Fas ligand-dependent inflammatory regulation in acute myocarditis induced by Trypanosoma cruzi infection

Physical Exercise Promotes a Reduction in Cardiac Fibrosis in the Chronic Indeterminate Form of Experimental Chagas Disease

Chagas disease (CD), caused by the protozoan Trypanosoma cruzi, is a neglected tropical disease and a health problem in Latin America. Etiological treatment has limited effectiveness in chronic CD; thus, new therapeutic strategies are required. The practice of physical exercises has been widely advocated to improve the quality of life of CD patients. The most frequent clinical CD manifestation is the chronic indeterminate form (CIF), and the effect of physical exercises on disease progression remains unknown. Here, in a CIF model, we aimed to evaluate the effect of physical exercises on cardiac histological, parasitological, mitochondrial, and oxidative metabolism, electro and echocardiographic profiles, and immunological features. To establish a CIF model, BALB/c and C57BL/6 mice were infected with 100 and 500 trypomastigotes of the Y T. cruzi strain. At 120 days postinfection (dpi), all mouse groups showed normal PR and corrected QT intervals and QRS complexes. Compared to BALB/c mice, C57BL/6 mice showed a lower parasitemia peak, mortality rate, and less intense myocarditis. Thus, C57BL/6 mice infected with 500 parasites were used for subsequent analyses. At 120 dpi, a decrease in cardiac mitochondrial oxygen consumption and an increase in reactive oxygen species (ROS) were detected. When we increased the number of analyzed mice, a reduced heart rate and slightly prolonged corrected QT intervals were detected, at 120 and 150 dpi, which were then normalized at 180 dpi, thus characterizing the CIF. Y-infected mice were subjected to an exercise program on a treadmill for 4 weeks (from 150 to 180 dpi), five times per week in a 30–60-min daily training session. At 180 dpi, no alterations were detected in cardiac mitochondrial and oxidative metabolism, which were not affected by physical exercises, although ROS production increased. At 120 and 180 dpi, comparing infected and non-infected mice, no differences were observed in the levels of plasma cytokines, indicating that a crucial biomarker of the systemic inflammatory profile was absent and not affected by exercise. Compared with sedentary mice, trained Y-infected mice showed similar parasite loads and inflammatory cells but reduced cardiac fibrosis. Therefore, our data show that physical exercises promote beneficial changes that may prevent CD progression.

The Liver and the Hepatic Immune Response in Trypanosoma cruzi Infection, a Historical and Updated View

Chagas disease was described more than a century ago and, despite great efforts to understand the underlying mechanisms that lead to cardiac and digestive manifestations in chronic patients, much remains to be clarified. The disease is found beyond Latin America, including Japan, the USA, France, Spain, and Australia, and is caused by the protozoan Trypanosoma cruzi. Dr. Carlos Chagas described Chagas disease in 1909 in Brazil, and hepatomegaly was among the clinical signs observed. Currently, hepatomegaly is cited in most papers published which either study acutely infected patients or experimental models, and we know that the parasite can infect multiple cell types in the liver, especially Kupffer cells and dendritic cells. Moreover, liver damage is more pronounced in cases of oral infection, which is mainly found in the Amazon region. However, the importance of liver involvement, including the hepatic immune response, in disease progression does not receive much attention. In this review, we present the very first paper published approaching the liver's participation in the infection, as well as subsequent papers published in the last century, up to and including our recently published results. We propose that, after infection, activated peripheral T lymphocytes reach the liver and induce a shift to a pro-inflammatory ambient environment. Thus, there is an immunological integration and cooperation between peripheral and hepatic immunity, contributing to disease control.

