Authors

Discussion

Introduction: Trypanosoma cruzi, the protozoan that causes Chagas disease, has a complex biological cycle. Upon entering the mammalian host, the parasite needs to effectively evade the attack of the complement system, which consists of the main humoral mechanism of the innate immune system. To guarantee infection, T. cruzi expresses different complement system inhibitors on its surface and quickly infects mammalian cells before their lysis. Our group showed that at that moment, extracellular vesicles (EVs) released by metacyclic trypomastigote forms in interaction with host cells participate by inhibiting the complement system and providing greater invasion of mammalian cells. Objective: Here, we wondered whether it would be possible to select parasites by exposure to normal human serum (NHS) and characterize the phenotype of this population. Methods: We selected a population of epimastigotes from T. cruzi (G strain) through two rounds of 30% normal human serum exposition, until reaching 30% of survivors, who were recovered (2R population). Then, the phenotype of the selected 2R population was evaluated through tests of resistance to complement-mediated lysis, capacity of invasion of cells (VERO cells) and release of extracellular vesicles (EVs). Results: The population of selected parasites presented greater resistance to lysis by the complement system and also greater infectivity to eukaryotic cells when compared to WT parasites. Metacyclic trypomastigotes from 2R were at least three times more infective to eukaryotic cells even in the presence of normal human serum. This phenotype seems to be explained by a greater expression of gp82 in the selected parasites. The production of EVs is similar among populations, but 2R parasites present higher resistance in the presence of EVs and WT invasion is increased by 2R EVs. It was seen that the virulence phenotype of the selected population remains in the trypomastigote form derived from cell culture, which has a higher rate of infection and also a rate of release of trypomastigotes from infected cells at least 3 fold higher than that of WT. Conclusion: It is possible to select a population of parasites more resistant to SNH. The resistance to the complement system is transient and becomes unstable over time. The selected parasites are more infective, even in the presence of normal human serum, possibly due to increased exposure of gp82, the main antigen related to metacyclic invasion. The perspectives for this work are to analyze the expression of genes related to complement resistance and invasion comparatively between the WT and 2R populations and to understand if the EVs derived from the 2R parasite can lead to greater infectivity of other parasites.