How are antibodies involved in the protective mechanism of susceptible mice infected with T. cruzi?

IgG Subclass Analysis in Patients with Chagas Disease 4 Years After Benznidazole Treatment

BACKGROUND

In humans, Trypanosoma cruzi infection is controlled by a complex immune response. Immunoglobulin G (IgG) is important for opsonizing blood trypomastigotes, activating the classic complement pathway, and reducing parasitemia. The trypanocidal activity of benznidazole is recognized, but its effects on the prevention and progression of Chagas disease is not well understood OBJECTIVE: We aimed to evaluate the levels of total IgG and cross-specific IgG subclasses in patients with chronic Chagas disease of different clinical forms before and after 4 years of benznidazole treatment.

METHODS

Eight individuals with the indeterminate form and nine with the cardiac form who completed the treatment protocol were evaluated. The levels of total IgG and IgG1, IgG2, IgG3, and IgG4 isotypes were quantified in the serum of each individual using the fluorescent immunosorbent assay. The results are expressed as relative fluorescence unit.

RESULTS

Patients with chronic Chagas disease presented decreased levels of total IgG at 48 months after benznidazole treatment. Increased IgG1 and decreased IgG3 levels were observed in patients with the cardiac form and those with exacerbated clinical forms. In addition, a decrease in the IgG3/IgG1 ratio was observed in individuals with the cardiac form of Chagas disease.

CONCLUSIONS

Benznidazole administration in the chronic phase differentially changes IgG subclasses in patients with cardiac and indeterminate forms, and monitoring the IgG3 level may indicate the possible prognosis to the cardiac form or worsening of the already established clinical form.

Experimental Nanovaccine Offers Protection Against Repeat Exposures to Trypanosoma cruzi Through Activation of Polyfunctional T Cell Response

A parasitic protozoan Trypanosoma cruzi (T. cruzi) is the etiologic agent of Chagas disease. Previously, we have identified T. cruzi antigens TcG2 and TcG4 as potential vaccine candidates, cloned in eukaryotic expression vector pCDNA3.1 (referred as p2/4) and tested their ability to elicit protection from T. cruzi infection. In the present study, we subcloned the two antigens in a nanoplasmid that is optimized for delivery, antigen expression, and regulatory compliance standards, and evaluated the nanovaccine (referred as nano2/4) for prophylactic protection against repeat T. cruzi infections. For this, C57BL/6 mice were immunized with two doses of p2/4 or nano2/4 at 21 days interval, challenged with T. cruzi 21 days after 2^nd immunization, and euthanized at 10- and 21-days post-infection (pi) corresponding to parasite dissemination and replication phase, respectively. Some mice were re-challenged 21 days pi and monitored at 7 days after re-infection. Without the help of a vaccine, T. cruzi elicited delayed and sub-par T cell activation and low levels of effector molecules that failed to control tissue dissemination and replication of the parasite and provided no protection against repeat challenge infection. The nano2/4 was most effective in eliciting an early activation and production of IFN-γ by CD4⁺T effector/effector memory (T_EM) cells and cytolytic perforin (PFN) and granzyme B (GZB) molecules by CD4⁺ and CD8⁺ T_EM subsets at 10 days pi that was followed by robust expansion of CD4⁺ and CD8⁺ T_EM and T_CM cells with further increase in IFN-γ production at 21 days pi. Consequently, nano2/4-immunized mice exhibited potent control of parasite dissemination at 10 days pi, and tissue parasite burden and tissue inflammatory infiltrate and necrosis were barely detectable at 21 days pi. Furthermore, nano2/4-immunized mice responded to re-challenge infection with high levels of effector molecules production by CD4⁺ and CD8⁺ T_EM subpopulations that offered even better control of tissue parasite burden than was observed after 1^st infection. In comparison, non-vaccinated/infected mice exhibited clinical features of sickness and 59% mortality within 7 days after re-infection. In conclusion, we show that delivery of TcG2 and TcG4 in nanoplasmid offers excellent, protective T cell immunity against repeat T. cruzi infections.

