The Pivotal Role of 5-Lipoxygenase-Derived LTB4 in Controlling Pulmonary Paracoccidioidomycosis

Leukotrienes (LTs) produced from arachidonic acid by the action of 5-lipoxygenase (5-LO) are classical mediators of inflammatory responses. However, studies published in the literature regarding these mediators are contradictory and it remains uncertain whether these lipid mediators play a role in host defense against the fungal pathogen Paracoccidioides brasiliensis. To determine the involvement of LTs in the host response to pulmonary infection, wild-type and LT-deficient mice by targeted disruption of the 5-lipoxygenase gene (knockout mice) were studied following intratracheal challenge with P. brasiliensis yeasts. The results showed that infection is uniformly fatal in 5-LO-deficient mice and the mechanisms that account for this phenotype are an exacerbated lung injury and higher fungal pulmonary burden. Genetic ablation or pharmacological inhibition of LTs resulted in lower phagocytosis and fungicidal activity of macrophages in vitro, suggesting that deficiency in fungal clearance seems to be secondary to the absence of activation in 5-LO^−/− macrophages. Exogenous LTB₄ restored phagocytosis and fungicidal activity of 5-LO^−/− macrophages. Moreover, P. brasiliensis killing promoted by LTB₄ was dependent on nitric oxide (NO) production by macrophages. Taken together, these results reveal a fundamental role for 5-LO-derived LTB₄ in the protective response to P. brasiliensis infection and identify relevant mechanisms for the control of fungal infection during the early stages of the host immune response.     

Eicosanoid pathway on host resistance and inflammation during Mycobacterium tuberculosis infection is comprised by LTB4 reduction but not PGE2 increment

The functions of eicosanoids, a family of potent biologically active lipid mediators, are not restricted to inflammatory responses and they also act as mediators of the pathogenesis process. However, the role of eicosanoids in tuberculosis remains controversial. To investigate the specific role of LTB₄ in Mycobacterium tuberculosis (Mtb) infection, we used 5-lipoxygenase-deficient (5-LO^−/−) mice and WT (sv129) mice inoculated intranasally with LTB₄ (encapsulated in PLGA microspheres). We showed that deficiency of the 5-LO pathway was related to resistance to Mtb infection. LTB₄ inoculation increased susceptibility to Mtb in 5-LO^−/− mice but not in WT mice, resulting in worsening of lung inflammation and tissue damage. In infected WT mice, most supplementary LTB₄ was metabolized to the inactive form 12-oxo-LTB₄ in the lung. A high amount of PGE₂ was detected during Mtb infection, and pharmacological inhibition of COX-2 induced a significant reduction of bacterial load and an improved innate immune response in the lungs, independently of baseline LTB₄ levels. COX-2 inhibition with celecoxib significantly reduced PGE₂ levels, enhanced IFN-γ production and NO release, and increased macrophage phagocytosis of Mtb. The results suggest that a balance between PGE₂/LTB₄ is essential in the pathogenesis process of tuberculosis to prevent severe inflammation. Moreover, optimal levels of PGE₂ are required to induce an effective innate response in the early phase of Mtb infection. Thus, pharmacological modulation of eicosanoid production may provide an important host-directed therapy in tuberculosis.     

Toxoplasma gondii: The role of IFN-gamma, TNFRp55 and iNOS in inflammatory changes during infection

In order to examine the role of IFN-γ, TNFRp55 and iNOS in inflammatory reaction during toxoplasmosis, IFN-γ^−/−, TNFRp55^−/− and iNOS^−/− mice were experimentally infected with Toxoplasma gondii ME-49 strain. The organs of the mice were evaluated for histology and immunohistochemistry in detection of tissue parasitism and iNOS positive cells. IFN-γ^−/− mice presented mild inflammation in peripheral organs associated with a high parasitism and mortality in the acute phase of infection. In contrast, the peripheral organs of WT, TNFRp55^−/− and iNOS^−/− mice, presented a significant inflammatory reaction and low tissue parasitism in the same period of infection. The inflammatory lesions and tissue parasitism were increased and more severe in the Central Nervous System (CNS) of TNFRp55^−/− and iNOS^−/− with a progression of infection, when compared to WT mice. In these knockout animals, the inflammatory changes were associated with low levels or no expression of iNOS in TNFRp55^−/− and iNOS^−/− mice, respectively.     

