Analyzing Nonspecific Cytotoxic Cells in Fish

The nonspecific cytotoxic cell (NCC) is believed to be the evolutionary precursor of the mammalian natural killer (NK) cell. Evidence for a phylogenetic linkage between NCCs of teleost fish and NK cells from higher vertebrates was first obtained functionally; that is, NCCs lyse many of the same target cells as human (K562), mouse (YAC-1) and rat NK cells (1 ,2 ). The best parallels between NK and NCC are found in the target cell recognition of NCC vs adherent lymphokine (interleukin-2 [IL-2]) activated killer cells (ALAK). Both ALAK and NCC kill promiscuously. Their wide range of targets include many different histological types of allogeneic tumor cells, xenogeneic tumor targets, protozoan parasites, as well as certain virus transformed cells (3 ,4 ). Beyond the observations that both types of cells kill the same targets, two other properties link NK cells with NCC.