Variation in susceptibility of Schistosoma mansoni to damage by polycations.

We have studied the characteristics of binding of the polycation poly-L-lysine to the schistosome surface. Two consequences of this binding were measured: (a) tegumental damage, as assessed by the uptake of the DNA binding stain Hoechst 33258, and (b) the effect of cation binding on the uptake of a lipid analogue, 5-(N-octadecanoyl) aminofluorescein. Schistosomes were incubated with a preparation of eosinophil cationic proteins; these naturally occurring polycations bound to and damaged the parasites in a manner similar to poly-L-lysine. The different developmental stages of the parasite vary in the degree to which the poly-L-lysine binds, in susceptibility to tegumental damage, and in the degree to which lipid uptake is affected. The lung stage is most resistant to damage, and 3-week-old worms are the most susceptible. The teguments of male and female adult worms differ in the binding of the poly-L-lysine. Individual schistosomula, and batches of schistosomula shed at different times, show non-genetic variation in binding and susceptibility to damage. These findings may relate to variation in immune killing in vivo.