Mannose-Binding Lectin Regulates Host Resistance and Pathology during Experimental Infection with Trypanosoma cruzi

Mannose-binding lectin (MBL) is a humoral pattern-recognition molecule important for host defense. Although recent genetic studies suggest an involvement of MBL/MASP2-associated pathways in Chagas’ disease, it is currently unknown whether MBL plays a role in host resistance to the intracellular protozoan Trypanosoma cruzi, the causative agent of Chagas’ disease. In this study we employed MBL^−/− mice to assess the role of MBL in resistance to experimental infection with T. cruzi. T. cruzi infection enhanced tissue expression of MBL both at the mRNA and protein level. Similarly, symptomatic acute Chagas’ disease patients displayed increased serum concentrations of MBL compared to patients with indeterminate, asymptomatic forms of the disease. Furthermore, increased parasite loads in the blood and/or tissue were observed in MBL^−/− mice compared to WT controls. This was associated with reduced systemic levels of IL-12/23p40 in MBL^−/− mice. Importantly, MBL^−/− mice infected with a cardiotropic strain of T. cruzi displayed increased myocarditis and cardiac fibrosis compared to WT controls. The latter was accompanied by elevated hydroxyproline content and mRNA levels of collagen-1 and -6 in the heart. These observations point to a previously unappreciated role for MBL in regulating host resistance and cardiac inflammation during infection with a major human pathogen.     

Deficiency in indoleamine-2, 3-dioxygenase induces upregulation of guanylate binding protein 1 and inducible nitric oxide synthase expression in the brain during cerebral infection with Toxoplasma gondii in genetically resistant BALB/c mice but not in genetically susceptible C57BL/6 mice

We examined the roles of indoleamine-2, 3-dioxygenase 1 (IDO1) in controlling cerebral Toxoplasma gondii infection in both genetically resistant and susceptible strains of mice. In susceptible C57BL/6 mice, IDO expression was immunohistochemically detected only in a minority (22.5%) of tachyzoite-infected cells in their brains during the later stage of infection. When C57BL-6-background IDO1-deficient (IDO1^?/?) mice were infected, their cerebral tachyzoite burden was equivalent to those of wild-type (WT) animals. In contrast, in resistant BALB/c mice, IDO expression was detected in a majority (84.0%) of tachyzoite-infected cerebral cells. However, tachyzoite burden in BALB/c-background IDO1^?/? mice remained as low as that of WT mice, which was 78 times less than those of C57BL/6 mice. Of interest, IDO1^?/? mice of only resistant BALB/c-background had markedly greater cerebral expressions of two other IFN-γ-mediated effector molecules, guanylate binding protein 1 (Gbp1) and nitric oxide synthase 2 (NOS2), than their WT mice. Therefore, it would be possible that IDO1 deficiency was effectively compensated by the upregulated expression of Gbp1 and NOS2 to control cerebral tachyzoite growth in genetically resistant BALB/c mice, whereas IDO1 did not significantly contribute to controlling cerebral tachyzoite growth in genetically susceptible C57BL/6 mice because of its suppressed expression in infected cells.     

Haeme oxygenase activity protects the host against excessive cardiac inflammation during experimental Trypanosoma cruzi infection

The infection with Trypanosoma cruzi induces a robust cardiac inflammation that plays a pathogenic role in the development of Chagas heart disease. In this study, we aimed at investigating the effects of Haem Oxygenase (HO) during experimental infection by T. cruzi in BALB/c and C57BL/6 mice. HO has recently emerged as a key factor modulating the immune response in diverse models of inflammatory diseases. In mice with two different genetic backgrounds, the pharmacologic inhibition of HO activity with zinc-protoporphyrin IX (ZnPPIX) induced enhanced myocarditis and reduced parasitaemia, which was accompanied by an amplified production of nitric oxide and increased influx of CD4⁺, CD8⁺ and IFN-γ⁺ cells to the myocardium in comparison with the control group. Conversely, treatment with haemin (an activator of HO) lead to a decreased number of intracardiac CD4⁺ (but not CD8⁺) cells compared to the control group. The mechanism involved in these observations is a modulation of the induction of regulatory T cells, because the stimulation or inhibition of HO was parallelled by an enhanced or reduced frequency of regulatory T cells, respectively. Hence, HO may be involved in the regulation of heart tissue inflammation and could be a potential target in conceiving future therapeutic approaches for Chagas disease.     