Human apoCIII transgenic mice with epicardial adipose tissue inflammation and PRESERVATION of the cardiac plexus

Hypertriglyceridemia is a result of the increase in the serum levels of lipoproteins, which are responsible for the transport of triglycerides and can be caused by genetic and/or metabolic factors. Animal models which either express or lack genes related to changes in the lipoproteins profile are useful to understand lipid metabolism. Apolipoprotein CIII (apoCIII) is an important modulator of hepatic production and peripheral removal of triglycerides. Mice that overexpress the apoCIII gene become hypertriglyceridemic, showing high concentrations of free fatty acids in the blood. Since hypertriglyceridemia is related to atherosclerosis, and the latter refers to cardiac alterations, this study aimed at evaluating the morphological, morphometric and quantitative profiles of the cardiac plexus, as well as the morphometric and histopathological aspects of the epicardial adipose tissue in human apoCIII transgenic mice. Therefore, 8-12-month-old male C57BL/6 mice that overexpressed human apoCIII (CIII) and their respective controls were used. Our results showed that overexpression of human apoCIII did not modify morphological or quantitative parameters of cardiac plexus neurons; however, age increased both, the area and the number of such cells. Furthermore, there was a direct correlation of this dyslipidemia to the thickening of periganglionar type 1 collagens. On the other hand, this overexpression caused epicardial adipose tissue inflammation and an increase in the area of the adipocytes, thus, favoring the recruitment of inflammatory cells in this tissue. In conclusion, this overexpression is harmful since it is related to an increase in cardiac adiposity, as well as to a predisposition to an inflammatory environment in the epicardial fat and to the incidence of cardiovascular diseases.

Multiparametric Color Tendency Analysis (MCTA): A Method to Analyze Several Flow Cytometry Labelings Simultaneously

Despite the remarkable evolution of flow cytometers, fluorescent probes, and flow cytometry analysis software, most users still follow the same ways for data analysis. Conventional flow cytometry analysis relies on the creation of dot plot sequences, based on two fluorescence parameters at a time, to evidence phenotypically distinct populations. Thus, reaching conclusions about the biological characteristics of the samples is a fragmented and challenging process. We present here the MCTA (Multiparametric Color Tendency Analysis), a method for data analysis that considers multiple labelings simultaneously, extending and complementing conventional analysis. The MCTA method executes the background fluorescence exclusion, spillover compensation, and a user-defined gating strategy for subpopulation analysis. The results are then presented in conventional FSC x SSC dot plots with statistical data. For each event, the method converts each of the multiple fluorescence colors under analysis into a vector, with longer vectors being attributed to more intense labelings. Then, the MCTA generates a resultant vector, which is therefore mostly influenced by predominant labelings. The radial position of this resultant vector corresponds to a resultant color, making it easy to visualize phenotypic modulations among cellular subpopulations. Besides, it is a deterministic method that quickly assigns a resulting color to all events that obey the gating strategy, with no polymeric regions defined by the user or downsampling. The MCTA application generates a single dot plot showing all events in the FCS file, but a resultant color is attributed only to those that obey the gating strategy. Therefore, it can also help to evidence rare events or unpredicted subpopulations naturally excluded from the regions defined by the user. We believe that the MCTA method adds a new perspective over multiparametric flow cytometry analysis while evidencing modulations of molecular labeling profiles based on multiple fluorescences. Availability and implementation: The instructions for the MCTA application is freely available at https://github.com/flowcytometry/MCTA.

CD43 sialoglycoprotein modulates cardiac inflammation and murine susceptibility to Trypanosoma cruzi infection

