Cell-free synthesis of Schistosoma mansoni surface antigens: stage specificity of their expression

Messenger RNA has been extracted from all stages of the life cycle of the parasitic multicellular helminth Schistosoma mansoni. In vitro translation of these mRNA preparations in rabbit reticulocyte lysates yielded in each case a large number of polypeptides. Immunoprecipitation of translation products either by serum from immune mice or from human patients demonstrated that relatively few, approximately 10, polypeptides are recognised as antigens. Two of the in vitro synthesised antigens, of mol. wts. 22 000 and 14 000, were demonstrated to correspond to schistosomula surface antigens. The expression of these antigens may show stage specificity. Both are readily detected from adult and sporocyst translation products, neither from schistosomula and only the 22 000 antigen from miracidia. This is an unexpected finding since similar polypeptide antigens occur on the surface of schistosomula. These results indicate that not only are schistosomula surface antigens preformed at the preceding sporocyst stage, i.e., within the snail host, but they also remain invariant throughout the life cycle in the vertebrate host. Two other prominent schistosomula surface antigens of mol. wts. 38 000 and 32 000, were not recognised amongst cell-free translation products directed by RNA from any life cycle stage. The demonstration that at least two schistosomula surface antigens are detectable amongst adult mRNA cell-free translation products demonstrates the feasibility of identifying the genes encoding them in cDNA libraries from adult worm mRNA.