ULTRASTRUCTURE OF NONSPECIFIC CYTOTOXIC-CELLS IN TELEOSTS .1. EFFECTOR-TARGET CELL-BINDING IN A MARINE AND A FRESH-WATER SPECIES (SEABREAM,SPARUS-AURATA L, AND CARP, CYPRINUS-CARPIO L)

Background: Fish cytotoxic effecters form a cell population whose ultr astructure and properties of conjugation with target cells have not be en completely established. We report the ultrastructure of the nonspec ific cytotoxic cells in a seawater teleost (Sparus aurata L.) and comp are it to a freshwater species (Cyprinus carpio L,). Methods: Blood le ucocytes were incubated with HeLa or B16 melanoma cells. Samples were processed for transmission electron microscopic study. Results: Conjug ates consisting of leucocytes binding targets were regularly observed after 30 min, 1 hr, or 2 hr of incubation. In both species leucocytes binding to targets showed ultrastructural features of either monocyte- like or lymphocyte-like cells. Monocyte-like cells usually appeared fl attened against the targets and seemed to enclose fragments of the tar get to form cytoplasmic vesicles and the content of their scarce cytop lasmic granules seemed to be delivered into these vesicles. In the sea bream lymphocyte-like cells, dense cytoplasmic granules occurred only occasionally, and neither microvilli nor cell processes were present a t the contact areas with the targets. In the carp, the contacts were m ore numerous and formed regularly interdigitating contact areas and th e lymphocytes showed granules with characteristic dense and fibrillar contents. Conclusions: We conclude that seabream and carp have a leuco cyte cell population with ultrastructural features of either monocytes or lymphocytes showing nonspecific cytotoxic ability. (C) 1994 Wiley- Liss, Inc.