Host-parasite dynamics in Chagas disease from systemic to hyper-local scales

Trypanosoma cruzi is a remarkably versatile parasite. It can parasitize almost any nucleated cell type and naturally infects hundreds of mammal species across much of the Americas. In humans, it is the cause of Chagas disease, a set of mainly chronic conditions predominantly affecting the heart and gastrointestinal tract, which can progress to become life threatening. Yet around two thirds of infected people are long-term asymptomatic carriers. Clinical outcomes depend on many factors, but the central determinant is the nature of the host-parasite interactions that play out over the years of chronic infection in diverse tissue environments. In this review, we aim to integrate recent developments in the understanding of the spatial and temporal dynamics of T. cruzi infections with established and emerging concepts in host immune responses in the corresponding phases and tissues.

In-solution behavior and protective potential of asparagine synthetase A from Trypanosoma cruzi

l-Asparagine synthetase (AS) acts in asparagine formation and can be classified into two families: AS-A or AS-B. AS-A is mainly found in prokaryotes and can synthetize asparagine from ammonia. Distinct from other eukaryotes, Trypanosoma cruzi produces an AS-A. AS-A from Trypanosoma cruzi (Tc-AS-A) differs from prokaryotic AS-A due to its ability to catalyze asparagine synthesis using both glutamine and ammonia as nitrogen sources. Regarding these peculiarities, this work uses several biophysical techniques to provide data concerning the Tc-AS-A in-solution behavior. Tc-AS-A was produced as a recombinant and purified by three chromatography steps. Circular dichroism, dynamic light scattering, and analytical size exclusion chromatography showed that Tc-AS-A has the same fold and quaternary arrangement of prokaryotic AS-A. Despite the tendency of protein to aggregate, stable dimers were obtained when solubilization occurred at pH ≤ 7.0. We also demonstrate the protective efficacy against T. cruzi infection in mice immunized with Tc-AS-A. Our results indicate that immunization with Tc-AS-A might confer partial protection to infective forms of T. cruzi in this particular model.

Could age and aging change the host response to systemic parasitic infections? A systematic review of preclinical evidence

The impact of age and aging in the evolution of systemic parasitic infections remains poorly understood. We conducted a systematic review from preclinical models of Chagas disease, leishmaniasis, malaria, sleeping sickness and toxoplasmosis. From a structured and comprehensive search in electronic databases, 29 studies were recovered and included in the review. Beyond the characteristics of the experimental models, parasitological and immunological outcomes, we also discussed the quality of current evidence. Our findings indicated that throughout aging, parasitemia and mortality were consistently reduced in Chagas disease and malaria, but were similar or increased in leishmaniasis and highly variable in toxoplasmosis. While a marked humoral response in older animals was related to the anti-T. cruzi protective phenotype, cellular responses mediated by a polarized Th1 phenotype were associated with a more effective defense against Plasmodium infection. Conversely, in leishmaniasis, severe infections and high mortality rates were potentially related to attenuation of humoral response and an imbalance between Th1 and Th2 phenotypes. Due to the heterogeneous parasitological outcomes and limited immunological data, the role of aging on toxoplasmosis evolution remains unclear. From a detailed description of the methodological bias, more controlled researches could avoid the systematic reproduction of inconsistent and poorly reproducible experimental designs.

Unconventional Pro-inflammatory CD4+ T Cell Response in B Cell-Deficient Mice Infected with Trypanosoma cruzi

