Reevaluation of the potential of Fasciola hepatica antigens for immunization against Schistosoma mansoni infection

Value of Haemonchus longistipes purified antigens in diagnosis of gastro-intestinal nematodes infection in camels

Fractionated Haemonchus longistipes crude antigen revealed 7 protein fractions at molecular weights of 93, 74, 67, 56, 32, 26 and 16 kDa. The bands at 56, 32 and 26 kDa reacted specifically with H. longistipes hyperimmune sera prepared in rabbit (1:100 dilution) using EITB technique. The eluted concentrated fractions as well as crude worm antigens were used in diagnosis of natural infection of Gastro-Intestinal Nematodes (GIN) only or associated with other parasites in camels using ELISA technique. H. longistipes crude antigen and fraction of 26 kDa induced high sensitivity in diagnosis of infection in animals harboring GIN only (sensitivity was 95-100%), while it was 85.0-93.3% with 32 kDa fraction and 55.5-73.3% with that of 56 kDa using ELISA technique. The two H. longistipes eluted protein fractions of 26 and 32 kDa showed higher sensitivity than their crude antigens in diagnosis of GIN infection mixed with other parasites. While, Protein bands of 26 kDa appeared more sensitive than the other protein bands in detection of anti- H. longistipes antibodies at higher serum dilution. With special superiority for fraction of 26 kDa, in comparison with the other antigens, sharp specificity or sensitivity in diagnosis, could not be achieved in this study especially in case of mixed infection with other parasites, where these animals might be immune-compromised.

Higher levels of passive compared with active immunity in rats immunized with larval antigens of Schistosoma mansoni

We have previously shown that it is the lung stage schistosomulum which is both the inducer and the target of immunity in rats vaccinated with irradiated cercariae but that rats can also be partially protected by immunization with detergent extracts of mechanically-transformed schistosomula. In the present study we therefore compared the immunogenicity of these and intermediate schistosomular stages. In the first experiment low levels of protection (13-24%) were induced by extracts of mechanically-transformed schistosomula cultured for 3 hours or 2 days but not by extracts of lung schistosomula. In a repeat experiment insignificant levels of protection were induced by extracts of 3 h schistosomula and lung schistosomula were again non-protective. Nevertheless, high levels of anti-schistosomula antibodies were demonstrated and sera from actively immunized rats conferred significant passive protection in five out of six trials. The levels of protection conferred by passive immunization (26-51%) were in each case higher than the levels of protection demonstrated in the respective serum donor groups, showing that some form of immunological blockade suppression is operating to prevent expression of protective immunity in the actively immunized rats.

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.