In vitro killing of S. mansoni schistosomula by lymphokine-activated mouse macrophages

Inflammatory macrophages from mice i.p. injected with FCS 24-hr before harvesting, activated by partly purified MAF from Con A-stimulated spleen cells, were shown to kill an average of 60.9% (SE +/- 5.3) of the parasites in cultures of Schistosoma mansoni schistosomula. On the contrary, resident macrophages were not cytotoxic under the same conditions. The degree of macrophage activation for the killing was dependent upon both lymphokine concentration and time of incubation in lymphokine. The capacity of macrophages to be activated to kill schistosomula as well as the schistosomulicidal activity of the lymphokine-activated macrophages were short-lived properties. The killing was strongly influenced by the effector-to-target ratio. The results are consistent with other data on the immune response in experimental infection and particularly the development of the delayed hypersensitivity. Therefore, among the immune mechanisms that participate in immunity to reinfection, cell-mediated immunity that involves inflammatory macrophages should no longer be restricted to microorganisms and protozoans and could be extended to multicellular parasites like schistosomes.