MIF synergizes with Trypanosoma cruzi antigens to promote efficient dendritic cell maturation and IL-12 production via p38 MAPK

Macrophage migration inhibitory factor (MIF) has been found to be involved in host resistance to several parasitic infections. To determine the mechanisms of the MIF-dependent responses to Trypanosoma cruzi, we investigated host resistance in MIF-/- mice (on the BALB/c background) during an intraperitoneal infection. We focused on the potential involvement of MIF in dendritic cell (DC) maturation and cytokine production. Following a challenge with 5 x 10³ T. cruzi parasites, wild type (WT) mice developed a strong IL-12 response and adequate maturation of the draining mesenteric lymph node DCs and were resistant to infection. In contrast, similarly infected MIF^-/- mice mounted a weak IL-12 response, displayed immature DCs in the early phases of infection and rapidly succumbed to T. cruzi infection. The lack of maturation and IL-12 production by the DCs in response to total T. cruzi antigen (TcAg) was confirmed by in vitro studies. These effects were reversed following treatment with recombinant MIF. Interestingly, TcAg-stimulated bone marrow-derived DCs from both WT and MIF^-/- mice had increased ERK1/2 MAPK phosphorylation. In contrast, p38 phosphorylation was only upregulated in WT DCs. Reconstitution of MIF to MIF^-/- DCs upregulated p38 phosphorylation. The MIF-p38 pathway affected MHC-II and CD86 expression as well as IL-12 production. These findings demonstrate that the MIF-induced early DC maturation and IL-12 production mediates resistance to T. cruzi infection, probably by activating the p38 pathway.     

Acute and Chronic Experimental Trypanosoma cruzi Infection in the Rat. Response to Systemic Treatment with Recombinant Rat Interferon-Gamma

We examined the effects of recombinant rat inteferon-gamma (IFN-γ) injections on the parasitologic, serologic, immunologic and histopathologic features of acute and chronic experimental Trypanosoma cruzi (T. cruzi) infections in “l” rats. Upon infection at weaning, two rat groups were allocated to receive a 20-day cycle of IFN-γ injections, 20,000 IU/rat each, which started at 1, and 7 days post-infection (pi). Treatment with IFN-γ, initiated at either 1 or 7 days pi, resulted in comparatively lower peak parasitemias (P<0.02) but in similar levels of anti-T. cruzi circulating antibodies and serum IFN-γ activities. The latter appeared significantly increased during acute infection whereas biologically active tumor necrosis factor was virtually undetectable in serum from infected rats regardless of whether they had been given IFN-γ or not. The prevalence of chronic focal myocarditis in IFN-γ-treated infected rats showed no differences with respect to the one recorded in control-infected counterparts. The inverse CD4/CD8 ratio of spleen and lymph node T cells that usually accompanies chronic infection was reversed by IFN-γ. Mononuclear cells carrying class III-A and I-E molecules, that were found to have increased at both compartments, appeared also modified upon IFN-γ treatment with an overincrease of I-A-positive cells, and a normalization of I-E-bearing cells.     

