T-cell responsiveness towards various synthetic peptides of the P28 antigen in rat and mouse models during Schistosoma mansoni infection.

It has recently been demonstrated that the Schistosoma mansoni P28 antigen can induce a strong protective immunity after direct immunization in various experimental models. T lymphocytes from Fischer rats immunized with the recombinant P28 antigen were cultured in vitro in the presence of seven synthetic peptides derived from the amino acid sequence of the P28. The most significant and reproducible proliferation was obtained with the 24-43 and 115-131 synthetic peptides. In order to analyze whether these located determinants were also exposed to the host's immune system during the natural S. mansoni infection or after immunization with crude antigenic extracts of various development stages of the parasite, the T-cell responsiveness of infected or immunized Fischer rats and BALB/c mice was tested towards these synthetic peptides. The results showed that, in both permissive (mouse) and non-permissive (rat) hosts, 24-43 and 115-131 synthetic peptides are recognized during the course of infection and that there is a dynamic variation of this recognition. These peptides are also recognized by T cells educated against crude antigenic extracts of different developmental stages of the parasite which contained the native form of the P28 molecule. Taken together, the results indicated that these synthetic peptides derived from the recombinant P28 antigen can activate T lymphocytes educated against the native P28 molecule during the development and maturation of the parasite in their hosts. Therefore, they might be useful for the construction of synthetic vaccines against schistosomiasis.