A histopathological analysis of the course of myocarditis in C3H/He mice infected with Trypanosoma cruzi clone Sylvio-X10/4

Persistent Biofluid Small-Molecule Alterations Induced by Trypanosoma cruzi Infection Are Not Restored by Parasite Elimination

Chagas disease (CD), caused by Trypanosoma cruzi (T. cruzi) protozoa, is a complicated parasitic illness with inadequate medical measures for diagnosing infection and monitoring treatment success. To address this gap, we analyzed changes in the metabolome of T. cruzi-infected mice via liquid chromatography tandem mass spectrometry of clinically accessible biofluids: saliva, urine, and plasma. Urine was the most indicative of infection status across mouse and parasite genotypes. Metabolites perturbed by infection in urine include kynurenate, acylcarnitines, and threonylcarbamoyladenosine. Based on these results, we sought to implement urine as a tool for the assessment of CD treatment success. Strikingly, it was found that mice with parasite clearance following benznidazole antiparasitic treatment had an overall urine metabolome comparable to that of mice that failed to clear parasites. These results provide a complementary hypothesis to explain clinical trial data in which benznidazole treatment did not improve patient outcomes in late-stage disease, even in patients with successful parasite clearance. Overall, this study provides insights into new small-molecule-based CD diagnostic methods and a new approach to assess functional responses to treatment.

Importance of CD40/CD40 dyad in the course of infection with Trypanosoma cruzi: Impact of its inhibition

Chagas heart disease (CHD), caused by the protozoan parasite Trypanosoma cruzi, consists of a progressive myocarditis which may lead to congestive heart failure or sudden death. Previous work from our laboratory has demonstrated that the experimental infection of mice with T. cruzi positively modulates the expression of CD40 by myocardial cells, whose ligation potentiates IFN-γ-induced IL-6 production. Herein, we investigate the role of the CD40/CD40L interaction during T. cruzi infection using a CD40-targeted peptide and evaluating parasitological, histopathological and serological parameters. To reproduce acute and chronic phases of theT. cruzi infection, we used two experimental models: Balb/c mice infected with RA strain of T. cruzi (Balb/c-RA) and C3H/HeN mice infected with Sylvio X-10/4 parasites (C3H/HeN-Sylvio), respectively. Balb/c-RA treated with CD40-tageted peptide since day 0 post infection (pi), were unable to control the acute infection dying within 23-26 days pi with marked tissue damage. In contrast, treatment of C3H/HeN-Sylvio treated with CD40-targeted peptide starting on day 30 pi resulted in amelioration of myocardial and skeletal muscle damage. Altogether, our results indicate a dual role of CD40/CD40L dyad in the control of T.cruzi infection as well as the associated pathology, depending on the timing of treatment initiation.

Assessment of a combined treatment with a therapeutic vaccine and benznidazole for the Trypanosoma cruzi chronic infection

The difficulties encountered in achieving treatments for chronic Chagas disease have promoted the investigation of new therapeutic strategies. In this study, we used two murine models of Trypanosoma cruzi chronic infection to determine the usefulness of applying a therapeutic vaccine alone or followed by benznidazole (Bz) chemotherapy. A vaccine formulation based on an N-terminal fragment of Trans-sialidase (TS) and Immunostimulant Particle Adjuvant (ISPA) - TSNt-ISPA was obtained. Firstly, the immunogenicity and protective capacity of TSNt-ISPA was demonstrated as a prophylactic formulation in an acute model of infection. Later, the formulation was assessed as a therapeutic vaccine alone or combined with (Bz) using two models of chronic infection. BALB/c mice chronically infected with Sylvio X10/4 or Tulahuen cl2 T. cruzi strains were not treated as control or treated only with the therapeutic vaccine TSNt-ISPA, with a combined treatment TSNt-ISPA+Bz (Bz applied after the vaccine), or only with Bz. The vaccination schedule consisted of TSNt-ISPA administration at days110, 120, and 130 post-infection (pi) and Bz administration was performed daily from day 140 to 170 pi. At day 273 pi, electrocardiographic (ECG) parameters, heart parasite load, myocarditis, and heart fibrosis were assessed. In both models, therapeutic administration of TSNt-ISPA reduced ECG alterations and the cardiac tissue damage observed in the chronic phase. Moreover, vaccine treatment significantly decreased heart parasite load in both Sylvio X10/4 and Tulahuen cl2 infected mice. The combined treatment, but not Bz or vaccine administration alone, allowed to restore ECG parameters in Tulahuen cl2 infected mice. The results indicate the usefulness of the therapeutic TSNt-ISPA formulation in BALB/c mice chronically infected with Sylvio X10/4 or Tulahuen cl2 strain. For the mice infected with T. cruzi Tulahuen cl2 strain, the combined treatment with the vaccine and Bz had a more positive effect on the course of heart disease than the individual treatments with the vaccine or Bz alone.

Experimental combination therapy using low doses of benznidazole and allopurinol in mouse models of Trypanosoma cruzi chronic infection

This study evaluated the effectiveness of low doses of benznidazole (BNZ) on continuous administration (BNZc), combined with allopurinol (ALO), in C57BL/6J and C3H/HeN mice infected with Trypanosoma cruzi Nicaragua strain and T. cruzi Sylvio-X10/4 clone. TcN-C57BL/6J was also treated with intermittent doses of BNZ (BNZit). The drug therapy started 3 months post infection (pi) in the chronic phase of mice with heart disease progression, followed-up at 6 months pi. TcN-C57BL/6J treated with BNZc was also monitored up to 12 months pi by serology and electrocardiogram. These mice showed severe electrical abnormalities, which were not observed after BNZc or BNZit. ALO only showed positive interaction with the lowest dose of BNZ. A clear parasitic effect, with significant reductions in antibody titres and parasitic loads, was achieved in all models with low doses of BNZ, and a 25% reduction of the conventional dose showed more efficacy to inhibit the development of the pathology. However, BNZ 75 showed partial efficacy in the TcSylvio-X10/4-C3H/HeN model. In our experimental designs, C57BL/6J allowed to clearly define a chronic phase, and through reproducible efficacy indicators, it can be considered a good preclinical model.

Curcumin exerts anti-inflammatory and vasoprotective effects through amelioration of NFAT-dependent endothelin-1 production in mice with acute Chagas cardiomyopathy

BACKGROUND

The anti-inflammatory and cardioprotective properties of curcumin (Cur), a natural polyphenolic flavonoid isolated from the rhizomes of Curcuma longa, are increasingly considered to have beneficial effects on the progression of Chagas heart disease, caused by the protozoan parasite Trypanosoma cruzi.

