A purified 28,000 dalton protein from Schistosoma mansoni adult worms protects rats and mice against experimental schistosomiasis.

We have purified a 28,000 dalton (P28) protein from Schistosoma mansoni adult worms and used it to immunize Fischer rats. Immunofluorescence assays demonstrated that the P28 antigen was mainly located in the parenchyma of the schistosomulum and of the adult worm, including the dorsal spines of the parasite. Western blot analysis revealed that this antigen was present in three species of schistosomes: S. mansoni, S. japonicum, and S. bovis. The antibody response raised against this protein was able to kill S. mansoni schistosomula in in vitro cytotoxicity assays in the presence of rat eosinophils. The inhibition of this cytotoxic activity by an aggregated myeloma IgG2a indicated that one of the major isotypes involved in this in vitro model is IgG2a. The passive transfer of P28 antisera induced a significant level of protection against experimental infection. Moreover, we have immunized Fischer rats and BALB/c mice with the purified 28,000 dalton protein and observed a marked decrease (up to 70%) in the parasite burden in both experimental infection models.