interacts with the different arms of the innate and adaptive host's immune response in a very complex and flowery manner. The history of host-parasite co-evolution has provided this protozoan with ...means of resisting, escaping or subverting the mechanisms of immunity and establishing a chronic infection. Despite many decades of research on the subject, the infection remains incurable, and the factors that steer chronic Chagas disease from an asymptomatic state to clinical onset are still unclear. As the relationship between
and the host immune system is intricate, so is the amount and diversity of scientific knowledge on the matter. Many of the mechanisms of immunity are fairly well understood, but unveiling the factors that lead each of these to success or failure, within the coordinated response as a whole, requires further research. The intention behind this Review is to compile the available information on the different aspects of the immune response, with an emphasis on those phenomena that have been studied and confirmed in the human host. For ease of comprehension, it has been subdivided in sections that cover the main humoral and cell-mediated components involved therein. However, we also intend to underline that these elements are not independent, but function intimately and concertedly. Here, we summarize years of investigation carried out to unravel the puzzling interplay between the host and the parasite.
The CD4
+
and CD8
+
T cell immune response against
T. cruzi
, the parasite causing Chagas disease, are relevant for both parasite control and disease pathogenesis. Several studies have been focused ...on their phenotype and functionally, but only a few have drilled down to identify the parasite proteins that are processed and presented to these cells, especially to CD4
+
T lymphocytes. Although approximately 10,000 proteins are encoded per haploid
T. cruzi
genome, fewer than 200 T cell epitopes from 49
T. cruzi
proteins have been identified so far. In this context, a detailed knowledge of the specific targets of T cell memory response emerges as a prime tool for the conceptualization and development of prophylactic or therapeutic vaccines, an approach with great potential to prevent and treat this chronic disease. Here, we review the available information about this topic in a comprehensive manner and discuss the future challenges in the field.
Chronic Chagas cardiomyopathy caused by Trypanosoma cruzi is the result of a pathologic process starting during the acute phase of parasite infection. Among different factors, the specific ...recognition of glycan structures by glycan-binding proteins from the parasite or from the mammalian host cells may play a critical role in the evolution of the infection.
Here we investigated the contribution of galectin-1 (Gal-1), an endogenous glycan-binding protein abundantly expressed in human and mouse heart, to the pathophysiology of T. cruzi infection, particularly in the context of cardiac pathology. We found that exposure of HL-1 cardiac cells to Gal-1 reduced the percentage of infection by two different T. cruzi strains, Tulahuén (TcVI) and Brazil (TcI). In addition, Gal-1 prevented exposure of phosphatidylserine and early events in the apoptotic program by parasite infection on HL-1 cells. These effects were not mediated by direct interaction with the parasite surface, suggesting that Gal-1 may act through binding to host cells. Moreover, we also observed that T. cruzi infection altered the glycophenotype of cardiac cells, reducing binding of exogenous Gal-1 to the cell surface. Consistent with these data, Gal-1 deficient (Lgals1-/-) mice showed increased parasitemia, reduced signs of inflammation in heart and skeletal muscle tissues, and lower survival rates as compared to wild-type (WT) mice in response to intraperitoneal infection with T. cruzi Tulahuén strain.
Our results indicate that Gal-1 modulates T. cruzi infection of cardiac cells, highlighting the relevance of galectins and their ligands as regulators of host-parasite interactions.
Summary
Trypanosoma cruzi cytosolic tryparedoxin peroxidase (c‐TXNPx) is a 2‐Cys peroxiredoxin (Prx) with an important role in detoxifying host cell oxidative molecules during parasite infection. ...c‐TXNPx is a virulence factor, as its overexpression enhances parasite infectivity and resistance to exogenous oxidation. As Prxs from other organisms possess immunomodulatory properties, we studied the effects of c‐TXNPx in the immune response and analysed whether the presence of the peroxidatic cysteine is necessary to mediate these properties. To this end, we used a recombinant c‐TXNPx and a mutant version (c‐TXNPxC52S) lacking the peroxidatic cysteine. We first analysed the oligomerization profile, oxidation state and peroxidase activity of both proteins by gel filtration, Western blot and enzymatic assay, respectively. To investigate their immunological properties, we analysed the phenotype and functional activity of macrophage and dendritic cells and the T‐cell response by flow cytometry after injection into mice. Our results show that c‐TXNPx, but not c‐TXNPxC52S, induces the recruitment of IL‐12/23p40‐producing innate antigen‐presenting cells and promotes a strong specific Th1 immune response. Finally, we studied the cellular and humoral immune response developed in the context of parasite natural infection and found that only wild‐type c‐TXNPx induces proliferation and high levels of IFN‐γ secretion in PBMC from chronic patients without demonstrable cardiac manifestations. In conclusion, we demonstrate that c‐TXNPx possesses pro‐inflammatory properties that depend on the presence of peroxidatic cysteine that is essential for peroxidase activity and quaternary structure of the protein and could contribute to rational design of immune‐based strategies against Chagas disease.