OBJECTIVE

To evaluate the effects of oral therapy with Cur on T. cruzi-mediated cardiovasculopathy in acutely infected mice and analyse the in vitro response of parasite-infected human microvascular endothelial cells treated with this phytochemical.

METHODS

Inflammation of heart vessels from Cur-treated and untreated infected mice were analysed by histology, with benznidazole (Bz) as the reference compound. Parasitaemia was monitored by the direct method. Capillary permeability was visualised by Evans-blue assay. Myocardial ET-1, IL-6, and TNF-α mRNA expressions were measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Microvascular endothelial HMEC-1 cells were infected in vitro with or without addition of Cur or Bz. Induction of the Ca2+/NFAT pathway was assessed by fluorometry, immunoblotting, and reporter assay.

FINDINGS

Oral Cur therapy of recently infected mice reduced inflammatory cell infiltration of myocardial arteries without lowering parasite levels. Compared to that of the phosphate-buffered saline-receiving group, hearts from Cur-treated mice showed significantly decreased vessel inflammation scores (p < 0.001), vascular permeabilities (p < 0.001), and levels of IL-6/TNF-α (p < 0.01) and ET-1 (p < 0.05) mRNA. Moreover, Cur significantly (p < 0.05 for transcript; p < 0.01 for peptide) downregulated ET-1 secretion from infected HMEC-1 cells. Remarkably, Cur addition significantly (p < 0.05 at 27.0 μM) interfered with T. cruzi-dependent activation of the Ca2+/NFATc1 signalling pathway that promotes generation of inflammatory agents in HMEC-1 cells.

CONCLUSIONS

Oral treatment with Cur dampens cardiovasculopathy in acute Chagas mice. Cur impairs the Ca2+/NFATc1-regulated release of ET-1 from T. cruzi-infected vascular endothelium. These findings identify new perspectives for exploring the potential of Cur-based interventions to ameliorate Chagas heart disease.

Macrophages Promote Oxidative Metabolism To Drive Nitric Oxide Generation in Response to Trypanosoma cruzi

Trypanosoma cruzi is the causative agent of chronic chagasic cardiomyopathy. Why macrophages (mφs), the early responders to infection, fail to achieve parasite clearance is not known. Mouse (RAW 264.7) and human (THP-1 and primary) mφs were infected for 3 h and 18 h with T. cruzi TcI isolates, SylvioX10/4 (SYL, virulent) and TCC (nonpathogenic), which represent mφ stimulation and infection states, respectively. Mφs incubated with lipopolysaccharide and gamma interferon (LPS/IFN-γ) and with interleukin-4 (IL-4) were used as controls. We monitored the cytokine profile (using enzyme-linked immunosorbent assay [ELISA]), reactive oxygen species (ROS; fluorescent probes), nitric oxide (·NO; Griess assay), and metabolic state using a custom-designed mitoxosome array and Seahorse XF24 Analyzer. LPS/IFN-γ treatment of mφs elicited a potent increase in production of tumor necrosis alpha (TNF-α) at 3 h and of ROS and ·NO by 18 h. Upon SYL infection, murine mφs elicited an inflammatory cytokine profile (TNF-α ≫ TGF-β + IL-10) and low levels of ·NO and ROS production. LPS/IFN-γ treatment resulted in the inhibition of oxidative metabolism at the gene expression and functional levels and a switch to the glycolytic pathway in mφs, while IL-4-treated mφs utilized oxidative metabolism to meet energy demands. SYL infection resulted in an intermediate functional metabolic state with increased mitoxosome gene expression and glycolysis, and IFN-γ addition shut down the oxidative metabolism in SYL-infected mφs. Further, TCC- and SYL-stimulated mφs exhibited similar levels of cell proliferation and production of TNF-α and ROS, while TCC-stimulated mφs exhibited up to 2-fold-higher levels of oxidative metabolism and ·NO production than SYL-infected mφs. Inhibiting ATP-coupled O₂ consumption suppressed the ·NO generation in SYL-infected mφs. Mitochondrial oxygen consumption constitutes a mechanism for stimulating ·NO production in mφs during T. cruzi infection. Enhancing the oxidative metabolism provides an opportunity for increased ·NO production and pathogen clearance by mφs to limit disease progression.

Mice with Genetic Deletion of Group VIA Phospholipase A2β Exhibit Impaired Macrophage Function and Increased Parasite Load in Trypanosoma cruzi-Induced Myocarditis

Trypanosoma cruzi infection, which is the etiological agent of Chagas disease, is associated with intense inflammation during the acute and chronic phases. The pathological progression of Chagas disease is influenced by the infiltration and transmigration of inflammatory cells across the endothelium to infected tissues, which are carefully regulated processes involving several molecular mediators, including adhesion molecules and platelet-activating factor (PAF). We have shown that PAF production is dependent upon calcium-independent group VIA phospholipase A2β (iPLA2β) following infection of human coronary artery endothelial cells (HCAECs) with T. cruzi, suggesting that the absence of iPLA2β may decrease the recruitment of inflammatory cells to the heart to manage parasite accumulation. Cardiac endothelial cells isolated from iPLA2β-knockout (iPLA2β-KO) mice infected withT. cruzi demonstrated decreased PAF production compared to that by cells isolated from wild-type (WT) mice but demonstrated increases in adhesion molecule expression similar to those seen in WT mice. Myocardial inflammation in iPLA2β-KO mice infected with T. cruzi was similar in severity to that in WT mice, but the iPLA2β-KO mouse myocardium contained more parasite pseudocysts. Upon activation, macrophages from iPLA2β-KO mice produced significantly less nitric oxide (NO) and caused lessT. cruzi inhibition than macrophages from wild-type mice. Thus, the absence of iPLA2β activity does not influence myocardial inflammation, but iPLA2β is essential forT. cruzi clearance.

Trypanosoma cruzi infection induces the expression of CD40 in murine cardiomyocytes favoring CD40 ligation-dependent production of cardiopathogenic IL-6

The inflammatory response in the myocardium is an important aspect of the pathogenesis of Chagas' heart disease raised by Trypanosoma cruzi. CD40, a transmembrane type I receptor belonging to the tumor necrosis factor receptor (TNFR) family, is expressed in a broad spectrum of cell types and is crucial in several inflammatory and autoimmune diseases. Activation of CD40 through ligation to CD40L (CD154) induces multiple effects, including the secretion of proinflammatory molecules. In the present study, we examined the ability of T. cruzi to trigger the expression of CD40 in cardiac myocytes in vitro and in a murine model of chagasic cardiomyopathy. Our results indicate, for the first time, that T. cruzi is able to induce the expression of CD40 in HL-1 murine cardiomyocytes. Moreover, ligation of CD40 receptor upregulated interleukin-6 (IL-6), associated with inflammation. Furthermore, the induction of this costimulatory molecule was demonstrated in vivo in myocardium of mice infected with T. cruzi. This suggests that CD40-bearing cardiac muscle cells could interact with CD40L-expressing lymphocytes infiltrating the heart, thus contributing to inflammatory injury in chagasic cardiomyopathy.

