Correction: Importance of TLR2 on Hepatic Immune and Non-Immune Cells to Attenuate the Strong Inflammatory Liver Response During Trypanosoma cruzi Acute Infection.

[This corrects the article DOI: 10.1371/journal.pntd.0000863.].

Signaling pathways that regulate Trypanosoma cruzi infection and immune response.

Current understanding of key cellular pathways, which are activated by the interaction between T. cruzi and host immunity, is crucial for controlling T. cruzi infection and also for limiting the development of the immunopathological symptoms of Chagas´ disease. Here, we focus on recent advances in the knowledge of modulation of innate receptors such as TLRs and NLRs, especially NLRP3, by T. cruzi in different cells of the immune system. On the other hand, the modulation of macrophage activation may be instrumental in allowing parasite persistence and long-term host survival. In this sense, we discuss the importance of the metabolism of two amino acids: L-arginine and tryptophan, and evaluate the role of iNOS, arginase and IDO enzymes in the regulation of innate and adaptive immune response during this infection; and, finally, we also discuss how T. cruzi exploits the AhR, mTOR and Wnt signaling pathways to promote their intracellular replication in macrophages, thus evading the host's immune response.

NLRP3 Inflammasome and Caspase-1/11 Pathway Orchestrate Different Outcomes in the Host Protection Against Trypanosoma cruzi Acute Infection.

Infection with protozoan parasite Trypanosoma cruzi results in activation of nucleotide-binding domain and leucine-rich repeat containing receptors (NLRs). NLR activation leads to inflammasome formation, the activation of caspase-1, and the subsequent cleavage of IL-1ß and IL-18. Considering that inflammasome activation and IL-1ß induction by macrophages are key players for an appropriate T cell response, we investigated the relevance of NLR pyrin domain-containing 3 (NLRP3) and caspase-1/11 to elucidate their roles in the induction of different T cell phenotypes and the relationship with parasite load and hepatic inflammation during T. cruzi-Tulahuen strain acute infection. We demonstrated that infected nlrp3-/- and C57BL/6 wild type (WT) mice exhibited similar parasitemia and survival, although the parasite load was higher in the livers of nlrp3-/- mice than in those of WT mice. Increased levels of transaminases and pro-inflammatory cytokines were found in the plasma of WT and nlrp3-/- mice indicating that NLRP3 is dispensable to control the parasitemia but it is required for a better clearance of parasites in the liver. Importantly, we have found that NLRP3 and caspase-1/11-deficient mice differentially modulate T helper (Th1, Th2, and Th17) and cytotoxic T lymphocyte phenotypes. Strikingly, caspase-1/11-/- mice showed the most dramatic reduction in the number of IFN-γ- and IL-17-producing CD4+ and CD8+ T cells associated with higher parasitemia and lower survival. Additionally, caspase-1/11-/- mice demonstrated significantly reduced liver inflammation with the lowest alanine aminotransferase (ALT) levels but the highest hepatic parasitic load. These results unequivocally demonstrate that caspase-1/11 pathway plays an important role in the induction of liver adaptive immunity against this parasite infection as well as in hepatic inflammation.

L-arginine supplementation reduces mortality and improves disease outcome in mice infected with Trypanosoma cruzi.

Chagas disease caused by Trypanosoma cruzi is a neglected disease that affects about 7 million people in Latin America, recently emerging on other continents due to migration. As infection in mice is characterized by depletion of plasma L-arginine, the effect on infection outcome was tested in mice with or without L-arginine supplementation and treatment with 1400W, a specific inhibitor of inducible nitric oxide synthase (iNOS). We found that levels of L-arginine and citrulline were reduced in the heart and plasma of infected mice, whereas levels of asymmetric dimethylarginine, an endogenous iNOS inhibitor, were higher. Moreover, L-arginine supplementation decreased parasitemia and heart parasite burden, improving clinical score and survival. Nitric oxide production in heart tissue and plasma was increased by L-arginine supplementation, while pharmacological inhibition of iNOS yielded an increase in parasitemia and worse clinical score. Interestingly, electrocardiograms improved in mice supplemented with L-arginine, suggesting that it modulates infection and heart function and is thus a potential biomarker of pathology. More importantly, L-arginine may be useful for treating T. cruzi infection, either alone or in combination with other antiparasitic drugs.

