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Serum antibody responses of mice exposed to Philippine isolates of Schistosoma japonicum have been analysed by immunoprecipitation of exogenously radiolabelled antigens extracted from adult worms. Attention was focused on labelled protein antigens differentially recognized by sera of mice that differ genetically in their resistance status. Mice of the inbred strain 129/J can show high level resistance to first or repeated infection with S. japonicum. Even after six percutaneous administrations of 25 cercariae, approximately 50% of 129/J mice remain healthy with no or very few worms present in the portal system. Sera from 129/J mice exposed to S. japonicum consistently and differentially recognise an antigen of adult worms of mol. wt. 26,000. This antigen, termed Sj26, is not immunoprecipitated from S. mansoni adult worms by sera from resistant 129/J mice. Serum antibodies to Sj26 are present in at least some patients with a history of schistosomiasis japonica. Whether immune responses to Sj26 are involved directly in expression of resistance to S. japonicum remains to be determined. However, this antigen produced by cloned DNA in expression vectors, or isolated from adult worms, is an obvious candidate to be tested for vaccination efficacy in mice.

Summary The radioisotopic assay for acute granulomatous hypersensitivity (AGH) to eggs of Schistosoma japonicum in mice sensitized with eggs in adjuvant has been examined in the high responder strain. C57BL/6. Responsiveness is expressed as the lung‐kidney ratio of radioactivity in mice challenged intravenously with eggs and injected with 123I‐iododeoxyuridine, Eggs vary in their AGH sensitizing and eliciting potency; eggs proven to be superior in the circumoval precipitation (COP) test for detection of human serum anti‐S. japonicum antibodies are superior in the C57BL/6 AGH assay. CBA/H are non responders and BALB/c are low to intermediate responders and are thus different from C57BL/6 mice. Short‐term infected CBA/H mice are low COP antibody responders relative to infected C57BL/6 and titres of IgM anti‐egg antibodies are low in the CRA/H strain as determined in a solid‐phase radioimmunoassay (RIA). Following egg sensitization. CBA/H mice are also lower responders than C57BL/6 mice in terms of antibodies with the specificity of a COP‐positive IgM hybridoma‐derived antibody, P.41, measured in a competitive RIA. No evidence has been obtained that alteration of the response to the target epitope of P.41 alters the responsiveness of C57BL/6 mice to S. japonicum eggs. Thus, large amounts of injected P.41 antibody do not alter lung AGH and induced anti‐idiotype responses to the P.41 protein do not influence AGH in egg‐sensitized C57BL/6 mice. However, immunization of C57BL/6 mice with another IgM anti‐schistosome hybridoma antibody, 1.39, results in partial inhibition of lung AGH responsiveness. The nature of the effect of 1.39 immunization on AGH to eggs remains unknown, but further analysis of the phenomenon may lead to novel approaches to the control of granulomatous inflammatory disease in high responders.

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