Acquisition of host antigens by young Schistosoma mansoni in mice: correlation with failure to bind antibody in vitro.

Young schistosomes collected after penetration through isolated mouse skin (3 h schistosomula) were cultured in medium containing immune rhesus monkey serum with a high titre of antibody known to kill schistosomula in the presence of complement. Morphological signs of damage in electron micrographs were confined to the surface tegument of the schistosomula. Antibodies in immune rhesus serum were shown to bind to the surface membrane of 3 h schistosomula using an antibody-enzyme bridge technique involving labelling with horseradish peroxidase and histochemical localization of the enzyme at the ultrastructural level. Schistosomula recovered from the lungs of mice 4 days after infection did not bind monkey antibodies at the surface and these 4-day schistosomula are not susceptible to damage by immune serum in vitro. Mouse erythrocyte antigens were detected on the surface of 4-day schistosomula using an appropriate antibody-enzyme bridge but these host antigens could not be found on 3 h schistosomula. This correlation between the presence of mouse host antigens on the surface of schistosomula and the inability of immune monkey antibodies to bind to the surface membrane is consistent with the hypothesis that host antigens are acquired by young schistosomes and serve to protect the surface membrane against antibody-mediated damage.