Nonspecific cell-mediated cytotoxicity in the seawater teleosts (Sparus aurata andDicentrarchus labrax): Ultrastructural study of target cell death mechanisms

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Abstract
Background In higher vertebrates, cytolytic lymphocytes lyse their targets by the mechanisms of cell death called necrosis and apoptosis. However, the mechanisms of target cell death mediated by fish cytotoxic cells have not been established. We report the ultrastructure of target cell death mediated by the seawater teleosts gilthead seabream (Sparus 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 electron microscopic studies. Results After incubation of tumor cells with leukocytes, substantial ultrastructural changes typically associated with both necrosis and apoptosis were observed in the plasmalemma, nucleus, and cytoplasm of the tumor cells. These morphological changes included loss of microvilli, the formation of long cytoplasmic processes and blebs, condensation and margination of the chromatin, swelling of the organelles, and vacuolation and condensation of the cytoplasm. Conclusions Our results indicate that leukocytes from gilthead seabream and sea bass are able to kill their targets by the mechanisms of necrosis and apoptosis, in a similar way to mammalian cytotoxic cells.