Chagas disease, caused by the parasite Trypanosoma cruzi, is endemic in Latin America but has become a global public health concern by migration of infected people. It has been reported that parasite persistence as well as the intensity of the inflammatory immune response are determinants of the clinical manifestations of the disease. Even though inflammation is indispensable for host defense, when deregulated, it can contribute to tissue injury and organ dysfunction. Here, we report the importance of B cells in conditioning T cell response in T. cruzi infection. Mice deficient in mature B cells (muMT mice) infected with T. cruzi exhibited an increase in plasma TNF concentration, TNF-producing CD4⁺ T cells, and mortality. The increase in TNF-producing CD4⁺ T cells was accompanied by a reduction in IFNγ⁺CD4⁺ T cells and a decrease of the frequency of regulatory Foxp3⁺, IL-10⁺, and IL17⁺CD4⁺ T cells populations. The CD4⁺ T cell population activated by T. cruzi infection, in absence of mature B cells, had a high frequency of Ly6C⁺ cells and showed a lower expression of inhibitory molecules such as CTLA-4, PD-1, and LAG3. CD4⁺ T cells from infected muMT mice presented a high frequency of CD62L^hiCD44^- cells, which is commonly associated with a naïve phenotype. Through transfer experiments we demonstrated that CD4⁺ T cells from infected muMT mice were able to condition the CD4⁺ T cells response from infected wild-type mice. Interestingly, using Blimp-flox/flox-CD23icre mice we observed that in absence of plasmablast/plasma cell T. cruzi-infected mice exhibited a higher number of TNF-producing CD4⁺ T cells. Our results showed that the absence of B cells during T. cruzi infection affected the T cell response at different levels and generated a favorable scenario for unconventional activation of CD4⁺ T cell leading to an uncontrolled effector response and inflammation. The product of B cell differentiation, the plasmablast/plasma cells, could be able to regulate TNF-producing CD4⁺ T cells since their absence favor the increase of the number of TNF⁺ CD4⁺ in T. cruzi-infected mice.

Modulation of immune response in experimental Chagas disease

Trypanosoma cruzi (T. cruzi), the etiological agent of Chagas disease, affects nearly 18 million people in Latin America and 90 million are at risk of infection. The parasite presents two stages of medical importance in the host, the amastigote, intracellular replicating form, and the extracellular trypomastigote, the infective form. Thus infection by T. cruzi induces a complex immune response that involves effectors and regulatory mechanisms. That is why control of the infection requires a strong humoral and cellular immune response; hence, the outcome of host-parasite interaction in the early stages of infection is extremely important. A critical event during this period of the infection is innate immune response, in which the macrophage’s role is vital. Thus, after being phagocytized, the parasite is able to develop intracellularly; however, during later periods, these cells induce its elimination by means of toxic metabolites. In turn, as the infection progresses, adaptive immune response mechanisms are triggered through the TH1 and TH2 responses. Finally, T. cruzi, like other protozoa such as Leishmania and Toxoplasma, have numerous evasive mechanisms to the immune response that make it possible to spread around the host. In our Laboratory we have developed a vaccination model in mice with Trypanosoma rangeli, nonpathogenic to humans, which modulates the immune response to infection by T. cruzi, thus protecting them. Vaccinated animals showed an important innate response (modulation of NO and other metabolites, cytokines, activation of macrophages), a strong adaptive cellular response and significant increase in specific antibodies. The modulation caused early elimination of the parasites, low parasitaemia, the absence of histological lesions and high survival rates. Even though progress has been made in the knowledge of some of these mechanisms, new studies must be conducted which could target further prophylactic and therapeutic trials against T. cruzi infection.

IL-17RA signaling reduces inflammation and mortality during Trypanosoma cruzi infection by recruiting suppressive IL-10-producing neutrophils

