Epitope mapping of trans-sialidase from Trypanosoma cruzi reveals the presence of several cross-reactive determinants

Trypanosoma cruzi, the agent of Chagas' disease, expresses bans-sialidase, a unique enzyme activity that enables the parasite to invade host cells by transferring sialyl residues from host glyconjugates to the parasite's surf ace acceptor molecules. The enzyme is also shed into the surrounding enviro nment, causing apoptosis in cells from the immune system. During infections , an antibody response against the catalytic region of the trans-sialidase that is coincident with the control of the parasitemia and survival of the host is observed. This low-titer humoral response is characterized by its p ersistence for many years in benznidazole-treated patients. Here we analyze d the antigenic structure of the molecule by phage-displayed peptide combin atorial libraries and SPOT synthesis. Several epitopes were defined and loc ated on the three-dimensional model of the enzyme. Unexpectedly, cross-reac tion was found among several epitopes distributed in different locations di splaying nonconsensus sequences. This finding was confirmed by the reactivi ty of three monoclonal antibodies able to recognize non-sequence-related pe ptides that together constitute the surface surrounding the catalytic site of the enzyme. The presence of cross-reacting epitopes within a single mole cule suggests a mechanism developed to avoid a strong humoral response by d isplaying an undefined target to the immune system.