Altered bone marrow lymphopoiesis and interleukin-6-dependent inhibition of thymocyte differentiation contribute to thymic atrophy during Trypanosoma cruzi infection.

Thymic atrophy occurs during infection being associated with apoptosis of double positive (DP) and premature exit of DP and double negative (DN) thymocytes. We observed for the first time that a significant bone marrow aplasia and a decrease in common lymphoid progenitors (CLPs) preceded thymic alterations in mice infected with Trypanosoma cruzi. In addition, depletion of the DN2 stage was previous to the DN1, indicating an alteration in the differentiation from DN1 to DN2 thymocytes. Interestingly, infected mice deficient in IL-6 expression showed higher numbers of DP and CD4+ thymocytes than wild type infected mice, while presenting similar percentages of DN1 thymocytes. Moreover, the drop in late differentiation stages of DN thymocytes was partially abrogated in comparison with wild type littermates. Thus, our results suggest that thymic atrophy involves a drop in CLPs production in bone marrow and IL-6-dependent and independent mechanisms that inhibits the differentiation of DN thymocytes.

Chronic Trypanosoma cruzi infection potentiates adipose tissue macrophage polarization toward an anti-inflammatory M2 phenotype and contributes to diabetes progression in a diet-induced obesity model.

Chronic obesity and Chagas disease (caused by the protozoan Trypanosoma cruzi) represent serious public health concerns. The interrelation between parasite infection, adipose tissue, immune system and metabolism in an obesogenic context, has not been entirely explored. A novel diet-induced obesity model (DIO) was developed in C57BL/6 wild type mice to examine the effect of chronic infection (DIO+I) on metabolic parameters and on obesity-related disorders. Dyslipidemia, hyperleptinemia, and cardiac/hepatic steatosis were strongly developed in DIO mice. Strikingly, although these metabolic alterations were collectively improved by infection, plasmatic apoB100 levels remain significantly increased in DIO+I, suggesting the presence of pro-atherogenic small and dense LDL particles. Moreover, acute insulin resistance followed by chronic hyperglycemia with hypoinsulinemia was found, evidencing an infection-related-diabetes progression. These lipid and glucose metabolic changes seemed to be highly dependent on TLR4 expression since TLR4-/- mice were protected from obesity and its complications. Notably, chronic infection promoted a strong increase in MCP-1 producing macrophages with a M2 (F4/80+CD11c-CD206+) phenotype associated to oxidative stress in visceral adipose tissue of DIO+I mice. Importantly, infection reduced lipid content but intensified inflammatory infiltrates in target tissues. Thus, parasite persistence in an obesogenic environment and the resulting host immunometabolic dysregulation may contribute to diabetes/atherosclerosis progression.

IL-6 Improves the Nitric Oxide-Induced Cytotoxic CD8+ T Cell Dysfunction in Human Chagas Disease.