Role of CCL3/MIP-1α and CCL5/RANTES during acute Trypanosoma cruzi infection in rats

Chagas’ disease is caused by Trypanosoma cruzi infection and is characterized by chronic fibrogenic inflammation and heart dysfunction. Chemokines are produced during infection and drive tissue inflammation. In rats, acute infection is characterized by intense myocarditis and regression of inflammation after control of parasitism. We investigated the role of CCL3 and CCL5 during infection by using DNA vaccination encoding for each chemokine separately or simultaneously. MetRANTES treatment was used to evaluate the role of CCR1 and CCR5, the receptors for CCL3 and CCL5. Vaccination with CCL3 or CCL5 increased heart parasitism and decreased local IFN-γ production, but did not influence intensity of inflammation. Simultaneous treatment with both plasmids or treatment with MetRANTES enhanced cardiac inflammation, fibrosis and parasitism. In conclusion, chemokines CCL3 and CCL5 are relevant, but not essential, for control of T. cruzi infection in rats. On the other hand, combined blockade of these chemokines or their receptors enhanced tissue inflammation and fibrosis, clearly contrasting with available data in murine models of T. cruzi infection. These data reinforce the important role of chemokines during T. cruzi infection but suggest that caution must be taken when expanding the therapeutic modulation of the chemokine system in mice to the human infection.     

Treatment of chronically Trypanosoma cruzi-infected mice with a CCR1/CCR5 antagonist (Met-RANTES) results in amelioration of cardiac tissue damage

The comprehension of the molecular mechanisms leading to Trypanosoma cruzi-elicited heart dysfunction might contribute to design novel therapeutic strategies aiming to ameliorate chronic Chagas disease cardiomyopathy. In C3H/He mice infected with the low virulence T. cruzi Colombian strain, the persistent cardiac inflammation composed mainly of CCR5⁺ T lymphocytes parallels the expression of CC-chemokines in a pro-inflammatory IFN-γ and TNF-α milieu. The chronic myocarditis is accompanied by increased frequency of peripheral CCR5⁺LFA-1⁺ T lymphocytes. The treatment of chronically T. cruzi-infected mice with Met-RANTES, a selective CCR1/CCR5 antagonist, led to a 20–30% decrease in CD4⁺ cell numbers as well as IL-10, IL-13 and TNF-α expression. Further, Met-RANTES administration impaired the re-compartmentalization of the activated CD4⁺CCR5⁺ lymphocytes. Importantly, Met-RANTES treatment resulted in significant reduction in parasite load and fibronectin deposition in the heart tissue. Moreover, Met-RANTES treatment significantly protected T. cruzi-infected mice against connexin 43 loss in heart tissue and CK-MB level enhancement, markers of heart dysfunction. Thus, our results corroborate that therapeutic strategies based on the modulation of CCR1/CCR5-mediated cell migration and/or effector function may contribute to cardiac tissue damage limitation during chronic Chagas disease.     

TIPE2 knockout reduces myocardial cell damage by inhibiting IFN-γ-mediated ferroptosis

Acute rejection of the transplanted heart is mediated by oxidative programmed cell death through the synergistic effects of the innate and adaptive immune systems. However, the role of ferroptosis, a newly discovered form of oxidative cell death, has not been widely evaluated. Tumor necrosis factor-α-induced protein-8 like 2 (TNFAIP8L2), also known as TIPE2, is required for maintaining immune homeostasis. To characterize the role of TIPE2 in mediating heart allografts, BALB/c hearts were transplanted into C57BL/6 wild-type (WT) and TIPE2^?/? recipient mice. In TIPE2^?/? recipient mice, allograft injury in BALB/c allograft hearts was significantly reduced through the inhibition of allograft ferroptosis. On day 3 and day 6 post-transplantation, the numbers of CD3⁺, CD4⁺, and CD8⁺ cells among splenocytes and draining lymph node cells were significantly decreased, and the activation of CD4⁺ and CD8⁺ cells in grafts was decreased in TIPE2^?/? recipient mice compared with WT mice. Moreover, CD4⁺ and CD8⁺ T cells in TIPE2^?/? recipient mice were characterized by deficient capacities for interferon-γ (IFN-γ) production through the TBK1 signaling axis and increased glutathione peroxidase 4 (GPX4). In cell experiments, treatment with IFN-γ enhanced ferroptosis-specific lipid peroxidation in myocardial cells and correlated inversely with GPX4 expression. Mechanistically, IFN-γ administration decreased the expression of GPX4 by inhibiting MEK/ERK phosphorylation. In summary, our findings demonstrated that TIPE2 deficiency inhibits T-cell production of IFN-γ to reduce ferroptosis in allografts by restraining lipid peroxidation.     

