Immunoparasitological studies of Trypanosoma cruzi low virulence clones from Panama: humoral immune responses and antigenic cross-reactions with Trypanosoma rangeli in experimentally infected mice.

The kinetics of humoral immune responses were investigated in mice experimentally infected with five clones of Trypanosoma cruzi isolated from different sources in Panama. Sera were collected at different timepoints post-infection. ELISA and IHA tests were used to detect antibodies against T. cruzi epimastigote antigens. The levels of T. cruzi specific antibodies increased during the course of infection; at day 90 post-infection the range was between 1:5120 and 1:10240. A high correlation was evident between ELISA and IHA results. Western blots revealed that these antibodies recognized polypeptides of 81, 76 and 71 KDa during the first weeks and 81, 76, 71, 50, 40, 28 and 12 KDa after 30-50 days. Only minor differences in antigen recognition patterns were demonstrated, suggesting that the major antigens may be represented in all clones. T. rangeli antigens were also recognized by T. cruzi seropositive sera. However, an ELISA test using antigens isolated from a genomic expression library of T. cruzi revealed that a hyperimmune rabbit serum against T. rangeli was unable to recognize the repeat sequence of SAPA (Shed Acute Phase Antigen) peptides but did recognize a number of other T. cruzi synthetic peptide antigens. The importance of these findings, in the context of Chagas' disease, is discussed.