Experimental Chagas' disease: I. Study of different immunization conditions in the infection course]

In previous works it has been demonstrated that Balb/c albino mice immunized with Trypanosoma rangeli developed cellular and humoral immune response to Tripanosoma cruzi. Moreover, the immunized animals were protected against lethal infection by virulent T. cruzi trypomastigotes. In fact, immunized mice had significantly lower parasitemias and longer survival than controls. To go further in this experimental model, the aim of the present work was to analyze the effect of the number of antigenic stimuli and the conservation of the antigen on the effectiveness of protective effect. For that purpose, three different immunization schedules injecting T. rangeli epimastigotes fixed with glutaraldehide and emulsified with Saponin (SAP) as adjuvant were assayed. Different lots of mice which received only phosphate buffer saline or SAP were used as controls. In another set of experiments the conservation of the antigen during 90 days at 4 degrees C was studied. In all the experiments mice were infected with 100 trypomastigotes of T. cruzi, Tulahuén strain. The parasitemias were analyzed on 13th, 16th and 21st post infection days, and the survival until the 60th day. The results revealed that one dose of antigen was inadequate to give an effective protection. On the other hand, mice immunized with 2 and 3 dose showed a significant decrease of parasitemia with regard to controls (p < 0.001 - p < 0.0001) and the survival were markedly increased. Likewise, the antigen kept during 90th days at 4 degrees C showed similar protective efficacy than fresh antigen. Both of these experimental groups showed significant differences with respect to control animals in parasitemia (p < 0.05 - p > 0.01) and survival (p < 0.01). In conclusion, the results of this work showed that in the experimental conditions assayed, the immunization with T. rangeli trigger and adequate immune response when mice received at least two antigenic stimuli. Likewise, it is interesting to point out the stability of the antigenic preparation during at least 90th days.