Use of recombinant antigens for the accurate immunodiagnosis of Chagas' disease

Technological advances in the serological diagnosis of Chagas disease in dogs and cats: a systematic review

Background

Chagas disease (CD) is caused by Trypanosoma cruzi, which is transmitted mainly through the feces/urine of infected triatomine bugs. The acute phase lasts 2–3 months and is characterized by high parasitemia and nonspecific symptoms, whereas the lifelong chronic phase features symptoms affecting the heart and/or digestive tract occurring in 30–40% of infected individuals. As in humans, cardiac abnormalities are observed in T. cruzi-infected dogs and cats. We reviewed the technological advances in the serological diagnosis of CD in dogs and cats.

Methods

A review of the published literature during the last 54 years (1968–2022) on the epidemiology, clinical features, diagnosis, treatment and prevention of CD in dogs and cats was conducted.

Results

Using predefined eligibility criteria for a search of the published literature, we retrieved and screened 436 publications. Of these, 84 original studies were considered for inclusion in this review. Dogs and cats are considered as sentinels, potentially indicating an active T. cruzi transmission and thus the risk for human infection. Although dogs and cats are reputed to be important for maintaining the T. cruzi domestic transmission cycle, there are no commercial tests to detect past or active infections in these animals. Most published research on CD in dogs and cats have used in-house serological tests prepared with native and/or full-length recombinant antigens, resulting in variable diagnostic performance. In recent years, chimeric antigens have been used to improve the diagnosis of chronic CD in humans with encouraging results. Some of them have high performance values (> 95%) and extremely low cross-reactivity rates for Leishmania spp., especially the antigens IBMP-8.1 to IBMP-8.4. The diagnostic performance of IBMP antigens was also investigated in dogs, showing high diagnostic performance with negligible cross-reactivity with anti-Leishmania infantum antibodies.

Conclusions

The development of a commercial immunodiagnostic tool to identify past or active T. cruzi infections in dogs and cats is urgently needed. The use of chimeric recombinant T. cruzi antigens may help to fill this gap and is discussed in this review.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05476-4.

Comparison of four PCR methods for efficient detection of Trypanosoma cruzi in routine diagnostics

Due to increased migration, Chagas disease has become an international health problem. Reliable diagnosis of chronically infected people is crucial for prevention of non-vectorial transmission as well as treatment. This study compared four distinct PCR methods for detection of Trypanosoma cruzi DNA for the use in well-equipped routine diagnostic laboratories. DNA was extracted of T. cruzi-positive and negative patients' blood samples and cultured T. cruzi, T. rangeli as well as Leishmania spp. One conventional and two real-time PCR methods targeting a repetitive Sat-DNA sequence as well as one conventional PCR method targeting the variable region of the kDNA minicircle were compared for sensitivity, intra- and interassay precision, limit of detection, specificity and cross-reactivity. Considering the performance, costs and ease of use, an algorithm for PCR-diagnosis of patients with a positive serology for T. cruzi antibodies was developed.

Accuracy of chimeric proteins in the serological diagnosis of chronic chagas disease - a Phase II study

BACKGROUND

The performance of current serologic tests for diagnosing chronic Chagas disease (CD) is highly variable. The search for new diagnostic markers has been a constant challenge for improving accuracy and reducing the number of inconclusive results.

METHODOLOGY/PRINCIPAL FINDINGS

Here, four chimeric proteins (IBMP-8.1 to -8.4) comprising immunodominant regions of different Trypanosoma cruzi antigens were tested by enzyme-linked immunosorbent assay. The proteins were used to detect specific anti-T. cruzi antibodies in the sera of 857 chagasic and 689 non-chagasic individuals to evaluate their accuracy for chronic CD diagnosis. The antigens were recombinantly expressed in Escherichia coli and purified by chromatographic methods. The sensitivity and specificity values ranged from 94.3% to 99.3% and 99.4% to 100%, respectively. The diagnostic odds ratio (DOR) values were 6,462 for IBMP-8.1, 3,807 for IBMP-8.2, 32,095 for IBMP-8.3, and 283,714 for IBMP-8.4. These chimeric antigens presented DORs that were higher than the commercial test Pathozyme Chagas. The antigens IBMP-8.3 and -8.4 also showed DORs higher than the Gold ELISA Chagas test. Mixtures with equimolar concentrations were tested in order to improve the diagnosis accuracy of negative samples with high signal and positive samples with low signal. However, no gain in accuracy was observed relative to the individual antigens. A total of 1,079 additional sera were used to test cross-reactivity to unrelated diseases. The cross-reactivity rates ranged from 0.37% to 0.74% even for Leishmania spp., a pathogen showing relatively high genome sequence identity to T. cruzi. Imprecision analyses showed that IBMP chimeras are very stable and the results are highly reproducible.

CONCLUSIONS/SIGNIFICANCE

Our findings indicate that the IBMP-8.4 antigen can be safely used in serological tests for T. cruzi screening in blood banks and for chronic CD laboratory diagnosis.

Expression of co-stimulatory molecules CD80 and CD86 is altered in CD14 + HLA-DR + monocytes from patients with Chagas disease following induction by Trypanosoma cruzi recombinant antigens

INTRODUCTION

The relationships between monocytes and lymphocytes through MHC class II molecules and costimulatory, are of utmost importance for the production of an efficient immune response. In this work, we assessed the expression of surface molecules CD80 and CD86 on CD14+HLA-DR+ monocytes from patients with Chagas disease.

METHODS:

The study population consisted of 31 patients with chronic clinical forms of Chagas disease. Patient blood samples were cultured in the presence of recombinant cytoplasmic repetitive antigen (CRA) and flagellar repetitive antigen (FRA).

RESULTS:

We found considerable differences in the expression profile of surface molecules involved in antigen presentation.

CONCLUSIONS:

CRA and FRA may contribute to host immune response evasion by Trypanozoma cruzi.

