Anti-Trypanosoma cruzi immunoglobulin G1 can be a useful tool for diagnosis and prognosis of human Chagas' disease

Challenges and advancements in the development of vaccines and therapies against Chagas disease

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, presents a substantial global health burden, affecting millions of individuals worldwide and posing a continual risk of infection. Despite the high mortality and morbidity rates, effective vaccines to prevent infection by the parasite remain elusive, and the drugs currently available are suboptimal. Understanding the intricate dynamics of parasite-host interactions and the resulting immune responses, which contribute to both protection and pathology, is crucial for the development of effective vaccines and therapies against Chagas disease. In this Series paper, we discuss the challenges associated with discovering and translating prophylactic and therapeutic strategies from the laboratory bench to clinical application. We highlight ongoing efforts in vaccine and new drug development, with a focus on more advanced candidates for vaccines and drugs. We also discuss potential solutions, emphasising the importance of collaborative research efforts, sustained funding, and a comprehensive understanding of host-parasite interactions and immunopathology to advance the development of new vaccines and therapies against Chagas disease.

IgG Isotypes Targeting a Recombinant Chimeric Protein of Trypanosoma cruzi in Different Clinical Presentations of Chronic Chagas Disease

Chagas disease (CD) is caused by the protozoan Trypanosoma cruzi, which leads to a spectrum of clinical presentations that range from asymptomatic to severe cardiac involvement. The host immune response plays a pivotal role in disease progression. Ig isotypes may contribute to disease pathogenesis. Investigating these components can provide insights into the immunopathogenic mechanisms underlying CD. This cross-sectional study aims to establish a correlation between the Ig profile of individuals infected with T. cruzi with the clinical forms of chronic CD. Serum samples were collected from partner institutions in different states of Brazil. Individuals diagnosed with chronic CD were categorized based on the clinical form of the disease. The indirect ELISA method using the recombinant chimeric Molecular Biology Institute of Paraná membrane protein 8.4 as the antigen was used to determine the Ig profile, including total IgG, IgG1, IgG2, IgG3, and IgG4. Ninety-seven serum samples from patients classified as negative (NEG, n = 38), indeterminate (IND, n = 24), mild cardiac (MC, n = 20), and severe cardiac (SC, n = 15) forms were analyzed. IgG1 exhibited greater levels compared with the other isotypes, showing a significant difference between the MC and IND groups. IgG3 levels were greater in individuals from the MC group compared with the SC group. IgG1 and IgG3 isotypes can serve as biomarkers to evaluate the progression of CD because they exhibit variations across clinical groups. Additional longitudinal studies are necessary to explore the relationship between antibody kinetics and the development of tissue damage.

Double-negative T cells: Setting the stage for disease control or progression

Double-negative (DN) T cells are present at relatively low frequencies in human peripheral blood, and are characterized as expressing the alpha-beta or gamma-delta T-cell receptor (TCR), but not the CD4 nor the CD8 co-receptors. Despite their low frequencies, these cells are potent producers of cytokines and, thus, are key orchestrators of immune responses. DN T cells were initially associated with induction of peripheral immunological tolerance and immunomodulatory activities related to disease prevention. However, other studies demonstrated that these cells can also display effector functions associated with pathology development. This apparent contradiction highlighted the heterogeneity of the DN T-cell population. Here, we review phenotypic and functional characteristics of DN T cells, emphasizing their role in human diseases. The need for developing biomarkers to facilitate the translation of studies from animal models to humans will also be discussed. Finally, we will examine DN T cells as promising therapeutic targets to prevent or inhibit human disease development.

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.

Assessing antibody decline after chemotherapy of early chronic Chagas disease patients

BACKGROUND

Chagas disease remains a significant public health problem in Latin America. There are only two chemotherapy drugs, nifurtimox and benznidazole, and both may have severe side effects. After complete chemotherapy of acute cases, seropositive diagnosis may revert to negative. However, there are no definitive parasitological or serological biomarkers of cure.

METHODS

Following a pilot study with seven Bolivian migrants to Spain, we tested 71 serum samples from chronic patients (mean age 12.6 years) inhabiting the Argentine Chaco region. Benznidazole chemotherapy (5-8 mg/kg day, twice daily for 60 days) was administered during 2011-2016. Subsequently, pre-and post-chemotherapy serum samples were analysed in pairs by IgG1 and IgG ELISA using two different antigens and Chagas Sero K-SeT rapid diagnostic tests (RDT). Molecular diagnosis by kDNA-PCR was applied to post-treatment samples.

RESULTS

Pilot data demonstrated IgG1 antibody decline in three of seven patients from Bolivia 1 year post-treatment. All Argentine patients in 2017 (averaging 5 years post-treatment), except one, were positive by conventional serology. All were kDNA-PCR-negative. Most (91.5%) pre-treatment samples were positive by the Chagas Sero K-SeT RDT, confirming the predominance of TcII/V/VI. IgG1 and IgG of Argentine patients showed significant decline in antibody titres post-chemotherapy, with either lysate (IgG, P = 0.0001, IgG1, P = 0.0001) or TcII/V/VI peptide antigen (IgG, P = 0.0001, IgG1, P = 0.0001). IgG1 decline was more discriminative than IgG. Antibody decline after treatment was also detected by the RDT. Incomplete treatment was associated with high IgG1 post-treatment titres against lysate (P = 0.013), as were IgG post-treatment titres to TcII/V/VI peptide (P = 0.0001). High pre-treatment IgG1 with lysate was associated with Qom ethnicity (P = 0.045). No associations were found between gender, age, body mass index and pre- or post-treatment antibody titres.

CONCLUSIONS

We show that following chemotherapy of early chronic Chagas disease, significant decline in IgG1 antibody suggests cure, whereas sustained or increased IgG1 is a potential indicator of treatment failure. Due to restricted sensitivity, IgG1 should not be used as a diagnostic marker but has promise, with further development, as a biomarker of cure. We show that following chemotherapy of early chronic Chagas disease, a significant decline in IgG1 antibody suggests cure, whereas sustained or increased IgG1 is a potential indicator of treatment failure. Due to restricted sensitivity, IgG1 should not be used as a diagnostic marker but has promise, with further development, as a biomarker of cure.

Recombinant antibody against Trypanosoma cruzi from patients with chronic Chagas heart disease recognizes mammalian nervous system

BACKGROUND

To deeply understand the role of antibodies in the context of Trypanosoma cruzi infection, we decided to characterize A2R1, a parasite antibody selected from single-chain variable fragment (scFv) phage display libraries constructed from B cells of chronic Chagas heart disease patients.

METHODS

Immunoblot, ELISA, cytometry, immunofluorescence and immunohistochemical assays were used to characterize A2R1 reactivity. To identify the antibody target, we performed an immunoprecipitation and two-dimensional electrophoresis coupled to mass spectrometry and confirmed A2R1 specific interaction by producing the antigen in different expression systems. Based on these data, we carried out a comparative in silico analysis of the protein target´s orthologues, focusing mainly on post-translational modifications.

FINDINGS

A2R1 recognizes a parasite protein of ~50 kDa present in all life cycle stages of T. cruzi, as well as in other members of the kinetoplastid family, showing a defined immunofluorescence labeling pattern consistent with the cytoskeleton. A2R1 binds to tubulin, but this interaction relies on its post-translational modifications. Interestingly, this antibody also targets mammalian tubulin only present in brain, staining in and around cell bodies of the human peripheral and central nervous system.

