Heterogeneity of channel catfish CTL with respect to target recognition and cytotoxic mechanisms employed

Two types of catfish alloantigen-dependent cytotoxic T cells were cloned fr om PBL from a fish immunized in vivo and stimulated in vitro with the allog eneic B cell line 3B11. Because these are the first clonal cytotoxic T cell lines derived from an ectothermic vertebrate, studies were undertaken to c haracterize their recognition and cytotoxic mechanisms. The first type of C TL (group 1) shows strict alloantigen specificity, i.e., they specifically kill and proliferate only in response to 3B11 cells. The second type (group II) shows broad allogeneic specificity, i.e., they kill and proliferate in response to several different allogeneic cells in addition to 3B11. "Cold" target-inhibition studies suggest that group II CTL recognize their target s via a single receptor, because the killing of one allotarget can be inhib ited by a different allotarget. Both types of catfish CTL form conjugates w ith and kill targets by apoptosis. Killing by Ag-specific cytotoxic T cells (group 1) was completely inhibited by treatment with EGTA or concanamycin A, and this killing is sensitive to PMSF inhibition, suggesting that killin g was mediated exclusively by the secretory perforin/granzyme mechanism. In contrast, killing by the broadly specific T cytotoxic cells (group II) was only partially inhibited by either EGTA or concanamycin A, suggesting that these cells use a cytotoxic mechanism in addition to that involving perfor in/granzyme. Consistent with the presumed use of a secretory pathway, both groups of CTL possess putative lytic granules. These results suggest that c atfish CTL show heterogeneity with respect to target recognition and cytoto xic mechanisms.