Recombinant tumour necrosis factor inhibits malaria parasites in vivo but not in vitro.

As tumour necrosis serum kills malarial parasites in vitro and inhibits the multiplication of some species of Plasmodium in mice, we examined the effect of recombinant mouse tumour necrosis factor (rTNF) on P. yoelii both in vitro and in vivo. Parasites incubated overnight with rTNF showed no loss of viability, but repeated injection of rTNF into infected mice reduced parasitaemia and significantly prolonged survival of mice infected with a lethal variant of the parasite. We conclude that TNF acts on blood-stage malaria in vivo via a host cell and that another molecule in tumour necrosis serum is involved in killing the parasite in vitro.