INTERPRETATION

Our findings demonstrate for the first time the existence of a human antibody against T. cruzi tubulin capable of cross-reacting with a human neural protein. This work re-emphasizes the role of molecular mimicry between host and parasitic antigens in the development of pathological manifestations of T. cruzi infection.

The influence of parasitism by Trypanosoma cruzi in the hematological parameters of the white ear opossum (Didelphis albiventris) from Campo Grande, Mato Grosso do Sul, Brazil

Considered ecologically generalist, Didelphis albiventris is reported as reservoir for different species of parasites, especially Trypanosoma cruzi. However, the knowledge about the influence of T. cruzi on hematological parameters of free-living opossum remains scarce. The present study aimed to evaluate the influence of T. cruzi on hematological parameters of white-ear opossums (D. albiventris) from Campo Grande, Mato Grosso do Sul, Brazil. The blood samples and biometric data were collected from 40 opossums captured by Tomahawk and Sherman traps in six urban forest fragments located in the city. The health of these animals was inferred, mainly, by means of blood parameters (PCV, RBC, WBC, MCV and WBC differential). Molecular detection of T. cruzi infection was performed by nested polymerase chain reaction (nPCR), using 18S and 24Sα rDNA region as target. Paired-t-test and simple linear regression were used for statistical analysis. No significant difference was observed between the averages of hematological variables in relation to gender and body condition. The molecular diagnosis showed that 32.5% (13/40) of the opossums were infected by T. cruzi, which presented lymphocytosis (3.4 ± 1.5) and eosinophilia (0.09 ± 0.13). Path analysis showed that T. cruzi infection resulted in increased numbers of lymphocytes and indirectly decreased the body condition of opossums. Moreover T. cruzi infection resulted in a direct effect on decrease of MCV. Overall, our results suggest that T. cruzi infection may represent a risk to health of opossums since the lymphocytosis may cause a secondary damage on body condition of infected animals.

Pathology and Pathogenesis of Chagas Heart Disease

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of people infected with the protozoan parasite Trypanosoma cruzi. One way T. cruzi is transmitted to people is through contact with infected kissing bugs, which are found in much of the Western Hemisphere, including in vast areas of the United States. The epidemiology of T. cruzi and Chagas heart disease and the varied mechanisms leading to myocyte destruction, mononuclear cell infiltration, fibrosis, and edema in the heart have been extensively studied by hundreds of scientists for more than 100 years. Despite this wealth of knowledge, it is still impossible to predict what will happen in an individual infected with T. cruzi because of the tremendous variability in clonal parasite virulence and human susceptibility to infection and the lack of definitive molecular predictors of outcome from either side of the host-parasite equation. Further, while several distinct mechanisms of pathogenesis have been studied in isolation, it is certain that multiple coincident mechanisms combine to determine the ultimate outcome. For these reasons, Chagas disease is best considered a collection of related but distinct illnesses. This review highlights the pathology and pathogenesis of the most common adverse sequela of T. cruzi infection-Chagas heart disease-and concludes with a discussion of key unanswered questions and a view to the future.

Outcomes of Trypanosoma cruzi and Trypanosoma evansi infections on health of Southern coati (Nasua nasua), crab-eating fox (Cerdocyon thous), and ocelot (Leopardus pardalis) in the Brazilian Pantanal

The occurrence of Trypanosoma spp. in wild carnivore populations has been intensively investigated during the last decades. However, the impact of these parasites on the health of free-living infected animals has been largely neglected. The Pantanal biome is the world’s largest seasonal wetland, harboring a great diversity of species and habitats. This includes 174 species of mammals, of which 20 belong to the order Carnivora. The present study aimed to investigate the effect of Trypanosoma evansi and Trypanosoma cruzi infections and coinfections on the health of the most abundant carnivores in the Pantanal: coati (Nasua nasua), crab-eating fox (Cerdocyon thous), and ocelot (Leopardus pardalis). We captured 39 coatis, 48 crab-eating foxes, and 19 ocelots. Diagnostic tests showed T. cruzi infection in 7 crab-eating foxes and 5 coatis. Additionally, 7 crab-eating foxes, 10 coatis, and 12 ocelots were positive for T. evansi. We observed coinfections in 9 crab-eating foxes, 8 coatis, and 2 ocelots. This is the first report of T. evansi and T. cruzi infection on the health of free-living ocelots and crab-eating foxes. We showed that single T. evansi or T. cruzi infection, as well as coinfection, caused some degree of anemia in all animals, as well as an indirect negative effect on body condition in coatis and crab-eating foxes via anemia indicators and immune investment, respectively. Furthermore, the vigorous immune investment observed in sampled coatis, crab-eating foxes and ocelots infected by T. evansi, T. cruzi and coinfected can be highly harmful to their health. Overall, our results indicate that single and combined infection with T. evansi and T. cruzi represent a severe risk to the health of wild carnivores in the Pantanal region.

Systems Biology Reveals Relevant Gaps in Fc-γR Expression, Impaired Regulatory Cytokine Microenvironment Interfaced With Anti-Trypanosoma cruzi IgG Reactivity in Cardiac Chagas Disease Patients

The systems biology approach has become an innovative tool when it comes to shedding light on the complex immune response underlying the development/maintenance of distinct clinical forms of Chagas disease. The goal of this study was to describe an integrative overview of Fc-γR expression, cytokine microenvironment and anti-Trypanosoma cruzi IgG interface in indeterminate-(IND) and cardiac-(CARD) patients. Data demonstrated that IND displayed an overall higher Fcγ-R expression (CD16; CD32; CD64) on neutrophils-(NEU), along with (CD16; CD64) on monocytes-(MON) as compared to CARD. Additionally, CARD presented an increased expression of CD32 in B-cells. While preserved frequency of IL-10-producing cells was observed in IND, decreased levels of IL-10+ phagocytes and enhanced TNF+ MON and NK-cells were observed in CARD. T. cruzi-antigen recall in vitro induces a general decrease of Fc-γR expression in Chagas disease patients, especially in CARD. Moreover, T. cruzi-antigen stimuli triggered a concomitant increase of IFN-γ+NEU/TNF+NK-cells and IL-10+MON/IL-10+B-cells in IND. Biomarker signatures further emphasized the contrasting Fc-γR expression and cytokine microenvironment observed in Chagas disease patients with distinct clinical forms. Up-regulation of Fc-γR expression (CD16 on NEU;MON;NK) was observed in IND, whereas a general decrease was reported for CARD. Moreover, while a mixed cytokine microenvironment (TNF; IL-10) was observed in IND, CARD presented a contrasting profile with up-regulation of TNF+NEU and IL-12+NEU. Integrative network analysis revealed a distinct assemblage of biomarkers, with CARD presenting a large number of negative internode connectivity in comparison with IND. The relevant gaps in Fc-γR expression and impaired regulatory cytokine microenvironment interfaced with the anti-T. cruzi IgG reactivity throughout an exacerbated negative connectivity may account for the development/maintenance of the clinical status of cardiac Chagas disease.

