Schistosoma mansoni: Cytotoxicity of hemocytes from susceptible snail hosts for sporocysts in plasma from resistant Biomphalaria glabrata

Sporocysts of Schistosoma mansoni (PR1 strain) survive and grow in Biomphalaria glabrata PR albino strain snails, whereas they are encapsulated and die in B. glabrata 10R2 strain snails. These processes also occur in an in vitro system in which the only living cells are those of sporocysts and snail hemolymph. Hemocytes of the susceptible snail are normally not effective in damaging sporocysts. However, when the encounter occurred in the presence of cell-free plasma from resistant snails, previously impotent hemocytes severely damaged sporocysts in 24 hr. The cytotoxic capacity of resistant strain hemocytes was not altered by plasma from susceptible snails. Furthermore, it was retained even when plasma was replaced by culture medium free of snail components. The nature of the plasma factor(s) which facilitated damage by otherwise impotent hemocytes is discussed, and evidence is evaluated for the hypothesis that snail resistance is dependent upon the specificity of cytophilic factors present both in the plasma and on the hemocyte plasma membranes.