Members of the IL-17 cytokine family play an important role in protection against pathogens through the induction of different effector mechanisms. We determined that IL-17A, IL-17E and IL-17F are produced during the acute phase of T. cruzi infection. Using IL-17RA knockout (KO) mice, we demonstrate that IL-17RA, the common receptor subunit for many IL-17 family members, is required for host resistance during T. cruzi infection. Furthermore, infected IL-17RA KO mice that lack of response to several IL-17 cytokines showed amplified inflammatory responses with exuberant IFN-γ and TNF production that promoted hepatic damage and mortality. Absence of IL-17RA during T. cruzi infection resulted in reduced CXCL1 and CXCL2 expression in spleen and liver and limited neutrophil recruitment. T. cruzi-stimulated neutrophils secreted IL-10 and showed an IL-10-dependent suppressive phenotype in vitro inhibiting T-cell proliferation and IFN-γ production. Specific depletion of Ly-6G+ neutrophils in vivo during T. cruzi infection raised parasitemia and serum IFN-γ concentration and resulted in increased liver pathology in WT mice and overwhelming wasting disease in IL-17RA KO mice. Adoptively transferred neutrophils were unable to migrate to tissues and to restore resistant phenotype in infected IL-17RA KO mice but migrated to spleen and liver of infected WT mice and downregulated IFN-γ production and increased survival in an IL-10 dependent manner. Our results underscore the role of IL-17RA in the modulation of IFN-γ-mediated inflammatory responses during infections and uncover a previously unrecognized regulatory mechanism that involves the IL-17RA-mediated recruitment of suppressive IL-10-producing neutrophils.

IL-17 family is comprised for six members (IL-17A to F) that have been reported to play protective effects in bacterial and fungal infections and contradictory roles in parasite infections. Using mice deficient in IL-17RA, the common receptor subunit for many IL-17 family members, we determined that these cytokines are required for host protection against the parasite Trypanosoma cruzi. In absence of IL-17 signaling, mice developed an aggravated infection with similar levels of parasite in blood but increased inflammation and tissue damage of vital organs such as liver. We evaluated the mechanisms underlying this increased susceptibility and determined that the absence of IL-17RA caused a reduced arrival of neutrophils to organs such as spleen and liver. Neutrophils are phagocytic cells with abilities to directly destroy pathogens and also to regulate the inflammatory response. Indeed, we determined that neutrophils from T. cruzi infected mice are poisoned to secrete the regulatory cytokine IL-10. Finally, by experiments of depletion and adoptive transfer of neutrophils we determined that, during T. cruzi infection, IL-17RA is required for the recruitment of neutrophils that destroy the parasite and that also regulate inflammatory responses and collateral tissue damage by secreting IL-10.

Mast cell function and death in Trypanosoma cruzi infection

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

Vaccination with Trypanosoma rangeli modulates the profiles of immunoglobulins and IL-6 at local and systemic levels in the early phase of Trypanosoma cruzi experimental infection

In America, there are two species of Trypanosoma that can infect humans: Trypanosoma cruzi, which is responsible for Chagas disease and Trypanosoma rangeli, which is not pathogenic. We have developed a model of vaccination in mice with T. rangeli epimastigotes that protects against T. cruzi infection. The goal of this work was to study the pattern of specific immunoglobulins in the peritoneum (the site of infection) and in the sera of mice immunized with T. rangeli before and after challenge with T. cruzi. Additionally, we studied the effects triggered by antigen-antibodies binding and the levels of key cytokines involved in the humoral response, such as IL-4, IL-5 and IL-6. The immunization triggered the production of antibodies reactive with T. cruzi in peritoneal fluid (PF) and in serum, mainly IgG1 and, to a lesser magnitude, IgG2. Only immunized mice developed specific IgG3 antibodies in their peritoneal cavities. Antibodies were able to bind to the surface of the parasites and agglutinate them. Among the cytokines studied, IL-6 was elevated in PF during early infection, with higher levels in non-immunized-infected mice. The results indicate that T. rangeli vaccination against T. cruzi infection triggers a high production of specific IgG isotypes in PF and sera before infection and modulates the levels of IL-6 in PF in the early periods of infection.

