In vitro encounters between Schistosoma mansoni primary sporocysts and hemolymph components of susceptible and resistant strains of Biomphalaria glabrata.

Encounters between axenically transformed sporocysts of the Puerto Rican 1 strain of Schistosoma mansoni and hemocytes and plasmaaa components of susceptible "M line" and resistant 10-R2 and 13-16-1 strains of Biomphalaria glabrata were studied in vitro. After 24 hours of incubation in susceptible hemolymph components, 94.4% of 36 observed sporocysts retained normal structure, whereas 9l.6% of 48 sporocysts were destroyed after 24 hours of incubation in resistant hemolymph components. Sporocysts preincubated for 6 hours in susceptible plasm were destroyed when subsequently incubated with resistant hemocytes in susceptible plasma. Sporocysts preincubated in resistant plasma were not destroyed when subsequently incubated with susceptible hemocytes and plasma. Susceptible hemocytes preincubated in resistant plasma, and then incubated for 24 hours with sporocysts in the presence of susceptible plasma were incapable of inflicting damage. The simultaneous incubation of sporocysts with susceptible hemocytes and resistant plasma produced variable results. The predominant trend was sporocyst destruction in five replicates and lack of substantial damage in six replicates. Results of these and previous experiments imply that differences between susceptible and resistant strains of snails in their ability to destroy sporocysts in vitro can be attributed primarily to differences in their hemocytes, although plasma factors may alter these responses in some cases. The results also suggest that if sporocysts do acquire a coat of host plasma components, this strategy is by itself insufficient to account for the persistence of sporocysts in susceptible snails.