NONSPECIFIC CELL-MEDIATED CYTOTOXICITY IN THE SEAWATER TELEOSTS (SPARUS-AURATA AND DICENTRARCHUS-LABRAX) - ULTRASTRUCTURAL-STUDY OF TARGET-CELL DEATH MECHANISMS

Background: In higher vertebrates, cytolytic lymphocytes lyse their ta rgets by the mechanisms of cell death called necrosis and apoptosis. H owever, the mechanisms of target cell death mediated by fish cytotoxic cells have not been established. We report the ultrastructure of targ et cell death mediated by the seawater teleosts gilthead seabream (Spa rus aurata) and sea bass (Dicentrarchus labrax). Methods: Head-kidney, blood, and peritoneal exudate leukocytes were incubated with HeLa or B16 melanoma tumor cells, as targets, and processed for transmission e lectron microscopic studies. Results: After incubation of tumor cells with leukocytes, substantial ultrastructural changes typically associa ted with both necrosis and apoptosis were observed in the plasmalemma, nucleus, and cytoplasm of the tumor cells. These morphological change s included loss of microvilli, the formation of long cytoplasmic proce sses and blebs, condensation and margination of the chromatin, swellin g of the organelles, and vacuolation and condensation of the cytoplasm . Conclusions: Our results indicate that leukocytes from gilthead seab ream and sea bass are able to kill their targets by the mechanisms of necrosis and apoptosis, in a similar way to mammalian cytotoxic cells. (C) 1996 Wiley-Liss, Inc.