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

Development and Application of an ELISA Assay Using Excretion/Secretion Proteins from Epimastigote Forms of T. cruzi (ESEA Antigens) for the Diagnosis of Chagas Disease

An indirect enzyme-linked immunoabsorbent assay (ELISA) for Trypanosoma cruzi was developed using epimastigote secretion/excretion proteins (ESEA antigens) obtained from axenic culture supernatants. A panel of 120 serum samples from subjects with confirmed Chagas disease (n = 50), healthy controls (n = 50), and patients with other parasitic diseases (n = 20) was used to evaluate the new ESEA-based ELISA (ELISA(ESEA)). This new test had excellent sensitivity (98%) and acceptable specificity (88%). Cross-reactivity was observed largely in sera from subjects with Leishmania and Ascaris infections. Using Western blotting and epimastigotes from two distinct T. cruzi isolates, several polypeptide bands with molecular masses ranging from 50 to 220 kDa were detected in pooled chagasic sera. However, the band pattern for each isolate was different. These data suggest that an inexpensive and technically simple ELISA based on ESEA antigens is a promising new tool for the diagnosis of Chagas disease.

ELISA versus PCR for diagnosis of chronic Chagas disease: systematic review and meta-analysis

Background

Most current guidelines recommend two serological tests to diagnose chronic Chagas disease. When serological tests are persistently inconclusive, some guidelines recommend molecular tests. The aim of this investigation was to review chronic Chagas disease diagnosis literature and to summarize results of ELISA and PCR performance.

Methods

A systematic review was conducted searching remote databases (MEDLINE, LILACS, EMBASE, SCOPUS and ISIWeb) and full texts bibliography for relevant abstracts. In addition, manufacturers of commercial tests were contacted. Original investigations were eligible if they estimated sensitivity and specificity, or reliability -or if their calculation was possible - of ELISA or PCR tests, for chronic Chagas disease.

Results

Heterogeneity was high within each test (ELISA and PCR) and threshold effect was detected only in a particular subgroup. Reference standard blinding partially explained heterogeneity in ELISA studies, and pooled sensitivity and specificity were 97.7% [96.7%-98.5%] and 96.3% [94.6%-97.6%] respectively. Commercial ELISA with recombinant antigens studied in phase three investigations partially explained heterogeneity, and pooled sensitivity and specificity were 99.3% [97.9%-99.9%] and 97.5% [88.5%-99.5%] respectively. ELISA's reliability was seldom studied but was considered acceptable. PCR heterogeneity was not explained, but a threshold effect was detected in three groups created by using guanidine and boiling the sample before DNA extraction. PCR sensitivity is likely to be between 50% and 90%, while its specificity is close to 100%. PCR reliability was never studied.

Conclusions

Both conventional and recombinant based ELISA give useful information, however there are commercial tests without technical reports and therefore were not included in this review. Physicians need to have access to technical reports to understand if these serological tests are similar to those included in this review and therefore correctly order and interpret test results. Currently, PCR should not be used in clinical practice for chronic Chagas disease diagnosis and there is no PCR test commercially available for this purpose. Tests limitations and directions for future research are discussed.

Role of the gp85/trans-sialidase superfamily of glycoproteins in the interaction of Trypanosoma cruzi with host structures

Invasion of mammalian cells by T. cruzi trypomastigotes is a multi-step and complex process involving several adhesion molecules, signaling events and proteolytic activities. From the blood to the cell target in different tissues the parasite has to interact with different cells and the extracellular matrix (ECM). The review focus on the role of the gp85/ trans-sialidase superfamily members in the interaction of the parasite with the host cell, particularly with ECM components, with emphasis on the significant variability among the ligands and receptors involved. Use of the SELEX technique to evolve nuclease-resistant RNA aptamers for receptor identification is briefly discussed.

Design, construction, and evaluation of a specific chimeric antigen to diagnose chagasic infection

Chagas' disease is routinely diagnosed by detecting specific antibodies (Abs) using serological methods. The methodology has the drawback of potential cross-reactions with Abs raised during other infectious and autoimmune diseases (AID). Fusion of DNA sequences encoding antigenic proteins is a versatile tool to engineer proteins to be used as sensitizing elements in serological tests. A synthetic gene encoding a chimeric protein containing the C-terminal region of C29 and the N-terminal region of TcP2beta was constructed. A 236-serum panel, composed of 104 reactive and 132 nonreactive sera to Chagas' disease, was used to evaluate the performance of the chimera. Among the nonreactive sera, 65 were from patients with AID (systemic lupus erythematosus and rheumatoid arthritis) or patients infected with Leishmania brasiliensis, Brucella abortus, Streptococcus pyogenes, or Toxoplasma gondii. The diagnostic performances of the complete TcP2beta (TcP2betaFL) and its N-terminal region (TcP2betaN) were evaluated. TcP2betaFL showed unspecific recognition toward leishmaniasis (40%) and AID Abs (58%), while TcP2betaN showed no unspecific recognition. The diagnostic utility of the chimera was evaluated by analyzing reactivity and comparing the results with those obtained with TcP2betaN. The chimera reactivity was higher than that of the peptide fractions (0.874 versus 0.564 optical density, P = 0.0017). The detectability and specificity were both 100% for the whole serum panel tested. We conclude that the obtained chimera shows an improved selectivity and sensitivity compared with other ones previously reported, therefore displaying an optimized performance for Trypanosoma cruzi infection diagnosis.