CD43 (leukosialin) is a large sialoglycoprotein abundantly expressed on the surface of most cells from the hematopoietic lineage. CD43 is directly involved in the contact between cells participating in a series of events such as signaling, adherence and host parasite interactions. In this study we examined the role of CD43 in the immune response against Trypanosoma cruzi, the protozoan parasite that causes Chagas’ disease, a potential life-threatening illness endemic in 21 Latin American countries according to the WHO. The acute stage of infection is marked by intense parasitemia and cardiac tissue parasitism, resulting in the recruitment of inflammatory cells and acute damage to the heart tissue. We show here that CD43^−/− mice were more resistant to infection due to increased cytotoxicity of antigen specific CD8+ T cells and reduced inflammatory infiltration in the cardiac tissue, both contributing to lower cardiomyocyte damage. In addition, we demonstrate that the induction of acute myocarditis involves the engagement of CD43 cytoplasmic tripeptide sequence KRR to ezrin-radixin-moiesin cytoskeletal proteins. Together, our results show the participation of CD43 in different events involved in the pathogenesis of T. cruzi infection, contributing to a better overall understanding of the mechanisms underlying the pathogenesis of acute chagasic cardiomyopathy.

Reverse Signaling of Tumor Necrosis Factor Superfamily Proteins in Macrophages and Microglia: Superfamily Portrait in the Neuroimmune Interface

The tumor necrosis factor (TNF) superfamily (TNFSF) is a protein superfamily of type II transmembrane proteins commonly containing the TNF homology domain. The superfamily contains more than 20 protein members, which can be released from the cell membrane by proteolytic cleavage. Members of the TNFSF function as cytokines and regulate diverse biological processes, including immune responses, proliferation, differentiation, apoptosis, and embryogenesis, by binding to TNFSF receptors. Many TNFSF proteins are also known to be responsible for the regulation of innate immunity and inflammation. Both receptor-mediated forward signaling and ligand-mediated reverse signaling play important roles in these processes. In this review, we discuss the functional expression and roles of various reverse signaling molecules and pathways of TNFSF members in macrophages and microglia in the central nervous system (CNS). A thorough understanding of the roles of TNFSF ligands and receptors in the activation of macrophages and microglia may improve the treatment of inflammatory diseases in the brain and periphery. In particular, TNFSF reverse signaling in microglia can be exploited to gain further insights into the functions of the neuroimmune interface in physiological and pathological processes in the CNS.

Histopathological lesions in encephalon and heart of mice infected with Toxoplasma gondii increase after Lycopodium clavatum 200dH treatment

In many cases, symptoms of toxoplasmosis are mistaken for the ones of other infectious diseases. Clinical signs are rare in immunocompetent people. However, when they arise, in the acute phase of infection, several organs are affected due to the rapid spread of tachyzoites through the bloodstream. In the present study, the reduction of tachyzoites in peripheral blood of mice of G72 (infected 72h after treatment) and G48 (infected 48h after treatment and treated three more times), when compared with IC (infected and non-treated), suggests protective effect exerted by Lycopodium clavatum. If on the one hand L. clavatum brought benefits, reducing parasitemia, on the other hand, the parasitism became exacerbated. Histopathological analysis demonstrated focal, multifocal and diffuse inflammatory infiltrates, ranging from absent, discreet, moderate to intense, in heart and encephalon of mice of NIC (non-infected and non-treated), IC, G48 and G72 groups, respectively. In the perivascular region and meninges, the injuries were enlarged. The presence of tachyzoites was demonstrated through immunohistochemical (IHC) assay in myocardium. Toxoplasma gondii induced increase of collagen fibers in myocardium of mice of G72 and G48 groups, compared with IC (p<0.05) and NIC (p<0.001). The presence of inflammatory infiltrates, as well as the progressive fibrosis, caused myocardial remodeling in animals treated with L. clavatum. Counterstaining with H&E suggests TGF-β expression by mononuclear cells in the inflammatory infiltrate. Based on our results, we can conclude that the adopted regimen and potency exerted a protective effect, reducing parasitemia. However, it intensified the histopathological lesions in encephalon and heart of mice infected with T. gondii.