The liver plays a major role in clearance and destruction of blood trypomastigotes in Trypanosoma cruzi chronically infected mice

Intravenous challenge with Trypanosoma cruzi can be used to investigate the process and consequences of blood parasite clearance in experimental Chagas disease. One hour after intravenous challenge of chronically infected mice with 5×10⁶ trypomastigotes, the liver constituted a major site of parasite accumulation, as revealed by PCR. Intact parasites and/or parasite remnants were visualized at this time point scattered in the liver parenchyma. Moreover, at this time, many of liver-cleared parasites were viable, as estimated by the frequency of positive cultures, which considerably diminished after 48 h. Following clearance, the number of infiltrating cells in the hepatic tissue notably increased: initially (at 24 h) as diffuse infiltrates affecting the whole parenchyma, and at 48 h, in the form of large focal infiltrates in both the parenchyma and perivascular spaces. Phenotypic characterization of liver-infiltrating cells 24 h after challenge revealed an increase in Mac1⁺, CD8⁺ and CD4⁺ cells, followed by natural killer (NK) cells. As evidence that liver-infiltrating CD4⁺ and CD8⁺ cells were activated, increased frequencies of CD69⁺CD8⁺, CD69⁺CD4⁺ and CD25⁺CD122⁺CD4⁺ cells were observed at 24 and 48 h after challenge, and of CD25⁻CD122⁺CD4⁺ cells at 48 h. The major role of CD4⁺ cells in liver protection was suggested by data showing a very high frequency of interferon (IFN)-γ-producing CD4⁺ cells 24 h after challenge. In contrast, liver CD8⁺ cells produced little IFN-γ, even though they showed an enhanced potential for secreting this cytokine, as revealed by in vitro T cell receptor (TCR) stimulation. Confirming the effectiveness of the liver immune response in blood parasite control during the chronic phase of infection, no live parasites were detected in this organ 7 days after challenge.

Chagas disease, a Latin American illness caused by the protozoan parasite Trypanosoma cruzi, has only rare spontaneous cure, and in most patients a small number of parasites persists for life in the blood and tissues, leading to chronic disorders such as cardiomyopathy. In a murine model of chronic T. cruzi infection we observed that the liver plays an important role in the clearance of blood-circulating parasites. Moreover, parasite accumulation in this organ is followed by their elimination, an effect that is not immediate but seems to depend on the recruitment of leukocytes and on the local production of IFN-γ, a cytokine known to increase the T. cruzi-killing capacity of phagocytes. Our findings contribute to the knowledge of T. cruzi-host interaction, showing the participation of a non-lymphoid organ in parasite control. In addition, they contribute to understanding the multifaceted role the liver plays in the immune response.

Characterising the KMP-11 and HSP-70 recombinant antigens' humoral immune response profile in chagasic patients

BACKGROUND

Antigen specificity and IgG subclass could be significant in the natural history of Chagas' disease. The relationship between the different stages of human Chagas' disease and the profiles of total IgG and its subclasses were thus analysed here; they were directed against a crude T. cruzi extract and three recombinant antigens: the T. cruzi kinetoplastid membrane protein-11 (rKMP-11), an internal fragment of the T. cruzi HSP-70 protein 192-433, and the entire Trypanosoma rangeli HSP-70 protein.

METHODS

Seventeen Brazilian acute chagasic patients, 50 Colombian chronic chagasic patients (21 indeterminate and 29 cardiopathic patients) and 30 healthy individuals were included. Total IgG and its subtypes directed against the above-mentioned recombinant antigens were determined by ELISA tests.

RESULTS

The T. cruzi KMP-11 and T. rangeli HSP-70 recombinant proteins were able to distinguish both acute from chronic chagasic patients and infected people from healthy individuals. Specific antibodies to T. cruzi crude antigen in acute patients came from IgG3 and IgG4 subclasses whereas IgG1 and IgG3 were the prevalent isotypes in indeterminate and chronic chagasic patients. By contrast, the specific prominent antibodies in all disease stages against T. cruzi KMP-11 and T. rangeli HSP-70 recombinant antigens were the IgG1 subclass.

CONCLUSION

T. cruzi KMP-11 and the T. rangeli HSP-70 recombinant proteins may be explored together in the immunodiagnosis of Chagas' disease. Polarising the IgG1 subclass of the IgG response to T. cruzi KMP-11 and T. rangeli HSP-70 recombinant proteins could have important biological effects, taking into account that this is a complement fixing antibody.