Reactive oxygen and nitrogen species are important microbicidal agents and are also involved in lymphocyte unresponsiveness during experimental infections. Many of the biological effects attributed to nitric oxide are mediated by peroxynitrites, which induce the nitration of immune cells, among others. Our group has demonstrated that nitric oxide is involved in the suppressive activity of myeloid-derived suppressor cells in Trypanosoma cruzi-infected mice, with a higher number of CD8+ T cells suffering surface-nitration compared to uninfected controls. Studying the functional and phenotypic features of peripheral CD8+ T cells from chagasic patients and human cells experimentally infected with T. cruzi, we found that different regulatory mechanisms impaired the effector functions of T cytotoxic population from seropositive patients. Peripheral leukocytes from chagasic patients showed increased nitric oxide production concomitant with increased tyrosine nitration of CD8+ T cells. Additionally, this cytotoxic population exhibited increased apoptotic rate, loss of the TCRζ-chain, and lower levels of CD107a, a marker of degranulation. Strikingly, IL-6 stimulation of in vitro-infected peripheral blood mononuclear cells obtained from healthy donors, blunted T. cruzi-induced nitration of CD3+CD8+ cells, and increased their survival. Furthermore, the treatment of these cultures with an IL-6 neutralizing antibody increased the percentage of T. cruzi-induced CD8+ T cell nitration and raised the release of nitric oxide. The results suggest that the under-responsiveness of cytotoxic T cell population observed in the setting of long-term constant activation of the immune system could be reverted by the pleiotropic actions of IL-6, since this cytokine improves its survival and effector functions.

Impact of tumor necrosis factor receptor p55 deficiency in susceptibility of C57BL/6 mice to infection with Leishmania (Leishmania) amazonensis.

Tumor necrosis factor (TNF) is involved in host resistance to several intracellular pathogens. Although the critical role of TNF receptor (TNFR)p55 in Leishmania (Leishmania) major infection has been demonstrated, the impact of TNFRp55 deficiency on L. (L.) amazonensis infection has not been explored. L. (L.) amazonensis-infected TNFRp55(-/-) mice failed to resolve lesions, whereas C57BL/6 wild-type mice completely healed. The susceptibility of the TNFRp55(-/-) mice was characterized by higher lesion size and histopathological damage in comparison with the wild-type mice. A marked increased of the splenic index was observed in the TNFRp55(-/-) mice after 15 weeks infection. These results show that in the absence of TNFRp55, L. (L.) amazonensis-infected knockout mice fail to resolve lesions, whereas wild-type mice completely heal.

Trypanosoma cruzi infection is a potent risk factor for non-alcoholic steatohepatitis enhancing local and systemic inflammation associated with strong oxidative stress and metabolic disorders.

BACKGROUND: The immune mechanisms underlying experimental non-alcoholic steatohepatitis (NASH), and more interestingly, the effect of T. cruzi chronic infection on the pathogenesis of this metabolic disorder are not completely understood. METHODOLOGY/PRINCIPAL FINDINGS: We evaluated immunological parameters in male C57BL/6 wild type and TLR4 deficient mice fed with a standard, low fat diet, LFD (3% fat) as control group, or a medium fat diet, MFD (14% fat) in order to induce NASH, or mice infected intraperitoneally with 100 blood-derived trypomastigotes of Tulahuen strain and also fed with LFD (I+LFD) or MFD (I+MFD) for 24 weeks. We demonstrated that MFD by itself was able to induce NASH in WT mice and that parasitic infection induced marked metabolic changes with reduction of body weight and steatosis revealed by histological studies. The I+MFD group also improved insulin resistance, demonstrated by homeostasis model assessment of insulin resistance (HOMA-IR) analysis; although parasitic infection increased the triglycerides and cholesterol plasma levels. In addition, hepatic M1 inflammatory macrophages and cytotoxic T cells showed intracellular inflammatory cytokines which were associated with high levels of IL6, IFNγ and IL17 plasmatic cytokines and CCL2 chemokine. These findings correlated with an increase in hepatic parasite load in I+MFD group demonstrated by qPCR assays. The recruitment of hepatic B lymphocytes, NK and dendritic cells was enhanced by MFD, and it was intensified by parasitic infection. These results were TLR4 signaling dependent. Flow cytometry and confocal microscopy analysis demonstrated that the reactive oxygen species and peroxinitrites produced by liver inflammatory leukocytes of MFD group were also exacerbated by parasitic infection in our NASH model. CONCLUSIONS: We highlight that a medium fat diet by itself is able to induce steatohepatitis. Our results also suggest a synergic effect between damage associated with molecular patterns generated during NASH and parasitic infection, revealing an intense cross-talk between metabolically active tissues, such as the liver, and the immune system. Thus, T. cruzi infection must be considered as an additional risk factor since exacerbates the inflammation and accelerates the development of hepatic injury.