Trypanosoma cruzi cytosolic tryparedoxin peroxidase (c‐TXNPx) is a 2‐Cys peroxiredoxin (Prx) with an important role in detoxifying host cell oxidative molecules during parasite infection. We investigated their immunological properties, using a recombinant c‐TXNPx and a mutant version (c‐TXNPxC52S) lacking the peroxidatic cysteine. We demonstrate that c‐TXNPx possesses pro‐inflammatory properties that depend on the presence of peroxidatic cysteine, essential for peroxidase activity and quaternary structure of the protein, and could contribute to rational design of immune‐based strategies against Chagas disease.
The discovery of T cell epitopes is essential not only for gaining knowledge about host response to infectious disease but also for the development of immune-intervention strategies. In Chagas ...disease, given the size and complexity of the Trypanosoma cruzi proteome and its interaction with the host's immune system, the fine specificity of T cells has not been extensively studied yet, and this is particularly true for the CD4+ T cell compartment. The aim of the present work was to optimize a protocol for the generation of parasite-specific memory T cell lines, representative of their in vivo precursor populations and capable of responding to parasite antigens after long-term culture. Accordingly, peripheral blood mononuclear cells (PBMC) from both chronic asymptomatic and cardiac patients, and from non-infected individuals, underwent different in vitro culture and stimulation conditions. Subsequently, cells were tested for their capacity to respond against T. cruzi lysate by measuring 3H-thymidine incorporation and interferon-γ and GM-CSF secretion. Results allowed us to adjust initial T. cruzi lysate incubation time as well as the number of expansions with phytohemagglutinin (PHA) and irradiated allogeneic PBMC prior to specificity evaluation. Moreover, our data demonstrated that parasite specific T cells displayed a clear and strong activation by using T. cruzi lysate pulsed, Epstein-Barr virus (EBV)-transformed human B lymphocytes (B-LCL), as autologous antigen presenting cells. Under these culture conditions, we generated a clone from an asymptomatic patient's memory CD4+ T cells which responded against epimastigote and trypomastigote protein lysate. Our results describe a culture method for isolating T. cruzi specific T cell clones from patients with Chagas disease, which enable the acquisition of information on functionality and specificity of individual T cells.
Antigen‐specific T cells are central to the adaptive immune response against T. cruzi infection and underpin the efficacy of on‐going vaccine strategies. In this context, the present study focuses on ...T‐cell assays that define the parasite‐specificity on the basis of upregulation of TCR stimulation‐induced surface markers. For this purpose, we tested different dual marker combinations (OX40, CD25, CD40L, CD137, CD69, PD‐L1, CD11a, CD49d, HLA‐DR, CD38) to reliably identify activated CD4+ and CD8+ T‐cell populations from PBMCs of chronic Chagas disease (CCD) patients after 12 or 24 h of stimulation with T. cruzi lysate. Results demonstrated that activation‐induced markers (AIM) assays combining the expression of OX40, CD25, CD40L, CD137, CD69 and/or PD‐L1 surface markers are efficient at detecting T. cruzi‐specific CD4+ T cells in CCD patients, in comparison to non‐infected donors, after both stimulation times. For CD8+ T cells, only PD‐L1/OX40 after 24 h of antigen exposure resulted to be useful to track a parasite‐specific response. We also demonstrated that the agnostic activation is mediated by different T. cruzi strains, such as Dm28c, CL Brener or Sylvio. Additionally, we successfully used this approach to identify the phenotype of activated T lymphocytes based on the expression of CD45RA and CCR7. Overall, our results show that different combinations of AIM markers represent an effective and simple tool for the detection of T. cruzi‐specific CD4+ and CD8+ T cells.
Activation‐induced markers (AIM) assay is useful to identify T. cruzi‐specific T cells in chronic Chagas disease patients. Several dual AIM markers designate CD4+ T‐cell activation, while only PD‐L1/OX40 identifies parasite‐specific CD8+ T lymphocytes. AIM assay allows the detection of T‐cell agnostic activation mediated by different T. cruzi strains, such as Dm28c, CL Brener or Sylvio.
