Morphological damage induced by isolated cytolytic granules in K562 target cells.

Early and late events leading to cell death in K562 target cells incubated with isolated cytolytic granules from NK-like cytolytic cell lines were analyzed by transmission, scanning and freeze-fracture electron microscopy. Particular focus was given to the possible morphological expression of nuclear envelope and chromatin alterations related to DNA fragmentation and <<programmed cell death>> of the target. Typical plasma membrane alterations could be induced by cytolytic granules after 5 min using high lytic amounts and after 30 min using sublytic doses. The architecture of the plasmalemma was also significantly modified, with a general redistribution of intra-membrane particles, which appear characteristically clustered. The nuclear envelope and chromatin structure were only little affected by the lytic process, chromatin condensation and nucleoplasm extraction being observed only in highly damaged cells, following osmotic lysis. These results show that the morphological expression of granule cytolysis in K562 target cells is similar to that induced by human NK lymphocytes. In this model nuclear alteration can be considered a consequence of osmotic cell lysis.