Chagas Disease Diagnostic Applications: Present Knowledge and Future Steps

Chagas disease, caused by the protozoan Trypanosoma cruzi, is a lifelong and debilitating illness of major significance throughout Latin America and an emergent threat to global public health. Being a neglected disease, the vast majority of Chagasic patients have limited access to proper diagnosis and treatment, and there is only a marginal investment into R&D for drug and vaccine development. In this context, identification of novel biomarkers able to transcend the current limits of diagnostic methods surfaces as a main priority in Chagas disease applied research. The expectation is that these novel biomarkers will provide reliable, reproducible and accurate results irrespective of the genetic background, infecting parasite strain, stage of disease, and clinical-associated features of Chagasic populations. In addition, they should be able to address other still unmet diagnostic needs, including early detection of congenital T. cruzi transmission, rapid assessment of treatment efficiency or failure, indication/prediction of disease progression and direct parasite typification in clinical samples. The lack of access of poor and neglected populations to essential diagnostics also stresses the necessity of developing new methods operational in point-of-care settings. In summary, emergent diagnostic tests integrating these novel and tailored tools should provide a significant impact on the effectiveness of current intervention schemes and on the clinical management of Chagasic patients. In this chapter, we discuss the present knowledge and possible future steps in Chagas disease diagnostic applications, as well as the opportunity provided by recent advances in high-throughput methods for biomarker discovery.

Serological based monitoring of a cohort of patients with chronic Chagas disease treated with benznidazole in a highly endemic area of northern Argentina

This study aimed to evaluate well-documented diagnostic antigens, named B13, 1F8 and JL7 recombinant proteins, as potential markers of seroconversion in treated chagasic patients. Prospective study, involving 203 patients treated with benznidazole, was conducted from endemic areas of northern Argentina. Follow-up was possible in 107 out of them and blood samples were taken for serology and PCR assays before and 2, 3, 6, 12, 24 and 36 months after treatment initiation. Reactivity against Trypanosoma cruzi lysate and recombinant antigens was measured by ELISA. The rate of decrease of antibody titers showed nonlinear kinetics with an abrupt drop within the first three months after initiation of treatment for all studied antigens, followed by a plateau displaying a low decay until the end of follow-up. At this point, anti-B13, anti-1F8 and anti-JL7 titers were relatively close to the cut-off line, while anti-T. cruzi antibodies still remained positive. At baseline, 60.8% (45/74) of analysed patients tested positive for parasite DNA by PCR and during the follow-up period in 34 out of 45 positive samples (75.5%) could not be detected T. cruzi DNA. Our results suggest that these antigens might be useful as early markers for monitoring antiparasitic treatment in chronic Chagas disease.

Modulation of Trypanosoma cruzi-specific T-cell responses after chemotherapy for chronic Chagas disease

The aim of this review is to describe the contributions of the knowledge of T-cell responses to the understanding of the physiopathology and the responsiveness to etiological treatment during the chronic phase of Chagas disease. T-helper (Th)1 and interleukin (IL)-10 Trypanosoma cruzi-specific T-cells have been linked to the asymptomatic phase or to severe clinical forms of the disease, respectively or vice versa, depending on the T. cruzi antigen source, the patient's location and the performed immunological assays. Parasite-specific T-cell responses are modulated after benznidazole (BZ) treatment in chronically T. cruzi-infected subjects in association with a significant decrease in T. cruzi-specific antibodies. Accumulating evidence has indicated that treatment efficacy during experimental infection with T. cruzi results from the combined action of BZ and the activation of appropriate immune responses in the host. However, strong support of this interaction in T. cruzi-infected humans remains lacking. Overall, the quality of T-cell responses might be a key factor in not only disease evolution, but also chemotherapy responsiveness. Immunological parameters are potential indicators of treatment response regardless of achievement of cure. Providing tools to monitor and provide early predictions of treatment success will allow the development of new therapeutic options.

Evaluation of recombinant antigens of Trypanosoma cruzi to diagnose infection in naturally infected dogs from Chaco region, Argentina

Dogs are considered the main mammal reservoir of Trypanosoma cruzi in domiciliary environments. Consequently, accurate detection of T. cruzi infection in canine populations is epidemiologically relevant. Here, we analysed the utility of the T. cruzi recombinant antigens FRA, SAPA, CP1, Ag1 and a SAPA/TSSA VI mixture, in an ELISA format. We used a positive control group of sera obtained from 38 dogs from the Chaco region in Argentina with positive homogenate-ELISA reaction, all of them also positive by xenodiagnosis and/or PCR. The negative group included 19 dogs from a nonendemic area. Sensitivity, specificity, area under the curve (AUC) of the receiver operating charactheristic (ROC) curve and Kappa index were obtained to compare the diagnostic efficiency of the tests. The SAPA/TSSA VI had the highest performance, with a sensitivity of 94.7% and an AUC ROC of 0.99 that indicates high accuracy. Among individual antigens, SAPA-ELISA yielded the highest sensitivity (86.8%) and AUC ROC (0.96), whereas FRA-ELISA was the least efficient test (sensitivity = 36.8%; AUC ROC = 0.53). Our results showed that the use of SAPA/TSSA VI in ELISAs could be a useful tool to study dogs naturally infected with T. cruzi in endemic areas.

Chagas disease-specific antigens: characterization of epitopes in CRA/FRA by synthetic peptide mapping and evaluation by ELISA-peptide assay

Background

The identification of epitopes in proteins recognized by medically relevant antibodies is useful for the development of peptide-based diagnostics and vaccines. In this study, epitopes in the cytoplasmic repetitive antigen (CRA) and flagellar repetitive antigen (FRA) proteins from Trypanosoma cruzi were identified using synthetic peptide techniques and pooled sera from Chagasic patients. The epitopes were further assayed with an ELISA assay based on synthetic peptides.