Accomplishing the genotype-specific serodiagnosis of single and dual Trypanosoma cruzi infections by flow cytometry Chagas-Flow ATE-IgG2a

The methods currently available for genotype-specific diagnosis of T. cruzi infection still present relevant limitations, especially to identify mixed infection. In the present investigation, we have evaluated the performance of Chagas-Flow ATE-IgG2a test for early and late differential diagnosis of single and dual genotype-specific T. cruzi infections. Serum samples from Swiss mice at early and late stages of T. cruzi infection were assayed in parallel batches for genotype-specific diagnosis of single (TcI, TcVI or TcII) and dual (TcI+TcVI, TcVI+TcII or TcII+TcI) infections. The intrinsic reactivity to TcI, TcVI and TcII target antigens, including amastigote (AI/AVI/AII), trypomastigote-(TI/TVI/TII) and epimastigote (EI/EVI/EII), at specific reverse of serum dilutions (500 to 64,000), was employed to provide reliable decision-trees for "early" vs "late", "single vs "dual" and "genotype-specific" serology. The results demonstrated that selective set of attributes "EII 500/EI 2,000/AII 500" were able to provide high-quality accuracy (81%) to segregate early and late stages of T. cruzi infection. The sets "TI 2,000/AI 1,000/EII 1,000" and "TI 8,000/AII 32,000" presented expressive scores to discriminate single from dual T. cruzi infections at early (85%) and late stages (84%), respectively. Moreover, the attributes "TI 4,000/TVI 500/TII 1,000", "TI 16,000/EI 2,000/EII 2,000/AI 500/TVI 500" showed good performance for genotype-specific diagnosis at early stage of single (72%) and dual (80%) T. cruzi infections, respectively. In addition, the attributes "TI 4,000/AII 1,000/EVI 1,000", "TI 64,000/AVI 500/AI 2,000/AII 1,000/EII 4,000" showed moderate performance for genotype-specific diagnosis at late stage of single (69%) and dual (76%) T. cruzi infections, respectively. The sets of decision-trees were assembled to construct a sequential algorithm with expressive accuracy (81%) for serological diagnosis of T. cruzi infection. These findings engender new perspectives for the application of Chagas-Flow ATE-IgG2a method for genotype-specific diagnosis in humans, with relevant contributions for epidemiological surveys as well as clinical and post-therapeutic monitoring of Chagas disease.

Lack of Efficacy of Liposomal Amphotericin B Against Acute and Chronic Trypanosoma cruzi Infection in Mice

Acute and chronic infection with Trypanosoma cruzi affects millions of people. The current therapeutic options are highly toxic and often not effective. Liposomal amphotericin B (LAMB) has been demonstrated previously to have some activity in murine models. In our studies, higher dosages given multiple times were tested for activity against acute or chronic disease, exploring whether intermittent and brief regimens could be effective, as might then prove useful in human, particularly outpatient, therapy. For acute infection, LAMB 25 mg/kg intravenously (i.v.) given one to three times prolonged survival and caused a rapid disappearance of Y strain trypomastigotes from the blood. However, even four or six doses of LAMB 30 mg/kg i.v., did not result in the cure of Y strain infection, with all mice relapsing after being immunosuppressed with cyclophosphamide. Similarly, chronic infection due to the CL strain was found to be unaltered by 1-3 treatments with LAMB 25 mg/kg. All surviving mice had histopathological evidence of infection in one or more tissues and equivalent antibody titers regardless of treatment regimen. Overall, LAMB at doses up to 30 mg/kg i.v. prolonged survival, but these doses were not curative in the regimens studied.

Evolution of anti-Trypanosoma cruzi antibody production in patients with chronic Chagas disease: Correlation between antibody titers and development of cardiac disease severity

Chagas disease is one of the most important endemic infections in Latin America affecting around 6–7 million people. About 30–50% of patients develop the cardiac form of the disease, which can lead to severe cardiac dysfunction and death. In this scenario, the identification of immunological markers of disease progression would be a valuable tool for early treatment and reduction of death rates. In this observational study, the production of anti-Trypanosoma cruzi antibodies through a retrospective longitudinal follow-up in chronic Chagas disease patients´ cohort and its correlation with disease progression and heart commitment was evaluated. Strong inverse correlation (ρ = -0.6375, p = 0.0005) between anti-T. cruzi IgG₁ titers and left ventricular ejection fraction (LVEF) in chronic Chagas cardiomyopathy (CCC) patients were observed after disease progression. Elevated levels of anti-T. cruzi IgG₃ titers were detected in all T. cruzi-infected patients, indicating a lack of correlation of this IgG isotype with disease progression. Furthermore, low levels of anti-T. cruzi IgG₂, IgG₄, and IgA were detected in all patients through the follow-up. Although without statistical significance anti-T. cruzi IgE tends to be more reactive in patients with the indeterminate form (IND) of the disease (p = 0.0637). As this study was conducted in patients with many years of chronic disease no anti-T. cruzi IgM was detected. Taken together, these results indicate that the levels of anti-T. cruzi IgG₁ could be considered to seek for promising biomarkers to predict the severity of chronic Chagas disease cardiomyopathy.

Trypanosoma cruzi is the etiological agent of Chagas disease that affects about 7 million people in Latin America, being considered one of the most important neglected diseases of developing countries. Chronic Chagas disease might be present in different forms as an asymptomatic indeterminate form or even with severe cardiac commitment, known as chronic Chagas cardiomyopathy. In fact, the cardiac form can lead to death due to disease progression. Seeking for biomarkers of cardiomyopathy progression has become important to understand the cardiac progression and to predict or even prevent the disease worsening and to improve the quality of life of affected individuals. In this work, we followed the anti-T. cruzi antibody profile in a retrospective longitudinal study in a cohort of chronic Chagas disease patients, and further correlate with heart commitment and cardiac disease progression. We found an inverse correlation between anti-T. cruzi IgG₁ titers and cardiac disease severity in patients with progressive disease. These data suggest that anti-T. cruzi IgG₁ levels could be considered a suitable candidate tool for early identification of cardiac disease progression.

Myocarditis in different experimental models infected by Trypanosoma cruzi is correlated with the production of IgG1 isotype

This study was designed to verify the relationship between IgG antibodies isotypes and myocarditis in Trypanosoma cruzi infection using mice and dogs infected with different T. cruzi strains. The animals were infected with benznidazole-susceptible Berenice-78 and benznidazole-resistant AAS and VL-10 strains. The IgG subtypes were measured in serum samples from dogs (IgG, IgG1, and IgG2) and mice (IgG, IgG1, IgG2a, and IgG2b). The infection of dogs with VL-10 strain induced the highest levels of heart inflammation while intermediate and lower levels were detected with Berenice-78 and AAS strains, respectively. Similar results were found in mice infected with VL-10, but not in those infected with AAS or Berenice-78 strains. The AAS strain induced higher levels of heart inflammation in mice, while Berenice-78 strain was not able to induce it. Correlation analysis between myocarditis and antibody reactivity index revealed very interesting results, mainly for IgG and IgG1, the latter being the most exciting. High IgG1 showed a significant correlation with myocarditis in both experimental models, being more significant in dogs (r=0.94, p<0.0001) than in mice (r=0.58, p=0.047). Overall, our data suggest that IgG1 could be a good marker to demonstrate myocarditis intensity in Chagas disease.