Granulocyte colony-stimulating factor partially repairs the damage provoked by Trypanosoma cruzi in murine myocardium

BACKGROUND

The hallmark of Trypanosoma cruzi infection is cardiomyopathy that leads to end-stage heart failure. We investigated whether G-CSF, known to induce heart tissue repair by bone marrow stem cell mobilization, ameliorates T. cruzi-induced myocarditis.

METHODS AND RESULTS

T. cruzi-infected C3H/He mice were treated with G-CSF and monitored for parasite burden, BMSC mobilization, cytokine profile and cardiac remodeling. G-CSF increased the expression of CXCR4, CD34, and c-Kit, indicating mobilization and migration of BMSC, some of which differentiated to cardiomyocytes as evidenced by increased levels of GATA4(+)/MEF2C(+) cells and desmin expression in chagasic hearts. G-CSF enhanced a mixed cytokine response (IL-10+TGF-β>IFN-γ+TNF-α>IL-4) associated with increased heart inflammation and no beneficial effect on parasite control. Further, G-CSF controlled T. cruzi-induced extracellular-matrix alterations of collagens (Col I and Col llI), hydroxyproline, and glycosaminoglycan contents and promoted compensatory cardiac remodeling; however, these responses were not sufficient to control T. cruzi-induced cardiomyocyte atrophy. Benznidazole treatment prior to G-CSF resulted in the control of parasitism and parasite-induced inflammation, and subsequently, G-CSF was effective in executing the tissue repair, as evidenced by extracellular-matrix homeostasis and normalization of cardiomyocyte size in chagasic hearts.

CONCLUSIONS

G-CSF treatment after T. cruzi infection enhanced migration and homing of BMSC, some of which differentiated to cardiomyocytes. Yet, G-CSF promoted a mixed (Treg>Th1>Th2) immune response that contributed to persistent inflammation and limited improvement in cardiac homeostasis. Combinatorial therapy (BZ → G-CSF) was beneficial in arresting inflammatory processes and tissue damage in chagasic hearts.

Elevated serum levels of macrophage migration inhibitory factor are associated with progressive chronic cardiomyopathy in patients with Chagas disease

Clinical symptoms of chronic Chagas disease occur in around 30% of the individuals infected with Trypanosoma cruzi and are characterized by heart inflammation and dysfunction. The pathogenesis of chronic chagasic cardiomyopathy (CCC) is not completely understood yet, partially because disease evolution depends on complex host-parasite interactions. Macrophage migration inhibitory factor (MIF) is a pleiotropic proinflammatory cytokine that promotes numerous pathophysiological processes. In the current study, we investigated the link between MIF and CCC progression.

Immunohistochemical analysis demonstrated MIF overexpression in the hearts from chronically T. cruzi-infected mice, particularly those showing intense inflammatory infiltration. We also found that MIF exogenously added to parasite-infected murine macrophage cultures is capable of enhancing the production of TNF-α and reactive oxygen species, both with pathogenic roles in CCC. Thus, the integrated action of MIF and other cytokines and chemokines may account for leukocyte influx to the infected myocardium, accompanied by enhanced local production of multiple inflammatory mediators. We further examined by ELISA the level of MIF in the sera from chronic indeterminate and cardiomyopathic chagasic patients, and healthy subjects. CCC patients displayed significantly higher MIF concentrations than those recorded in asymptomatic T. cruzi-infected and uninfected individuals. Interestingly, increased MIF levels were associated with severe progressive Chagas heart disease, in correlation with elevated serum concentration of high sensitivity C-reactive protein and also with several echocardiographic indicators of left ventricular dysfunction, one of the hallmarks of CCC. Our present findings represent the first evidence that enhanced MIF production is associated with progressive cardiac impairment in chronic human infection with T. cruzi, strengthening the relationship between inflammatory response and parasite-driven pathology. These observations contribute to unravel the elements involved in the pathogenesis of CCC and may also be helpful for the design of novel therapies aimed to control long-term morbidity in chagasic patients.

ECG detection of murine chagasic cardiomyopathy

Chagas' disease, induced by Trypanosoma cruzi , is a common cause of infectious myocarditis. Recent clinical treatment trials and vaccine studies indicate that chagasic immunopathology is directed against the parasite and not self-antigens. Therefore, vaccines may have the potential to protect against disease progression. Certain combinations of mouse and parasite strains produce significant histopathology and can be used for safety analyses of new vaccination strategies. The goals of this study were to determine (1) whether the development of chagasic cardiomyopathy in the murine model could be identified by electrocardiogram (ECG); and (2) whether these potential chagasic ECG changes would correlate with histopathologic findings. Groups of BALB/c, C57BL/6, and C3H mice were infected with different parasite strains (Tulahuén, Brazil, or Sylvio-X10/4) and evaluated weekly by ECG. Selected tissues from subsets of mice were harvested periodically for blinded histologic evaluation. Significantly increased proportions of BALB/c mice infected with Brazil and Tulahuén strain parasites displayed prolonged QT intervals. Prolonged mean QT intervals detected in infected BALB/c mice significantly correlated with chagasic histopathologic changes. These results indicate that ECG can be used as a non-invasive method to screen for immune-mediated damage resulting in chagasic cardiomyopathy in the murine model.

The role of selenium in intestinal motility and morphology in a murine model of Typanosoma cruzi infection

Infection with Trypanosoma cruzi causes megasyndromes of the gastrointestinal (GI) tract in humans and animals. In the present study, we employed magnetic resonance imaging to non-invasively monitor the effect of selenium supplementation on alterations in the GI tract of T. cruzi-infected mice. CD1 mice infected with T. cruzi (Brazil strain) exhibited dilatation of the intestines similar to that we recently reported in infected C57Bl/6 mice. The average intestine lumen diameter increased by 65% and the increase was reduced to 29% in mice supplemented with 2 ppm selenium in the drinking water. When supplemented with 3 ppm selenium in chow the lumen diameter was also significantly reduced although the difference between the infected and infected supplemented mice was smaller. Intestinal motility in infected mice fed with selenium-enriched chow was increased compared with infected mice fed with normal unsupplemented chow and was not significantly different from intestinal motility in uninfected mice. We suggest that Se may be used to modulate the inflammatory, immunological, and/or antioxidant responses involved in intestinal disturbances caused by T. cruzi infection.