Nitric oxide synthase 2 (NOS2) expression in histologically normal margins of oral squamous cell carcinoma.

UNLABELLED: The activity of Nitric Oxide Synthase 2 (NOS2) was found in oral squamous cell carcinomas (OSCC) but not in normal mucosa. Molecular changes associated to early carcinogenesis have been found in mucosa near carcinomas, which is considered a model to study field cancerization. The aim of the present study is to analyze NOS2 expression at the histologically normal margins of OSCC. STUDY DESIGN: Eleven biopsy specimens of OSCC containing histologically normal margins (HNM) were analyzed. Ten biopsies of normal oral mucosa were used as controls. The activity of NOS2 was determined by immunohistochemistry. Salivary nitrate and nitrite as well as tobacco and alcohol consumption were also analyzed. The Chi-squared test was applied. RESULTS: Six out of the eleven HNM from carcinoma samples showed positive NOS2 activity whereas all the control group samples yielded negative (p=0.005). No statistically significant association between enzyme expression and tobacco and/or alcohol consumption and salivary nitrate and nitrite was found. CONCLUSION: NOS2 expression would be an additional evidence of alterations that may occur in a state of field cancerization before the appearance of potentially malignant morphological changes.

Myeloid-derived suppressor cells are key players in the resolution of inflammation during a model of acute infection.

Myeloid-derived suppressor cells (MDSCs) are key players in the immune suppressive network. During acute infection with the causative agent of Chagas disease, Trypanosoma cruzi, BALB/c mice show less inflammation and better survival than C57BL/6 (B6) mice. In this comparative study, we found a higher number of MDSCs in the spleens and livers of infected BALB/c mice compared with infected B6 mice. An analysis of the two major MDSCs subsets revealed a greater number of granulocytic cells in the spleens and livers of BALB/c mice when compared with that in B6 mice. Moreover, splenic MDSCs purified from infected BALB/c mice inhibited ConA-induced splenocyte proliferation. Mechanistic studies demonstrated that ROS and nitric oxide were involved in the suppressive activity of MDSCs, with a higher number of infected CD8(+) T cells suffering surface-nitration compared to uninfected controls. An upregulation of NADPH oxidase p47 phox subunit and p-STAT3 occurred in MDSCs and infected IL-6 KO mice showed less recruitment of MDSCs and impaired survival. Remarkably, in vivo depletion of MDSCs led to increased production of IL-6, IFN-γ, and a Th17 response with very high parasitemia and mortality. These findings demonstrate a new facet of MDSCs as crucial regulators of inflammation during T. cruzi infection.

Trypanosoma cruzi, the causative agent of Chagas disease, modulates interleukin-6-induced STAT3 phosphorylation via gp130 cleavage in different host cells.

