Schistosoma mansoni: further studies of the interaction between schistosomula and granulocyte-derived cationic proteins in vitro.

Purified eosinophil and neutrophil cationic proteins isolated from the lysosomal secretion granules of human leucocytes have been tested for cytotoxic capacity against lung-stage schistosomula of Schistosoma mansoni in vitro. Eosinophil cationic protein (ECP) caused paralysis but not death at high concentration; this effect was reversible and involved no gross pathological manifestations. Eosinophil protein X (EPX) and neutrophil cationic protein (NCP) were highly toxic at concentrations of 10(-5) mol/l, and induced paralysis at sublethal concentrations. These two proteins exerted their cidal effect principally against the subtegumental musculature and internal tissues of the parasite rather than against the surface syncytium and tegumental outer membrane. ECP and NCP were shown to bind to lung worms at paralysing concentrations, but this binding occurred independently of the charge on the parasite surface. Of several control proteins tested, only protamine was capable of destroying lung-stage parasites; the manifestations of damage were different, however, from those induced by the granulocyte-derived proteins. Parallel assays demonstrated that EPX also possessed cytotoxic capacity against newly transformed schistosomula, but it was less efficient than ECP in this respect. The data are discussed in relation to potential post-skin mechanisms of challenge attrition in the immunized host.