Plasmid DNA immunization with Trypanosoma cruzi genes induces cardiac and clinical protection against Chagas disease in the canine model

Abstract

The only existing preventive measure against American trypanosomosis, or Chagas disease, is the control of the transmitting insect, which has only been effective in a few South American regions. Currently, there is no vaccine available to prevent this disease. Here, we present the clinical and cardiac levels of protection induced by expression to Trypanosoma cruzi genes encoding the TcSP and TcSSP4 proteins in the canine model. Physical examination, diagnostic chagasic serology, and serial electrocardiograms were performed before and after immunization, as well as after experimental infection. We found that immunization with recombinant plasmids prevented hyperthermia in the acute phase of experimental infection and produced lymphadenomegaly as an immunological response against the parasite and additionally prevented heart rate elevation (tachycardia) in the acute and/or chronic stages of infection. Immunization with T. cruzi genes encoding the TcSP and TcSSP4 antigens diminished the quality and quantity of the electrocardiographic abnormalities, thereby avoiding progression to more severe developments such as right bundle branch block or ventricular premature complexes in a greater number of dogs.

Figure 1

rSSP4 and rSP protein expression in the HeLa plasmid transfected cells. (A) SDS-PAGE and (B) western blot analysis of the pBCSSP4 plasmid transfected cell extracts; samples were taken at different time points; Lanes: 2 and 3, 8 h; 4 and 5, 24 h; 6 and 7, 48 h; 8 and 9, 56 h. The membrane was probed with the anti-MBP::SSP4 antibody. (C) SDS-PAGE and (D) western blot analysis of the pBCSP plasmid transfected cell extracts; samples were taken at different time points; Lanes: MWM, molecular weight marker; 2, 8 h; 3, 24 h; 4, 48 h; 5, 56 h, and 6, 72 h. The membrane was probed with the anti-epimastigote whole extract antibody. Lanes 1 in (A), (B), (C), and (D) are the samples corresponding to control empty vector pBK-CMV HeLa transfected cells.

Figure 2

Body temperature of DNA-immunized dogs with experimental T. cruzi infection. Rectal temperature recordings from each experimental group (plasmid DNA immunized- and SS mock-immunized dogs) were compared with those of the control group (uninfected healthy animals). The values are the average of the temperature recordings ± S.D. Two-way ANOVA statistical test (* P ≤ 0.05).

Figure 3

Heart rate of DNA-immunized dogs with experimental T. cruzi infection. Heart beat recordings from each experimental group (plasmid DNA immunized- and SS mock-immunized dogs) were compared with those of the control group (uninfected healthy animals). Heart rates exceeding 160 beats per minute were considered tachycardic. The values represent the average of the heart rate recordings ± S.D. Two-way ANOVA statistical test (* P ≤ 0.05).