Interleukin-6 mediates host defense and cell survival mainly through the activation of the transcription factor STAT3 via the glycoprotein gp130, a shared signal-transducing receptor for several IL-6-type cytokines. We have reported that the cardiotrophic parasite Trypanosoma cruzi protects murine cardiomyocytes from apoptosis. In agreement, an intense induction of the anti-apoptotic factor Bcl-2 is found in cardiac fibers during the acute phase of infection, establishing a higher threshold against apoptosis. We report here that inactive cruzipain, the main cysteine protease secreted by the parasite, specifically triggered TLR2 and the subsequent release of IL-6, which acted as an essential anti-apoptotic factor for cardiomyocyte cultures. Although comparable IL-6 levels were found under active cruzipain stimulation, starved cardiac cell monolayers could not be rescued from apoptosis. Moreover, cardiomyocytes treated with active cruzipain completely abrogated the STAT3 phosphorylation and nuclear translocation induced by recombinant IL-6. This inhibition was also observed on splenocytes, but it was reverted when the enzyme was complexed with chagasin, a parasite cysteine protease inhibitor. Furthermore, the inhibition of IL-6-induced p-STAT3 was evidenced in spleen cells stimulated with pre-activated supernatants derived from trypomastigotes. To account for these observations, we found that cruzipain enzymatically cleaved recombinant gp130 ectodomain, and induced the release of membrane-distal N-terminal domain of this receptor on human peripheral blood mononuclear cells. These results demonstrate, for the first time, that the parasite may modify the IL-6-induced response through the modulation of its cysteine protease activity, suggesting that specific inhibitors may help to improve the immune cell activation and cardioprotective effects.

Toll-like receptor-2 and interleukin-6 mediate cardiomyocyte protection from apoptosis during Trypanosoma cruzi murine infection.

Local innate immunity plays a key role in initiating and coordinating homeostatic and defense responses in the heart. We have previously reported that the cardiotropic parasite Trypanosoma cruzi, the etiological agent of Chagas disease, protects cardiomyocytes against growth factor deprivation-induced apoptosis. In this study, we investigated cardiomyocyte innate immune response to T. cruzi infection and its role in cellular protection from apoptosis. We found that Toll-like receptor (TLR) 2-expressing cells were strongly increased by the parasite in BALB/c neonatal mouse cardiomyocyte cultures. Using a dominant-negative system, we showed that TLR2 mediated cardiomyocyte survival and the secretion of interleukin (IL) 6, which acted as an essential anti-apoptotic factor. Moreover, IL6 released by infected cells, as well as the recombinant bioactive cytokine, induced the phosphorylation of the signal transducers and activators of transcription-3 (STAT3) in cultured cardiomyocytes. In accord with the in vitro results, during the acute phase of the infection, TLR2 expression increased 2.9-fold and the anti-apoptotic factor Bcl-2 increased 4.5-fold in the cardiac tissue. We have clearly shown a cross-talk between the intrinsic innate response of cardiomyocytes and the pro-survival effect evoked by the parasite.

Nonimmune Cells Contribute to Crosstalk between Immune Cells and Inflammatory Mediators in the Innate Response to Trypanosoma cruzi Infection.

Chagas myocarditis, which is caused by infection with the intracellular parasite Trypanosoma cruzi, remains the major infectious heart disease worldwide. Innate recognition through toll-like receptors (TLRs) on immune cells has not only been revealed to be critical for defense against T. cruzi but has also been involved in triggering the pathology. Subsequent studies revealed that this parasite activates nucleotide-binding oligomerization domain- (NOD-)like receptors and several particular transcription factors in TLR-independent manner. In addition to professional immune cells, T. cruzi infects and resides in different parenchyma cells. The innate receptors in nonimmune target tissues could also have an impact on host response. Thus, the outcome of the myocarditis or the inflamed liver relies on an intricate network of inflammatory mediators and signals given by immune and nonimmune cells. In this paper, we discuss the evidence of innate immunity to the parasite developed by the host, with emphasis on the crosstalk between immune and nonimmune cell responses.

The role of Toll-like receptors and adaptive immunity in the development of protective or pathological immune response triggered by the Trypanosoma cruzi protozoan.

Trypanosoma cruzi, the causal agent of Chagas disease, is an intracellular protozoan parasite that predominantly invades macrophages and cardiomyocytes, leading to persistent infection. Several members of the Toll-like receptor family are crucial for innate immunity to infection and are involved in maintaining tissue homeostasis. This review focuses on recent experimental findings of the innate and adaptive immune response in controlling the parasite and/or in generating heart and liver tissue injury. We also describe the importance of the host's genetic background in the outcome of the disease and emphasize the importance of studying the response to specific parasite antigens. Understanding the dual participation of the immune response may contribute to the design of new therapies for Chagas disease.

