促进凋亡细胞的吞噬作用。结果表明，ic3b包被的凋亡细胞被巨噬细胞吞噬的速度明显快于未包被的细胞。抗ic6b抗体和抗CR3可抑制巨噬细胞吞噬ic6b包被的凋亡细胞，提示凋亡细胞上的ic3b可能与巨噬细胞上的CR3相互作用，促进巨噬细胞对凋亡细胞的清除。因此，补体不仅是一种宿主防御系统，也是一种清除不必要细胞（如凋亡细胞）的生理系统。少

We investigated the mechanism of autologous complement activation by apoptotic cells and biological significance of complement activation in the clearance of apoptotic cells by macrophages.1. Activator of the autologous complement pathway in apoptotic cells. Complement activation does not occur on homologous live cells.We observed the activation of the autologous complement pathway by human apoptotic cells, suggesting the appearance of a novel complement activator on apoptotic cells.To characterize the novel activator, Jurkat Y cell line was allowed to spoptosis and its cell proteins were subjected to SDS-PAGE and subsequently treated with human serum as a source of complement.Complemnt activation occurred on a 50 KDa protein, which was become deposited with C3b, suggesting the presence of 50 KDa molecule capable of activating autologous complement.The same molecule was detected in the membrane fraction of live cells. Based on these data, we proposed that the 50 KDa activator protein i … More s located in the membrane fraction of live cells and become exposed to cell surface upon apoptosis.Studies on the isolation of the novel complement activator are now in progress.2. The effect of complement activation upon phagocytosis of qpoptotic cells by macrophages.We found that serum-treated apoptotic cells were labeled with ic3b, which is known as an opsonin. This suggested that ic3b on apoptotic cells might interact with CR3 of macrophages and promote the phagocytosis of apoptotic cells.The ic3b-coated apoptotic cells were found to be phagocytosed much more quickly than ic3b-noncoated cells by macrophages.The phagocytosis of ic6b-coated apoptotic cells by macrophages was found to be inhibited by anti-ic6b antibodies and anti-CR3, indicating that ic3b on apoptotic cells should interact with CR3 on macrophages and promote the clearance of apoptotic cells by phagocytes.Thus, complement is not only a host defense system but also a physiological system to remove unnecessary cells, such as apoptotic cells. Less