FC-TRIPLEX Chagas/Leish IgG1: a multiplexed flow cytometry method for differential serological diagnosis of chagas disease and leishmaniasis

Differential serological diagnosis of Chagas disease and leishmaniasis is difficult owing to cross-reactivity resulting from the fact that the parasites that cause these pathologies share antigenic epitopes. Even with optimized serological assays that use parasite-specific recombinant antigens, inconclusive test results continue to be a problem. Therefore, new serological tests with high sensitivity and specificity are needed. In the present work, we developed and evaluated the performance of a new flow cytometric serological method, referred to as FC-TRIPLEX Chagas/Leish IgG1, for the all-in-one classification of inconclusive tests. The method uses antigens for the detection of visceral leishmaniasis, localized cutaneous leishmaniasis, and Chagas disease and is based on an inverted detuned algorithm for analysis of anti-Trypanosomatidae IgG1 reactivity. First, parasites were label with fluorescein isothiocyanate or Alexa Fluor 647 at various concentrations. Then serum samples were serially diluted, the dilutions were incubated with suspensions of mixed labeled parasites, and flow cytometric measurements were performed to determine percentages of positive fluorescent parasites. Using the new method, we obtained correct results for 76 of 80 analyzed serum samples (95% overall performance), underscoring the outstanding performance of the method. Moreover, we found that the fluorescently labeled parasite suspensions were stable during storage at room temperature, 4 °C, and -20 °C for 1 year. In addition, two different lots of parasite suspensions showed equivalent antigen recognition; that is, the two lots showed equivalent categorical segregation of anti-Trypanosomatidae IgG1 reactivity at selected serum dilutions. In conclusion, we have developed a sensitive and selective method for differential diagnosis of Chagas disease, visceral leishmaniasis, and localized cutaneous leishmaniasis.

Experimental benznidazole treatment of Trypanosoma cruzi II strains isolated from children of the Jequitinhonha Valley, Minas Gerais, Brazil, with Chagas disease

Trypanosoma cruzi strains from distinct geographic areas show differences in drug resistance and association between parasites genetic and treatment response has been observed. Considering that benznidazole (BZ) can reduce the parasite burden and tissues damage, even in not cured animals and individuals, the goal is to assess the drug response to BZ of T. cruzi II strains isolated from children of the Jequitinhonha Valley, state of Minas Gerais, Brazil, before treatment. Mice infected and treated with BZ in both phases of infection were compared with the untreated and evaluated by fresh blood examination, haemoculture, polymerase chain reaction, conventional (ELISA) and non-conventional (FC-ALTA) serologies. In mice treated in the acute phase, a significant decrease in parasitaemia was observed for all strains. Positive parasitological and/or serological tests in animals treated during the acute and chronic (95.1-100%) phases showed that most of the strains were BZ resistant. However, beneficial effect was demonstrated because significant reduction (p < 0.05%) and/or suppression of parasitaemia was observed in mice infected with all strains (acute phase), associated to reduction/elimination of inflammation and fibrosis for two/eight strains. BZ offered some benefit, even in not cured animals, what suggest that BZ use may be recommended at least for recent chronic infection of the studied region.

Specific IgM, IgG and IgG1 directed against Toxoplasma gondii detected by flow cytometry and their potential as serologic tools to support clinical indirect fundoscopic presumed diagnosis of ocular disease

In the present study we evaluated the anti-Toxoplasma gondii immunoglobulin profiles of a group of 118 individuals living in an endemic area. The aim of the study was to select biomarkers to support the ophthalmological diagnosis of retinal/retinochoroidal scars presumably caused by T. gondii infection. Overall anti-T. gondii reactivity of the IgM, IgG, IgA, IgE and IgG subclasses was investigated by flow cytometry-based anti-fixed tachyzoite antibodies (FC-AFTA) in four groups of subjects, referred to as: i) TOXO(L)--seropositive patients with retinal/retinochoroidal scars presumably caused by T. gondii infection; these patients were further subdivided according to morphological aspects of their ocular scar lesions as A, B or C; ii) TOXO(NL)--seropositive patients without ocular scar lesions; iii) NEG(L)--T. gondii seronegative patients presenting retinal lesions; and iv) NEG(NL)--T. gondii seronegative without retinal lesions (negative controls). Our data demonstrated that anti-T. gondii IgG profiles were able to discriminate the mean reactivity of TOXO(L) from all other clinical groups. Analysis of anti-T. gondii immunoglobulin profiles revealed that IgM and IgG were good biomarkers capable of discriminating between individual reactivity in patients with retinal/retinochoroidal scars presumably caused by T. gondii infection [TOXO(L)] from those caused by other clinical conditions. Furthermore, anti-T. gondii IgG1 reactivity was able to discriminate TOXO(L) from all other clinical groups. In conclusion, the pre-selected IgM, IgG and IgG1 anti-T. gondii antibody subclasses were able to segregate both TOXO(L) and the other subgroups, including the scar lesion group types (A, B, C), from other clinical conditions. These results suggest the applicability of this technique in the clinical laboratory to detect putative biomarker for diagnosis of ocular lesions in T. gondii-infected patients. Studies in other areas implementing the methods described in the present study would be of value and enable evaluation of a system for classification of presumed ocular toxoplasmosis scar lesions. This classification would make comparative studies on ocular toxoplasmosis conducted in different regions around the world possible.

Oral multicomponent DNA vaccine delivered by attenuated Salmonella elicited immunoprotection against American trypanosomiasis

We have reported that attenuated Salmonella (S) carrying plasmids encoding the cysteine protease cruzipain (Cz) protects against Trypanosoma cruzi infection. Here, we determined whether immunoprotection could be improved by the oral coadministration of 3 Salmonella carrying the plasmids that encode the antigens Cz, Tc52, and Tc24. SCz+STc52+STc24-immunized mice presented an increased antibody response against each antigen compared with those in the single antigen-immunized groups, as well as higher trypomastigotes antibody-mediated lyses and cell invasion inhibition compared with controls. SCz+STc52+STc24-immunized and -challenged mice rendered lower parasitemia. Weight loss after infection was detected in all mice except those in the SCz+STc52+STc24 group. Moreover, cardiomyopathy-associated enzyme activity was significantly lower in SCz+STc24+STc52-immunized mice compared with controls. Few or no abnormalities were found in muscle tissues of SCz+STc24+STc52-immunized mice, whereas controls presented with inflammatory foci, necrosis, and amastigote nests. We conclude that a multicomponent approach that targets several invasion and metabolic mechanisms improves protection compared with single-component vaccines.

Altered distribution of peripheral blood memory B cells in humans chronically infected with Trypanosoma cruzi

Numerous abnormalities of the peripheral blood T cell compartment have been reported in human chronic Trypanosoma cruzi infection and related to prolonged antigenic stimulation by persisting parasites. Herein, we measured circulating lymphocytes of various phenotypes based on the differential expression of CD19, CD4, CD27, CD10, IgD, IgM, IgG and CD138 in a total of 48 T. cruzi-infected individuals and 24 healthy controls. Infected individuals had decreased frequencies of CD19+CD27+ cells, which positively correlated with the frequencies of CD4+CD27+ cells. The contraction of CD19+CD27+ cells was comprised of IgG+IgD-, IgM+IgD- and isotype switched IgM-IgD- memory B cells, CD19+CD10+CD27+ B cell precursors and terminally differentiated CD19+CD27+CD138+ plasma cells. Conversely, infected individuals had increased proportions of CD19+IgG+CD27-IgD- memory and CD19+IgM+CD27-IgD+ transitional/naïve B cells. These observations prompted us to assess soluble CD27, a molecule generated by the cleavage of membrane-bound CD27 and used to monitor systemic immune activation. Elevated levels of serum soluble CD27 were observed in infected individuals with Chagas cardiomyopathy, indicating its potentiality as an immunological marker for disease progression in endemic areas. In conclusion, our results demonstrate that chronic T. cruzi infection alters the distribution of various peripheral blood B cell subsets, probably related to the CD4+ T cell deregulation process provoked by the parasite in humans.