Infection by the Sylvio X10/4 clone of Trypanosoma cruzi: relevance of a low-virulence model of Chagas' disease

The physiopathology of Chagas' disease has been largely defined in murine infections with virulent strains which partially represent parasite diversity. This report reviews our studies with Sylvio X10/4 parasites, a Trypanosoma cruzi clone that induces no acute phase but in C3H/He mice leads to chronic myocarditis resembling the human disease.

Synthesis and antimalarial activity of new isotebuquine analogues

Amodiaquine (AQ) and tebuquine are 4-aminoquinoline antimalarials with Mannich base side chain and are highly effective against chloroquine (CQ)-resistant strains of Plasmodium falciparum. Clinical use of AQ has been severely restricted due to hepatoxicity and agranulocytosis side effects associated with its long term use. Lysosomal accumulation and bioactivation to generate reactive quinoneimine metabolite are implicated to be the cause of the observed AQ toxicities. To avoid the quinoneimine formation and thus the toxicity, a series of isotebuquine analogues and their Nomega-oxides with hydroxy group meta to the amino rather than in para position of the aniline moiety were prepared. The new Mannich bases are highly active against both CQ-sensitive (D6) and -resistant (W2 and TM91C235) clones of P. falciparum with IC50 in the range of 0.3-120 ng/mL. New compounds are1000-fold less toxic (IC50 = 0.7-6 microg/mL) to mouse macrophage cell line than to parasite cell lines. Mono-Mannich bases are more active than bis-Mannich bases. Mono-Mannich base 1a (IC50 = 0.3 ng/mL) is 20-fold more active than the corresponding trifluoromethyl analogue 1b. No appreciable difference in either toxicity or efficacy were observed between the new Mannich bases (m-hydroxyaniline derivatives) 1a or 2a and the corresponding p-hydroxyaniline derivatives.

Real time PCR strategy for the identification of major lineages of Trypanosoma cruzi directly in chronically infected human tissues

Two evolutionary lineages, called Trypanosoma cruzi I and II, have been identified in T. cruzi, the etiologic agent of human Chagas disease. Here, we describe a molecular strategy for direct genetic typing of these major groups of T. cruzi directly in human tissues. The protocol is based on heminested PCR amplification of the D7 region of the 24Salpha ribosomal DNA (rDNA), followed by identification of the products using denaturation curves in real time PCR. The repetitive nature of the gene, and the heminested PCR format insured the high sensitivity necessary to detect the presence of the very scarce T. cruzi DNA present in the chronically infected human tissues. There is 80% DNA sequence homology between the two 24Salpha rDNA alleles that define the T. cruzi I and II groups, sufficient to produce different thermal denaturation curves with melting temperature (TM) values of 81.7+/-0.43 and 78.2+/-0.33 degrees C (mean+/-SEM). Using this technical approach, we analysed tissue samples (esophagi, hearts and colon) from 25 different patients with the gastrointestinal or cardiac forms of Chagas disease; in all of them we found only the presence of T cruzi II. Previous epidemiological and immunological findings had already led to the idea that chronic human infections occurring in Brazil and Argentina might be primarily due to T. cruzi II strains, but all the evidence available had been indirect. Our findings provide definitive proof of this hypothesis and will also allow the establishment of which group of T. cruzi is responsible for Chagas disease in other countries.

Trypanosoma cruzi carrying a targeted deletion of a Tc52 protein-encoding allele elicits attenuated Chagas' disease in mice

The intracellular protozoan parasite Trypanosoma cruzi is the etiological agent of Chagas' disease. We have previously characterized a T. cruzi virulence factor named Tc52 sharing structural and functional properties with the thioredoxin and glutaredoxin protein family. Single mutant parasite clones (Tc52(+/-)) exhibiting low virulence in vitro and in vivo were obtained by targeted Tc52 gene replacement. In this report, we have extended our study to analyze the immune response and the disease phenotype in Tc52(+/-)-infected BALB/c mice, during the acute and chronic phases of the disease. Significantly lower parasitemia were found in Tc52(+/-)-infected mice, as compared to wild-type parasite (WT)-infected ones. However, the expansion of all classes of lymphocytes and macrophages was similar for both clones. Furthermore, except for IgG2b levels which were higher in the case of WT-infected mice, all classes of Ig presented no significant difference for WT and Tc52(+/-)-infected animals. Interestingly, a lack of suppression of IL-2 production and of T-cell proliferation inhibition was observed in the case of spleen cells from Tc52(+/-)-infected mice. Finally, the pattern of inflammation process was different and characterized as diffused in the case of Tc52(+/-)-infected mice, or presenting numerous foci in the case of WT-infected mice. Localization of the Tc52 protein in tissue sections and infected heart cell primary cultures by immunofluorescence and immunogold labeling, respectively, revealed the presence of Tc52 at the amastigote surface and associated to aggregates within host cell vesicles. Taken together, these results reinforce the notion of Tc52 being a virulence factor playing a role in the phenotype of the immune response associated to the infection and on the course of the disease.

Views on the autoimmunity hypothesis for Chagas disease pathogenesis

Initially, the notion that the pathogenesis of Chagas disease has an autoimmune component was based on the finding that sera from Trypanosoma cruzi-infected patients or laboratory animals contain antibodies that recognize both parasite and host tissue antigens. Subsequent work suggested that T lymphocytes from chagasic patients and animals also displayed such cross-reactivity. However, the autoimmunity hypothesis has remained controversial because of experimental pitfalls, incomplete or inadequate controls, difficulties in reproducing some key results, and a lack of persuasive evidence that the cross-reactive antibodies or lymphocytes can truly effect the multifaceted pathological features of Chagas disease. Whether the immunologic autoreactivities described to date cause chagasic pathology or result from it is another unresolved question. Discussed herein are the most recent contributions to this topic and the reservations they have raised.

Rapid quantitation of Trypanosoma cruzi in host tissue by real-time PCR

A real-time PCR technique that allows for accurate and sensitive quantitation of tissue parasite burden in animals infected with the protozoan parasite Trypanosoma cruzi was developed. The utility of this method was demonstrated by confirmation of higher parasite load in mice with acute infections in comparison to chronically infected mice, detection of tissue-restricted parasite persistence in different parasite:host strain combinations, and the observation of increased tissue parasite burden with higher infective doses. This method should be a useful tool for monitoring parasite burden in hosts under various treatment regimens.

