Neutrophilic granulocytes in carp, Cyprinus carpio, possess a spontaneous cytotoxic activity.

This study demonstrates for the first time that carp (Cyprinus carpio) neutrophilic granulocytes from the head kidney possess potent spontaneous cytotoxic activity against several human tumor cell lines. Carp head kidney cells isolated at a density of 1.09 g/mL contained more than 90% neutrophilic granulocytes. These cells were round and approximately 10 millimicrons in diameter with reniform or polymorphic nuclei and slightly eosinophilic cytoplasm when stained with Giemsa. Electron microscopy revealed that the cytoplasm contained numerous oval granules, some of which contained a dense rod-shaped core. The neutrophilic granulocytes readily formed conjugates with the human target cells and rapidly killed them. The neutrophilic granulocytes killed human derived target cells better than murine derived target cells. Inhibition of cytotoxicity by catalase suggested that the production of H2O2 is involved as a mediator in the cytotoxic reaction. The size and granularity of the carp effector cells indicate that they are different from the small agranular nonspecific cytotoxic cells (NCC) described in the channel catfish.