Identification of phenotypic markers of B cells from patients with Chagas disease

Chagas disease was discovered more than a hundred years ago, but its pathogenesis is still not completely understood. Autoimmunity is one of the mechanisms shown to contribute to its pathogenesis, which may indicate an important participation of B lymphocytes. Patients with Chagas disease have shown increased percentage of B cells producing IL-10. However, there are no reports of the phenotypic markers of B cells producing IL-10 in patients with Chagas disease. For the first time in the literature, we evaluated the phenotypic profile of distinct markers of B cells from peripheral blood of noninfected individuals and patients with Chagas disease. Our results showed that patients with Chagas disease had a higher expression of CD21 and CD24 on the surface of CD19+ B cells, while CD43 and CD23 were expressed equally in all groups. Moreover, the expression of MHC-II (HLA-DR), CD80, CD86, caspase-3, granzyme B and intracellular IL-10 and TGF-β by CD19+ B cells was higher in patients with Chagas disease. The results of IL-10 production within CD19+ CD5+ CD1d+ B cells showed a higher percentage of this cytokine in patients with Chagas disease. Thus, our data bring a new knowledge about distinct markers of B cells in immune responses of Chagas disease.

TcVac3 induced control of Trypanosoma cruzi infection and chronic myocarditis in mice

We characterized the immune responses elicited by a DNA-prime/MVA-boost vaccine (TcVac3) constituted of antigenic candidates (TcG2 and TcG4), shown to be recognized by B and T cell responses in Trypanosoma cruzi (Tc) infected multiple hosts. C57BL/6 mice immunized with TcVac3 elicited a strong antigen-specific, high-avidity, trypanolytic antibody response (IgG2b>IgG1); and a robust antigen- and Tc-specific CD8⁺T cell response with type-1 cytokine (IFN-γ⁺TNF-α>IL-4⁺IL-10) and cytolytic effector (CD8⁺CD107a⁺IFN-γ⁺Perforin⁺) phenotype. The vaccine-induced effector T cells significantly expanded upon challenge infection and provided >92% control of T. cruzi. Co-delivery of IL-12 and GMCSF cytokine adjuvants didn’t enhance the TcVac3-induced resistance to T. cruzi. In chronic phase, vaccinated/infected mice exhibited a significant decline (up to 70%) in IFN-γ⁺CD8⁺T cells, a predominance of immunoregulatory IL-10⁺/CD4⁺T and IL10⁺/CD8⁺T cells, and presented undetectable tissue parasitism, inflammatory infiltrate, and fibrosis in vaccinated/infected mice. In comparison, control mice responded to challenge infection by a low antibody response, mixed cytokine profile, and consistent activation of pro-inflammatory CD8⁺T cells associated with parasite persistence and pathologic damage in the heart. We conclude that TcVac3 elicited type-1 effector T cell immunity that effectively controlled T. cruzi infection, and subsequently, predominance of anti-inflammatory responses prevented chronic inflammation and myocarditis in chagasic mice.

Antigenicity and diagnostic potential of vaccine candidates in human Chagas disease

Background

Chagas disease, caused by Trypanosoma cruzi, is endemic in Latin America and an emerging infectious disease in the US and Europe. We have shown TcG1, TcG2, and TcG4 antigens elicit protective immunity to T. cruzi in mice and dogs. Herein, we investigated antigenicity of the recombinant proteins in humans to determine their potential utility for the development of next generation diagnostics for screening of T. cruzi infection and Chagas disease.

Methods and Results

Sera samples from inhabitants of the endemic areas of Argentina-Bolivia and Mexico-Guatemala were analyzed in 1^st-phase for anti-T. cruzi antibody response by traditional serology tests; and in 2^nd-phase for antibody response to the recombinant antigens (individually or mixed) by an ELISA. We noted similar antibody response to candidate antigens in sera samples from inhabitants of Argentina and Mexico (n = 175). The IgG antibodies to TcG1, TcG2, and TcG4 (individually) and TcG_mix were present in 62–71%, 65–78% and 72–82%, and 89–93% of the subjects, respectively, identified to be seropositive by traditional serology. Recombinant TcG1- (93.6%), TcG2- (96%), TcG4- (94.6%) and TcG_mix- (98%) based ELISA exhibited significantly higher specificity compared to that noted for T. cruzi trypomastigote-based ELISA (77.8%) in diagnosing T. cruzi-infection and avoiding cross-reactivity to Leishmania spp. No significant correlation was noted in the sera levels of antibody response and clinical severity of Chagas disease in seropositive subjects.

Conclusions

Three candidate antigens were recognized by antibody response in chagasic patients from two distinct study sites and expressed in diverse strains of the circulating parasites. A multiplex ELISA detecting antibody response to three antigens was highly sensitive and specific in diagnosing T. cruzi infection in humans, suggesting that a diagnostic kit based on TcG1, TcG2 and TcG4 recombinant proteins will be useful in diverse situations.

Chagas disease is the most common cause of congestive heart failure related deaths among young adults in the endemic areas of South and Central America and Mexico. Diagnosis and treatment of T. cruzi infection has remained difficult and challenging after 100 years of its identification. In >95% of human cases, T. cruzi infection remains undiagnosed until several years later when chronic evolution of progressive disease results in clinical symptoms associated with cardiac damage. Diagnosis generally depends on the measurement of T. cruzi–specific antibodies that can result in false positives. A conclusive diagnosis of T. cruzi infection thus often requires multiple serological tests, in combination with epidemiological data and clinical symptoms. In this study, we investigated the antibody response to TcG1, TcG2, and TcG4 in clinically characterized chagasic patients. These antigens were identified as vaccine candidates and shown to elicit protective immunity to T. cruzi and Chagas disease in experimental animals. Our data show the serology test developed using the TcG_mix (multiplex ELISA) is a significantly better alternative to epimastigote extracts currently used in T. cruzi serodiagnosis or the trypomastigote lysate used in this study for comparison purposes.

A flow cytometry-based workflow for detection and quantification of anti-plasmodial antibodies in vaccinated and naturally exposed individuals

Background

Antibodies play a central role in naturally acquired immunity against Plasmodium falciparum. Current assays to detect anti-plasmodial antibodies against native antigens within their cellular context are prone to bias and cannot be automated, although they provide important information about natural exposure and vaccine immunogenicity. A novel, cytometry-based workflow for quantitative detection of anti-plasmodial antibodies in human serum is presented.

Methods

Fixed red blood cells (RBCs), infected with late stages of P. falciparum were utilized to detect malaria-specific antibodies by flow cytometry with subsequent automated data analysis. Available methods for data-driven analysis of cytometry data were assessed and a new overlap subtraction algorithm (OSA) based on open source software was developed. The complete workflow was evaluated using sera from two GMZ2 malaria vaccine trials in semi-immune adults and pre-school children residing in a malaria endemic area.

Results

Fixation, permeabilization, and staining of infected RBCs were adapted for best operation in flow cytometry. As asexual blood-stage vaccine candidates are designed to induce antibody patterns similar to those in semi-immune adults, serial dilutions of sera from heavily exposed individuals were compared to naïve controls to determine optimal antibody dilutions. To eliminate investigator effects introduced by manual gating, a non-biased algorithm (OSA) for data-driven gating was developed. OSA-derived results correlated well with those obtained by manual gating (r between 0.79 and 0.99) and outperformed other model-driven gating methods. Bland-Altman plots confirmed the agreement of manual gating and OSA-derived results. A 1.33-fold increase (p=0.003) in the number of positive cells after vaccination in a subgroup of pre-school children vaccinated with 100 μg GMZ2 was present and in vaccinated adults from the same region we measured a baseline-corrected 1.23-fold, vaccine-induced increase in mean fluorescence intensity of positive cells (p=0.03).