Methods

Twenty-two overlapping synthetic peptides representing the coding sequence of the T. cruzi CRA and FRA proteins were assessed by a Spot-synthesis array analysis using sera donated by patients with Chagas disease. Shorter peptides were selected that represented the determined epitopes and synthesized by solid phase synthesis to evaluate the patterns of cross-reactivities and discrimination through an ELISA-diagnostic assay.

Results

The peptide Spot-synthesis array successfully identified two IgG antigenic determinants in the CRA protein and four in FRA. Bioinformatics suggested that the CRA antigens were unique to T. cruzi while the FRA antigen showed similarity with sequences present within various proteins from Leishmania sp. Subsequently, shorter peptides representing the CRA-1, CRA-2 and FRA-1 epitopes were synthesized by solid phase synthesis and assayed by an ELISA-diagnostic assay. The CRA antigens gave a high discrimination between Chagasic, Leishmaniasis and T. cruzi-uninfected serum. A sensitivity and specificity of 100% was calculated for CRA. While the FRA antigen showed a slightly lower sensitivity (91.6%), its specificity was only 60%.

Conclusions

The epitopes recognized by human anti-T. cruzi antibodies have been precisely located in two biomarkers of T. cruzi, CRA and FRA. The results from screening a panel of patient sera through an ELISA assay based on peptides representing these epitopes strongly suggest that the sequences from CRA would be useful for the development of diagnostic reagents that could improve upon the sensitivity and specificity of currently available diagnostic tests. Overall, the results provide further evidence of the usefulness of identifying specific linear B-cell epitopes for improving diagnostic tools.

Performance of different Trypanosoma cruzi antigens in the diagnosis of Chagas disease in patients with American cutaneous leishmaniasis from a co-endemic region in Argentina

OBJECTIVE

To determine the ability of recombinant antigens to detect cases of infection with Trypanosoma cruzi among cases of infection with Leishmania spp. by serological methods.

METHODS

Sera from 41 patients infected with Leishmania spp. were evaluated with ELISA using single (FRA, CP1 and TSSAVI) or pooled (commercial Rec-ELISA) recombinant proteins or homogenate antigens (commercial H-ELISA). As there is no gold standard antigen to discriminate Chagas disease from leishmaniasis, the correlation of results between defined antigens and the homogenate was made with Kappa Index (KI), the level of correlation considered being used as a criterion of specificity.

RESULTS

Single recombinant antigens and Rec-ELISA showed good correlation (KI > 0.8). A low correlation (KI < 0.66) was observed between the results from single recombinant antigens or the commercial recombinant kit and H-ELISA.

CONCLUSIONS

The highly correlated results between T. cruzi single or pooled recombinant proteins are indicative of the usefulness of recombinant antigens for Chagas diagnosis. Our results also indicate that in the city of Oran in Argentina, between 12% and 17% of patients with leishmaniasis are also infected with Chagas disease. The high KI values between TSSAVI and the other recombinant proteins suggest that in these patients, the infection may be caused by T. cruzi II and/or V and/or VI lineages.

IL-10 and IFN-γ gene expression in chronic Chagas disease patients after in vitro stimulation with recombinant antigens of Trypanosoma cruzi

Along with several other aspects of Chagas disease, the mechanisms responsible for the different clinical outcomes observed in chronic infected individuals have not yet been clarified. It is believed that the host immune response to the parasite plays an important role in the development of the pathology. Therefore, the aim of this study was to evaluate the relationship between IL-10 and IFN-γ gene expression profile, after in vitro stimulation of peripheral blood mononuclear cells (PBMC) with Trypanosoma cruzi recombinant antigens CRA (cytoplasmatic repetitive antigen) and FRA (flagellar repetitive antigen), and the clinical forms of chronic Chagas disease. Twenty patients with the cardiac form of the disease (CARD), of whom 10 had the mild cardiac form (CARD 1) and 10 the severe cardiac form (CARD 2), and 20 patients with the indeterminate form (IND), were selected at the Chagas Disease Unit of the Oswaldo Cruz University Hospital, University of Pernambuco, Recife, Pernambuco, Brazil. The PBMCs of these individuals were cultured in the presence of CRA or FRA for 3 days and IL-10 and IFN-γ gene expression was evaluated by detection of its messenger RNA using Real Time Quantitative PCR. Although no significant difference was observed between the groups of individuals studied, we found that most patients with IND displayed high levels of IFN-γ gene expression, while the majority of patients with CARD 1 presented high levels of IL-10. The results of this study thus highlight the important role that inflammatory cytokines play in patients with the IND group controlling for parasite replication, and that anti-inflammatory cytokines play in determining susceptibility to progression to symptomatic clinical forms of the disease.

Highly effective serodiagnosis for Chagas' disease

Many proteins of Trypanosoma cruzi, the causative agent of Chagas' disease, contain characteristic arrays of highly repetitive immunogenic amino acid motifs. Diagnostic tests using these motifs in monomeric or dimeric form have proven to provide markedly improved specificity compared to conventional tests based on crude parasite extracts. However, in many cases the available tests still suffer from limited sensitivity. In this study we produced stable synthetic genes with maximal codon variability for the four diagnostic antigens, B13, CRA, TcD, and TcE, each containing between three and nine identical amino acid repeats. These genes were combined by linker sequences encoding short proline-rich peptides, giving rise to a 24-kDa fusion protein which was used as a novel diagnostic antigen in an enzyme-linked immunosorbent assay setup. Validation of the assay with a large number of well-characterized patient sera from Bolivia and Brazil revealed excellent diagnostic performance. The high sensitivity of the new test may allow future studies to use blood collected by finger prick and dried on filter paper, thus dramatically reducing the costs and effort for the detection of T. cruzi infection.

Diagnosis of Chagas disease: what has been achieved? What remains to be done with regard to diagnosis and follow up studies?

