Induction of target cell apoptosis by channel catfish cytotoxic cells

This study examines cytotoxic mechanisms used by channel catfish peripheral blood-derived effector cells. Transmission electron microscopy (TEM), coup led with [H-3]thymidine DNA fragmentation (JAM) and terminal deoxynucleotid yl nick-end labeling (TUNEL) assays, provided the first evidence that catfi sh peripheral blood cytotoxic effecters killed allogeneic targets via an ap optotic pathway. TEM demonstrated that the effector cell population present within peripheral blood leukocytes (PBLs) was composed of agranular lympho cytes that formed conjugates with, and induced apoptosis in, allogeneic tar get cells. Both JAM and TUNEL assays showed that PBLs induced target cell D NA fragmentation within 1 h of coculture. In addition, fixed effecters did not induce target cell necrosis or apoptosis, and target cell lysis was com pletely inhibited by chelation of free Ca2+ by EGTA. These results suggest that catfish peripheral blood-derived effector cells utilize a secretory me chanism rather than a ligand-based mechanism to trigger apoptosis. (C) 1999 Academic Press.