Protective immunity and pathology induced by inoculation of mice with different subcellular fractions of Trypanosoma cruzi.

Mice were immunized with subcellular fractions obtained by differential centrifugation from epimastigotes of Trypanosoma cruzi (Tulahuén strain). In a chronic model of Chagas' disease, they were challenged each with 25 bloodstream trypomastigotes. Non-immunized, non-challenged and non-immunized challenged animals were kept as controls. Among the challenged mice, those immunized with 105,000 g pellet (Mc) and 105,000 g supernatant (Cs) fractions presented positive xenodiagnosis, myocarditis and myositis similar to those shown by non-immunized challenged controls. The fractions enriched in flagella, the 5000 g pellet (P5) and the flagellar fraction (F) resulted in fewer animals with positive xenodiagnosis and in hosts partially protected from the development of myocarditis. In the absence of infection, Mc and Cs induced an intense myocarditis while F induced mild lesions similar to those found in the controls. P5 caused a myocarditis intermediate between that elicited by Mc and that in the controls. 50% of the animals immunized with Cs presented pathological electrocardiograms in the absence of challenge. The animals immunized with F and P5 and challenged were protected against the development of pathological electrocardiograms, whereas those immunized with Mc and Cs behaved like the non-immunized controls. The immunized, non-challenged animals presented anti-T. cruzi IgG antibodies, with titres which were lower than those shown by the immunized and challenged mice.--The results show the possibility of obtaining tissue lesions with antigenic preparations of T. cruzi in the absence of infection, and suggest that the mechanisms involved in the generation of myocarditis and electrocardiographic alterations are probably different, since these pathologies can be elicited by different subcellular fractions. Among the antigenic components of the parasite, the flagellar fraction gave the best immunoprotective properties, with little or no immunoaggressive effects.