Cardioprotective effects of phosphoramidon on myocardial structure and function in murine Chagas' disease

Chagas' disease is an important cause of cardiomyopathy. Endothelin-1, a vasoactive peptide has been implicated in the pathogenesis of chagasic cardiomyopathy. C57BL/6 x 129sv and CD1 mice were thus, infected with trypomastigotes of Trypanosoma cruzi (Brazil strain) and these infected mice were compared with infected mice treated with phosphoramidon. This compound inhibits endothelin-converting enzyme and neutral endopeptidases and does not affect the growth of the parasite in culture. Phosphoramidon was given in a dose of 10mg/kg for the initial 15 days post-infection None of the C57Bl/6 x 129sv mice died as a result of infection. However, there was marked myocardial inflammation and fibrosis in infected, untreated mice. The hearts of the infected, phosphoramidon-treated mice showed significantly less pathology. Cardiac magnetic resonance imaging of infected mice revealed right ventricular dilation that was less severe in those treated with phosphoramidon. Phosphoramidon-treated CD1 mice survived the acute infection. Transthoracic echocardiography demonstrated left ventricular dilation and reduced percent fractional shortening and relative wall thickness. These alterations were also attenuated as a result of phosphoramidon treatment. These data suggest that endothelin-1 contributes to the pathogenesis of chagasic cardiomyopathy and interventions that inhibit the synthesis of endothelin-1 and/or neutral endopeptidase might have a protective effect on myocardial structure and function in murine Chagas' disease.

Cardioprotective effects of verapamil on myocardial structure and function in a murine model of chronic Trypanosoma cruzi infection (Brazil Strain): an echocardiographic study

Verapamil has been shown to attenuate the extent of myocardial injury in murine models of chronic Trypanosoma cruzi infection. Infected mice treated with verapamil have significantly lower myocardial expression of inducible nitric oxide synthase and cytokines and substantially less inflammatory infiltrate and myocyte necrosis at necropsy. In the present study, we examined the cardiac structural and functional correlates of verapamil treatment in CD1 mice infected with the Brazil strain of T. cruzi using serial transthoracic echocardiography. There were four groups: uninfected- untreated control, uninfected-verapamil-treated, infected-untreated control, and infected-verapamil-treated. Verapamil was given in drinking water (1 gm/l) continuously from the day of infection for a total of 120 days. Mice were evaluated at baseline, 40 and 150 days p.i. Mice in the untreated-infected group compared with the mice in the infected-verapamil-treated group showed thinning of the left ventricular wall (0.84 +/- 0.02-vs-0.92 +/- 0.04, P<0.05 mm), increase in the left ventricular end-diastolic diameter (3.27 +/- 0.15-vs-2.74 +/- 0.05 mm, P<0.05) and reduction in percent fractional shortening (37 +/- 2-vs-53 +/- 4%, P<0.05). No differences in these parameters were noted among mice in the uninfected-untreated and uninfected-verapamil-treated groups. Furthermore, right ventricular dilation was more severe in mice from the infected-untreated group as compared with those in the infected- verapamil-treated group (visual grade 1.9 +/- 0.4-vs-1.0 +/- 0.2, P<0.05). At necropsy, the extent of myocardial injury, as determined histologically, was significantly greater in the infected-untreated mice. These data provide cardiac structural and functional correlates for the previously observed cardioprotective effects of verapamil in chronic chagasic cardiomyopathy.

Trypanosoma cruzi: acute infection affects expression of alpha-2-macroglobulin and A2MR/LRP receptor differently in C3H and C57BL/6 mice

Although a complete cellular and humoral immune response is elicited in Chagas' disease, recent data suggest that other natural elements of innate immunity may also contribute to the initial host primary defense. alpha-Macroglobulins are a family of plasma proteinase inhibitors that are acute-phase reactants in Trypanosoma cruzi-infected mice and humans. Mice contain a tetrameric alpha-2-macroglobulin (MAM) and a monomeric murinoglobulin (MUG). Heterogeneity in their reactions was observed in murine T. cruzi-infected plasma A2M levels despite an overall increase. In addition, up-regulation of the A2M receptor (A2MR/LRP) was observed in peritoneal macrophages during T. cruzi infection. Here, we show that during T. cruzi infection (Y strain), the MAM and MUG hepatic mRNA levels and the corresponding plasma protein levels were up-regulated in C3H and C57BL/6 (B6) mice, but with different kinetics. On the contrary, A2MR/LRP mRNA levels increased in acutely infected C3H mice, but decreased in B6 mice, in both liver and heart. Immunocytochemistry of infected B6 heart cryosections confirmed a less intense endothelium labeling by the fluoresceinated ligand for A2MR/LRP. On the other hand, infected B6 spleen cells displayed higher F-A2M-FITC binding and MAC1 expression, confirming higher A2MR/LRP expression in macrophages. In uninfected mice, as well as after T. cruzi infection, higher A2M plasma levels were measured in C3H mice than in B6 mice. The lower tissue T. cruzi parasitism found in C3H-infected mice could reflect an inhibitory effect of A2M on parasite invasion. Our present data further contribute to clarifying aspects of the role of A2MR/LRP in a model of acute Chagas' disease in different mouse strains.

A role for extracellular amastigotes in the immunopathology of Chagas disease

In spite of the growing knowledge obtained about immune control of Trypanosoma cruzi infection, the mechanisms responsible for the variable clinico-pathological expression of Chagas disease remain unknown. In a twist from previous concepts, recent studies indicated that tissue parasitism is a pre-requisite for the development of chronic myocarditis. This fundamental concept, together with the realization that T. cruzi organisms consist of genetically heterogeneous clones, offers a new framework for studies of molecular pathogenesis. In the present article, we will discuss in general terms the possible implications of genetic variability of T. cruzi antigens and proteases to immunopathology. Peptide epitopes from a highly polymorphic subfamily of trans-sialidase (TS) antigens were recently identified as targets of killer T cell (CTL) responses, both in mice and humans. While some class I MHC restricted CTL recognize epitopes derived from amastigote-specific TS-related antigens (TSRA), others are targeted to peptide epitopes originating from trypomastigote-specific TSRA. A mechanistic hypothesis is proposed to explain how the functional activity and specificity of class I MHC restricted killer T cells may control the extent to which tissue are exposed to prematurely released amastigotes. Chronic immunopathology may be exacerbated due the progressive accumulation of amastigote-derived antigens and pro-inflammatory molecules (eg. GPI-mucins and kinin-releasing proteases) in dead macrophage bodies.