Conclusions

The current workflow advances detection and quantification of anti-plasmodial antibodies through improvement of a bias-prone, low-throughput to an unbiased, semi-automated, scalable method. In conclusion, this work presents a novel method for immunofluorescence assays in malaria research.

Current understanding of immunity to Trypanosoma cruzi infection and pathogenesis of Chagas disease

Chagas disease caused by Trypanosoma cruzi remains an important neglected tropical disease and a cause of significant morbidity and mortality. No longer confined to endemic areas of Latin America, it is now found in non-endemic areas due to immigration. The parasite may persist in any tissue, but in recent years, there has been increased recognition of adipose tissue both as an early target of infection and a reservoir of chronic infection. The major complications of this disease are cardiomyopathy and megasyndromes involving the gastrointestinal tract. The pathogenesis of Chagas disease is complex and multifactorial involving many interactive pathways. The significance of innate immunity, including the contributions of cytokines, chemokines, reactive oxygen species, and oxidative stress, has been emphasized. The role of the components of the eicosanoid pathway such as thromboxane A(2) and the lipoxins has been demonstrated to have profound effects as both pro- and anti-inflammatory factors. Additionally, we discuss the vasoconstrictive actions of thromboxane A(2) and endothelin-1 in Chagas disease. Human immunity to T. cruzi infection and its role in pathogen control and disease progression have not been fully investigated. However, recently, it was demonstrated that a reduction in the anti-inflammatory cytokine IL-10 was associated with clinically significant chronic chagasic cardiomyopathy.

Delivery of antigenic candidates by a DNA/MVA heterologous approach elicits effector CD8(+)T cell mediated immunity against Trypanosoma cruzi

In this study, we have characterized the immune mechanisms elicited by antigenic candidates, TcG2 and TcG4, delivered by a DNA-prime/MVA-boost approach, and evaluated the host responses to Trypanosoma cruzi infection in C57BL/6 mice. Immunization of mice with antigenic candidates elicited antigen-specific, high-avidity, trypanolytic antibody response (IgG2b>IgG1) and CD8(+)T cells that exhibited type-1 cytolytic effector (CD8(+)CD107a(+)IFN-γ(+)Perforin(+)) phenotype. The extent of TcG2-dependent type 1 B and T cell immunity was higher than that noted in TcG4-immunized mice, and expanded accordingly in response to challenge infection with T. cruzi. The progression of chronic phase in immunized mice was associated with persistence of IgGs, 55-90% reduction in the frequency of proinflammatory (IFN-γ(+) or TNF-α(+)) CD8(+)T cells, and an increase or emergence of immunoregulatory (IL-10(+)) CD4/CD8 T cells. The tissue parasitism, infiltration of inflammatory infiltrate, parasite persistence, and fibrosis were decreased by 82-92% in heart and skeletal muscle of immunized/chronically infected mice. Control mice exhibited a significantly low antibody response, consistent activation of effector CD8(+)T cells dominated by pro-inflammatory phenotype and mixed cytokine profile (IFN-γ+TNF-α>IL-4+IL-10), parasite persistence and pathologic damage in chagasic hearts. We conclude that delivery of TcG2 or TcG4 by DNA-rMVA approach elicits effective antibody and CD8(+)T cell mediated immunity against T. cruzi and Chagas disease. The emergence of type 2 cytokine and T cell response in chronic phase was indicative of prevention of clinical disease.

In-house ELISA method to analyze anti-Trypanosoma cruzi IgG reactivity for differential diagnosis and evaluation of Chagas disease morbidity

INTRODUCTION: The goal was to develop an in-house serological method with high specificity and sensitivity for diagnosis and monitoring of Chagas disease morbidity. METHODS: With this purpose, the reactivities of anti-T. cruzi IgG and subclasses were tested in successive serum dilutions of patients from Berilo municipality, Jequitinhonha Valley, Minas Gerais, Brazil. The performance of the in-house ELISA was also evaluated in samples from other relevant infectious diseases, including HIV, hepatitis C (HCV), syphilis (SYP), visceral leishmaniasis (VL), and American tegumentary leishmaniasis (ATL), and noninfected controls (NI). Further analysis was performed to evaluate the applicability of this in-house methodology for monitoring Chagas disease morbidity into three groups of patients: indeterminate (IND), cardiac (CARD), and digestive/mixed (DIG/Mix), based on their clinical status. RESULTS: The analysis of total IgG reactivity at serum dilution 1:40 was an excellent approach to Chagas disease diagnosis (100% sensitivity and specificity). The analysis of IgG subclasses showed cross-reactivity, mainly with NI, VL, and ATL, at all selected serum dilutions. Based on the data analysis, the IND group displayed higher IgG3 levels and the DIG/Mix group presented higher levels of total IgG as compared with the IND and CARD groups. CONCLUSIONS: These findings demonstrated that methodology presents promising applicability in the analysis of anti-T. cruzi IgG reactivity for the differential diagnosis and evaluation of Chagas disease morbidity.

Pathogenesis of Chagas disease: time to move on

Trypanosoma cruzi is the etiologic agent of Chagas disease. The contributions of parasite and immune system for disease pathogenesis remain unresolved and controversial. The possibility that Chagas disease was an autoimmune progression triggered by T. cruzi infection led some to question the benefit of treating chronically T. cruzi-infected persons with drugs. Furthermore, it provided the rationale for not investing in research aimed at a vaccine which might carry a risk of inducing autoimmunity or exacerbating inflammation. This viewpoint was adopted by cash-strapped health systems in the developing economies where the disease is endemic and has been repeatedly challenged by researchers and clinicians in recent years and there is now a considerable body of evidence and broad consensus that parasite persistence is requisite for pathogenesis and that antiparasitic immunity can be protective against T. cruzi pathogenesis without eliciting autoimmune pathology. Thus, treatment of chronically infected patients is likely to yield positive outcomes and efforts to understand immunity and vaccine development should be recognized as a priority area of research for Chagas disease.

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 use of IgG antibodies in conventional and non-conventional immunodiagnostic tests for early prognosis after treatment of Chagas disease

Treatment success of chronically infected Chagas disease patients is laborious and a positive prognosis often is made only after repetitive serological and/or parasitological examinations with continuous negative results. Recently, we have developed a non-conventional flow-cytometric method in order to detect immunoglobulin G antibodies against live trypomastigote forms of Trypanosoma cruzi and showed its usefulness in the prognosis of treatment success. In the present study, we investigated the performance of flow-cytometric anti-live trypomastigote IgG antibodies (FC-ALTA) and flow-cytometric anti-fixed epimastigote IgG antibodies (FC-AFEA), as well as conventional serological methods, for early monitoring of benznidazole treated Chagas disease patients, e.g. 5years after treatment. The analysis of individual FC-ALTA reactivity along the titration curve before and after treatment, we were able to show, that between 4% and 13% of treated patients under evaluation presented with reduced serological reactivity and segregated from the other patient groups. Similar results were obtained with semi-quantitative, conventional indirect hemagglutination or indirect immunofluorescence. Our data therefore suggest that the combined use of conventional and non-conventional serological methods could provide more suitable cure criteria in early post-therapeutic prognosis of Chagas disease.