Chagas disease is caused by the parasite
. In humans, it evolves into a chronic disease, eventually resulting in cardiac, digestive, and/or neurological disorders. In the present study, we ...characterized a novel
antigen named Tc323 (TcCLB.504087.20), recognized by a single-chain monoclonal antibody (scFv 6B6) isolated from the B cells of patients with cardiomyopathy related to chronic Chagas disease. Tc323, a ~323 kDa protein, is an uncharacterized protein showing putative quinoprotein alcohol dehydrogenase-like domains. A computational molecular docking study revealed that the scFv 6B6 binds to an internal domain of Tc323. Immunofluorescence microscopy and Western Blot showed that Tc323 is expressed in the main developmental forms of
, localized intracellularly and exhibiting a membrane-associated pattern. According to phylogenetic analysis, Tc323 is highly conserved throughout evolution in all the lineages of
so far identified, but it is absent in
spp. and
. Most interestingly, only plasma samples from patients infected with
and those with mixed infection with
spp. reacted against Tc323. Collectively, our findings demonstrate that Tc323 is a promising candidate for the differential serodiagnosis of chronic Chagas disease in areas where
and
spp. infections coexist.
Despite the growing importance of the regulatory function of B cells in many infectious diseases, their immunosuppressive role remains elusive in chronic Chagas disease (CCD). Here, we studied the ...proportion of different B cell subsets and their capacity to secrete IL-10 ex vivo in peripheral blood from patients with or without CCD cardiomyopathy. First, we immunophenotyped peripheral blood mononuclear cells from patients according to the expression of markers CD19, CD24, CD38 and CD27 and we showed an expansion of total B cell and transitional CD24
CD38
B cell subsets in CCD patients with cardiac involvement compared to non-infected donors. Although no differences were observed in the frequency of total IL-10 producing B cells (B10) among the groups, CCD patients with cardiac involvement showed an increased proportion of naïve B10 cells and a tendency to a higher frequency of transitional B10 cells compared to non-infected donors. Our research demonstrates that transitional B cells are greatly expanded in patients with the cardiac form of CCD and these cells retain the ability to secrete IL-10. These findings provide insight into the phenotypic distribution of regulatory B cells in CCD, an important step towards new strategies to prevent cardiomyopathy associated with T. cruzi infection.
T cells are central to the adaptive immune response against Trypanosoma cruzi infection. In chronic Chagas disease (CCD), circulating parasite-specific memory T cells show reduced functionality and ...increased expression of inhibitory receptors as a result of persistent antigenic stimulation. This phenotype has been linked to progression of cardiac pathology, whereas the presence of polyfunctional T cells shows association with therapeutic success. In this study, we demonstrate that T. cruzi-specific human CD4+ T cells can be identified by their expression of OX40 and CD25 upon in vitro stimulation. We characterized the expression of the inhibitory receptors T cell immunoreceptor with Ig and ITIM domains (TIGIT), T cell Ig and mucin-domain containing-3 (TIM-3), and lymphocyte activation gene 3 (LAG-3) in CD4+ T cells from CCD patients with and without cardiac alterations. Our results show that, independently of their clinical stage, CCD patients present an increased frequency of CD4+ T cells expressing TIGIT in comparison with non-T. cruzi-infected donors. Exposure to parasite Ags increases the expression of TIM-3 in CD4+ T cells from CCD patients, especially in those with cardiac compromise. Upregulation of LAG-3 was also detected in CCD individuals without cardiac manifestations, predominantly within the subpopulation of cells that did not become activated upon stimulation. Further differences were found between groups in the coexpression of these receptors. Blockade of each individual receptor did not affect activation or the production of IFN-γ and IL-10 by CD4+ T cells in response to parasite Ags. Our results suggest a role for TIGIT, TIM-3, and LAG-3 in the modulation of inflammatory phenomena thought to ultimately lead to tissue damage and cardiac pathology.
, the protozoan parasite causative agent of Chagas disease, affects about seven million people worldwide, representing a major global public health concern with relevant socioeconomic consequences, ...particularly in developing countries. In this review, we discuss the multiple roles of galectins, a family of β-galactoside-binding proteins, in modulating both
infection and immunoregulation. Specifically, we focus on galectin-driven circuits that link parasite invasion and inflammation and reprogram innate and adaptive immune responses. Understanding the dynamics of galectins and their β-galactoside-specific ligands during the pathogenesis of
infection and elucidating their roles in immunoregulation, inflammation, and tissue damage offer new rational opportunities for treating this devastating neglected disease.
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