HMGB1 release triggered by the interaction of live retinal cells and uveitogenic T cells is Fas/FasL activation-dependent

Background

It is not clear how invading autoreactive T cells initiate the pathogenic process inside the diseased organ in T cell-mediated organ-specific autoimmune disease. In experimental autoimmune uveitis (EAU) induced by adoptive transfer of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells in mice, we have previously reported that intraocular inflammation was initiated by infiltrating IRBP-specific T cells that directly interacted with retinal cells and resulted in the active release of high mobility group box 1 (HMGB1), an important member of damage associate molecular patterns (DAMPs). Furthermore, blockade of HMGB1 in our murine model reduced intraocular inflammation via suppression of IRBP-specific T cell functions. These results have demonstrated that HMGB1 is an early and critical mediator of induction of intraocular inflammation. The present study identified the cell surface molecule that triggers HMGB1 secretion.

Methods

Retinal explants from Fas-deficient (Fas^lpr) and wild-type (Wt) C57BL/6 (B6) mice were cultured with activated IRBP 1–20 peptide-specific T cells or with a Fas-activating antibody (Jo2), and then the level of HMGB1 in culture supernatants were detected by ELISA. In addition, released HMGB1 was examined in the eye of Fas^lpr and Wt mice after IRBP-specific T cell transfer. Uveitis was evaluated in the IRBP-specific T cell transferred Fas^lpr mice after recombinant HMGB1 was restored within the eye and in the IRBP-specific T cell transferred Wt mice after they were treated with a Fas antagonist (Met12).

Results

In contrast to retinal explants from Wt mice, those from Fas^lpr mice did not release HMGB1 after exposure to IRBP-specific T cells or to Jo2. The release of HMGB1 by Wt retinal explants was suppressed by Met 12. Moreover, after IRBP-specific T cell injection, Fas^lpr mice did not release HMGB1 in the eye or develop EAU, but intravitreous injection of HMGB1 resulted in intraocular inflammation. Finally, tEAU in Wt mice was attenuated by local treatment with Met 12. Unlike HMGB1, Fas-induced IL-1 and IL-18 were not essential for tEAU induction.

Conclusion

Our results show that interaction of retinal cells with infiltrating uveitogenic T cells leads to rapid release of HMGB1 via the Fas/FasL inflammatory signaling pathway.

Moderate physical exercise protects myenteric metabolically more active neurons in mice infected with Trypanosoma cruzi

BACKGROUND

Trypanosoma cruzi causes neuronal myenteric depopulation compromising intestinal function.

AIM

The purpose of this study was to evaluate the influence of moderate physical exercise on NADH diaphorase (NADH-d)-positive neurons in the myenteric plexus and intestinal wall of the colon in mice infected with T. cruzi.

MATERIALS AND METHODS

Forty 30-day-old male Swiss mice were divided into the following groups: trained infected (TI), sedentary infected (SI), trained control (TC), and sedentary control. The TC and TI groups were subjected to a moderate physical exercise program on a treadmill for 8 weeks. Three days after finishing physical exercise, the TI and SI groups were intraperitoneally inoculated with 1,300 blood trypomastigotes of the Y strain of Trypanosoma cruzi. Parasitemia was evaluated from days 4 to 61 after inoculation. On day 75 of infection, myenteric neurons in the colon were quantified (NADH-d), and inflammatory foci were counted. Tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β) levels were evaluated in plasma. The results were compared using analysis of variance and the Kruskal-Wallis test at a 5 % significance level.

RESULTS

Moderate physical exercise reduced the parasite peak on day 8 of infection (p = 0.0132) and total parasitemia (p = 0.0307). It also prevented neuronal depopulation (p < 0.01), caused hypertrophy of these cells (p < 0.05), prevented the formation of inflammatory foci (p < 0.01), and increased the synthesis of TNF-α (p < 0.01) and TGF-β (p > 0.05).

CONCLUSION

These results reinforce the therapeutic benefits of moderate physical exercise for T. cruzi infection.