The role of parasite persistence in pathogenesis of Chagas heart disease

Chagas disease (CD) is caused by the infection with the protozoan haemoflagellate Trypanosoma cruzi. This disease is still a great menace to public health, and is largely neglected as it affects mostly the poorest populations of Latin America. Nonetheless, there are neither effective diagnostic markers nor therapeutic options to accurately detect and efficiently cure this chronic infection. In spite of the great advances in the knowledge of the biology of natural transmission, as well as the immunobiology of the host-parasite interaction, the understanding of the pathogenesis of CD remains largely elusive. In the recent decades, a controversy in the research community has developed about the relevance of parasite persistence or autoimmune phenomena in the development of chronic cardiac pathology. One of the most notable aspects of chronic CD is the progressive deterioration of cardiac function, derived mostly from structural derangement, as a consequence of the intense inflammatory process. Here we review the evidence supporting the multifactorial nature of Chagas heart disease comprising pathogen persistence and altered host immunoregulatory mechanisms.

Perforin-expressing cytotoxic cells contribute to chronic cardiomyopathy in Trypanosoma cruzi infection

Understanding the dual participation of the immune response in controlling the invader and at the same time causing tissue damage might contribute to the design of effective new vaccines and therapies for Chagas disease. Perforin, a cytolytic protein product of killer cells, is involved in resistance to acute Trypanosoma cruzi infection. However, the contribution of perforin in parasite control and chronic chagasic cardiomyopathy is unclear. Perforin-positive cells were detected in the heart tissue during the acute and chronic phases of infection of C57BL/6 mice inoculated with low dose (10(2) parasites) of the Colombian T. cruzi strain. This protocol led to acute phase survival in both wild-type and perforin null (pfp(-/-)) mice lineages. During the chronic infection, parasitism and inducible nitric oxide synthase (iNOS) as well as interleukin (IL)-4+ and, mainly, interferon (IFN)-gamma+ cells were more elevated in the heart tissue of pfp(-/-) mice. Higher levels of circulating NO and anti-parasite immunoglobulin (Ig)G2c and IgG3, paralleled by a prominent frequency of IFN-gamma+ and IL-10+ splenocytes, were present in pfp(-/-)-infected mice. Therefore, although the perforin-dependent pathway plays a role, it is not crucial for anti-T. cruzi immunity and acute phase survival of mice infected with a low inoculum. Further, perforin deficiency resulted in lower activity of creatine kinase-muscle brain isoform (CK-MB) isoenzyme in serum and a more restricted connexin 43 loss, both of which are markers of the cardiomyocyte lesion. Moreover, perforin deficiency hampered the development of severe electrocardiographic abnormalities. Hence, our results corroborate that perforin-bearing cytotoxic cells might contribute to cardiomyocyte lesion and heart dysfunction during chronic T. cruzi infection, shedding light on immunopathogenesis of chronic chagasic cardiomyopathy.

Trypanosoma cruzi: Immunological predictors of benznidazole efficacy during experimental infection

C3H/HeN male mice were infected with a lethal population of Trypanosoma cruzi and treated with benznidazole (Bz). Parasitemia, body weight and survival rate were registered during the therapy with significant improvement for T. cruzi-infected Bz-treated animals. Besides, flow cytometry resulted a useful method to discriminate between cured animals from those not cured by monitoring IgG(1) bound to live trypomastigotes levels. At the end of Bz therapy, the LT splenocyte compartment was studied for activation/memory cell surface markers (CD(69)(+) and CD(44)(+)). Cytofluorometric analysis showed that T. cruzi-infected untreated mice increased their activated LT numbers and this effect was completely abolished only in cured mice at the end of Bz administration. The same behavior was observed for the memory LT subpopulation correlating to an effector memory (CD(62L)(-)) displayed by T. cruzi infection. Bz treatment was able to modulate the immunological response by reducing the deleterious effect of the acute phase in all T. cruzi-infected mice.

Performance of IgG and IgG1 anti-HTLV-1 reactivity by an indirect immunofluorescence flow cytometric assay for the identification of persons infected with HTLV-1, asymptomatic carriers and patients with myelopathy

In this study, the performance of IgG and IgG1 anti-HTLV-1 reactivity obtained by a flow cytometric assay was evaluated to verify its applicability for the diagnosis of persons infected with HTLV-1, including asymptomatic carriers and patients with myelopathy. The ability to identify patients with myelopathy among persons infected with HTLV-1 was also examined. Western blot assays were performed to assess the reactivity profiles of sera from asymptomatic carriers and patients with myelopathy against viral proteins. The data showed that IgG1 detected by flow cytometric assay is effective for the diagnosis of persons infected with HTLV-1 with 97% sensitivity and 100% specificity. IgG and IgG1 exhibited high performance in distinguishing patients with myelopathy from asymptomatic carriers. Using serum dilutions and cut-off points established previously a second HTLV-1 carrier group was tested using flow cytometric assay to detect IgG and IgG1. The data demonstrated sensitivity of 93% and 98%, respectively, confirming the high reactivity of persons infected with HTLV-1 detected by this method. Western blot assays confirmed the high specificity of MT-2 cells as a reliable source of viral antigen since only sera from persons infected with HTLV-1 recognised MT-2 proteins. Furthermore, a high reactivity to Gag and Env proteins was observed, especially among patients with myelopathy. These data suggest that flow cytometric detection of IgG1 is a valuable, non-conventional serological method to diagnose HTLV-1 infection and for research purposes.

Trypanosoma cruzi: Genetic diversity influences the profile of immunoglobulins during experimental infection

The clonal evolution model postulated for Trypanosoma cruzi predicts a correlation between the phylogenetic divergence of T. cruzi clonal genotypes and their biological properties. In the present study, the linkage between phylogenetic divergence of the parasite and IgG, IgG1, IgG2a and IgG2b response has been evaluated during the acute and chronic phases of the experimental infection. Eight laboratory-cloned stocks representative of this phylogenetic diversity and including the lineages T. cruzi I (genotypes 19 and 20), T. cruzi II (genotype 32) and T. cruzi (genotype 39) have been studied. The results showed that the pattern of humoral immune response was correlated with T. cruzi genotype, and that stocks included in genotype 20 were responsible for the high IgG response in the acute and chronic phases. Moreover, T. cruzi I lineage was more efficient in over-expressing all subclasses of specific anti-parasite IgG than either T. cruzi II or T. cruzi lineages. Curiously, the alteration in the pattern of antibodies induced by Benznidazole treatment was related to the phase of the infection but not to the genotype of the parasite. The data suggest that genotypes of T. cruzi are able to drive levels/subclasses of specific IgG, hence giving rise to further concerns about the sensitivity of serological assays in the diagnosis of human Chagas disease.

Trypanosoma cruzi: immunoglobulin isotype profiles during the acute phase of canine experimental infection with metacyclic or blood trypomastigotes

A detailed investigation has been carried out about the serological profiles of groups of dogs experimentally infected with metacyclic (MT) or blood (BT) trypomastigotes of Berenice-78 Trypanosoma cruzi strain. Peripheral blood was collected from infected dogs and uninfected controls, weekly during 35 days following the acute phase of infection, and immunoglobulin profiles were determined by ELISA. Dogs infected with BT exhibited unaltered levels of IgG2, increases in IgM, IgE, IgA, IgG and IgG1. In contrast, dogs infected with MT presented unaltered levels of IgE and IgG1 and an increase in IgM, IgA, IgG and IgG2 levels. Compared with the MT group, animals infected with BT showed significant increases in IgM on days 7, 14 and 28, in IgA on days 7, 14 and 21, in IgE on days 7 and 14, in IgG on days 14 and 28, and in IgG1 on days 7, 14 and 21. Parasitemia levels of the infected animals were measured over the same time period. No correlations were found between the immunoglobulin profiles and the parasitemia levels. The results demonstrated that the inoculum source (BT or MT) influence the immunoglobulin isotype profile that may drive distinct outcome of acute canine Chagas disease.

