Abstract
BackgroundTrypanosoma cruzi infection is associated with severe T cell unresponsiveness to antigens and mitogens and is characterized by decreased IL-2 synthesis. In addition, the acquisition of the anergic phenotype is correlated with upregulation of “gene related to anergy in lymphocytes” (GRAIL) protein in CD4 T cells. We therefore sought to examine the role of GRAIL in CD4 T cell proliferation during T. cruzi infection.Methodology/Principal FindingsBalb/c mice were infected intraperitoneally with 500 blood-derived trypomastigotes of Tulahuen strain, and spleen cells from control non-infected or infected animals were obtained. CD4 T cell proliferation was assessed by CFSE staining, and the expression of GRAIL in splenic T cells was measured by real-time PCR, flow cytometry and Western blot. We found increased GRAIL expression at the early stages of infection, coinciding with the peak of parasitemia, with these findings correlating with impaired proliferation and poor IL-2 and IFN-γ secretion in response to plate-bound antibodies. In addition, we showed that the expression of GRAIL E3-ubiquitin ligase in CD4 T cells during the acute phase of infection was complemented by a high expression of inhibitory receptors such as PD-1 and CTLA-4. We demonstrated that GRAIL expression during infection was modulated by the mammalian target of the rapamycin (mTOR) pathway, since addition of IL-2 or CTLA-4 blockade in splenocytes from mice 21 days post infection led to a reduction in GRAIL expression. Furthermore, addition of IL-2 was able to activate the mTOR pathway, inducing Otubain-1 expression, which mediated GRAIL degradation and improved T cell proliferation.ConclusionsWe hypothesize that GRAIL expression induced by the parasite may be maintained by the increased expression of inhibitory molecules, which blocked mTOR activation and IL-2 secretion. Consequently, the GRAIL regulator Otubain-1 was not expressed and GRAIL maintained the brake on T cell proliferation. Our findings reveal a novel association between increased GRAIL expression and impaired CD4 T cell proliferation during Trypanosoma cruzi infection.
Highlights
Chagas disease, caused by the intracellular protozoa Trypanosoma cruzi, is one of the major human health problems in Latin America
We demonstrated that GRAIL expression during infection was modulated by the mammalian target of the rapamycin pathway, since addition of IL-2 or CTLA-4 blockade in splenocytes from mice 21 days post infection led to a reduction in GRAIL expression
We hypothesize that GRAIL expression induced by the parasite may be maintained by the increased expression of inhibitory molecules, which blocked mammalian target of the rapamycin (mTOR) activation and IL-2 secretion
Summary
Chagas disease, caused by the intracellular protozoa Trypanosoma cruzi, is one of the major human health problems in Latin America. It evolves from an acute to a chronic phase, where subjects may be clinically asymptomatic or show progressive heart disease and leads to an endstage dilated cardiomyopathy in 20–30% of infected individuals. Even in cases in which these responses are sufficiently stimulated to be able to control the acute infection, T. cruzi is not completely eradicated, but instead persists in infected hosts for decades [3]. A number of both host-dependent and parasite-induced mechanisms have been previously shown to affect immune regulation [9,10]. T cells from infected hosts are largely unresponsive to antigens and mitogens, resulting in reduced IL-2 synthesis [8]. Trypanosoma cruzi infection is associated with severe T cell unresponsiveness to antigens and mitogens and is characterized by decreased IL-2 synthesis. We sought to examine the role of GRAIL in CD4 T cell proliferation during T. cruzi infection
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