Glycosidase activities in plasma of naive and schistosome-infected Biomphalaria glabrata (Gastropoda)

Activity of the following glycosidases was detected in the plasma of the fr eshwater snail Biomphalaria glabrata: beta-D-fucosidase, P-D-glucosidase, P -D-galactosidase, P-D-mannosidase, P-D-glucuronidase, N-acetyl-beta-D-galac tosaminidase, N-acetyl-beta-D-glucosaminidase, and lysozyme. At the physiol ogical pH (7.2-7.4 ) of snail haemolymph, enzymatic activity was about 10-5 0 % of the maximum activity at each enzyme's respective acid pH-optimum. Sc histosome-susceptible B. glabrata showed lower plasma protein concentration and significantly lower enzymatic activities (U/mg protein) than schistoso me-resistant snails. Changes in glycosidase activity levels correlate with the progress of infection. After successful schistosome invasion, activitie s of plasma glycosidases but not the concentration of total plasma proteins increased significantly during the first 2 days in both snail strains. Thu s, most tegumental glycoproteins of schistosome larvae can be altered by hu moral host glycosidases. The detection of only very low activities of hexos aminidases leads to the hypothesis that GalNAc/GlcNAc may be involved in th e process of non-self recognition. At 4 days post-infection, glycosidase ac tivities were identical or slightly below the levels found in naive snails. ,At this time of infection the parasite is encapsulated and destroyed by ha emocytes of resistant snails. In susceptible snails, however, the schistoso mes have transformed into sporocysts and will complete their life-cycle wit hout eliciting effective defence reactions. After > 30 days post-infection, when cercariae are fully developed in susceptible snails, plasma protein c oncentration decreased significantly, whereas glycosidase activities were e levated.