Acquired immunity in schistosomiasis with purified Fasciola hepatica cross-reactive antigens.

We have previously demonstrated that a Fasciola hepatica-derived adult worm antigen, which is cross-reactive with Schistosoma mansoni and designated FhSmIII(M), induces resistance to challenge infection with S. mansoni in mice. The current review concerns the methods developed to isolate and partially characterize a major component of FhSmIII(M), a 12-kDa polypeptide, as well as immunity studies involving this antigen. Utilizing conventional gel filtration, followed by diethylaminoethyl (DEAE) Sephadex A-120 and monitoring the fractions by polyacrylamide gel electrophoresis (PAGE) and enzyme-linked immunoelectrotransfer blot techniques (EITB), we were able to isolate the 12-kDa antigenic polypeptide to homogeneity. Conventional gel filtration chromatography was followed by high-pressure, liquid anion, exchange chromatography, when highly purified material was needed, although the effective yields diminished drastically with the latter. Mice, rabbits and calves with a primary infection of F. hepatica developed antibodies (detectable in enzyme linked immunosorbent assay (ELISA) to the F. hepatica 12-kDa polypeptide within 2 weeks of infection. Mice with a primary infection of S. mansoni developed significant, but low, levels of anti-12-kDa antibodies by 7 weeks post-infection. Immunization of mice with microgram amounts of this 12-kDa polypeptide in Freunds' adjuvant resulted in the development of up to 77% less S. mansoni worms than the controls. Treatment with either endoglycosidase H, neuraminidase or dithiothreitol had no effect on the protein's mobility on sodium dodecyl sulfate (SDS)-PAGE or in its recognition by antibodies, suggesting the absence of carbohydrate moieties or disulphide bonds in relation to its antigenic determinants. Degradation by proteinase K further confirmed its polypeptide nature and points to recombinant DNA technology for the large-scale manufacture of this potential vaccine. Further use of this antigen in immunity studies should greatly contribute to the clarification of the mechanisms involved in cross-resistance against schistosomiasis.

Successful vaccination against murine Schistosoma mansoni infection with a purified 12 Kd Fasciola hepatica cross-reactive antigen.

A 12 Kd antigen was isolated from Fasciola hepatica adult worm extracts by gel filtration in Sephadex G-50 and ion exchange chromatography using DEAE Sephadex A-120. Mice immunized with this Fasciola-derived 12 Kd antigen developed antibodies to Schistosoma mansoni adult worm extracts, demonstrating its cross-reactivity with schistosomes. Vaccination of mice with microgram amounts of the antigen in Freund's adjuvant induced up to 77% reduction in worm burdens after challenge with S. mansoni cercariae. F. hepatica 12 Kd degraded by proteinase K to lower molecular weight polypeptides which still retain their antigenicity as determined by the enzyme-linked immunoelectrotransfer blot technique. Treatment with either Endoglycosidase H, neuraminidase, or dithiothreitol had no effect on its mobility in sodium dodecyl sulfate polyacrylamide gels, or in its recognition by antibody, suggesting the absence of carbohydrate moieties or disulphide bonds in relation to its antigenic determinants and also suggesting that the antigen is a pure polypeptide. These studies establish that a molecularly defined cross-reactive component of one parasitic trematode (F. hepatica) induces resistance to challenge infection with another parasitic trematode (S. mansoni). Its polypeptide nature makes recombinant DNA technology an alternative for the manufacture of a vaccine.