Polypeptides synthesized in vitro by Biomphalaria glabrata hemocytes bind to Schistosoma mansoni primary sporocysts.

In vitro labeled polypeptides secreted by schistosome-susceptible and -resistant Biomphalaria glabrata were tested for their ability to bind the surface tegument of Schistosoma mansoni primary (= mother) sporocysts. Out of a complex pattern of SDS-PAGE-separated hemocyte polypeptides, only two (19 and 46 kDa) bound to sporocysts. The 19-kDa polypeptide consistently bound to both live and fixed sporocysts, although fixed larvae usually bound more than living sporocysts. The 46-kDa component bound primarily to fixed sporocysts. A similar pattern of binding was seen when sporocysts were exposed to polypeptides secreted into culture medium by both resistant and susceptible snail hemocytes. However, previous work indicates that sporocyst secretory products, in the presence of homologous snail plasma components, can differentially influence the quantity of these two polypeptides. Therefore, it is hypothesized that "regulation" of the interaction of snail hemocyte polypeptides with the parasite may lie in the sporocyst-mediated differential effect on synthesis and/or secretion of the 19- and 46-kDa polypeptides by hemocytes of these two snail strains. Thus, the hemocyte polypeptides reported in this study may represent potential mediators of self/non-self-recognition or hemocyte activation in the B. glabrata internal defense system.