In the acute phase and in the chronic forms of Chagas disease, the etiological diagnosis may be performed by detection of the parasite using direct or indirect parasitological methods and by the presence of antibodies in the serum by way of serological tests. Several techniques are easily available, ranging from the simplest wet smear preparation to immuno-enzymatic assays with recombinant antigens that will meet most diagnostic needs. Other tests under evaluation include a molecular test using polymerase chain reaction, which has shown promising results and may be used as a confirmatory test both in the acute and chronic phases of the disease. Better rapid tests are needed for diagnosis, some of which are already under evaluation. Additionally, there is a need for tools that can identify patients cured shortly after specific treatment. Other needs include a marker for prognosis and early diagnosis of congenital transmission.

Comparison of recombinant Trypanosoma cruzi peptide mixtures versus multiepitope chimeric proteins as sensitizing antigens for immunodiagnosis

The aim of this work was to determine the best strategy to display antigens (Ags) on immunochemical devices to improve test selectivity and sensitivity. We comparatively evaluated five Trypanosoma cruzi antigenic recombinant peptides, chose the three more sensitive ones, built up chimeras bearing these selected Ags, and systematically compared by enzyme-linked immunosorbent assay the performance of the assortments of those peptides with that of the multiepitope constructions bearing all those peptides lineally fused. The better-performing Ags that were compared included peptides homologous to the previously described T. cruzi flagellar repetitive Ag (here named RP1), shed acute-phase Ag (RP2), B13 (RP5), and the chimeric recombinant proteins CP1 and CP2, bearing repetitions of RP1-RP2 and RP1-RP2-RP5, respectively. The diagnostic performances of these Ags were assessed for discrimination efficiency by the formula +OD/cutoff value (where +OD is the mean optical density value of the positive serum samples tested), in comparison with each other either alone, in mixtures, or as peptide-fused chimeras and with total parasite homogenate (TPH). The discrimination efficiency values obtained for CP1 and CP2 were 25% and 52% higher, respectively, than those of their individual-Ag mixtures. CP2 was the only Ag that showed enhanced discrimination efficiency between Chagas' disease-positive and -negative samples, compared with TPH. This study highlights the convenience of performing immunochemical assays using hybrid, single-molecule, chimeric Ags instead of peptide mixtures. CP2 preliminary tests rendered 98.6% sensitivity when evaluated with a 141-Chagas' disease-positive serum sample panel and 99.4% specificity when assessed with a 164-Chagas' disease-negative serum sample panel containing 15 samples from individuals infected with Leishmania spp.

Cellular immune response from Chagasic patients to CRA or FRA recombinant antigens of Trypanosoma cruzi

We propose to analyze the relation between the cellular immune response of Chagas' disease patients after in vitro stimulation of peripheral blood mononuclear cells (PBMC) with recombinant antigens cytoplasmatic repetitive antigen (CRA) or flagellar repetitive antigen (FRA) of T. cruzi and the chronic clinical forms of disease. Cells were stimulated using phytohemagglutinin, CRA, FRA, or a soluble antigen of Epimastigota (Ag-Epi) for 24 hr, 72 hr, or 6 days. The proliferation of cells was evaluated after 6 days of culture by quantification of incorporated 3H-thymidine. Cytokines were measured in the supernatants obtained after 24 hr (tumor necrosis factor [TNF]-alpha and interleukin [IL]-4), 72 hr (IL-10), and 6 days (interferon [IFN]-gamma) using enzyme-linked immunosorbent assay (ELISA). Cells of the Chagas patients stimulated with the recombinant antigens exhibited higher proliferation responses compared with that of non-Chagas (NC) individuals. However, when proliferation was compared between patients with the cardiac form (CF) or indeterminate form (IF), it was not possible to establish a difference in the response. So far as the cytokines secreted in the culture supernatants after stimulation in vitro with T. cruzi antigens were concerned, the results showed that CRA, as well as Epi-Ag, were able to stimulate the production of TNF-alpha and IFN-gamma in Chagas patients as compared with NC individuals. However, the cytokine levels after stimulation with the T. cruzi antigens were not different between the patients with CF and IF. CRA was capable of inducing a T helper type 1 (Th1) immune response, with elevated production of TNF-alpha and IFN-gamma in Chagas patients that are carriers of CF and IF clinical forms.

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.

Leishmania (Viannia) braziliensis: epidemiology of canine cutaneous leishmaniasis in the State of Paraná (Brazil)

The present study examines the role that dogs play in the maintenance of the Leishmania cycle in the State of Paraná, Southern Brazil. Dogs were examined in three regions where cutaneous leishmaniasis is endemic or epidemic (R1-Vale da Ribeira; R2-Central region of Paraná State and R3-Northern region). To determine serum prevalence rates ELISA was used. In regions endemic for Trypanosoma cruzi (R1 and R3), serum from dogs seroreactive towards Leishmania antigen was subjected to T. cruzi adsorption in order to eliminate cross-reaction with common antigen epitopes. Concomitantly, dogs with cutaneous lesions were biopsied to isolate and identify parasites using RAPD. Leishmania were classified by the phenetic method using the Jaccard coefficient of similarity, and grouped by Unweighted Pair-Group Method using an Arithmetic Average (UPGMA). A total of 410 dogs were studied. In R1 (Vale da Ribeira) 159 dogs were evaluated of which 10 had anti-Leishmania antibody. In R2 (Central Paraná), 39 animals were examined of which 8 were seropositive. In R3 (the North) 212 dogs were evaluated of which 39 animals were seropositive. Thirteen dogs had cutaneous lesions and the parasites were isolated from a dog with mucocutaneous lesion in R1, two animals with simple skin lesions in R2 and 10 dogs with multiple lesions in R3. The identification of the parasite by molecular methods showed it to be L. (Viannia) braziliensis. Based on this information, the role of domestic dogs in Leishmania infection of cutaneous leishmaniasis in Paraná is discussed.

