Schistosoma mansoni in baboons. Antibody-dependent cell-mediated damage to 51Cr-labelled schistosomula

A technique is described for estimating cell-mediated damage to the larval stages of Schistosoma mansoni that occur in the mamalian host (schistosomula), by measuring release of 51Cr from labelled organisms. This technique, although widely used for assaying cytotoxicity to single cell suspensions or monolayers, has not previously been applied to a multicellular parasite. It is more objective than microscopical assays, and allows the processing of larger numbers of samples. The new method has been used for the detection and quantification of cell-dependent cytotoxic antibodies in infected baboons. The effector cell in normal baboon peripheral blood, as in man, is associated with a neutrophil- and eosinophil-enriched fraction. Cytotoxic antibodies appear in the serum about 4 weeks after a primary infection, rising to a peak at 7-10 weeks, and then declining. In some animals, a second rise towards 30 weeks was observed. There were no consistent differences between groups of baboons exposed to 1000 cercariae, 200 cercariae, and 200 cercariae administered at each of five monthly intervals. The possible relationship between cell-dependent cytotoxic antibodies and resistance to reinfection in infected animals is discussed.