L-arginine metabolism through arginases and inducible nitric oxide synthase (NOS2) constitutes a fundamental axis for the resolution or progression of Chagas disease. Infection with Trypanosoma cruzi can cause a wide spectrum of disease, ranging from acute forms contained by the host immune response to chronic ones, such as the chronic chagasic cardiomyopathy. Here, we analyzed, in an in vitro model, the ability of two T. cruzi isolates, with different degrees of virulence, to regulate the metabolism of L-arginine through arginase 1 (Arg-1) and NOS2 in macrophages and through arginase 2 (Arg-2) and NOS2 in cardiomyocytes. Stimulation of bone marrow-derived macrophages (BMMΦ), obtained from CD1 mice, with TNF-α + IFN-γ induced their polarization into classically activated macrophages (CAMΦ), which expressed functional NOS2, while stimulation with IL-4 induced their polarization into alternatively activated macrophages (AAMΦ), which expressed functional Arg-1. Interestingly, stimulation of cardiomyocytes, obtained from hearts of CD1 neonatal mice, with TNF-α + IFN-γ or IL-4 also resulted in functional NOS2 and arginase expression, as observed in CAMΦ and AAMΦ, but Arg-2 was the arginase isoform expressed instead of Arg-1. We observed that infection of BMMΦ with the more virulent T. cruzi isolate (QRO) importantly diminished NOS2 expression and nitric oxide (NO) production in CAMΦ, allowing parasite survival, while infection with the less virulent isolate (CI2) did not diminish NOS2 activity and NO production in CAMΦ to a great extent, which resulted in parasite killing. Regarding Arg-1, infection of BMMΦ with the QRO isolate significantly induced Arg-1 expression and activity in AAMΦ, which resulted in a higher parasite load than the one in the unstimulated BMMΦ. Even though infection with CI2 isolate did not increase Arg-1 expression and activity in AAMΦ, the parasite load was higher than the one in the unstimulated BMMΦ but at a lesser magnitude than that observed during infection with the QRO isolate. On the other hand, infection of cardiomyocytes with either QRO or CI2 isolates and further stimulation with TNF-α + IFN-γ inhibited NOS2 expression and NO production, leading to amelioration of infection. Surprisingly, infection of cardiomyocytes with either QRO or CI2 isolates and further stimulation with IL-4 strongly inhibited Arg-2 expression and function, which resulted in parasite loads similar to those observed in unstimulated cardiomyocytes. Our results suggest that T. cruzi isolates that exhibit variable virulence or pathogenicity degrees differentially regulate L-arginine metabolism through Arg-1/2 and NOS2 in macrophages and cardiomyocytes.

Dendritic cells (DC) along with macrophages are the main host cells of the intracellular parasite Leishmania. DC traverse a process of maturation, passing through an immature state with phagocytic ability to a mature one where they can modulate the immune response through the secretion of cytokines. Several studies have demonstrated that Leishmania inhibits DC maturation. Nevertheless, when cells are subjected to a second stimulus such as LPS/IFN-γ, they manage to mature. In the maturation process of DC, several signaling pathways have been implicated, importantly MAPK. On the other hand, Akt is a signaling pathway deeply involved in cell survival. Some Leishmania species have shown to activate MAPK and Akt in different cells. The aim of this work was to investigate the role of ERK and Akt in the maturation of monocyte-derived DC (moDC) infected with L. mexicana. moDC were infected with L. mexicana metacyclic promastigotes, and the phosphorylation of ERK and Akt, the expression of MHCII and CD86 and IL-12 transcript, and secretion were determined in the presence or absence of an Akt inhibitor. We showed that L. mexicana induces a sustained Akt and ERK phosphorylation, while the Akt inhibitor inhibits it. Moreover, the infection of moDC downregulates CD86 expression but not MHCII, and the Akt inhibitor reestablishes CD86 expression and 12p40 production. Thus, L. mexicana can modulate DC maturation though Akt signaling.