Diagnosis of canine visceral leishmaniasis: biotechnological advances

Human visceral leishmaniasis (HVL) is endemic in the tropical and sub-tropical regions of Africa, Asia, the Mediterranean, Southern Europe and South and Central America, with approximately 500,000 new cases reported annually. As dogs are considered to be the major reservoirs for HVL, the accurate diagnosis of disease in these animals is important. Diagnosis of canine visceral leishmaniasis (CVL) is performed mainly by direct parasitological methods that can yield false-negative results, either because of the very low number of Leishmania spp. organisms in clinical samples (bone marrow and lymph nodes) or because morphological identification is difficult. In addition, these methods are invasive. Conventional serological techniques are limited by cross-reactivity with other parasitic diseases and because several technical procedures have not been standardised. The development of polymerase chain reaction based approaches and immunoassays based on the use of recombinant antigens aimed at improving the sensitivity and specificity of CVL diagnosis is discussed.

Assessment of chemiluminescence and PCR effectiveness in relation to conventional serological tests for the diagnosis of Chagas' disease

While testing 414 sera for the diagnosis of Chagas' disease, the conventional reactions of indirect hemagglutination, indirect immunofluorescence and the immunosorbent assay showed a sensitivity of 95.7%, 100% and 98.2% and a specificity of 98%, 98% and 96.4%, respectively, and an excellent association using Fisher's exact test. Chemiluminescence presented 100% sensitivity and 89.6% specificity, while PCR showed 100% specificity and 1.2% sensitivity. It is believed that the three conventional serological reactions are still adequate for diagnosing Chagas' disease.

The flagellar attachment zone of Trypanosoma cruzi epimastigote forms

The flagellar attachment zone (FAZ) is an adhesion region of Trypanosoma cruzi epimastigote forms where the flagellum emerges from the flagellar pocket and remains attached to the cell body. This region shows a junctional complex which is formed by a linear series of apposed macular structures that are separated by amorphous material and clusters of intramembranous particles. Two protein groups appear to be important in the FAZ region: a membrane glycoprotein of 72kDa and several high molecular weight proteins. To gain a better understanding of the FAZ region, we compared wild-type Y strain T. cruzi epimastigotes with a mutant cell in which the 72-kDa surface glycoprotein (Gp72), involved in cell body-flagellum adhesion, had been deleted by target gene replacement. Using immunofluorescence confocal microscopy and electron microscopy techniques to analyze the FAZ region the results suggest that, in the absence of Gp72, other proteins involved in the formation of FAZ remain concentrated in the flagellar pocket region. The analysis of a 3-D reconstruction model of wild-type epimastigotes showed that the endoplasmic reticulum and mitochondrion are in intimate association with FAZ, in contrast to the null mutant cells where the endoplasmic reticulum was not visualized.

Otimização de ELISA empregando a proteína Tc85-11 e planejamento fatorial

A doença de Chagas é causada pelo Trypanosoma cruzi (T. cruzi) e a detecção de anticorpos anti-T. cruzi no soro é um método para diagnosticar a doença. Neste trabalho, ELISA indireto foi otimizado para a detecção de anticorpos no soro de pacientes com doença de Chagas empregando a proteína Tc85-11 (Ag) da superfície do parasita tripomastigota. Na otimização das condições experimentais foi aplicado planejamento fatorial completo para os parâmetros tempo de incubação, diluições do Ag (0,08 mg mL-1), anticorpo primário (Ac) e anti-IgG conjugada com a peroxidase (Ac*). Os melhores resultados foram obtidos nas seguintes condições: 0,14 mg Ag/poço, 60 min para o tempo de incubação, diluições de 1:35 e 1:1000 para Ac e Ac*, respectivamente. O valor do limiar de reatividade ("cut off") foi A450nm = 0,371. O ELISA indireto foi aplicado em amostras de soros de pacientes infectados com doença de Chagas e pacientes com diferentes doenças sistêmicas. A proteína Tc85-11, a qual está envolvida com a adesão do parasita na célula hospedeira, é também apropriada para o diagnóstico sorológico da doença de Chagas.

Immunization with cytoplasmic repetitive antigen and flagellar repetitive antigen of Trypanosoma cruzi stimulates a cellular immune response in mice

In previous studies, we demonstrated that CRA and FRA recombinant proteins, used for diagnosis of Chagas' disease, elicited a humoral immune response in susceptible and resistant mice. To understand better the immune response to these proteins, we have evaluated, the cellular immune response in CRA- and in FRA-immunized BALB/c and C57BL/6 mice. A specific cellular lymphoproliferative response was observed in both strains of mice. Spleen cell cultures mainly from CRA-immunized C57BL/6 and FRA-immunized BALB/c mice produced high levels of IFN-y, indicating the induction of a Type 1 immune response. Regarding the T cell subsets, CD4+ T cells were the major source of IFN-y in CRA- and FRA-immunized mice. These results suggest that CRA and FRA are important immunogens in inducing a Type 1 immune response and that they may be considered as potential vaccine antigens.

Humoral and cellular immune responses in BALB/c and C57BL/6 mice immunized with cytoplasmic (CRA) and flagellar (FRA) recombinant repetitive antigens, in acute experimental Trypanosoma cruzi infection

In previous studies, cytoplasmic repetitive antigen (CRA) and flagellar repetitive antigen (FRA) proteins induced specific humoral and cellular immune responses in susceptible and resistant mice in the absence of Trypanosoma cruzi infection with a significant induction of the Interferon-gamma (IFN-gamma) production in those animals. In this follow-up paper, the immunostimulatory and protective effects of these proteins were evaluated by immunizing with CRA or FRA antigens, BALB/c and C57BL/6 mice and challenging with a T. cruzi (Y strain). Both proteins induced humoral response with high levels of IgG isotypes as well as cellular immunity with high levels of IFN-gamma when compared to controls. However, the lymphocyte proliferative response was minimal. The survival rate at 30 days post-infection was significant in CRA (60%) or FRA (50%)--immunized BALB/c mice and CRA (83.3%)--immunized C57BL/6 mice. Taken as a whole these findings indicate that CRA and FRA are immunogenic and potentially important for protective immunity.

