Trypanosoma cruzi glutathione-binding proteins (TcGBP): protection induced by native proteins in an experimental model and analysis of the antibody response.

Three Trypanosoma cruzi glutathione-binding proteins (TcGBP) of 45, 30 and 25 kDa presenting glutathione S transferase activity were characterized from T. cruzi epimastigotes. We show here that immunization of mice using TcGBP and complete Freund's adjuvant (CFA) did not protect the animals against a challenge with bloodstream trypomastigotes. In contrast, immunization of mice using TcGBP in association with Bordetella pertussis plus alum (BpAI) resulted in greatly diminished parasitaemia and significantly protected the animals from lethal infection. Using TcGBP mixed with BpAI and a lower challenge dose, we obtained strongly diminished parasitaemia and 100% protection in terms of survival. Only sera from mice immunized with TcGBP plus BpAI were able to kill trypomastigotes by complement-mediated lysis, whereas sera from mice immunized with TcGBP plus CFA did not. Interestingly, sera from mice immunized with TcGBP plus BpAI showed significant levels of specific IgE, IgG2a and IgG2b antibodies, whereas these isotypes were not detected in sera from mice immunized with TcGBP in CFA. All these levels were increased in sera of protected animals. These results demonstrate that TcGBP antigens can confer resistance to T. cruzi acute infection in mice, and suggest a possible functional role for both IgE and IgG2 isotypes in the induction of protective immunity.