Purified excreted-secreted antigens from Trypanosoma cruzi trypomastigotes as tools for diagnosis of Chagas' disease

There is currently no "gold standard" test for the diagnosis of late-stage Chagas' disease. As a result, protection of the blood supply in areas where Chagas' disease is endemic remains problematic. A panel of 709 serum samples from subjects with confirmed Chagas' disease (n = 195), healthy controls (n = 400), and patients with other parasitic diseases (n = 114) was used to assess enzyme-linked immunosorbent assays (ELISAs) based on a concentrated extract of excretory-secretory antigens from either Brazil or Tulahuen strain Trypanosoma cruzi trypomastigotes (total trypomastigote excretory-secretory antigens [TESAs]). The total TESA-based assays had excellent overall sensitivity (100%) and specificity (>94%), except for cross-reactivity with Leishmania-infected sera. In an attempt to increase the specificity of the assay, immunoaffinity chromatography was used to purify the TESA proteins (TESA(IA) proteins). By Western blotting, a series of polypeptide bands with molecular masses ranging from 60 to 220 kDa were recognized by pooled sera positive for Chagas' disease. An ELISA based on TESA(IA) proteins had a slightly lower sensitivity (98.6%) but an improved specificity (100%) compared to the sensitivity and specificity of the total TESA protein-based ELISAs. A 60-kDa polypeptide was identified as a major contributor to the cross-reactivity with Leishmania. These data suggest the need for field validation studies of TESA- and TESA(IA)-based assays in regions where Chagas' disease is endemic.

Use of full-length recombinant calflagin and its c fragment for improvement of diagnosis of Trypanosoma cruzi infection

Serological diagnosis of Trypanosoma cruzi infection is hampered by issues related to test specificity due to the cross-reactivity of most antigens with proteins of related parasites such as Leishmania spp. The recombinant calflagins are considered relevant antigens for the diagnosis of infection by Trypanosoma cruzi. In the present work, we describe two genes coding for putative calflagins in Leishmania major with the N-terminal moieties presenting high similarity with T. cruzi genes. This fact raised questions about their role in some cross-recognition of this antigen by sera from Leishmania spp.-infected individuals. The complete T. cruzi calflagin and two fragments of the protein, consisting of 146 amino acids of the N-terminal and 65 amino acids of the C-terminal regions, were expressed and evaluated against a panel of sera, which included well-characterized samples from T. cruzi, and Leishmania-infected patients. We were able to show that sera from Leishmania (Viannia) braziliensis-infected individuals recognized the recombinant full-length calflagin. Both the N-terminal and the complete protein presented the same high sensitivity (98.5% of sera from T. cruzi-infected patients was detected) but different specificities (94% and 98%, respectively, when evaluated against sera from people not infected by T. cruzi, including 15 sera from people infected with L. braziliensis). The C-terminal fragment presented low sensitivity (70%) but 100% specificity. We propose the use of these antigens in two sequential assays to optimize the serological diagnosis of T. cruzi infection in humans in geographic areas where Leishmania spp. infection is coendemic.

The diagnostic performance of recombinant Trypanosoma cruzi ribosomal P2beta protein is influenced by its expression system

In the present work, we have determined the effect of expression vectors and their corresponding host bacteria on the antigenic performance of Trypanosoma cruzi P2beta (TcP2beta) full-length recombinant protein. The gene encoding the TcP2beta ribosomal protein was cloned in pMAL-c2 and pET-32a vectors that allow the expression of high levels of soluble fusion proteins. A panel of 32 positive and 32 negative sera was assayed with the purified proteins expressed using pMal-c2 (TcP2beta-MBP) and pET-32a (TcP2beta-TRX) vectors and with MBP and TRX purified from pMAL-c2 and pET-32a vectors, respectively. The antigenic behavior of each TcP2beta recombinant protein differed in the diagnostic performance in terms of DI(+) (93.7 for TcP2beta-MBP vs 100% for TcP2beta-TRX), in DI(-) (90.5 for TcP2beta-MBP vs 100% for TcP2beta-TRX) and in cross-reaction with negative sera. To determine if the higher reactivity of expressed pMAL-c2 protein was due to folding during protein expression or to a steric effect related to the protein adsorption at the titration plate, the reactivity of sera against soluble proteins was assessed by ELISA inhibition assays. As each soluble protein preserved its level of reactivity, we concluded that differences in reactivity were due to intrinsic characteristics of the proteins and not to differences in patterns of adsorption to the plates.