5-Lypoxygenase Products Are Involved in Renal Tubulointerstitial Injury Induced by Albumin Overload in Proximal Tubules in Mice

The role of albumin overload in proximal tubules (PT) in the development of tubulointerstitial injury and, consequently, in the progression of renal disease has become more relevant in recent years. Despite the importance of leukotrienes (LTs) in renal disease, little is known about their role in tubulointerstitial injury. The aim of the present work was to investigate the possible role of LTs on tubulointerstitial injury induced by albumin overload. An animal model of tubulointerstitial injury challenged by bovine serum albumin was developed in SV129 mice (wild-type) and 5-lipoxygenase-deficient mice (5-LO^–/–). The changes in glomerular morphology and nestin expression observed in wild-type mice subjected to kidney insult were also observed in 5-LO^–/– mice. The levels of urinary protein observed in the 5-LO^–/– mice subjected or not to kidney insult were lower than those observed in respective wild-type mice. Furthermore, the increase in lactate dehydrogenase activity, a marker of tubule damage, observed in wild-type mice subjected to kidney insult did not occur in 5-LO^–/– mice. LTB₄ and LTD₄, 5-LO products, decreased the uptake of albumin in LLC-PK1 cells, a well-characterized porcine PT cell line. This effect correlated with activation of protein kinase C and inhibition of protein kinase B. The level of proinflammatory cytokines, tumor necrosis factor-α and interleukin (IL)-6, increased in mice subjected to kidney insult but this effect was not modified in 5-LO^–/– mice. However, 5-LO^–/– mice subjected to kidney insult presented lower macrophage infiltration and higher levels of IL-10 than wild-type mice. Our results reveal that LTs have an important role in tubulointerstitial disease induced by albumin overload.     

Insights into CX3CL1/Fractalkine during experimental Trypanosoma cruzi infection

Trypanosoma cruzi triggers a progressive myocarditis in mammalians through activation and recruitment of leukocytes and release of inflammatory mediators. The chemokine CX3CL1 has been highlighted for its potential role in the parasite controlling in end-pathological status of infected hosts. This study investigated the systemic and cardiac release of CX3CL1 in experimental T. cruzi infection and how this chemokine correlates with endothelin-1 and TNF. Male Fisher rats (n = 20) were infected, or not, by the Y strain of T. cruzi and parasitemia was daily evaluated and immunoassays performed in the cardiac tissue macerated supernatant and in serum to evaluate CX3CL1, endothelin, and TNF production on days 5 and 15 of infection. T. cruzi infection induced a higher serum and cardiac production of these mediators on days 5 and 15 of infection. In both periods of infection, respectively, CX3CL1 showed a positive correlation with TNF (r = 0.833, p < 0.001 and r = 0.723, p < 0.001) and endothelin-1 (r = 0.801, p < 0.05 and r = 0.857, p < 0.001), which reinforce its participation in the T. cruzi-induced myocarditis development.     

NLRP3 Controls Trypanosoma cruzi Infection through a Caspase-1-Dependent IL-1R-Independent NO Production

