Benznidazole therapy in Trypanosoma cruzi-infected mice blocks thymic involution and apoptosis of CD4+CD8+ double-positive thymocytes

Several alterations involving peripheral lymphoid organs have been extensively described after experimental Trypanosoma cruzi infection. Thymic involution occurs as well in infected mice, with both structural and functional alterations in the organ. Despite these abnormalities, specific immune response proceeds to control parasitemia and the participation of T lymphocytes is essential. However, there are relatively few studies on the impact of benznidazole (N-benzyl-2-nitroimidazole acetamide) upon this response. In this present work, we decided to evaluate the impact of benznidazole treatment upon the thymus involution following acute T. cruzi infection in mice. We have provided evidence that benznidazole treatment controls the severe abnormalities seen in the thymus due to T. cruzi infection. The thymocyte loss related to the depletion of double-positive CD4(+)CD8(+) thymocytes was clearly prevented, corroborating the idea that the mechanism responsible for the prevention of thymus involution is related to the decrease of apoptosis rate in this subset after benznidazole treatment. Furthermore, we demonstrated the prevention of enhanced extracellular matrix deposition in the thymus. In conclusion, the preservation of thymus homeostasis, even though partial, was accomplished after benznidazole treatment. Our data are consistent with the notion that different outcomes of T. cruzi infection may be linked to differences in the parasite load concomitant to fine tuning of the host immune response.

Activation of transforming growth factor β by Trypanosoma cruzi

The anti-inflammatory cytokine, transforming growth factor beta (TGFbeta), plays an important role in Chagas disease, which is caused by the protozoan parasite Trypanosoma cruzi. In the current study, we show that the addition of an anti-TGFbeta antibody inhibited T. cruzi infection of cardiomyocytes, demonstrating the requirement for active endogenous TGFbeta. As TGFbeta is synthesized as a biologically inactive precursor, which is proteolytically processed to yield a mature, active homodimer, we hypothesized that T. cruzi could activate latent TGFbeta. To test this, we added recombinant latent TGFbeta to a TGFbeta-responsive reporter cell line in the presence of T. cruzi. We observed that T. cruzi was able to activate latent recombinant TGFbeta in this cellular model. We then investigated the ability of T. cruzi to activate latent TGFbetain vitro. We found that live T. cruzi, or cytosolic extracts of T. cruzi, activated latent TGFbeta in a dose- and temperature-dependent manner. The agent involved in TGFbeta activation was shown to be thermolabile and hydrophobic. Taken together, our studies demonstrate that T. cruzi directly activates latent TGFbeta. This activation is required for parasite entry into the mammalian cells and is likely to play an important role in modulating the outcome of T. cruzi infection.

Trypanosoma cruzi-cardiomyocytes: new contributions regarding a better understanding of this interaction

The present paper summarizes new approaches regarding the progress done to the understanding of the interaction of Trypanosoma cruzi-cardiomyocytes. Mannose receptors localized at the surface of heart muscle cell are involved in binding and uptake of the parasite. One of the most striking events in the parasite-heart muscle cells interaction is the disruption of the actin cytoskeleton. We have investigated the regulation of the actin mRNA during the cytopathology induced in myocardial cells by the parasite. T. cruzi invasion increases calcium resting levels in cardiomyocytes. We have previously shown that Ca2+ ATPase of the sarcoplasmic reticulum (SERCA) is involved in the invasion of T. cruzi in cardiomyocytes. Treating the cells with thapsigargin, a drug that binds to all SERCA ATPases and causes depletion of intracellular calcium stores, we found a 75% inhibition in the T. cruzi-cardiomyocytes invasion.

Acute-phase proteins and serologic profiles of chagasic children from an endemic area in Bolivia

Chagas' disease represents a major public health problem in Latin America. In endemic areas, it is important to detect acute and even asymptomatic infections in children so that specific therapy can be started immediately. We studied 203 sera from children from the region of Cochabamba, Bolivia. A high percentage of seropositive individuals was found in the three villages studies. Levels of alpha-2 macroglobulin (A2M) and C-reactive protein (CRP) increased in a significant number of children with acute Chagas' disease. The combined analysis of serologic and biochemical parameters can define the different stages of acute infection by Trypanosoma cruzi: 1) an early stage, with an increase only in specific immunoglobulin M (IgM) levels; 2) intermediate stages, with high specific IgM and IgG levels and/or high anti-galactose (anti-Gal) levels and increased A2M and/or CRP levels; and 3) a late acute stage, with low IgM levels but high A2M, CRP, anti-Gal, and specific IgG levels. The detection of high IgG levels alone is indicative of the chronic/indeterminate stage of Chagas' disease. We also show serologic differences between seropositive asymptomatic villagers and symptomatic patients undergoing medical care; asymptomatic cases presented higher levels of A2M and lower levels of specific antibodies.

