Carbohydrate inhibition of Biomphalaria glabrata embryonic (Bge) cell adhesion to primary sporocysts of Schistosoma mansoni

Due to shared characteristics with snail haemocytes, the Biomphalaria glabrata embryonic (Bge) cell line has been used as a model in vitro system for the study of snail-trematode interactions. In this study Bge cells were used to characterize the adherence of snail host cells to schistosome primary sporocysts, and to test the effect of carbohydrates as inhibitors of this behaviour. Bge cells bound to the surface of > 90% of Schistosoma mansoni sporocysts and, based on a semi-quantitative cell adhesion scale of 1-4, exhibited a cell adhesion index (CAI) of 2.45. This cellular adhesion was significantly inhibited in the presence of selected carbohydrate-containing substances. Fucoidan,vas the most potent inhibitor, reducing Bge cell-binding prevalence to approximately 50% and the CAI to 1.6. Other inhibitory compounds included mannose-6-phosphate, heparin, dextran sulfate, and various forms of the polysaccharide carrageenan. Fluoresceinated-fucoidan was found to attach to Bge cells confirming their ability to associate with sugar moieties. These results were further supported by the specific binding of surface biotinylated Bge cell proteins to sporocyst tegumental glycoproteins ranging from 40 to 120 kDa. X-linked tegumental carbohydrates appeared to represent ligands for Bge cell proteins since N-glycosidase treatment of blotted tegumental glycoproteins completely abolished biotinylated Bge protein binding. We hypothesize that the involvement of lectins as potential host cellular receptors in snail cell-sporocyst interactions, and suggest that negatively charged (mainly sulfated) carbohydrate moieties may represent the schistosome surface ligand(s).