Moderate physical exercise reduces parasitaemia and protects colonic myenteric neurons in mice infected with Trypanosoma cruzi

This study evaluated the influence of moderate physical exercise on the myenteric neurons in the colonic intestinal wall of mice that had been infected with Trypanosoma cruzi. Parasitology and immunological aspects of the mice were considered. Forty-day-old male Swiss mice were divided into four groups: Trained Infected (TI), Sedentary Infected (SI), Trained Control (TC), and Sedentary Control (SC). The TC and TI were subjected to a moderate physical exercise program on a treadmill for 8 weeks. Three days after finishing exercise, the TI and SI groups were inoculated with 1,300 blood trypomastigotes of the Y strain-T. cruzi. After 75 days of infection results were obtained. Kruskal-Wallis or Analyze of variance (Tukey post hoc test) at 5% level of significance was performed. Moderate physical exercise reduced both the parasite peak (day 8 of infection) and total parasitemia compared with the sedentary groups (P < 0.05). This activity also contributed to neuronal survival (P < 0.05). Exercise caused neuronal hypertrophy (P < 0.05) and an increase in the total thickness of the intestinal wall (P < 0.05). The TI group exhibited an increase in the number of intraepithelial lymphocytes (P > 0.05). In trained animals, the number of goblet cells was reduced compared with sedentary animals (P < 0.05). Physical exercise prevented the formation of inflammatory foci in the TI group (P < 0.05) and increased the synthesis of TNF-α (P < 0.05) and TGF-β (P > 0.05). The present results demonstrated the benefits of moderate physical exercise, and reaffirmed the possibility of that it may contribute to improving clinical treatment in Chagas' disease patients.

Evolution of infection in mice inoculated by the oral route with different developmental forms of Trypanosoma cruzi I and II

Oral infection has become the most important transmission mechanism of Chagas disease in Brazil. For this study, the development of Trypanosoma cruzi infection in mice, induced by the oral and intraperitoneal (IP) routes, was compared. Four groups of Swiss mice were used to evaluate the influence of parasite genetics, number of parasites, inoculation volume and developmental stages on the development of the orally induced infection: 1 - blood trypomastigotes (BT) via oral; 2 - BT via IP; 3 - culture metacyclic trypomastigotes (MT) via oral; and 4 - culture MT via IP. Animals inoculated orally showed levels of parasitemia, as well as infectivity and mortality rates, lower than animals inoculated via IP, regardless of DTU (discrete typing unit) and inoculum. Animals infected with TcII showed higher levels of these parameters than did animals infected with TcI. The larger volume of inoculum showed a greater capacity to cause an infection when administered via the oral route. BT infection was more virulent than culture MT infection for both routes (oral and IP). However, mice inoculated orally with BT showed lower levels than via IP, while mice inoculated orally with culture MT showed similar levels of infection to those inoculated via IP. Mice inoculated with culture MT showed more histopathological changes than those inoculated with BT, regardless of the inoculation route. These results indicate that this alternative experimental model is useful for evaluating infection by T. cruzi isolates with subpatent parasitemia and low virulence, such as those belonging to the TcI and TcIV DTUs, which are prevalent in outbreaks of orally transmitted Chagas disease.

Defective T-lymphocyte migration to muscles in dystrophin-deficient mice

Duchenne muscular dystrophy (DMD), an X-linked recessive disorder affecting 1 in 3500 males, is caused by mutations in the dystrophin gene. DMD leads to degeneration of skeletal and cardiac muscles and to chronic inflammation. The mdx/mdx mouse has been widely used to study DMD; this model mimics most characteristics of the disease, including low numbers of T cells in damaged muscles. In this study, we aimed to assess migration of T cells to the heart and to identify any alterations in adhesion molecules that could possibly modulate this process. In 6-week-old mdx/mdx mice, blood leukocytes, including T cells, were CD62L(+), but by 12 weeks of age down-modulation was evident, with only approximately 40% of T cells retaining this molecule. Our in vitro and in vivo results point to a P2X7-dependent shedding of CD62L (with high levels in the serum), which in 12-week-old mdx/mdx mice reduces blood T cell competence to adhere to cardiac vessels in vitro and to reach cardiac tissue in vivo, even after Trypanosoma cruzi infection, a known inducer of lymphoid myocarditis. In mdx/mdx mice treated with Brilliant Blue G, a P2X7 blocker, these blood lymphocytes retained CD62L and were capable of migrating to the heart. These results provide new insights into the mechanisms of inflammatory infiltration and immune regulation in DMD.

