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

Previous workers have reported that significant resistance to Schistosoma mansoni cercarial challenge can be induced in mice by immunization with various Fasciola hepatica antigen preparations. We have attempted to reproduce these observations and have also carried out similar experiments in rats. In our hands, however, CBA mice did not develop either antibodies against the schistosomular surface, or significant resistance to challenge after immunization with heterologous antigens. Similar results were obtained in Fischer rats, but rats did develop significant resistance after immunization with homologous (schistosomular) antigens, even without adjuvant, and the homologous 'protective' antigens could be separated by antibody-affinity chromatography using serum from rats vaccinated with irradiated cercariae. Thus, we found no evidence for the existence of shared 'protective' antigens between S. mansoni and F. hepatica, and suggest that this is further evidence that where heterologous resistance can be demonstrated between these two parasites, it is probably due to immunologically non-specific mechanisms.