The validity of serologic tests for Trypanosoma cruzi and the effectiveness of transfusional screening strategies in a hyperendemic region

BACKGROUND

This study aims at obtaining unbiased estimates of the sensitivity and specificity of existing screening tests for Trypanosoma cruzi and at simulating the effectiveness of alternative screening strategies at different prevalence rates.

STUDY DESIGN AND METHODS

A systematic random sample of 400 was taken from 1200 banked serum samples of donors screened between August 1998 and January 1999 in Santa Cruz, Bolivia. Samples were tested with indirect hemagglutination test (IHA), indirect immunofluorescence assay (IFA), and four enzyme-linked immunosorbent assays (ELISAs). Sensitivity and specificity of tests were estimated through latent class analysis.

RESULTS

The sensitivity of individual tests ranged from 96.5 to 100 percent, and their specificity from 87.0 to 98.9 percent. Combinations of two tests used in parallel would, even at 40 percent prevalence, only miss approximately 1 infected unit per 10,000 screened. At 5 percent prevalence, however, they would yield 75 to 120 false-positive units per 1000 units screened. Parallel testing with IHA plus ELISA or with IHA plus IFA is marginally more cost-effective, compared to single IHA testing, than single ELISA or single IFA testing, regardless of the T. cruzi prevalence.

CONCLUSIONS

Routine blood donor screening for T. cruzi with a single test results in unacceptable numbers of false-negative samples in highly endemic areas or in at risk population groups. Adding a second test seems mandatory, but which one to choose depends on local cost components and feasibility.

On the possibility of autochthonous Chagas disease in Roraima, Amazon region, Brazil, 2000-2001

Chagas disease has been almost entirely eradicated from the arid zones in Central and Northeastern Brazil where rare or no autochthonous cases have been reported. However, in the last 10 years the disease has increasingly been registered in the Amazon Region. Aiming to investigate the possibility of the occurrence of autochthonous cycle of Chagas disease in Roraima, triatomine collections, vectorial susceptibility studies (this one to be shown elsewhere), parasitological and serological analyses were conducted in three agricultural settlement areas (Rorainópolis, Passarão Project and Ilha Community). Blood-donor candidates were also investigated. This is the first epidemiological survey on Chagas disease conducted in agricultural settlements in Roraima. Triatomine species found were Triatoma maculata, Rhodnius pictipes, Rhodnius robustus and Panstrongylus geniculatus. Trypanosoma cruzi detection analyses included xenodiagnosis, indirect immunofluorescence, indirect hemaglutination, ELISA and kinetoplast PCR amplification. Natural triatomine infection was not found in intestinal contents. Twenty-five adult settlers (1.4% out of 1821, all > 15 year-old, 20 migrants) presented anti-T. cruzi antibodies. Two migrant settlers (from Minas Gerais and Maranhão) tested positive for more than two serological tests, besides either being positive for xenodiagnosis or PCR. Results show that Chagas disease is not endemic in the areas studied. However, all elements of the transmission cycle are present, demanding for an adequate and continuous vigilance.

Serodiagnosis of chronic and acute Chagas' disease with Trypanosoma cruzi recombinant proteins: results of a collaborative study in six Latin American countries

An enzyme-linked immunosorbent assay to diagnose Chagas' disease by a serological test was performed with Trypanosoma cruzi recombinant antigens (JL8, MAP, and TcPo). High sensitivity (99.4%) and specificity (99.3%) were obtained when JL8 was combined with MAP (JM) and tested with 150 serum samples from chagasic and 142 nonchagasic individuals. Moreover, JM also diagnosed 84.2% of patients in the acute phase of T. cruzi infection.

Impedimetric evaluation for diagnosis of Chagas’ disease: antigen–antibody interactions on metallic eletrodes

A polypeptide chain formed by recombinant antigens, cytoplasmic repetitive antigen (CRA) and flagellar repetitive antigen (FRA) (CF-Chimera) of Trypanosoma cruzi, was adsorbed on gold and platinum electrodes and investigated by electrochemical impedance spectroscopy on phosphate buffer saline solutions (PBS) containing a redox couple. It was found that the adsorption is strongly sensitive to the oxide layer on the electrode surface. In the majority of the experiments the antigens retained their activity as observed through their interaction with sera from chronic chagasic patients. The results expressed in terms of the charge transfer resistance across the interface, indicate the viability of using the impedance methodology for the development of a biosensor for serological diagnosis of Chagas' disease.

Antibody isotype responses in Balb/c mice immunized with the cytoplasmic repetitive antigen and flagellar repetitive antigen of Trypanosoma cruzi

In the present report we analyzed the levels of IgG1, IgG2a, IgG2b and IgG3 isotypes from Balb/c mice immunized with cytoplasmic repetitive antigen (CRA), and flagellar repetitive antigen (FRA) of Trypanosoma cruzi. The immunization was done by subcutaneous route three times (20 days apart) and the analysis was performed 14 days after each treatment. CRA-immunized mice produced high levels of all IgG isotypes, mainly IgG3 and IgG1. FRA-immunization elicited only high levels of IgG1.

Chagas' disease diagnosis: comparative analysis of recombinant ELISA with conventional ELISA and the haemagglutination test

BACKGROUND AND OBJECTIVES

Serological screening for Chagas' disease in the blood banks of South America is carried out by using two different assays that generally show a high number of inconclusive results. To establish a combination of two tests that can minimize the number of inconclusive results, we compared a recombinant enzyme-linked immunosorbent assay (ELISA) with two conventional tests.

MATERIALS AND METHODS

Serum samples from chagasic patients (n = 112), from non-chagasic individuals (n = 143) and from patients with other diseases (n = 32) were tested using three assays: recombinant ELISA (Rec-ELISA); conventional ELISA (Con-ELISA); and the indirect haemagglutination (IHA) test.

