The interferon compartment of the immune response in human malaria: I. Interferon inducers in Plasmodium falciparum cultures.

The present study concerns the interferon (IFN) compartment of the immune response in human malaria. It was undertaken with Plasmodium falciparum parasitized human red blood cell culture supernatants (PF-RBCS). Investigations were conducted in order to verify whether supernatants of such protozoa cultures had the capacity to induce gamma interferon previously identified in sera of P. falciparum infected patients and to verify whether a T-cell mitogen recently characterized in vitro could be correlated with the eventual IFN-inducing activity. Investigations were performed with nonsynchronized P. falciparum cultures and highly synchronized PF-RBC cycles. Results obtained with the first type of experiment demonstrated the presence of an immune interferon inductor in PF-RBCS controlled for their positive mitogenic activity. In supernatants from highly synchronized PF-RBC cycles it was possible to further correlate the mitogen activity with the capacity to induce IFN-gamma. Both activities were found in the time-interval situated near the end of the parasite cycle shortly previous of the merozoite stage. At an earlier time, at the peak of the ring stage, when no mitogen activity was detected, an interferon-induction activity, solely of IFN-alpha, was also demonstrated.