Chagas' disease and the autoimmunity hypothesis

The notion that the pathology of Chagas' disease has an autoimmune component was initially based on the finding of circulating antibodies binding heart tissue antigens in patients and mice chronically infected with Trypanosoma cruzi. Later, T lymphocytes reactive with heart or nerve tissue antigens were found in chagasic mice and patients, extending the concept to include cell-mediated immunity. However, there is disagreement about whether the observed immunologic autoreactivities are triggered by T. cruzi epitopes and then affect host tissue antigens by virtue of molecular mimicry or are elicited by host antigens exposed to lymphocytes after tissue damage caused by the parasite. There is also disagreement about the relevance of immunologic autoreactivities to the pathogenesis of Chagas' disease because of the lack of reproducibility of some key reports supporting the autoimmunity hypothesis, conflicting data from independent laboratories, conclusions invalidated by advances in our understanding of the immunologic mechanisms underlying cell lysis, and, last but not least, a lack of direct, incontrovertible evidence that cross-reacting antibodies or autoreactive cells mediate the typical pathologic changes associated with human Chagas' disease. The data and views backing and questioning the autoimmunity hypothesis for Chagas' disease are summarized in this review.

Detection of live Trypanosoma cruzi in tissues of infected mice by using histochemical stain for beta-galactosidase

The pathogenesis of tissue damage in chronic Trypanosoma cruzi infection has been a subject of long-standing debate. Conventional staining methods reveal a paucity of parasites in tissues from chronically infected individuals, which has led to the theory that the pathologic findings may be primarily autoimmune in origin. Immunostaining for T. cruzi antigens or in situ PCR methods show evidence for parasite components in chronic tissues; however, these methods do not address whether the stained material represents parasite debris or live organisms. An improved method for detecting intact T. cruzi in tissues was developed by making a genetically engineered strain that expresses Escherichia coli beta-galactosidase. The expression of this enzyme allows the detection of T. cruzi in tissues by using the histochemical stain 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal). The technique was used to monitor tissue parasitism and its relation to pathologic findings in the mouse model of Chagas' disease. Parasites were easily visible as bright blue structures in skeletal muscle, heart, bladder, peripheral nerve, liver, spleen, adrenal gland, brain, and adipose tissue in acutely infected mice. The number of viable parasites diminished >100-fold when tissues from 3-week-infected mice were compared with those from 10-month-infected mice. However, even at the lower level, parasites were clearly recognizable in sections of skeletal muscle and bladder at the 10-month time point. Inflammation remained robust in skeletal muscle, bladder, and sciatic nerve despite the near disappearance of parasites, suggesting three possibilities: exuberant host reactions to the few remaining parasites, autoimmune inflammation, or reactions to retained parasite antigens in the tissues.

Enhanced prevalence of T cells expressing TCRBV8S2 and TCRBV8S3 in hearts of chronically Trypanosoma cruzi-infected mice

We have analysed the relative T cell receptor (TCR) BV gene usage in T cells from hearts and spleens of CBA/HJ mice chronically infected with the Tulahuén strain of Trypanosoma cruzi. During chronic infection, CBA/HJ mice recruit T cells at the major site of inflammation (i.e. the heart), with over-representation of certain TCRBV gene subfamilies (TCRBV8S2 and TCRBV8S3). In contrast, no signal or a very weak message from a limited number of T cells was recorded from one heart of the control group. No alteration of TCRBV distribution was recorded in spleens of chronically infected CBA/HJ. Our findings indicate that there is a preferential TCRBV gene usage in the T cell response in the hearts of chronically infected mice. Furthermore, the pattern of CDR3 lengths in inflammatory T cells was altered.

"Autoimmune rejection" of neonatal heart transplants in experimental Chagas disease is a parasite-specific response to infected host tissue

Infection with the protozoan parasite Trypanosoma cruzi often results in chronic heart- and gut-associated disease known as Chagas disease. In this study we show that contrary to previous reports, neonatal hearts transplanted into mice chronically infected with T. cruzi do not exhibit signs of autoimmune-type rejection or any significant inflammatory response. In addition to an absence of inflammation, these syngeneic heart transplants survive for more than 1 year and are absolutely free of parasites as determined by in situ PCR analysis. However, if well-established transplanted hearts in chronically infected mice are directly injected with live parasites, a rapid and dramatic inflammatory response ensues that results in cessation of heart function. Likewise, transplanted hearts established in mice prior to systemic infection with T. cruzi or hearts transplanted into mice during the acute stage of T. cruzi infection become parasitized and develop inflammatory foci. In these cases where the transplanted hearts become parasitized, the ensuing inflammatory response is nearly identical to that observed in the native hearts of T. cruzi-infected mice in terms of cell types present and adhesion molecules and cytokines expressed. Importantly, this response is strikingly different from that observed in the allogeneic heart rejection. These results clearly document that parasitization of heart tissue is both necessary and sufficient for the induction of tissue damage in Chagas disease and strongly argue against a principal autoimmune etiology for this disease.

Comparison of PCR and microscopic methods for detecting Trypanosoma cruzi

The diagnosis of acute infection with Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease, is generally made by detecting parasites by microscopic examination of fresh blood. Although highly specific, this approach often lacks sensitivity. Several years ago, PCR assays for the detection of T. cruzi were described, but the sensitivities and specificities of these tests have not yet been defined precisely. In the present study, we first compared the sensitivities of PCR methods that differ in sample processing as well as in the target sequences that are amplified. Then, we challenged eight mice with T. cruzi, and on 31 days over a 380-day period, we compared the ability of the PCR method with the highest sensitivity to detect parasites in blood with that of microscopic examination. During the acute phase of the infections, parasites were detected on average 3.9 days earlier by the PCR method than by microscopy. Furthermore, the infected mice were consistently positive by the PCR method during the chronic phase, while parasites were intermittently detected by microscopic examination during that period. Overall, among the 248 comparisons, in 84 the PCR method was positive and no parasites were seen by microscopic examination, whereas the reverse was true in only 1 case, a difference that is highly significant. These findings suggest that this approach should be in patients suspected of having acute Chagas' disease. Moreover, the higher sensitivity of the PCR method observed in both the acute and chronic phases of the T. cruzi infections in the mice that we studied indicates that this approach should be useful in evaluating experimental drugs in T. cruzi-infected laboratory animals.

