TRYPANOSOMA-CRUZI - IMMUNITY-INDUCED IN MICE AND RATS BY TRYPOMASTIGOTE EXCRETORY-SECRETORY ANTIGENS AND IDENTIFICATION OF A PEPTIDE SEQUENCE CONTAINING A T-CELL EPITOPE WITH PROTECTIVE ACTIVITY

In the present study, we investigate the immunoprotective properties o f trypomastigote excretory-secretory Ag (ESA) in experimental models. In the case of BALB/c mice, the immunization with ESA resulted in the reduction of parasitemia during acute infection and a significant leve l of protection in terms of mortality with more than 60% survival, whe reas none of the mice in the control groups survived after 39 days pos tinfection. The same experiments performed in Fischer rats showed a hi gh degree of protection against acute lethal infection with 100% survi val, whereas 20 to 40% of rats in the control groups survived the acut e phase of T. cruzi infection. Mouse and rat immune sera presented try panolytic activity against Trypanosoma cruzi infective forms, and reco gnized two major parasite components of 85 and 24 kDa. The analysis of specific isotype profiles showed a predominance of IgG1, IgG2a, and I gG2b antibody responses. Rat antisera to ESA were then used to screen a trypomastigote cDNA library. Several clones were identified, all of which encoded for the 24-kDa protein. Using a mAb (Tcr7) produced agai nst the native protein, the 31-kDa recombinant fusion protein was puri fied by affinity chromatography. The antisera to the recombinant prote in used in IFA and immunoelectron microscopy showed that the localizat ion of the 24-kDa protein differs among T. cruzi developmental stages. Protection experiments were performed in BALB/c mice using two synthe tic peptides (20-40 and 109-124) derived from the primary sequence of the 24-kDa polypeptide. The results obtained clearly indicated that th e peptide 109 to 124 containing a putative T cell epitope represents t he most protective epitope, which induced 30 to 50% of protection agai nst mortality during acute infection, whereas the percent survival in the control groups (OVA and 20-40 OVA peptide-immunized mice) was arou nd 16%. Moreover, analysis of T. cell proliferation in response to OVA -coupled peptides clearly indicated that only the 109 to 124 peptide h ad the capacity to induce the proliferation of T. cells from peptide-i mmunized mice. Interestingly, only the 109 to 124-coupled peptide indu ced the proliferation of T. cells from T. cruzi-infected mice.