Trypanosoma cruzi (T. cruzi) is an intracellular protozoan parasite and the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people worldwide. Although the role of TLR and Nod1 in the control of T. cruzi infection is well-established, the involvement of inflammasomes remains to be elucidated. Herein, we demonstrate for the first time that T. cruzi infection induces IL-1β production in an NLRP3- and caspase-1-dependent manner. Cathepsin B appears to be required for NLRP3 activation in response to infection with T. cruzi, as pharmacological inhibition of cathepsin B abrogates IL-1β secretion. NLRP3^−/− and caspase1^−/− mice exhibited high numbers of T. cruzi parasites, with a magnitude of peak parasitemia comparable to MyD88^−/− and iNOS^−/− mice (which are susceptible models for T. cruzi infection), indicating the involvement of NLRP3 inflammasome in the control of the acute phase of T. cruzi infection. Although the inflammatory cytokines IL-6 and IFN-γ were found in spleen cells from NLRP3^−/− and caspase1^−/− mice infected with T. cruzi, these mice exhibited severe defects in nitric oxide (NO) production and an impairment in macrophage-mediated parasite killing. Interestingly, neutralization of IL-1β and IL-18, and IL-1R genetic deficiency demonstrate that these cytokines have a minor effect on NO secretion and the capacity of macrophages to control T. cruzi infection. In contrast, inhibition of caspase-1 with z-YVAD-fmk abrogated NO production by WT and MyD88^−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3^−/− and caspase-1^−/− macrophages. Taken together, our results demonstrate a role for the NLRP3 inflammasome in the control of T. cruzi infection and identify NLRP3-mediated, caspase-1-dependent and IL-1R-independent NO production as a novel effector mechanism for these innate receptors.     

Plasminogen activator inhibitor type I may contribute to transient, non-specific changes in immunity in the subacute phase of murine tuberculosis

Tuberculosis, caused by Mycobacterium (M.) tuberculosis, is a devastating infectious disease causing many deaths worldwide. Non-specific host defense mechanisms such as the coagulation and fibrinolytic system may give insight in possible new therapeutic targets. Plasminogen activator inhibitor type-1 (PAI-1), an important regulator of inflammation and fibrinolysis, might be of interest as tuberculosis patients have elevated plasma levels of PAI-1. In this study we set out to investigate the role of PAI-1 during tuberculosis in vivo. Wildtype (WT) and PAI-1 deficient (PAI-1^?/?) mice were intranasally infected with M. tuberculosis H37rv and sacrificed after 2, 5 and 29 weeks. Five weeks post-infection, bacterial loads in lungs of PAI-1^?/? mice were significantly higher compared to WT mice, while no differences were seen 2 and 29 weeks post-infection. At two weeks post-infection increased influx of macrophages and lymphocytes was observed. PAI-1 deficiency was associated with a reduced cytokine response in the lungs; however, upon stimulation with tuberculin purified protein derivative (PPD), PAI-1^?/? splenocytes released increased levels of IFN-γ compared to WT. No clear differences were found between PAI-1^?/? and WT mice at 29 weeks after infection. In conclusion, these data suggest that PAI-1 contributes to transient, non-specific changes in immunity during the early phase of murine tuberculosis.     

Therapeutic Efficacy of a Subunit Vaccine in Controlling Chronic Trypanosoma cruzi Infection and Chagas Disease Is Enhanced by Glutathione Peroxidase Over-Expression

Trypanosoma cruzi-induced oxidative and inflammatory responses are implicated in chagasic cardiomyopathy. In this study, we examined the therapeutic utility of a subunit vaccine against T. cruzi and determined if glutathione peroxidase (GPx1, antioxidant) protects the heart from chagasic pathogenesis. C57BL/6 mice (wild-type (WT) and GPx1 transgenic (GPx^tg) were infected with T. cruzi and at 45 days post-infection (dpi), immunized with TcG2/TcG4 vaccine delivered by a DNA-prime/Protein-boost (D/P) approach. The plasma and tissue-sections were analyzed on 150 dpi for parasite burden, inflammatory and oxidative stress markers, inflammatory infiltrate and fibrosis. WT mice infected with T. cruzi had significantly more blood and tissue parasite burden compared with infected/GPx^tg mice (n = 5-8, p<0.01). Therapeutic vaccination provided >15-fold reduction in blood and tissue parasites in both WT and GPx^tg mice. The increase in plasma levels of myeloperoxidase (MPO, 24.7%) and nitrite (iNOS activity, 45%) was associated with myocardial increase in oxidant levels (3-4-fold) and non-responsive antioxidant status in chagasic/WT mice; and these responses were not controlled after vaccination (n = 5-7). The GPx^tg mice were better equipped than the WT mice in controlling T. cruzi-induced inflammatory and oxidative stress markers. Extensive myocardial and skeletal tissue inflammation noted in chagasic/WT mice, was significantly more compared with chagasic/GPx^tg mice (n = 4-6, p<0.05). Vaccination was equally effective in reducing the chronic inflammatory infiltrate in the heart and skeletal tissue of infected WT and GPx^tg mice (n = 6, p<0.05). Hypertrophy (increased BNP and ANP mRNA) and fibrosis (increased collagen) of the heart were extensively present in chronically-infected WT and GPx^tg mice and notably decreased after therapeutic vaccination. We conclude the therapeutic delivery of D/P vaccine was effective in arresting the chronic parasite persistence and chagasic pathology; and GPx1 over-expression provided additive benefits in reducing the parasite burden, inflammatory/oxidative stress and cardiac remodeling in Chagas disease.     