Experimental Chagas' disease in orchiectomized Calomys callosus infected with the CM strain of Trypanosoma cruzi

The incidence and progression of disorders associated with an unbalanced immune response has among many factors the gender as a contributory factor. The aims of this work were to evaluate the effects of orchiectomy and the immune response during the experimental Trypanosoma cruzi infection. Young adult, male Calomys callous were i.p. inoculated with 1 x 10(5) blood trypomastigotes of the CM strain of T. cruzi and divided in groups: Control, Sham and Castrated. Castrated group displayed significantly lower values for prostate and seminal vesicle weights indicating a drastic drop of testosterone plasmatic levels. Orchiectomized animals also displayed lesser number of blood parasites, enhanced lytic antibody percentage, splenocyte proliferation and NO concentration when compared to its sham and control counterparts, indicating that steroid gonadal ablation actually influences immune response triggering a more efficient cellular and humoral response which led animals to become more resistant against 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.

Geographical clustering of Trypanosoma cruzi I groups from Colombia revealed by low-stringency single specific primer-PCR of the intergenic regions of spliced-leader genes

A low-stringency single-primer polymerase chain reaction (LSSP-PCR) typing procedure targeted to the intergenic regions of spliced-leader genes (SL) was designed to profile Trypanosoma cruzi I stocks from endemic regions of Colombia. Comparison between SL-LSSP-PCR profiles of parasite DNA from vector faeces and cultures isolated from those faeces showed more conservative signatures than profiles using LSSP-PCR targeted to the minicircle variable regions (kDNA). This was also observed by analysing 15 parasite clones from one stock as well as serial samples of a same stock after in vitro culturing or inoculation into mice. Thus, SL-LSSP-PCR appears more appropriate than kDNA-LSSP-PCR for reliable typing of major T. cruzi I groups from in vitro cultured stocks and triatomine faeces. SL-LSSP-PCR grouped 46 of 47 T. cruzi I Colombian stocks according to their geographical procedences in four clusters: Cluster Cas from Casanare Department, Cluster Mg from Northern Magdalena department, Cluster Mom from Momposina Depression in Southern Magdalena and finally Cluster NW from northwestern Colombia, including Sucre, Chocó, Córdoba and Antioquia departments. Sequence analysis identified punctual mutations among amplicons from each cluster. Within Cluster Mg, sequence polymorphism allowed association with different sylvatic vector species. Novel SL sequences and LSSP-PCR profiles are reported from T. cruzi I infecting Eratyrus cuspidatus, Panstrongylus geniculatus and Rhodnius pallescens vectors.

Trypanosoma cruzi: orchiectomy and dehydroepiandrosterone therapy in infected rats

The ability of gonadal hormones to influence and induce diverse immunological functions during the course of a number of parasitic infections has been extensively studied in the latest decades. Dehydroepiandrosterone and its sulfate are the most abundant steroid hormones secreted by the human adrenal cortex and are considered potent immune-activators. The effects of orchiectomy on the course of Trypanosoma cruzi infection in rats, treated and untreated with DHEA were examined, by comparing blood and cardiac parasitism, macrophage numbers, nitric oxide and IFN-gamma levels. Orchiectomy enhanced resistance against infection with elevated numbers of macrophages, enhanced concentrations of NO and IFN-gamma and reduced amastigote burdens in heart when compared to control animals. DHEA replacement exerted a synergistic effect, up-modulating the immune response. Male sex steroids appear to play fundamental role in determining the outcome of disease, through the regulation and modulation of the activity of the immune response.

The clinical immunology of human Chagas disease

Human infection with the protozoan parasite Trypanosoma cruzi leads to Chagas disease, which affects approximately 17 million people in Latin America. A significant percentage of the infected population will develop clinical symptoms or present changes in laboratory and/or image evaluation. The existence of a large spectrum of clinical manifestations--with patients ranging from asymptomatic to severe cardiac involvement--emphasizes the need to use standardized and well-defined clinical criteria among different research groups. In this article, we carry out a systematic review of the immunology in human Chagas disease, discussing recent findings in the context of a clinical perspective.