Chagas' disease: IgG isotypes against cytoplasmic (CRA) and flagellar (FRA) recombinant repetitive antigens of Trypanosoma cruzi in chronic Chagasic patients

The wide range of clinical Chagas' disease manifestations, of which heart involvement is the most significant, because of its characteristics, frequency and consequences, and lack of treatment and cure, justify research in this area. Specific immunoglobulin G (IgG) antibody subclasses have been associated with human Chagas' disease. Thus, in this study, the profile of IgG subclasses against cytoplasmic (CRA) and flagellar (FRA) recombinant repetitive T. cruzi-specific antigens was correlated with cardiac (CARD, n=33), cardiodigestive (CD, n=7), and indeterminate (IND, n=20) forms of Chagas' disease by indirect enzyme-linked immunosorbent assay (ELISA). IgG subclasses were detected in almost all Chagas patients studied. Nevertheless, only specific IgG2 isotype FRA was found with a significant statistical difference in CARD patients when compared to IND patients. This result suggests the potential use of this isotype for prognostic purposes, for monitoring the progression of chronic Chagas' disease, and for predicting the risk of CARD damage. This is important information, as it could help physicians to evaluate and manage the treatment of their patients. However, a follow-up study is necessary to confirm our result.

Impact of dual infections on chemotherapeutic efficacy in BALB/c mice infected with major genotypes of Trypanosoma cruzi

The aim of this work was to investigate the impact of dual infections with stocks of Trypanosoma cruzi major genotypes on benznidazole (BZ) treatment efficacy. For this purpose, T. cruzi stocks representative of the genetic T. cruzi lineages, displaying different susceptibilities to BZ, belonging to the major T. cruzi genotypes broadly dispersed in North and South America and important in Chagas' disease epidemiology were used. Therapeutic efficacy was observed in 27.8% of the animals treated. Following BZ susceptibility classification, significant differences were observed in dual infections on the major genotype level, demonstrating that combinations of genotypes 19+39 and genotypes 19+32 led to a shift in the expected BZ susceptibility profile toward the resistance pattern. Analysis on the T. cruzi stock level demonstrated that 9 out of 24 dual infections shifted the expected BZ susceptibility profile compared with the respective single infections, including shifts toward lower and higher BZ susceptibilities. Microsatellite identification was able to identify a mixture of T. cruzi stocks in 7.7% of the T. cruzi isolates from infected and untreated mice (6.9%) and infected and treated but not cured mice (9.0%), revealing in some mixtures of BZ-susceptible and -resistant stocks that the T. cruzi stock identified after BZ treatment was previously susceptible in single infections. Considering the clonal structure and evolution of T. cruzi, an unexpected result was the identification of parasite subpopulations with distinct microsatellite alleles in relation to the original stocks observed in 12.2% of the isolates. Taken together, the data suggest that mixed infections, already verified in nature, may have an important impact on the efficacy of chemotherapy.

Trypanosoma cruzi: populations bearing opposite virulence induce differential expansion of circulating CD3+CD4-CD8- T cells and cytokine serum levels in young and adult rats

The JG strain is the least virulent while the CL-Brener clone is one of the most virulent Trypanosoma cruzi populations in young rats. In this study, we determined that the parasitemia peak values in CL-Brener clone-infected adult rats were 50-fold lower than in young rats and that mortality was null as compared to 45% death in young rats. Low parasitemia, milder and sustained myocarditis and myositis characterized JG infections. CL-Brener clone caused a significantly higher production of pro-inflammatory cytokines and higher expansion of CD3(+)CD4(-)CD8(-), double-negative (DN) T cells, during the acute phase in both adult and young rats. DN T cell frequencies correlated with IFN-gamma levels. These findings may explain the higher inflammation and fast acute phase resolution in CL-Brener infection. In young rats, IL-10 levels were similar in both infections. The IL-10/IFN-gamma ratio was higher in JG acute infection in accordance with the milder inflammation and parasite persistence leading to a chronic phase. In conclusion, virulence and pathogenicity depend on T. cruzi ability to induce expansion of DN T cells and production of specific cytokines.

Non-conventional flow cytometry approaches to detect anti-Trypanosoma cruzi immunoglobulin G in the clinical laboratory

We have recently developed a flow cytometric approach to detect anti-live trypomastigote and anti-fixed epimastigote IgG antibodies (FC-ALTA and FC-AFEA) in sera from individuals infected by Trypanosoma cruzi. Here, we present the first evaluation of the applicability of FC-AFEA-IgG as a diagnostic tool for Chagas disease. Performance analysis demonstrated that FC-AFEA-IgG has a sensitivity of 82% and a specificity of 100%. The assessment for prognosis performed by FC-ALTA-IgG1 and FC-AFEA-IgG, after classification of chagasic patients as belonging to indeterminate (IND), cardiac (CARD) or digestive (DIG) clinical forms, showed that most of IND have higher amounts of IgG than individuals' carrying CARD or DIG Chagas disease. FC-AFEA-IgG was also evaluated as a method to monitor chemotherapy efficacy in individuals classified into three distinct categories: not treated (NT), treated but not cured (TNC), and treated and cured (TC). Performance analysis demonstrated that FC-AFEA-IgG has an extraordinary capacity as a serological criterion to assess cure after therapeutic intervention in Chagas disease. These results represent a great advance in the application of serological techniques for clinical investigations on Chagas disease, and they clearly define new directions and perspectives. We intend to continue this field research focusing our attention on the influence of the degree of clinical damage on the FC-ALTA-IgG1 and FC-AFEA-IgG reactivity.

Clinical value of anti-live Leishmania (Viannia) braziliensis immunoglobulin G subclasses, detected by flow cytometry, for diagnosing active localized cutaneous leishmaniasis

OBJECTIVE

To evaluate the clinical value of flow cytometry anti-live promastigate antibody (FC-ALPA), for diagnosing active cutaneous leishmaniasis.

METHOD

Serum samples from 145 individuals living in endemic areas for localized cutaneous leishmaniasis (population 1) were classified as having the disease or not and then tested for their IgG reactivity by indirect immunofluorescence assay and FC-ALPA-IgG. The results of FC-ALPA-IgG were expressed as percentage of positive fluorescent parasite. Both tests were also evaluated in serum samples of people with visceral leishmaniasis and Chagas disease (population 1A).

RESULTS

In population 1, FC-ALPA-IgG performed better than the immunofluorescence assay regarding sensitivity, specificity and predictive values. Analysis of the results according to the likelihood ratios indicated that a percentage of positive fluorescent parasite <or=60 practically excludes the diagnosis of localized cutaneous leishmaniasis (likelihood ratio=0.07), whereas at >60% it reinforces diagnosis of the disease (likelihood ratio = 7.0). Immunofluorescent assay is of little value (likelihood ratio=2.04). In population 1A, both tests performed worse, but FC-ALPA-IgG achieved better statistical indexes than immunofluorescent assay.

CONCLUSION

The FC-ALPA-IgG is a valuable method for serological diagnosis of localized cutaneous leishmaniasis. FC-ALPA-IgG1/ALPA-IgG2 combined analysis is an additional serological tool for discriminating localized visceral leishmaniasis, Chagas disease and visceral leishmaniasis in areas where these infections co-exist.