Trypanosoma cruzi antigen immunization induces a higher B cell survival in BALB/c mice, a susceptible strain, compared to C57BL/6 B lymphocytes, a resistant strain to cardiac autoimmunity.

Chagas disease, caused by Trypanosoma cruzi, is endemic in Latin America and represents the most common infectious myocarditis worldwide. Autoimmunity is one of the mechanisms contributing to its pathogenesis. Although the cellular interactions that promote this autoimmune response are still poorly understood, several studies have demonstrated a key role for B lymphocytes since they secrete antibodies, cytokines and present antigens. Recently, we reported that immunization with cruzipain, an immunodominant T. cruzi antigen, induces a higher activation state in B cells from BALB/c mice (susceptible to cardiac autoimmunity) than B lymphocytes from C57BL/6 (a resistant strain). Here, we focused on the study of B cell survival in both mouse strains after cruzipain immunization and demonstrated an increased survival rate of B cells from BALB/c compared to C57BL/6 mice. This phenomenon was associated with a decreased expression of Fas/FasL and an increased expression of anti-apoptotic Bcl-2/Bcl-xL proteins. With the purpose to gain more knowledge about the mechanisms involved, we found that IL-4 produced by BALB/c B cells played a key role in the survival in an autocrine way whereas the addition of this bioactive cytokine rescued C57BL/6 B lymphocytes from apoptosis. Our findings suggest that in the absence of infection, both enhanced B cell activation induced by the immunization with a single parasite antigen and insufficient negative regulation can potentially contribute to autoimmunity seen in cruzipain immune BALB/c mice.

Importance of TLR2 on hepatic immune and non-immune cells to attenuate the strong inflammatory liver response during Trypanosoma cruzi acute infection.

BACKGROUND: Toll-like receptors (TLR) and cytokines play a central role in the pathogen clearance as well as in pathological processes. Recently, we reported that TLR2, TLR4 and TLR9 are differentially modulated in injured livers from BALB/c and C57BL/6 (B6) mice during Trypanosoma cruzi infection. However, the molecular and cellular mechanisms involved in local immune response remain unclear. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we demonstrate that hepatic leukocytes from infected B6 mice produced higher amounts of pro-inflammatory cytokines than BALB/c mice, whereas IL10 and TGFß were only released by hepatic leukocytes from BALB/c. Strikingly, a higher expression of TLR2 and TLR4 was observed in hepatocytes of infected BALB/c mice. However, in infected B6 mice, the strong pro-inflammatory response was associated with a high and sustained expression of TLR9 and iNOS in leukocytes and hepatic tissue respectively. Additionally, co-expression of gp91- and p47-phox NADPH oxidase subunits were detected in liver tissue of infected B6 mice. Notably, the pre-treatment previous to infection with Pam3CSK4, TLR2-agonist, induced a significant reduction of transaminase activity levels and inflammatory foci number in livers of infected B6 mice. Moreover, lower pro-inflammatory cytokines and increased TGFß levels were detected in purified hepatic leukocytes from TLR2-agonist pre-treated B6 mice. CONCLUSIONS/SIGNIFICANCE: Our results describe some of the main injurious signals involved in liver immune response during the T. cruzi acute infection. Additionally we show that the administration of Pam3CSk4, previous to infection, can attenuate the exacerbated inflammatory response of livers in B6 mice. These results could be useful to understand and design novel immune strategies in controlling liver pathologies.

Association of clomipramine and allopurinol for the treatment of the experimental infection with Trypanosoma cruzi.