Characterization of cytokine production in murine Trypanosoma cruzi infection by in situ immunocytochemistry: lack of association between susceptibility and type 2 cytokine production

Cytokine production in the spleens of mice infected with the protozoan parasite Trypanosoma cruzi was analyzed in three models which differ in the outcome of the infection. Using immunocytochemical techniques to detect cytokine-producing cells, the production of type 1 [interleukin-2 (IL-2) and interferon (IFN)-gamma], type 2 (IL-4, IL-5, IL-10), inflammatory [tumor necrosis factor (TNF)-alpha, IL-1 alpha, IL-6] and regulatory (transforming growth factor-beta) cytokines were examined. With the exception of IL-4 and IL-5, cells producing all of the cytokines assayed were detected in both the resistant and susceptible models of T. cruzi infection. Cells producing IL-4 and IL-5 were not detected until later in infection in the resistant mice (> 34 days), at about the time animals of the susceptible strain succumb to the infection. Mice of the susceptible model showed a slight delay in the appearance of cells producing the type 1 cytokines IL-2 and IFN-gamma and an earlier appearance of TNF-producing cells, in comparison to resistant mice. Cells producing IL-2 or IL-10 were transient in their appearance in the spleen while cells producing IL-1, IL-4, IL-5, IL-6, IFN-gamma, TNF, or TGF-beta were first detectable in either the acute or post-acute stage of the infection and persisted up to 700 days post infection in two different resistant models of the infection. Cells producing IFN-gamma, TNF-alpha and TGF-beta were particularly numerous even very late in the infection. Double-staining techniques were used to show that the vast majority of the IFN-gamma-producing cells in the spleen were CD4-, CD8- alpha/beta TCR+T cells. This study confirms the transience of IL-2 production in the acute stage of T. cruzi infection and the persistent and simultaneous production of type 1 and type 2 cytokines during the late-acute and chronic stages of the infection. Susceptibility or resistance to T. cruzi infection does not associate with a Th2 pattern of cytokine production in the three models examined in this study. The overlapping pattern of type 1 and type 2 cytokine-producing cells in both the acute and chronic stages of T. cruzi infection demonstrates that longterm infections do not necessarily lead to a dominance of either type 1 or type 2 cytokine production.

Changes in the total content of iron, copper, and zinc in serum, heart, liver, spleen, and skeletal muscle tissues of rats infected with Trypanosoma cruzi

The effects of the Trypanosoma cruzi infection on the total content of the essential trace elements iron (Fe), copper (Cu), and zinc (Zn) in serum, heart, liver, spleen, and skeletal muscle were determined in "Wistar" rats inoculated with reticulotropic "Y" strain trypanosomes (Tryps) in their slender blood form. The 250 rats were divided in two groups of 80 rats (L-1 and L-2) and one of 90 (C) used as controls. L-1 and L-2 were inoculated with 2 x 10(5) and 5 x 10(2) Tryps, respectively. Ten rats of the C group were killed the inoculation day (i), and ten rats of each group chosen at random were killed and blood parasitemia determined at 5, 10, 15, 20, 25, 30, 60, and 90 post-i days covering the infection acute-phase myocarditis. Previously cryohomogenized and lyophilized tissues were digested in an HNO3- H2O2 mixture with the aid of a microwave oven, and the elements Fe, Cu, and Zn were determined by Flame Atomic Absorption Spectrometry. Generally, more intense changes were observed in the L-1 group. Serum Fe and Zn levels are lower and Cu levels higher in groups L-1 and L-2 than in C. However, Fe is not significantly sequestered in the liver during the acute phase of the infection as expected, but of the tissues studied, the spleen was the main site of Fe binding. Zn tended to increase in all tissues, except in the spleen, where during the acute phase of the infection, the total content of Zn in groups L-1 and L-2 was lower than in group C. Cu increased mainly in the spleen and muscle. In general, each tissue presented its own pattern of redistribution related to its nature, functions, and number of parasites inoculated, and these patterns may have been altered by the tropism of the parasite.

Susceptibility of beta 2-microglobulin-deficient mice to Trypanosoma cruzi infection

The beta 2-microglobulin (beta 2m) protein associates with the products of the class I major histocompatibility (MHC) loci; this combination functions in the thymic development of and antigen presentation to CD8+ T cells. Mice in which the beta 2m gene has been disrupted by homologous recombination fail to express class I MHC gene products, and therefore lack CD8+ T cells and measurable cytotoxic T-cell responses. However, beta 2m- mice appear to have normal development of both CD4+ alpha/beta T-cell receptor (TCR+) and gamma/delta TCR+ T cells and are not overtly more susceptible than beta 2m+ mice to potential environmental agents of infection or to experimental viral infection. Here we show that beta 2m- mice suffer high parasitaemias and early death when infected with the obligate cytoplasmic protozoan parasite Trypanosoma cruzi. Despite this increased susceptibility, the beta 2m- mice are more responsive than their beta 2m+ littermates in terms of lymphokine production, making higher levels of both interleukin-2 and interferon-gamma in response to mitogen stimulation. In addition, the beta 2m- mice show essentially no inflammatory response in parasite-infected tissues. These results confirm previous experiments on mice depleted of CD8+ cells using antibody treatment in demonstrating the importance of CD8+ T cells in immune protection in T. cruzi infection. They also implicate CD8+ T cells and/or class I MHC molecules in regulation of lymphokine production and recruitment of inflammatory cells.

Apheresis for severe malaria complicated by cerebral malaria, acute respiratory distress syndrome, acute renal failure, and disseminated intravascular coagulation

Malaria has become a very uncommon disease in Italy. Recently a variety of circumstances, such as travel to tropical countries as well as immigration from Asia and Africa, have combined to increase the number of malaria cases recorded annually. In this report we describe the use of red cell exchange transfusion and plasma exchange in the treatment of a patient with hyperparasitemic malaria (51% erythrocytes or more parasitized). When first observed the patient was in shock and had signs of cerebral malaria, disseminated intravascular coagulation, and acute respiratory distress syndrome, which in the following 2 days were complicated by acute renal failure. After mefloquine therapy combined with 3 red blood cell exchanges, 2 plasma exchanges, and 10 dialysis sessions over 14 days, the patient recovered completely. This case of severe malaria with multiple complications, treated with mefloquine in conjunction with both exchange transfusion and plasmapheresis, had a successful outcome and lends further support to the possible beneficial role of exchange transfusion in complicated malaria.

