In the present study, we investigate the immunoprotective properties of 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 level of protection in terms of mortality with more than 60% survival, whereas none of the mice in the control groups survived after 39 days postinfection. The same experiments performed in Fischer rats showed a high degree of protection against acute lethal
infection with 100% survival, whereas 20 to 40% of rats in the control groups survived the acute phase of T. cruzi
infection. Mouse and rat
immune sera presented trypanolytic activity against Trypanosoma cruzi infective forms, and recognized two major parasite components of 85 and 24 kDa. The analysis of specific isotype profiles showed a predominance of
IgG1,
IgG2a, and
IgG2b 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 against the native
protein, the 31-kDa
recombinant fusion protein was purified by affinity chromatography. The
antisera to the
recombinant protein used in IFA and immunoelectron microscopy showed that the localization of the 24-kDa
protein differs among T. cruzi developmental stages. Protection experiments were performed in BALB/c mice using two synthetic
peptides (20-40 and 109-124) derived from the primary sequence of the 24-kDa
polypeptide. The results obtained clearly indicated that the
peptide 109 to 124 containing a putative
T cell epitope represents the most protective
epitope, which induced 30 to 50% of protection against mortality during acute
infection, whereas the percent survival in the control groups (OVA and 20-40 OVA
peptide-immunized mice) was around 16%. Moreover, analysis of T cell proliferation in response to OVA-coupled
peptides clearly indicated that only the 109 to 124
peptide had the capacity to induce the proliferation of T cells from
peptide-immunized mice. Interestingly, only the 109 to 124-coupled
peptide induced the proliferation of T cells from T. cruzi-infected mice.