Mast cell function and death in Trypanosoma cruzi infection

Although the roles of mast cells (MCs) are essential in many inflammatory and fibrotic diseases, their role in Trypanosoma cruzi-induced cardiomyopathy is unexplored. In this study, we treated infected CBA mice with cromolyn, an MC stabilizer, and observed much greater parasitemia and interferon-γ levels, higher mortality, myocarditis, and cardiac damage. Although these data show that MCs are important in controlling acute infection, we observed MC apoptosis in the cardiac tissue and peritoneal cavity of untreated mice. In the heart, pericardial mucosal MC die, perhaps because of reduced amounts of local stem cell factor. Using RT-PCR in purified cardiac MCs, we observed that infection induced transcription of P2X(7) receptor and Fas, two molecules reportedly involved in cell death and inflammatory regulation. In gld/gld mice (FasL(-/-)), apoptosis of cardiac, but not peritoneal, MCs was decreased. Conversely, infection of P2X(7)(-/-) mice led to reduced peritoneal, but not cardiac, MC death. These data illustrate the immunomodulatory role played by MCs in T. cruzi infection and the complexity of molecular interactions that control inflammatory pathways in different tissues and compartments.

Inflammation and Chagas disease some mechanisms and relevance

Chagas cardiomyopathy is caused by infection with flagellated protozoan Trypanosoma cruzi. In patients, there is a fine balance between control of the replication and the intensity of the inflammatory response so that the host is unable to eliminate the parasite resulting in the parasite persisting as a lifelong infection in most individuals. However, the parasite persists in such a way that it causes no or little disease. This chapter reviews our understanding of many of the mediators of inflammation and cells which are involved in the inflammatory response of mammals to T. cruzi infection. Particular emphasis is given to the role of chemokines, endothelin and lipid mediators. Understanding the full range of mediators and cells present and how they interact with each other in Chagas disease may shed light on how we modulate disease pathogenesis and define new approaches to treat or prevent the disease.

Apoptosis induced by parasitic diseases

Fatalities caused by parasitic infections often occur as a result of tissue injury that results from a form of host-cell death known as apoptosis. However, instead of being pathogenic, parasite-induced apoptosis may facilitate host survival. Consequently, it is of utmost importance to decipher and understand the process and the role of apoptosis induced or controlled by parasites in humans. Despite this, few studies provide definitive knowledge of parasite-induced host-cell apoptosis. Here, the focus is on a consideration of host-cell apoptosis as either a pathogenic feature or as a factor enabling parasite survival and development.

Cell death by apoptotic-like mechanisms could be described as a ride to death with a return ticket, as initiation of the pathway may be reversed, with the potential that it could be manipulated for therapeutic purposes. The management of host-cell apoptosis could thus be an adjunctive factor for parasitic disease treatment. Evidence that the apoptotic process could be reversed by anti-apoptotic drugs has recently been obtained, leading to the possibility of host-cell rescue after injury. An important issue will be to predict the beneficial or deleterious effects of controlling human cell death by apoptotic-like mechanisms during parasitic diseases.

Targeting caspases in intracellular protozoan infections

Caspases are cysteine aspartases acting either as initiators (caspases 8, 9, and 10) or executioners (caspases 3, 6, and 7) to induce programmed cell death by apoptosis. Parasite infections by certain intracellular protozoans increase host cell life span by targeting caspase activation. Conversely, caspase activation, followed by apoptosis of lymphocytes and other cells, prevents effective immune responses to chronic parasite infection. Here we discuss how pharmacological inhibition of caspases might affect the immunity to protozoan infections, by either blocking or delaying apoptosis.