Pathophysiological insights into the cardiomyopathy of Chagas' disease

The evidence gained from both human and animal studies of chronic chagasic cardiomyopathy suggests that the disease occurs as a consequence of several discrete and progressive pathophysiological processes occurring after infection, the ultimate expression of which depends on a host of unidentified factors. Collectively, the infection-associated events compromise microvasculature function and result in hypoperfusion, with consequences indistinguishable from those observed in other, nonparasitological cardiomyopathic diseases secondary to hypoperfusion. Therefore, chronic chagasic cardiomyopathy may share similar pathophysiological abnormalities with other chronic congestive cardiomyopathic states.

Modulation of Trypanosoma cruzi adhesion to host muscle cell membranes by ligands of muscarinic cholinergic and beta adrenergic receptors

Plasma membrane vesicles (PMVs) of Trypanosoma cruzi adhered to L6 myoblast host cells as a function of time and concentration in saturation phenomena in a similar fashion to that reported in a previous publication. The initial adhesion rate (A0) of T. cruzi PMVs to L6 myoblasts in tissue culture was inhibited by acetylcholine (10(-5) M), isoproterenol (10(-5) M) and norepinephrine (10(-8) M) (range 29.1-50.3% of control). Atropine, the antagonist of muscarinic cholinergic receptors (10(-5) M), and propranolol or pindolol, the antagonists of beta-adrenergic receptors (10(-5) M), were also equal inhibitors of the T. cruzi PMV to L6 myoblast adhesion rate (range 26.1 to 55.5% of control). The alpha-adrenergic receptor ligands yohimbine and phentolamine (10(-5) M) showed no A0 inhibitory activity in similar assays. The interaction of T. cruzi PMVs with type I host muscle sarcolemma receptors was clearly defined in assays which used porcine heart atrial membranes (PAMs) immobilized on cationic polyacrylamide beads. In this parasite membrane-host cell membrane assay system, 10(-10) M atropine and 5 x 10(-9) M propranolol produced a shift of an S-shaped T. cruzi PMV to PAM saturation isotherm to the right, suggesting that a negative cooperative interaction was produced between the intramembrane ligand binding site and another, surface heterotropic T. cruzi PMV adhesion site. Atropine and propranolol were equieffective inhibitors of the T. cruzi striated muscle sarcolemma recognition process, raising the possibility that T. cruzi attachment molecules annexed pairs of muscarinic cholinergic and beta-adrenergic receptors to effect adhesion of the two membrane surfaces.

The effect of interleukin-2 on parasitemia and myocarditis in experimental Chagas' disease

Previous investigations showed that interleukin-2 (IL-2) administered in vivo into mice infected with Trypanosoma cruzi reduced levels of parasitemia and increased longevity. Present experiments examined the effect of administration of different doses of IL-2 at different times during infection in mice on parasitemia and histopathology of heart tissue. Two different doses of IL-2 (1,500 or 10,000 U) given at 3 different times during infection were equivalent in reducing parasitemia. All of the IL-2 treated groups of mice had significantly lower numbers of circulating trypomastigotes as compared with controls not receiving this lymphokine. This IL-2 treatment of T. cruzi-infected mice resulted also in lower numbers of pseudocysts in all 4 ventricular regions in the hearts. This was particularly evident in the more severely infected right ventricular wall; however, a similar decrease was not as apparent in the less severely infected left ventricular wall. The IL-2 treated, infected mice showed minimal or no effect in reducing inflammation of myocardial cells. However, the mildest inflammation of ventricular wall tended to occur in mice receiving IL-2 treatment either as a low dose (1,500 U) or a high dose (10,000 U) at 5, 7 and 9 days after infection as compared with mice treated later on. It was concluded that IL-2 treatment of infected mice produced a significant decrease in parasitemia and decreased infection of myocardial cells.

Complementary surface epitopes, myotropic adhesion and active grip in Trypanosoma cruzi-host cell recognition

Plasma membranes with complementary surface epitopes and with essentially the same orientation as tissue infective metacyclic trypomastigotes and epimastigotes of Trypanosoma cruzi adhere to L6 myoblast host cells preferentially to smooth muscle and epithelial cells as a function of time, surface area and concentration in saturation phenomena at 4 and 37 degrees C. The initial adhesion rates are partially calcium ion dependent and, at saturation, they are also dependent on high energy phosphorylated intermediates, exerting an active grip on adherent parasite membranes. These phenomena are consistent with the existence of parasite attachment molecules on the external surface of the plasma membrane and complementary host cell receptor structures with the capacity to bind them.

Comparative studies of the infection of Lewis rats with four Trypanosoma cruzi clones

Quantitative and qualitative differences in parasitaemia levels and histopathological characteristics occurred in Lewis rats infected with four Trypanosoma cruzi clones. Rats infected with clone Sylvio-X10/7 sustained high parasitaemias and died during the acute phase whereas rats infected with clones Sylvio-X10/4, Miranda/78 or Miranda/80 did not. Myocardial fibrosis was more extensive in rats chronically infected with clone X10/4 than in rats infected with the 2 Miranda clones. Myocardial fibrosis developed more rapidly in rats than has been reported in mice. These characteristics are advantageous in developing animal models of human chagasic myocardiopathy.

Trypanosoma cruzi: constancy of clone pathogenicity for inbred mice during long-term in vitro maintenance

The reproducibility of infection of C3H/He mice with T. cruzi clones Sylvio-X10/4 and Sylvio-X10/7 maintained in the laboratory for 946 and 496 days respectively was assayed. Clone X10/7 from 15 different in vitro passages consistently induced an acute lethal infection (94.3% mortality) and constant survival time (Mean = 24.6 d.p.i.). Female mice survived significantly longer than males and mice older than 30 days at the time of infection survived significantly longer than younger mice. The mortality of mice infected with clone X10/4 from 23 different in vitro passages was lower (5.1%) and their survival longer (Mean = 42.7 d.p.i.) than mice infected with clone X10/7. High anti-T. cruzi IgG titres were detected in the plasma of all mice killed after 30 d.p.i. Histologically, the heart, skeletal muscles and/or large intestine contained intracellular parasites in 59% of the mice; parasites were found in mice of all groups tested. The hearts of all mice were comparably inflammed regardless of parasite passage number or duration of infection. These data demonstrate that the presentation and course of infection of inbred mice with two T. cruzi clones is not changed by either the duration or protocol used for in vitro maintenance; the reported loss or change in virulence of T. cruzi strains during long-term in vitro maintenance did not occur. Consequently, T. cruzi clones and inbred mice provide a dependable and reproducible means to study host-parasite interactions.