Characteristics of protective immunity in mice induced by drug-attenuated larvae of Schistosoma mansoni. Antigen localization and antibody responses.

Partial resistance to reinfection developed in mice with immature infections of Schistosoma mansoni treated with the drug Ro11-3128, whereas mice vaccinated with irradiated cercariae and treated in a similar way did not become immune. Persistence of drug-treated parasites in the skin and draining lymph nodes, which prolonged the opportunity for efficient Ag presentation, was necessary for the development of protective immunity. Death and clearance of parasites solely in the skin, was not sufficient to induce protection. The expansion in the number of lymphocytes in the skin-draining nodes after vaccination, was reflected in the contrasting levels of resistance induced by the different drug-treatment regimes. Challenge parasites were eliminated predominantly after they reached the lungs. An investigation of antibody reactivity revealed an immunodominant response against a doublet of Ag of Mr 97 to 99 kDa. Recognition of this complex by antisera from different groups of mice was not related to their immune status. Western blots and inhibition analysis showed that this doublet has epitopes in common with the Sm97/paramyosin protective Ag, originally identified by antisera reactivity from mice immunized with a nonliving vaccine.