Deficient control of Trypanosoma cruzi infection in C57BL/6 mice is related to a delayed specific IgG response and increased macrophage production of pro-inflammatory cytokines

Earlier work in Trypanosoma cruzi-infected C57BL/6 and BALB/c mice revealed an acute disease, of lethal outcome in the former group and lesser severity in BALB/c mice. Fatal course was not accompanied by an increased parasite load, but by a substantial imbalance between pro- and anti-inflammatory cytokine serum levels. To better characterise the mechanisms allowing the host to restrain the infection, we have now studied the specific IgG production and in vitro behaviour of peritoneal macrophages (PMs) when exposed to T. cruzi. BALC/c mice displayed higher serum levels of specific immunoglobulins in the first weeks of acute infection. In vitro infected PMs showed no between-group differences in the number of intracellular parasites, although TNFalpha levels were significantly higher in culture supernatants from C57BL/6 mice. Because an LPS-based pretreatment (desensitisation protocol followed by a sublethal LPS dose) reduced disease severity of C57BL/6 mice, we next explored the features of the in vitro infection in PMs from mice subjected to such protocol. PMs from LPS-pretreated mice had a decreased production of TNFalpha and IL-1beta, becoming more permissive to parasite replication. It is concluded that deficient control of T. cruzi infection in C57BL/6 mice may also involve a less satisfactory specific IgG response and increased TNFalpha production by PMs. Improved disease outcome in LPS-pretreated mice may be associated with the reduced inflammatory cytokine production by PMs, but the impaired ability of these cells to control parasite growth suggests that compensatory mechanisms are operating in the in vivo situation.

Utility of the Trypanosoma cruzi sequence database for identification of potential vaccine candidates by in silico and in vitro screening

Glycosylphosphatidylinositol (GPI)-anchored proteins are abundantly expressed in the infective and intracellular stages of Trypanosoma cruzi and are recognized as antigenic targets by both the humoral and cellular arms of the immune system. Previously, we demonstrated the efficacy of genes encoding GPI-anchored proteins in eliciting partially protective immunity to T. cruzi infection and disease, suggesting their utility as vaccine candidates. For the identification of additional vaccine targets, in this study we screened the T. cruzi expressed sequence tag (EST) and genomic sequence survey (GSS) databases. By applying a variety of web-based genome-mining tools to the analysis of approximately 2,500 sequences, we identified 348 (37.6%) EST and 260 (17.4%) GSS sequences encoding novel parasite-specific proteins. Of these, 19 sequences exhibited the characteristics of secreted and/or membrane-associated GPI proteins. Eight of the selected sequences were amplified to obtain genes TcG1, TcG2, TcG3, TcG4, TcG5, TcG6, TcG7, and TcG8 (TcG1-TcG8) which are expressed in different developmental stages of the parasite and conserved in the genome of a variety of T. cruzi strains. Flow cytometry confirmed the expression of the antigens encoded by the cloned genes as surface proteins in trypomastigote and/or amastigote stages of T. cruzi. When delivered as a DNA vaccine, genes TcG1-TcG6 elicited a parasite-specific antibody response in mice. Except for TcG5, antisera to genes TcG1-TcG6 exhibited trypanolytic activity against the trypomastigote forms of T. cruzi, a property known to correlate with the immune control of T. cruzi. Taken together, our results validate the applicability of bioinformatics in genome mining, resulting in the identification of T. cruzi membrane-associated proteins that are potential vaccine candidates.

