CYTOTOXIC ACTIVITY GENERATED FROM CHANNEL CATFISH PERIPHERAL-BLOOD LEUKOCYTES IN MIXED LEUKOCYTE-CULTURES

In previous work, lysis of allotargets was routinely observed with PBL from nonimmune channel catfish. In the work reported here, greatly in creased (similar to 100-fold) cytotoxic responses were generated by st imulation of channel catfish PBL with irradiated cells of allogeneic c loned B cell lines in mixed leukocyte cultures (MLC). This increased c ytotoxicity did not appear to be simply a consequence of cell prolifer ation since stimulation of catfish PBL proliferative responses with po lyclonal mitogens did not result in increased lysis. Somewhat surprisi ngly, the MLC-generated cytotoxicity did not exhibit allospecificity; i.e., allogeneic targets from other fish were as susceptible to lysis as were the cells used as stimulators. This apparent lack of allospeci ficity in MLC-generated cytotoxicity was confirmed by ''cold'' target inhibition assays. However, autologous targets were not killed, clearl y demonstrating that MLC-generated effecters could distinguish ''self' from ''nonself' at the level of lysis/recognition. Although their ori gin is unresolved, the MLC-generated effecters may be a source of high ly enriched fish cytotoxic cells and thus facilitate directly addressi ng questions pertaining to the evolution of such cells. (C) 1997 Acade mic Press.