Immunobiochemical significance of Trypanosoma rangeli in the study of Trypanosoma cruzi

Abstract: Trypanosoma rangeli is a haemoflagellate that infects humans nonpathogenicallyin some areas in which T. cruzi, the causative agent of Chagas' disease, is endemic.Since common biological and immunochemical characteristics have been described forthese parasites, a detailed study of their relationship is needed. In the presentwork, experimental murine infections demonstrated that T cruzi induces antibodiesthat recognize several T. rangeli antigenic polypeptides. In the same manner, antibodiesgenerated by T. rangeli infections recognize T. cruzi antigens. It is suggested thatthe IgM isotype is the predominant immunoglobulin produced during a T. rangeli infection,these antibodies also present cross-reactivities with T. cruzi antigens. Biotin labellingof surface proteins and the recognition of polypeptides by labelled lectins havedemonstrated the existence of a heterogeneous T. rangeli population and permitteddiagnostic indentification of both species. Immunoblotting analysis, using anti-T. rangeli and anti- T. cruzi antibodies, suggest 50% antigenic similarity betweenthese parasites. Nevertheless, antigens of 38, 43 and 48 KDa were identified as specificT. rangeli polypeptides. These fractions were purified, used for immunization ofmice and basically characterized. By immunoblotting analysis these molecules werenot detected in T. cruzi epimastigotes and Leishmania sp promastigotes. The moleculeof 38 Kda presents common and specific antigenic moieties, most of which are carbohydrates.Peptide mapping revealed that there are differences in the numbers and sizes of recognizedpeptides of T. rangeli (Trp38) and T. cruzi (Tcp38) proteins. The Trp48 is expresseduniformly by the T. rangeli cell population during axenic culture, a particular subcellularlocalization being proposed for this antigen. The antigenic relationship betweenT. rangeli and other trypanosomatids (5 genera) was also evaluated. The results demonstratethat several proteins are widely expressed among trypanosomatids (eg. 34, 29 and20 KDa), while others are more restricted to the genus Trypanosoma (41 and 24/23KDa). Finally, the antigenic characterization and releasing conditions of a T. rangelisialidase was investigated, demonstrating that the enzyme is secreted until supposedlysaturating extracellular levels are reached, perhaps to complete an as yet unknownbiological funtion. Purified sialidase presented a Mr of 73 KDa; antibodies generatedagainst the enzyme did not recognize T. cruzi, active sialidase/trans-sialidase polypeptidesor Clostiridium perfringes and Vibrio cholerae purified sialidases. These observationmay indicate the expression of different antigenic domains in T. rangeli, T cruziand bacterial sialidases. This study provides information of T. rangeli immunochemicalcharacteristics which may be useful for the understanding of its biology and biochemicalrelationship with T. cruzi.

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