Host and parasite apoptosis following Trypanosoma cruzi infection in in vitro and in vivo models

The mechanism of cell death which occurs during Chagas' cardiopathy is disputed. To address this issue we analyzed the molecular pathways implicated in the death of cardiomyocytes during T. cruzi invasion and found that they undergo apoptosis during both in vitro and in vivo infections. However, the death rates and onset were related to the parasite stocks belonging to different biodemes, which can be correlated to the different histological inflammation findings that have already been reported. Our in vitro data provide additional support for this hypothesis since higher levels and earlier apoptosis induction were noted during the interaction with the Dm28c (type I) as compared to the Y and CL stocks (type II). Modifications of the surface carbohydrates of the infected cardiomyocytes were observed and these molecular events may be acting as "eat me" tags for their final engulfment by macrophages and/or other non-professional phagocytes. The analysis of other host cell types showed that the in vitro infection of fibroblasts did not result in host apoptosis even when a highly infective stock was used. Conversely, infected macrophages undergo apoptosis but at a higher degree than cardiomyocytes. Apoptotic intracellular parasites were observed to varied extents depending on the T. cruzi stock, which was related to the parasite invasion and proliferation. In summary, our results show that during T. cruzi infection, the extent of apoptosis varies according to the host cell type and the parasite stocks. The apoptosis of both host and T. cruzi can contribute to the silent spreading and persistence of the parasite without triggering an exacerbated inflammatory response.