An inhibition ELISA to determine alpha macroglobulin levels in mouse plasma

A sensitive method for quantifying mouse plasma alpha-macroglobulins (AM) using an inhibition ELISA is described. AM are important plasma proteinase inhibitors that possibly act also as immunomodulatory molecules. The standard protocol developed in our experiments involves coating well with 10 micrograms/ml A2M in carbonate buffer, followed by incubation with a 1:1 (v/v) mixture of the plasma to be tested (diluted 1/1000) and goat anti-AM (diluted 1/1250). This is followed by further incubation, first with the enzyme-conjugated antibody and with the substrate prior to the reading of absorbance levels of the reaction products. Standard curve samples must be included in each plate, employing known amounts of the purified Murine Alpha-2-Macroglobulin (MuA2M) used for coating, with concentrations ranging from 0.001 to 10 micrograms/ml. Using test samples in triplicates and a 6-point standard curve in a single ELISA plate, 25 plasma samples can be tested accurately. The method offers an useful tool for establishing AM levels in small samples of mouse plasma.

Improved enzyme-linked immunoadsorbent assay (ELISA) for the study of Trypanosoma cruzi-host cell interaction in vitro

We herein present an improved assay for detecting the presence of Trypanosoma cruzi in infected cultures. Using chagasic human sera (CHS), we were able to detect T. cruzi infection in primary cultures of both peritoneal macrophages and heart muscle cells (MHC). To avoid elevated background levels--hitherto observed in all experiments especially in those using HMC--CHS were preincubated with uninfected cells in monolayers or suspensions prior to being used for detection of T. cruzi in infected monolayers. Preincubation with cell suspensions gave better results than with monolayers, reducing background by up to three times and increasing sensitivity by to twenty times. In addition, the continuous fibroblastic cell line L929 was shown to be suitable for preadsorption of CHS. These results indicate that the high background levels observed in previous reports may be due to the presence of human autoantibodies that recognize surface and/or extracellular matrix components in cell monolayers. We therefore propose a modified procedure that increases the performance of the ELISA method, making it an useful tool even in cultures that would otherwise be expected to present low levels of infection or high levels of background.

Trypanosoma cruzi: enhanced alpha-macroglobulin levels correlate with the resistance of BALB/cj mice to acute infection

Trypanosoma cruzi proteinases are very likely involved in host-cell invasion. Physiological plasma-proteinase inhibitors from the macroglobulin (MG) family, among them alpha-2-macroglobulin (A2M), are found in tissues and in the plasma of mammals. By complexing to all classes of proteinases, MGs inhibit their action on high-molecular-weight substrates. In vitro studies have shown that A2M impairs T. cruzi proteases and, consequently, the parasite's ability to invade host cells and enhances the phagocytic and microbicidal actions of resident macrophages against T. cruzi. To test the hypothesis of a putative "protective" effect for MG, we quantified it in BALB/cj mice during the course of an experimental T. cruzi infection, comparing a posteriori the levels in mice that died with those in animals that survived, which were considered as being susceptible and resistant to the infection, respectively. The results showed that surviving mice showed an increase in plasma concentrations of MG during the first few weeks after the infection, whereas the levels in mice that died during the acute phase did not differ significantly from those in non-infected mice. These findings and the previous in vitro data indicate a role for physiological proteinase inhibitors, particularly alpha-macroglobulins, in resistance to T. cruzi infection, whereby a balance between parasite proteases and host protease inhibitors may be crucial. MG may thus participate in the complex network of reactions involved in the early acute phase of the disease and contribute by conferring to the host an ability to survive the infection.

Biological aspects of the Dm 28c clone of Trypanosoma cruzi after metacyclogenesis in chemically defined media

The biological characterization of the Trypanosoma cruzi clone Dm 28c in terms of its growth in LIT medium, cell-cycle, infectivity to mice and interaction with professional and non-professional phagocytic cells shows that it behaves as a bona fide T. cruzi representant. The biological properties of this myotropic clone do not change according to the origin of the trypomastigote forms (i. e., from triatomines, infected mice, cell-culture or from the chemically defined TAUP and TAU3AAG media). In addition Dm 28c metacyclic trypomastigotes from TAU3AAG medium display a high infectivity level to fibroblasts and muscle cells. Experiments on binding of cationized ferritin to trypomastigotes surface show the existence of cap-like structures of ferritin in regions near the kinetoplast, however the nature and role of these anionic sites remain to be determined. The results indicate that metacyclic trypomastigotes from the Dm 28c clone obtained under chemically defined conditions reproduce the biological behaviour of T. cruzi, rendering this system very suitable for the study of cell-parasite interactions and for the isolation of trypanosome relevant macromolecules.