Malarial parasites and tumour cells are killed by the same component of tumour necrosis serum

Tumour necrosis serum (TNS), from animals primed with macrophage activating agents and challenged with endotoxin, causes necrosis of some tumours and can kill certain tumour lines in vitro and malarial parasites in vitro and in vivo. We have tested the possibility that the same factor is responsible for killing both tumour cells and malarial parasites. In competitive inhibition experiments, parasitized erythrocytes, but not normal erythrocytes, inhibited the cytotoxicity of TNS against a tumour cell line. Conversely, the tumour cells inhibited the killing of Plasmodium yoelii in vitro by TNS. When rabbit TNS was fractionated by ion exchange chromatography followed by gel filtration and the fractions at each step were pooled according to their ability to kill the tumour cells, in vitro parasite killing activity was found to correlate with tumour cell cytotoxicity, to a final sample which was purified more than 600-fold. Our results suggest that in terms of function, at least, the same component of TNS is responsible for the killing of both tumour cells and malarial parasites.