Intravenous immunoglobulin increases survival time in the acute phase of experimental Chagas disease

Chagas disease induced by Trypanosoma cruzi (Tc) infection is an important cause of mortality and morbidity affecting the cardiovascular system for which presently available therapies are insufficient and largely inadequate. Intravenous immunoglobulin (IVIg) is a therapeutic preparation containing normal polyspecific IgG obtained from plasma pools of several thousand healthy donors and is used in several autoimmune, inflammatory and infectious diseases. In the study of heart from mice chronically infected with Tc, we observed that IVIg restores type 1 atrioventricular block or bradycardia. In the present study, we investigated the effects of IVIg in acute Tc infection. Intravenous immunoglobulin administration after the first week of infection was associated with an increase in survival time. Taken together, results observed in the chronic and in the acute phase associate IVIg treatment with a favourable outcome in T. cruzi infection.

The role of FasL and Fas in health and disease

The FS7-associated cell surface antigen (Fas, also named CD95, APO-1 or TNFRSF6) attracted considerable interest in the field of apoptosis research since its discovery in 1989. The groups of Shin Yonehara and Peter Krammer were the first reporting extensive apoptotic cell death induction upon treating cells with Fas-specific monoclonal antibodies.1,2 Cloning of Fas3 and its ligand,4,5 FasL (also known as CD178, CD95L or TNFSF6), laid the cornerstone in establishing this receptor-ligand system as a central regulator of apoptosis in mammals. Therapeutic exploitation of FasL-Fas-mediated cytotoxicity was soon an ambitous goal and during the last decade numerous strategies have been developed for its realization. In this chapter, we will briefly introduce essential general aspects of the FasL-Fas system before reviewing its physiological and pathophysiological relevance. Finally, FasL-Fas-related therapeutic tools and concepts will be addressed.

Fas (CD95) induces rapid, TLR4/IRAK4-dependent release of pro-inflammatory HMGB1 from macrophages

Although Fas (CD95) is recognized as a death receptor that induces apoptosis, recent studies indicate that the Fas/FasL system can induce pro-inflammatory cytokine production by macrophages independent of conventional caspase-mediated apoptotic signaling. The precise mechanism(s) by which Fas activates macrophage inflammation is unknown. We hypothesized that Fas stimulates rapid release of high mobility group box 1 (HMGB1) that acts in an autocrine and/or paracrine manner to stimulate pro-inflammatory cytokine production via a Toll-like receptor-4 (TLR4)/Interleukin-1 receptor associated kinase-4 (IRAK4)-dependent mechanism. Following Fas activation, HMGB1 was released within 1 hr from viable RAW267.4 cells and primary murine peritoneal macrophages. HMGB1 release was more rapid following Fas activation compared to LPS stimulation. Neutralization of HMGB1 with an inhibitory anti-HMGB1 monoclonal antibody strongly inhibited Fas-induced production of tumor necrosis factor (TNF) and macrophage inflammatory protein-2 (MIP-2). Both Fas-induced HMGB1 release and associated pro-inflammatory cytokine production were significantly decreased from Tlr4^-/- and Irak4^-/- macrophages, but not Tlr2^-/- macrophages. These findings reveal a novel mechanism underlying Fas-mediated pro-inflammatory physiological responses in macrophages. We conclude that Fas activation induces rapid, TLR4/IRAK4-dependent release of HMGB1 that contributes to Fas-mediated pro-inflammatory cytokine production by viable macrophages.

