NONSPECIFIC CYTOTOXIC RESPONSE AGAINST TUMOR TARGET-CELLS MEDIATED BYLEUKOCYTES FROM SEAWATER TELEOSTS, SPARUS-AURATA AND DICENTRARCHUS-LABRAX - AN ULTRASTRUCTURAL-STUDY

The in vitro cytotoxic reaction of leucocytes from the seawater teleos ts gilthead seabream (Sparus aurata) and sea bass (Dicentrarchus labra x) against tumor target cells was studied by transmission and scanning electron microscopy. Head-kidney, blood or peritoneal exudate leucocy tes were incubated with HeLa or B16 melanoma cells. After incubation, conjugates of leucocytes (effecters) and tumor cells (targets) were ob served. Both the effector-target cell binding and target cell lysis st eps of the cytotoxic process were characterized. Usually more than one effector was bound to the same target. The effecters exhibited ultras tructural features of either monocyte or lymphocyte cells. Monocyte-li ke effecters possessed an oval or kidney-shaped heterochromatinic nucl eus and a few granules. They were flattened against the targets over a broad area or, occasionally, made several punctuated contacts. Lympho cyte-like effecters had a large, rounded or indented nucleus, numerous free ribosomes and occasional cytoplasmic granules. These effecters e stablished spot contacts with the target. Contacts between monocyte-li ke and lymphocyte-like effecters were also recognizable. After incubat ion, some targets appeared virtually intact, while others had a smooth surface or showed cell processes and surface blebs. These ultrastruct ural changes in the targets are similar to those described as mediated by mammalian cytotoxic cells.