Schistosoma mansoni: identification and protective immunity of adult worm antigens recognized by T lymphocytes of outbred Swiss mice immunized with irradiated cercariae.

Percutaneous exposure of outbred Swiss mice to 500 Schistosoma mansoni (Egyptian strain) cercariae attenuated by 25,000 rad gamma radiation, twice at a 4-week interval, led to 80% protection against challenge with 100 live unattenuated cercariae compared to unimmunized control mice. The S. mansoni molecules that induce protective immunity in this model are not as yet identified. The capacity of an immunogen to induce efficient protective immunity depends largely on its T-cell-activating potential, as T cells are required both for eliciting long-lasting antibody formation and for antibody-independent cell-mediated immunity. To define such T cell antigen in S. mansoni, soluble adult worm antigens (SAWA) were separated by SDS-PAGE and electrotransferred onto nitrocellulose paper. Thirteen bands, identified by their M(r) were tested in T cell Western assays for their ability to stimulate proliferation of lymph node cells from 23 mice immunized with irradiated cercariae for the second time 2-5 weeks earlier. Lymphocytes from all mice responded to only a few (maximum of 6) bands. The response rate for the 13 SAWA bands tested ranged from 0-43%. These findings suggest a heterogeneity in T cell responses of individual mice to each of the SAWA bands and have implications that should be considered in the selection of immunogens to be assayed for anti-Schistosomiasis mansoni protective capacity. A highly significant protection against S. mansoni challenge in outbred Swiss mice was obtained exclusively following vaccination with a cocktail of soluble adult worm T cell immunogens that are recognized by 30-40% of individuals.