Absence of Fas-L aggravates renal injury in acute Trypanosoma cruzi infection

Trypanosoma cruzi infection induces diverse alterations in immunocompetent cells and organs, myocarditis and congestive heart failure. However, the physiological network of disturbances imposed by the infection has not been addressed thoroughly. Regarding myocarditis induced by the infection, we observed in our previous work that Fas-L-/- mice (gld/gld) have very mild inflammatory infiltration when compared to BALB/c mice. However, all mice from both lineages die in the early acute phase. Therefore, in this work we studied the physiological connection relating arterial pressure, renal function/damage and cardiac insufficiency as causes of death. Our results show that a broader set of dysfunctions that could be classified as a cardio/anaemic/renal syndrome is more likely responsible for cardiac failure and death in both lineages. However, gld/gld mice had very early glomerular deposition of IgM and a more intense renal inflammatory response with reduced renal filtration, which is probably responsible for the premature death in the absence of significant myocarditis in gld/gld.

Is the Fas/Fas-L pathway a promising target for treating inflammatory heart disease?

The elucidation of the intricate molecular network of costimulus and regulatory pathways of the immune system led to the design of molecular therapies that specifically inactivate some cellular responses and ameliorate some autoimmune and inflammatory diseases. This innovative concept opens a new class of therapies, and one of the central components that could be targeted in future molecular therapies is the Fas-based pathway. Both soluble and membrane-bound Fas and Fas-L molecules exert a wide range of proinflammatory functions through the secretion of cytokines and chemokines, cellular chemotaxis, transcriptional regulation, cellular death, and others. Accordingly, many chronic inflammatory diseases, including myocarditis, are attenuated in mice lacking either molecule. Although it is tempting to speculate that the Fas/Fas-L pathway could be targeted for in vivo myocarditis therapy, the plurality of Fas/Fas-L functions can be an obstacle, leading to important side effects. In this review, we suggest that the injection of nonagonistic antibodies raised against the Fas molecule or the inactivation of downstream Fas-1,4,5-inositol triphosphate cascade are possible targets for myocarditis treatment.

Alterations in myocardial gene expression associated with experimental Trypanosoma cruzi infection

Chagas disease, characterized by acute myocarditis and chronic cardiomyopathy, is caused by infection with the protozoan parasite Trypanosoma cruzi. We sought to identify genes altered during the development of parasite-induced cardiomyopathy. Microarrays containing 27,400 sequence-verified mouse cDNAs were used to analyze global gene expression changes in the myocardium of a murine model of chagasic cardiomyopathy. Changes in gene expression were determined as the acute stage of infection developed into the chronic stage. This analysis was performed on the hearts of male CD-1 mice infected with trypomastigotes of T. cruzi (Brazil strain). At each interval we compared infected and uninfected mice and confirmed the microarray data with dye reversal. We identified eight distinct categories of mRNAs that were differentially regulated during infection and identified dysregulation of several key genes. These data may provide insight into the pathogenesis of chagasic cardiomyopathy and provide new targets for intervention.

The involvement of CD4+CD25+ T cells in the acute phase of Trypanosoma cruzi infection

The infection with Trypanosoma cruzi leads to a vigorous and apparently uncontrolled inflammatory response in the heart. Although the parasites trigger specific immune response, the infection is not completely cleared out, a phenomenon that in other parasitic infections has been attributed to CD4+CD25+ T cells (Tregs). Then, we examined the role of natural Tregs and its signaling through CD25 and GITR in the resistance against infection with T. cruzi. Mice were treated with mAb against CD25 and GITR and the parasitemia, mortality and heart pathology analyzed. First, we demonstrated that CD4+CD25+GITR+Foxp3+ T cells migrate to the heart of infected mice. The treatment with anti-CD25 or anti-GITR resulted in increased mortality of these infected animals. Moreover, the treatment with anti-GITR enhanced the myocarditis, with increased migration of CD4+, CD8+, and CCR5+ leukocytes, TNF-alpha production, and tissue parasitism, although it did not change the systemic nitric oxide synthesis. These data showed a limited role for CD25 signaling in controlling the inflammatory response during this protozoan infection. Also, the data suggested that signaling through GITR is determinant to control of the heart inflammation, parasite replication, and host resistance against the infection.