Immunogenicity and phylogenetic relationship of tapeworm antigens produced by Hymenolepis nana and Hymenolepis diminuta.

The tapeworms and share three major antigens in the cell sap. Two of these show identical specificity while the third exhibits common as well as uncommon determinants peculiar to the dwarf tapeworm, . Shared antigens are not, however, immunogenic during infection of mice with the dwarf tapeworm although there is a well defined response to specific antigens. On the other hand infection of rats with elicits a weak response yielding serum antibodies which cross-react with the dwarf tapeworm. Cross-reactive antibodies engendered in rabbits against worm homogenates are insensitive to mercaptoethanol treatment whereas non-cross-reactive antibodies present at 3 weeks post-infection with the dwarf tapeworm are primarily IgM globulins. The rapid formation and subsequent release of these antigens may relate to a persistence of immunogenicity. Antibody levels reach a peak after a 4-week period of infection and the drop in titre observed at 6 weeks is preceded by a reduction in worm load. Resistance to infection following artificial immunization with worm homogenates is consistent with that developed as a result of actual infection with the dwarf tapeworm. Over one-half of mice immunized did not become infected following challenge with ova. Worm loads of mice that did become infected were reduced to approximately 1 per cent that of non-immunized animals.