RESULTS

When we evaluated the data by matching the Rec-ELISA and the IHA test, 52 inconclusive results were obtained. When Rec-ELISA and Con-ELISA were matched, only four inconclusive results were observed.

CONCLUSIONS

Our investigation indicates that the use of two ELISAs with different antigen preparations provides an effective test combination for blood bank screening of Chagas' disease.

Evaluation of the immune response to CRA and FRA recombinant antigens of Trypanosoma cruzi in C57BL/6 mice

Humoral and cellular immune responses were evaluated in 44 C57BL/6 mice immunized with the Trypanosoma cruzi recombinant antigens CRA and FRA. Both antigens induced cutaneous immediate-type hypersensitivity response. The levels of IgG1, IgG2a, IgG2b and IgG3 were high in CRA immunized mice. IgG3 was the predominant isotype. Although no difference in antibody levels was observed in FRA-immunized mice when compared to control mice, both antigens were able to induce lymphoproliferation in immunized mice. Significant differences were observed between incorporation of [ H]- thymidine by spleen cell stimulated in vitro with CRA or FRA and the control group. These results suggest that CRA and FRA could be involved in mechanisms of resistance to Trypanosoma cruzi infection.

Purification of the 67-kDa lectin-like glycoprotein of Trypanosoma cruzi, LLGP-67, and its evaluation as a relevant antigen for the diagnosis of human infection

In the present work we propose a simple method for affinity purification of the 67-kDa lectin-like glycoprotein (LLGP-67) from Trypanosoma cruzi, the causative agent of Chagas' disease. The LLGP-67, which presents galactose binding activity and participates in the host cell recognition process, was previously purified by methods based on its interaction with galactose residues on erythrocytic membranes. We describe herein results showing that this protein can be purified from T. cruzi in a direct way using non-derivatized agarose as a chromatographic ligand. We also demonstrate the relevance of LLGP-67 as an antigen for human diagnosis of chagasic infection. Sensitivity and specificity for this antigen were calculated, being 98 and 98.11% respectively.

An improved serodiagnostic test for Chagas' disease employing a mixture of Trypanosoma cruzi recombinant antigens

BACKGROUND

Blood transfusion is one of the most important transmission routes of Chagas' disease, a major parasitic infection in Latin America. Therefore, screening for antibodies to Trypanosoma cruzi is mandatory in blood banks in South America. Most of the commercial serologic tests employ epimastigote antigens and show a high number of inconclusive and false-positive results, with high economic and social costs.

STUDY DESIGN AND METHODS

An ELISA using a mixture of three T. cruzi recombinant antigens, B13, 1F8, and H49 (mix-ELISA), was evaluated, first with a panel of well-characterized sera from 617 patients with Chagas' disease and 277 nonchagasic individuals, living in nine countries of South and Central America. Subsequently, the mix-ELISA was evaluated with 451 samples, from an endemic area of Brazil (Goiás), that were rejected from several blood banks because they presented discrepant results by two commercially available kits (indirect immunofluorescence assay, indirect hemagglutination assay, and/or ELISA).

RESULTS

The mix-ELISA exhibited 99.7 percent sensitivity and 98.6 percent specificity in the first evaluation with the 894 samples. In the second evaluation, 451 sera that had discrepant results in the first screening for Chagas' disease were further analyzed with the mix-ELISA. Upon consideration of the consensus results obtained with the trypomastigote excreted-secreted antigens blot test, a confirmatory test for Chagas' disease, the mix-ELISA led to a reduction in 99.6 percent in the number of discordant sera.

CONCLUSION

The combination of three T. cruzi recombinant antigens in a multiantigen immunoassay was highly sensitive and specific for Chagas' disease diagnosis. It is proposed that it can be applicable in blood bank screening in conjunction with the conventional serologic tests.

Trypanosoma cruzi recombinant complement regulatory protein: a novel antigen for use in an enzyme-linked immunosorbent assay for diagnosis of Chagas' disease

Currently, diagnosis of Chagas' disease is based on serological methods, but due to the high occurrence of inconclusive results, more reliable methods are needed. The use of recombinant antigens for serodiagnosis of Chagas' disease is recommended in order to increase the sensitivity and specificity of the serological tests. The Trypanosoma cruzi complement regulatory protein (CRP) is a surface glycoprotein present on the trypomastigote forms of the parasite, and the recombinant CRP (rCRP) was cloned in a mammalian expression system and purified by affinity chromatography. The purified recombinant protein was used as an antigen in an enzyme-linked immunosorbent assay (rCRP ELISA) in order to verify its sensitivity and specificity compared with other established methods. In this evaluation, a panel of 184 serum samples distributed among chronic chagasic patients (n = 65), blood bank donors (n = 100), and patients infected with Leishmania spp. (n = 19) was used. The sensitivity and specificity of the rCRP ELISA were 100% when compared to conventional serology and complement-mediated lysis tests from these groups. When hemoculture and PCR tests were evaluated for diagnosis of chronic chagasic patients, using the rCRP ELISA as a reference test, the positivities were found to be 64.62 and 81.54%, respectively, showing a higher degree of sensitivity of the test. The data demonstrate that rCRP ELISA was able to discriminate between chronic chagasic patients and nonchagasic individuals, such as blood donors and patients with leishmaniasis. Thus, the rCRP is an excellent antigen for use in Chagas' disease diagnosis, due to the absence of false-negative or false-positive results.

Use of the EIE-recombinant-Chagas-biomanguinhos kit to monitor cure of human Chagas' disease

We used the EIE-Recombinant-Chagas-Biomanguinhos kit (EIE-Rec kit) developed by the Oswaldo Cruz Foundation, Brazil, to monitor cure of chagasic patients who were treated during the acute phase of T. cruzi infection. Treated patients were previously studied by parasitological and serological tests and classified as cured patients (CP) (n = 10), dissociated patients (DP) (n = 6), and noncured patients (NCP) (n = 6). When sera of these patients were assayed by EIE-Rec kit all sera from NCP and all sera from CP showed positive and negative reactions, respectively. These results were in full agreement with those obtained previously by the classical tests. Two DP showed a positive reaction; the remaining four displayed a negative reaction, similar to that observed in sera from nonchagasic (NCh) individuals, and could therefore be considered CP. Our results suggest that the EIE-Rec kit could be used to monitor the efficacy of Chagas' disease treatment.

