Elevated agglutination titres in plasma of Biomphalaria glabrata exposed to Echinostoma paraensei: characterization and functional relevance of a trematode-induced response.
Production of elevated haemolymph agglutination titres by Biomphalaria glabrata following exposure to Echinostoma paraensei miracidia was investigated, to characterize this parasite-induced response and to understand its functional relevance. Both the dose of infection (1, 10 or 100 miracidia per snail) or the number of separate exposures to infection (between one and three, over a 4 or 8 day interval) were varied, and assuming a threshold dosage (10 miracidia per snail or higher) was exceeded, titres of juvenile snails peaked at 8-16 times the values for unexposed control snails, regardless of the exposure regimen. Adult snails, which are relatively refractory to infection, have slightly higher resting titres than juveniles, but exhibit only a 2- to 4-fold increase in titre following exposure. Juveniles exposed to infection but lacking demonstrable infection had lower titres than snails with confirmed infections. Exposure to infection increased heterogeneity of plasma agglutinins and provoked production of unique specificities not found in unexposed snails. However, the overall pattern of agglutination responses for snails with successfully developed parasites did not differ from those in which parasite development was unsuccessful. Agglutinating activity was inhibitable by several different monosaccharides, although plasma from infected snails was relatively unaffected by N-acetyl-glucosamine or N-acetyl-galactosamine. Wounding of snails provoked no change in plasma agglutination activity. As the highest agglutination titres were produced in snails with successfully developing parasites and agglutinin composition did not differ between snails with successful or unsuccessful parasites, the functional relevance of the response remains enigmatic. The production of unique agglutinins following exposure deserves additional study.