Rapidly progressive course of Trypanosoma cruzi infection in mice heterozygous for hexamethylene bis-acetamide inducible 1 (Hexim1) gene

Infection with Trypanosoma cruzi causes Chagas disease and results in myocardial inflammation and cardiomyopathy. Downregulated Hexim1 expression, as in Hexim1^+/? mice, reduces cardiac inflammation and fibrosis following ischemic stress. We asked whether reduced expression of Hexim1 would also afford protection against T. cruzi-induced cardiomyopathy. C57BL/6J (wild type – WT) and Hexim1^+/? mice were infected with sub-lethal doses of T. cruzi (Brazil strain), and cardiac function, serologic markers of inflammation and tissue pathology were examined. Infected Hexim1^+/? mice had compromised cardiac function, altered expression of both pro- and anti-inflammatory cytokines, and increased inflammation and fibrosis. Cardiac failure was evidenced by severely diminished heart rate, compensatory increase in respiratory rate, and abnormally high left ventricular mass with severe transmural inflammation. Lungs displayed intense peribronchial inflammation and fibrosis extending into the parenchyma. We also observed Smad3-serine²⁰⁸ phosphorylation in hearts and lungs of infected mice, suggesting increased TGF-β signaling pathway activity. This was more pronounced in Hexim1^+/? mice and correlated with increased fibrosis in these tissues. Conspicuous splenomegaly in the Hexim1^+/? mice most likely resulted from the observed extensive white pulp expansion. T. cruzi infection induced colonic dilatation and marked villous atrophy in both the WT and Hexim1^+/? mice but more so in the latter. The profound exacerbation of pathologic findings suggests a protective role for Hexim1 in T. cruzi infection.     

Coinfection with different Trypanosoma cruzi strains interferes with the host immune response to infection

A century after the discovery of Trypanosoma cruzi in a child living in Lassance, Minas Gerais, Brazil in 1909, many uncertainties remain with respect to factors determining the pathogenesis of Chagas disease (CD). Herein, we simultaneously investigate the contribution of both host and parasite factors during acute phase of infection in BALB/c mice infected with the JG and/or CL Brener T. cruzi strains. JG single infected mice presented reduced parasitemia and heart parasitism, no mortality, levels of pro-inflammatory mediators (TNF-α, CCL2, IL-6 and IFN-γ) similar to those found among naïve animals and no clinical manifestations of disease. On the other hand, CL Brener single infected mice presented higher parasitemia and heart parasitism, as well as an increased systemic release of pro-inflammatory mediators and higher mortality probably due to a toxic shock-like systemic inflammatory response. Interestingly, coinfection with JG and CL Brener strains resulted in intermediate parasitemia, heart parasitism and mortality. This was accompanied by an increase in the systemic release of IL-10 with a parallel increase in the number of MAC-3⁺ and CD4⁺ T spleen cells expressing IL-10. Therefore, the endogenous production of IL-10 elicited by coinfection seems to be crucial to counterregulate the potentially lethal effects triggered by systemic release of pro-inflammatory mediators induced by CL Brener single infection. In conclusion, our results suggest that the composition of the infecting parasite population plays a role in the host response to T. cruzi in determining the severity of the disease in experimentally infected BALB/c mice. The combination of JG and CL Brener was able to trigger both protective inflammatory immunity and regulatory immune mechanisms that attenuate damage caused by inflammation and disease severity in BALB/c mice.