We have previously shown that clomipramine and allopurinol used separately are effective in preventing chronic chagasic cardiomyopathy. The aim of the present study was to evaluate the effect of the association of clomipramine (Clo--5 mg/kg/day/90 days) and allopurinol (Allo--5, 10, or 15 mg/kg/day/90 days) for the treatment of experimental Chagas disease in the acute stage. Treatment effectiveness was evaluated through parasitemia, survival, electrocardiography, serology, and cardiac histopathology. Groups treated showed no electrocardiographic abnormalities, in contrast to those untreated which presented 25% of mice with conduction alterations. The myocardium of treated mice (Clo, Allo10+Clo, and Allo15+Clo) presented no structural alterations. Cardiac b-receptor affinity was preserved in mice treated with Clo or Clo+Allo at the different doses; receptor density of the Clo and Allo15+Clo groups did not differ from the non-infected group. Anti-cruzipain antibody levels were similar in treated and untreated groups. Survival was significantly increased in the treated groups (p < 0.05), with Clo and all the Clo+Allo groups presenting the highest rates. These results show that the association of clomipramine + allopurinol is effective for Chagas disease treatment and has the same effect as clomipramine alone.

Induction of NADPH oxidase activity and reactive oxygen species production by a single Trypanosoma cruzi antigen.

Trypanosoma cruzi is an intracellular protozoan parasite that predominantly invades mononuclear phagocytes and is able to establish a persistent infection. The production of reactive oxygen species (ROS) by phagocytes is an innate defence mechanism against microorganisms. It has been postulated that ROS such as superoxide anion (O(2)), hydrogen peroxide and peroxynitrite, may play a crucial role in the control of pathogen growth. However, information on parasite molecules able to trigger ROS production is scarce. In this work, we investigated whether cruzipain, an immunogenic glycoprotein from T. cruzi, was able to trigger the oxidative burst by murine cells. By employing chemiluminiscense and flow-cytometric analysis, we demonstrated that cruzipain induced ROS production in splenocytes from non-immune and cruzipain immune C57BL/6 mice and in a Raw 264.7 macrophage cell line. We also identified an O(2)(-) molecule as one of the ROS produced after antigen stimulation. Cruzipain stimulation induced NOX2 (gp91(phox)) and p47(phox) expression, as well as the co-localisation of both NADPH oxidase enzyme subunits. In the current study, we provide evidence that cruzipain not only increased ROS production but also promoted IL-6 and IL-1ß cytokine production. Taken together, we believe these results demonstrate for the first time that cruzipain, a single parasite molecule, in the absence of infection, favors oxidative burst in murine cells. This represents an important advance in the knowledge of parasite molecules that interact with the phagocyte defence mechanism.

TLR2, TLR4 and TLR9 are differentially modulated in liver lethally injured from BALB/c and C57BL/6 mice during Trypanosoma cruzi acute infection.

Toll-like receptor (TLR) family is crucial for microbial elimination and homeostasis, and has an important immunoregulatory role. In this study, we comparatively analyze innate immune response and tissular injury elicited in BALB/c and C57BL/6 (B6) mice during acute Trypanosoma cruzi infection. The liver was the most affected tissue with numerous cellular infiltrates, apoptotic cells and necrotic areas. The apoptotic rate, evaluated by Hoescht stain, was highest in liver of B6. Infection increased transaminase activities in both mouse strains, although they were highest in B6. BALB/c showed sixfold higher parasitemias than B6 but the latter presented higher mortality (80%) than BALB/c (40%). To gain insight into the molecular basis, we investigated the TLRs commitment in liver. We found that, TLR2 and TLR4 were up-regulated in BALB/c while they were down-regulated in B6. However, TLR9 showed a diminution in BALB/c and an increase in B6 at the end of infection. Moreover, an intensified pro-inflammatory cytokine profile was observed in B6 and F4/80+ and Gr1+ leukocytes were the predominant cells in liver from both mouse strains. Thus, altered TLR2, TLR4 and TLR9 signalling and exacerbate inflammatory cytokine profile could be responsible of the fatal hepatic damage observed in infected B6.