RESUMO
Protein and glycoprotein fractions are used for Chagas' disease diagnosis, but they are degraded by parasite endogenous proteases. Therefore protease inhibitors are used for their conservation increasing the antigen cost. The possibility of using protease-resistant glycosidic fractions could solve this problem allowing to obtain stable antigens, with a high sensitivity at a lower cost. This proposal is reinforced by the existence of anti-galactosyl antibodies against T. cruzi oligosaccharic fractions in sera from chagasic patients. The aim of this work was to obtain T. cruzi glycosidic fractions and to evaluate their possible use for Chagas' disease serologic diagnosis. Total protein and glycoproteins from the four stages of T. cruzi were obtained. The glycosidic fractions were obtained by exhaustive proteolysis with Proteinase K. Protein, glycoprotein and glycosidic profiles were analysed by SDS-PAGE followed by staining proteins (Coomassie/silver) or glycoproteins and glycosidic fractions (APABGP). Antigenicity of the different fractions was determined by Western Blot and luminography, using control hyperimmune serum anti-epimastigote and a "pool" of chagasic human sera. Finally, the capacity of the glycosidic fractions to discriminate chagasic and non-chagasic human sera and the sensitivity of the fractions respect to control serum, were determined by ELISA. Main findings were: a) there are peptides, glycopeptides and glycosidic fractions that are common and specific to parasite stages; b) there are more antigenic glycoproteins in epimastigotes and metacyclics than in trypomastigotes and amastigotes; c) there is a correlation between the glycosidic fraction-pattern and the host type; d) glycosidic fractions can be used as antigens to discriminate, by ELISA, chagasic and non chagasic patients, but show lower titers with respect to total proteic and glycoprotein antigens. It is concluded that it is possible to develop a diagnostic kit for Chagas' disease employing glycosidic fractions, eliminating the disadvantages of the current kits.
