ULTRASTRUCTURE OF MULTINUCLEATED GIANT-CELL APOPTOSIS IN FOREIGN-BODYGRANULOMA

To elucidate the role of apoptosis in the disappearance of multinuclea ted giant cells from the granulation tissue in cases of foreign-body g ranuloma, we induced a foreign-body reaction by implanting a collagen sponge into the dorsum of the rat and observed apoptotic changes withi n the multinucleated giant cells using electron microscopy. Two types of multinucleated giant cells were identified presenting apoptotic cha racteristics morphologically. One was characterized by apoptosis of on ly one nucleus, followed by cytoplasmic changes, rupture of the plasma membrane and necrosis evoking an inflammatory reaction. The other sho wed typical apoptotic changes in the majority or in all of the nuclei, followed by phagocytosis of the apoptotic syncytia. The results of th e present study suggest that apoptosis occurring within only one nucle us might be triggered by overexpression of the p53 protein, because DN A abnormalities are confined to this single nucleus. In contrast apopt osis occurring simultaneously in the majority or all of the nuclei is most probably due to cell death caused by senescence.