Immunobiochemical significance of Trypanosoma rangeli in the study of Trypanosoma cruzi

Trypanosoma rangeli is a haemoflagellate that infects humans nonpathogenically in some areas in which T. cruzi, the causative agent of Chagas' disease, is endemic. Since common biological and immunochemical characteristics have been described for these parasites, a detailed study of their relationship is needed. In the present work, experimental murine infections demonstrated that T cruzi induces antibodies that recognize several T. rangeli antigenic polypeptides. In the same manner, antibodies generated by T. rangeli infections recognize T. cruzi antigens. It is suggested that the IgM isotype is the predominant immunoglobulin produced during a T. rangeli infection, these antibodies also present cross-reactivities with T. cruzi antigens.

Biotin labelling of surface proteins and the recognition of polypeptides by labelled lectins have demonstrated the existence of a heterogeneous T. rangeli population and permitted diagnostic indentification of both species. Immunoblotting analysis, using anti-T. rangeli and anti-T. cruzi antibodies, suggest 50% antigenic similarity between these parasites. Nevertheless, antigens of 38, 43 and 48 KDa were identified as specific T. rangeli polypeptides. These fractions were purified, used for immunization of mice and basically characterized. By immunoblotting analysis these molecules were not detected in T. cruzi epimastigotes and Leishmania sp promastigotes. The molecule of 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 recognized peptides of T. rangeli (Trp38) and T. cruzi (Tcp38) proteins. The Trp48 is expressed uniformly by the T. rangeli cell population during axenic culture, a particular subcellular localization being proposed for this antigen. The antigenic relationship between T. rangeli and other trypanosomatids (5 genera) was also evaluated. The results demonstrate that several proteins are widely expressed among trypanosomatids (eg. 34, 29 and 20 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 supposedly saturating extracellular levels are reached, perhaps to complete an as yet unknown biological function. Purified sialidase presented a Mr of 73 KDa; antibodies generated against the enzyme did not recognize T. cruzi, active sialidase/trans-sialidase polypeptides or Clostiridium perfringes and Vibrio cholerae purified sialidases. These observation may indicate the expression of different antigenic domains in T. rangeli, T cruzi and bacterial sialidases. This study provides information of T. rangeli immunochemical characteristics which may be useful for the understanding of its biology and biochemical relationship with T. cruzi.