Influence of trypanosoma cruzi and host genetic variability on chagas disease immunopathology

Résumé

Chagas disease is an important problem of public health in the Americas, is caused by the intracellular parasite Trypanosoma cruzi. It is a complex disease with great variety of reservoirs and vectors, different ways transmission and parasite high genetic variability. For this reason the immunopathology is still not completely understood and there is no efficient treatment. Due to its high genetic variability T. cruzi has been classified into six different Discrete Typing Units. Studies evaluating the immunopathology in Chagas disease have been performed using single T. cruzi strains, thus, the role of the genetic variability of the parasite has not been taken in account. On the other hand, studies using a unique parasite strain and different mouse genetic backgrounds showed numerous inconsistences. For this reason it is important to evaluate the role of parasite genetic variability and the mouse genetic background, to better understand the immunopathology of Chagas disease. Previous studies in the laboratory demonstrated the importance of Toll-Like receptor 2 (TLR2) and Signaling Lymphocytic Activation Molecule Family 1 receptor (SLAMF1), during the infection with T. cruzi in vivo and in vitro using the Y parasite strain. The aim of this project was to evaluate the immunopathology of Chagas Disease using different reference strains of T. cruzi in vivo and in vitro, in mice with different mouse genetic background and deficient in the expression of TLR2 and SLAMF1 receptors. We found that macrophages from C57BL/6 mice were more resistant to in vitro infection with all T. cruzi strains evaluated compared to BALB/c, being the rate of infection variable depending on the strain. TLR2 was crucial during the interaction phase of macrophages and all the different strains potentiating parasite internalization. In contrast, SLAMF1 played an important role as a microbial sensor by suppressing NAPDH oxidase 2 (NOX2) expression and Reactive Oxygen Species (ROS) production for all the T. cruzi strains evaluated, except for VFRA cl1. In vivo results with BALB/c and Slamf1-/- mice infected with Dm28c, Y and VFRA cl1 strains, where in agreement with in vitro results. Thus, Slamf1 -/- mice infected Dm28c and Y were more resistant to infection compared with infected BALB/c mice, but more susceptible when infected with VFRA cl1 strain. Infections with the Y strain denoted the inverse correlation between the presence of Myeloid-derived Suppressor Cells (MDSCs) in the heart (denoted by expression of Arg-1, iNOS and COX-2 MDSCs markers) and mice survival, which was 30% and 100% in BALB/c and Slamf1 -/- mice, respectively. Dm28c and VFRA cl1 parasite strains caused lower levels of MDSCs in heart, but higher immune response in spleen and liver, indicating a more efficient control of the infection that impedes infected MDSCs reaching the heart that as a “Trojan horse”, deliver the parasites, causing cardiac damage and the death of the mice. Finally, we showed for the first time that immune-responsive gene 1 (Irg1) levels were high in mice hearts during T. cruzi infection. In vitro studies using epimastigotes showed a high IC50 for itaconic acid, a metabolite produced by Irg1 that inhibits pathogen’s isocitrate lyase, thus, the last constitutes a new drug target for Chagas disease treatment.