Ultrastructure of encapsulation of Schistosoma mansoni mother sporocysts by hemocytes of juveniles of the 10-R2 strain of Biomphalaria glabrata.

Dynamic aspects of the cellular responses of juvenile (2-3 mm shell diameter) 10-R2 strain Biomphalaria glabrata to newly penetrated Schistosoma mansoni (NIH-Sm-PR-1 strain) were studied at the ultrastructural level. As early as 3 hr postexposure (PE), host hemocytes had contacted the parasite's surface and by 7.5 hr, had phagocytosed sporocyst microvilli and small pieces of underlying tegument. Most sporocysts observed at 24 hr PE lacked tegumental cytoplasm, and germinal cells and other internal structures showed extensive pathological changes. By 48 hr, capsules were filled with hemocytes containing numerous, large phagosomes, and only scattered remnants of sporocyst material remained. Capsules were difficult to find at 4 days PE, suggesting that hemocytes participating in the encapsulation response had dispersed. Hemocytes responsible for the rapid and consistent destruction of S. mansoni sporocysts in the head-foot region typically formed extensive pseudopodia and contained large numbers of lysosomelike bodies, characteristics associated with granulocytes of B. glabrata. No evidence was found to suggest that hemocytes were lysed, or formed multinuclear syncytia, during the encapsulation response.