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.