Enzyme-linked immunosorbent assay for serological diagnosis of Chagas' disease employing a Trypanosoma cruzi recombinant antigen that consists of four different peptides

Serological tests to detect Trypanosoma cruzi antibodies have been used for screening blood donors, for epidemic studies, and for diagnosis of probably infected persons. Among different tests, the enzyme-linked immunosorbent assay (ELISA) with total, semipurified, or synthetic antigens has been widely used, mainly due to its easy automation. Aiming to improve serological studies concerning Chagas' disease, we have developed and evaluated a new test, the TcF-ELISA, using an artificially engineered recombinant antigen, which contains tandem sequences of different T. cruzi-specific peptides. The sensibility of the TcF-ELISA was determined with 101 serum samples from chagasic patients well-defined by clinical and epidemiological criteria. The specificity was determined with 39 serum samples from leishmaniasis or kala-azar patients and 150 serum samples from nonchagasic blood donors from Sao Paulo, Brazil. The TcF-ELISA showed 100% sensitivity and 98.94% of specificity. Compared with conventional ELISA (with semipurified T. cruzi epimastigote antigens), the TcF-ELISA showed advantages; for example, it distinguishes better between reagent and nonreagent serum and provides better precision and a lower occurrence of leishmaniasis cross-reactions. Our studies demonstrate high reproducibility between two different lots of the TcF ELISA and its applicability for the serological diagnosis of Chagas' disease.

Antibodies to an epitope from the Cha human autoantigen are markers of Chagas' disease

Chagas' disease is a prevalent disease in South America that is thought to have an autoimmune etiology. We previously identified human Cha as a new autoantigen recognized by chagasic sera. Those sera recognized an epitope spanning amino acids 120 to 129 of Cha, named R3. In the present study we have used the synthetic R3 peptide for the detection of serum immunoglobulin G antibodies from patients at different stages of Chagas' disease, including a therapeutically treated group. The immunoreactivity with R3 by enzyme-linked immunosorbent assay (ELISA) showed 92.4% sensitivity and 100% specificity for Chagas' disease sera. This sensitivity and specificity were higher than for any other autoantigen described to date. No anti-R3 antibodies were detected in sera from Leishmania-infected or idiopathic dilated cardiomyopathy patients or healthy controls from the same areas. Moreover, anti-R3 antibody reactivity detected by ELISA correlated with conventional serological tests as indirect immunofluorescence and ELISA assays with Trypanosoma cruzi extracts and other diagnostic tests as indirect hemagglutination. The levels of anti-R3 antibodies increased with progression and symptomatology of Chagas' disease. More interestingly, a statistically significant fall in anti-R3 antibody titer was observed in patients treated with antiparasitic drugs. Those results suggest that the presence of anti-R3 antibodies is a highly specific marker of Chagas' disease and that R3 ELISA could be helpful in the diagnosis and monitoring of this disease.

Excretory-secretory antigens of Trypanosoma cruzi are potentially useful for serodiagnosis of chronic Chagas' disease

The reactivities of sera from chronic chagasic patients against the trypomastigote excreted-secreted antigens (TESA) of Trypanosoma cruzi strains with different biodemes were analyzed by TESA-blot and TESA-enzyme-linked immunosorbent assay (ELISA). Although both tests presented high sensitivity and specificity, TESA-ELISA is more appropriate for screening a larger number of samples.

Chagas disease: recombinant Trypanosoma cruzi antigens for serological diagnosis

Diagnosis of individuals infected by Trypanosoma cruzi is performed mainly by serological tests using crude antigens, which might crossreact with other infections. In the past ten years, many recombinant T. cruzi proteins and synthetic peptides have been described, and some are already on the market. Managers of laboratories and blood banks need to make decisions on a cost-benefit basis whether to include these new-generation tests. Here, we indicate antigens that are likely to prove most useful.

Serodiagnosis of chronic Chagas infection by using EIE-Recombinant-Chagas-Biomanguinhos kit

A kit based on an enzyme immunoassay, EIE-Recombinant-Chagas-Biomanguinhos, developed by the Oswaldo Cruz Foundation, was evaluated for the serodiagnosis of chronic Chagas disease. Evaluation was performed with 368 serum samples collected from individuals living in an endemic area for Chagas disease: 131 patients in the chronic phase with confirmed clinical, epidemiological, and serological diagnosis (indirect immunofluorescence, indirect hemagglutination or enzyme-linked immunosorbent assay) and 237 nonchagasic seronegative individuals were considered negative control. The EIE-Recombinant-Chagas-Biomanguinhos kit showed high sensitivity, 100% (CI 95%: 96.4-100%) and high specificity, 100% (CI 95%: 98-100%). The data obtained were in full agreement with clinical and conventional serology data. In addition, no cross-reaction was observed with sera from patients with cutaneous (n=14) and visceral (n=3) leishmaniasis. However, when these sera were tested by conventional serological assays for Chagas disease, cross-reactions were detected in 14.3% and 33.3% of the patients with cutaneous and visceral leishmaniasis, respectively. No cross-reactions were observed when sera from nonchagasic seronegative patients bearing other infectious disease (syphilis, n=8; HTLV, n=8; HCV, n=7 and HBV, n=12) were tested. In addition, sera of patients with inconclusive results for Chagas disease by conventional serology showed results in agreement with clinical evaluation, when tested by the kit. These results are relevant and indicate that the referred kit provides a safe immunodiagnosis of Chagas disease and could be used in blood bank screening.