Age-related increase in resistance to acute Trypanosoma cruzi infection in rats is associated with an appropriate antibody response

Inoculation at weaning with Trypanosoma cruzi in inbred "l" rats resulted in a self-resolving acute infection characterized by marked parasitaemias, whereas challenge to adult rats revealed a mild disease with extremely low parasitaemias. To explore the mechanisms underlying such age-associated differences in disease outcome, we analysed the in vitro replication of T. cruzi, nitric oxide and tumour necrosis factor-alpha (TNF-alpha) production in peritoneal macrophages (PMs), the serum concentrations of the specific immunoglobulins (Igs) IgM and IgG, antibodies exhibiting lytic activity against bloodstream forms of T. cruzi and circulating levels of nitrate, TNF-alpha and interferon-gamma (IFN-gamma). Macrophages from young rats were as effective as their adult counterparts for restraining intracellular parasite replication. When stimulated with IFN-gamma, culture supernatants from young PMs contained higher amounts of nitrite and TNF-alpha. Serum samples from 4 and 7 days post infection revealed easily detectable amounts of nitrate, with values being further augmented by day 7 post infection and significantly higher in the young group. TNF-alpha levels were only detected in the young group by day 7 post infection. Both groups had increased amounts of IFN-gamma in their sera, although in adult rats, this trend was followed by a significant drop at day 7, with young rats showing values still higher by the same time point evaluation. In contrast, young rats presented significantly lower levels of IgM and IgG antibodies during the first week of infection. Increased resistance in adult rats seems to be the result of a more appropriate antibody production.

Experimental Trypanosoma cruzi infection alters the shaping of the central and peripheral T-cell repertoire

We investigated the thymic and peripheral T-lymphocyte subsets in BALB/c mice undergoing acute or chronic Trypanosoma cruzi infection, in terms of expression of particular Vbeta rearrangements of the T-cell receptor. We first confirmed the severe depletion of CD4(+)CD8(+) thymocytes following acute T. cruzi infection. By contrast, the numbers of CD4(+)CD8(+) cells in subcutaneous lymph nodes increased up to 16 times. In subcutaneous lymph nodes, we found CD4(+)CD8(+) cells that expressed prohibited segments TCRVbeta5 and TCRVbeta12 (which are physiologically deleted in the thymus of BALB/c mice), as did some mature single-positive cells (CD4(+)CD8(-) and CD4(-)CD8(+)). In the thymus of infected animals, although higher numbers of immature cells bearing such Vbeta segments were seen, they were no longer detected in the mature single-positive stage, suggesting that negative selection occurs normally. We also found increased numbers of cells bearing the potentially autoreactive phenotype TCRVbeta5(+) and TCRVbeta12(+) in T-lymphocyte subsets from subcutaneous lymph nodes of T. cruzi chronically infected mice. In conclusion, our data indicate that immature T lymphocytes bearing prohibited TCRVbeta segments leave the thymus and gain the lymph nodes, where they further differentiate into mature CD4(+) or CD8(+) cells. Conjointly, these findings show changes in the shaping of the central and peripheral T-cell repertoire in both acute and chronic phases of murine T. cruzi infection. The release of potentially autoreactive T cells in the periphery of the immune system may contribute to the autoimmune process found in both murine and human Chagas' disease.

Maternal Trypanosoma cruzi infection upregulates capacity of uninfected neonate cells To produce pro- and anti-inflammatory cytokines

The possibility of maternal in utero modulation of the innate and/or adaptive immune responses of uninfected newborns from Trypanosoma cruzi-infected mothers was investigated by studying the capacity of their whole blood cells to produce cytokines in response to T. cruzi lysate or lipopolysaccharide-plus-phytohemagglutinin (LPS-PHA) stimulation. Cells of such newborns occasionally released gamma interferon (IFN-gamma) and no interleukin-2 (IL-2) and IL-4 upon specific stimulation, while their mothers responded by the production of IFN-gamma, IL-2, and IL-4. Infection in mothers was also associated with a hyperactivation of maternal cells and also, strikingly, of cells of their uninfected neonates, since their release of proinflammatory (IL-1beta, IL-6, and tumor necrosis factor alpha [TNF-alpha]) as well as of anti-inflammatory (IL-10 and soluble TNF receptor) cytokines or factors was upregulated in the presence of LPS-PHA and/or parasite lysate. These results show that T. cruzi infection in mothers induces profound perturbations in the cytokine response of their uninfected neonates. Such maternal influence on neonatal innate immunity might contribute to limit the occurrence and severity of congenital infection.