Optimized broad-range real-time PCR-based method for bacterial screening of platelet concentrates

Bacterial contamination of blood components remains a major challenge in transfusion medicine, particularly, platelet concentrates (PCs) due to the storage conditions that support bacterial proliferation. In this study, we develop a rapid, sensitive and specific real-time PCR protocol for bacterial screening of PCs. An internally controlled real-time PCR-based method was optimized and validated with our proprietary 16S Universal PCR Master Mix (IBMP/Fiocruz), which targets a conserved region of the bacterial 16S rRNA gene. Nonspecific background DNA was completely eliminated by treating the PCR Master Mix with ethidium monoazide (EMA). A lower limit of detection was observed for 10 genome equivalents with an observed Ct value of 34±1.07 in calibration curve generated with 10-fold serial dilutions of E. coli DNA. The turnaround time for processing, including microbial DNA purification, was approximately 4 hours. The developed method showed a high sensitivity with no non-specific amplification and a lower time-to-detection than traditional microbiological methods, demonstrating it to be an efficient means of screening pre-transfusion PCs.

Electrospinning induced surface activation (EISA) of highly porous PMMA microfiber mats for HIV diagnosis

Schematic of biological coupling to both dry substrate (DS) and wet substrate (WS) deposited fibers. (A) DS fibers without coupling, (B) WS fibers coupled to AbPE and GFP fluorescent proteins, (C) WS fibers assay coupled to HIV.

DNA sequencing of 13 cytokine gene fragments of Aotus infulatus and Saimiri sciureus, two non-human primate models for malaria

Aotus and Saimiri are non-human primate models recommended by the World Health Organization for experimental studies in malaria, especially for vaccine pre-clinical trials. However, research using these primates is hindered by the lack of specific reagents to evaluate immune responses to infection or vaccination. As a step toward developing molecular tools for cytokine expression studies in these species, primer pairs for 18 cytokine gene fragments were designed based on human DNA sequences and used to amplify the corresponding genes in Aotus infulatus and Saimiri sciureus genomic DNA samples. IFNγ, TNFα, LTA, IL2, IL3, IL4, IL5, IL6, IL10, IL12, IL13, CSF2 and TGFβ2 gene fragments were amplified and sequenced. Primer pairs for IL8, IL17, IL18, IL27 and MIF failed to generate amplification products. When compared to the available corresponding human and non-human primate sequences, most--except IL3 and IL4--showed identity degrees above 90%. Small variations in sequence can help to explain the failure to amplify certain genes or the amplification only at lower annealing temperatures as compared to human DNA samples for several primer pairs. The sequences made available provide the basis for designing molecular tools such as primers for real time PCR specific for A. infulatus and/or S. sciureus. The nucleotide sequences reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned accession numbers DQ985386 to DQ985389, DQ989356 to DQ989369, FJ89020 to FJ89024, and FJ89029.

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.

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.

Cloning and characterization of the metacyclogenin gene, which is specifically expressed during Trypanosoma cruzi metacyclogenesis

We isolated a gene that is differentially expressed during Trypanosoma cruzi metacyclogenesis by the representation of differential expression (RDE) method, using differentiating epimastigotes cultured in chemically defined medium. This gene, the metacyclogenin gene, encodes a 630-nucleotide mRNA that is specifically associated with the polysomes of epimastigotes allowed to differentiate for 24 h. We sequenced and characterized the metacyclogenin gene and found that there were at least three copies of the gene organized into tandem 2.8 kb repeats in the genome of T. cruzi Dm28c. We analyzed the repeats and found that they contained two other genes, one encoding tryparedoxin peroxidase and the other encoding a 0.6 kb mRNA (named associated gene or AG) with sequences showing no significant similarity to those in the GenBank database. Northern blot analysis of polysomal RNA extracted from replicating and differentiating epimastigotes showed that metacyclogenin and AG genes displayed similar patterns of expression. Their products were detected only in differentiating epimastigotes, whereas tryparedoxin peroxidase was detected only in the polysomal RNA fraction of replicating and differentiating epimastigotes. In Northern blots of total RNA from differentiating and replicating epimastigotes, the genes studied were detected in both cell populations. The differential expression of the metacyclogenin gene was confirmed by immunocytochemistry studies showing that the protein is detected only in differentiating (adhered) epimastigote. The results suggest that mRNA mobilization to polysomes is an important mechanism in the regulation of gene expression in T. cruzi.

Trypanosoma cruzi: a gene family encoding chitin-binding-like proteins is posttranscriptionally regulated during metacyclogenesis

The development of the representation of differential expression method has lead to the cloning of Trypanosoma cruzi stage-specific genes. We used this method to characterize a multicopy gene family differentially expressed during metacyclogenesis. The genomic and cDNA clones sequenced encoded three short cysteine-rich polypeptides, of two types, with predicted molecular masses of 7.1, 10.4, and 10.8 kDa. We searched GenBank for similar sequences and found that the sequences of these clones were similar to that encoding the wheat germ agglutinin protein. The region of similarity corresponds to the chitin-binding domain, with eight similarly positioned half-cysteines and conserved aromatic residues involved in chitin recognition. Multiple copies of the genes of this family are present on a high- molecular-mass chromosome. We studied the expression of genes of this family during metacyclogenesis by determining messenger RNA (mRNA) levels. The mRNAs for the members of this gene family were present in the total RNA fraction but were mobilized to the polysomal fraction of adhered (differentiating) epimastigotes during metacyclogenesis, with a peak of accumulation at 24 of differentiation. Polyclonal antisera were raised against a recombinant protein and a synthetic peptide. The specific sera obtained detected 7- and 11-kDa proteins in T. cruzi total protein extracts. The 11-kDa protein was present in similar amounts in the various cell populations, whereas the 7-kDa protein displayed differential synthesis during metacyclogenesis, with maximal levels in 24-h-adhered (differentiating) epimastigotes.

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.

Differential gene expression during Trypanosoma cruzi metacyclogenesis

The transformation of epimastigotes into metacyclic trypomastigotes involves changes in the pattern of expressed genes, resulting in important morphological and functional differences between these developmental forms of Trypanosoma cruzi. In order to identify and characterize genes involved in triggering the metacyclogenesis process and in conferring to metacyclic trypomastigotes their stage specific biological properties, we have developed a method allowing the isolation of genes specifically expressed when comparing two close related cell populations (representation of differential expression or RDE). The method is based on the PCR amplification of gene sequences selected by hybridizing and subtracting the populations in such a way that after some cycles of hybridization-amplification genes specific to a given population are highly enriched. The use of this method in the analysis of differential gene expression during T. cruzi metacyclogenesis (6 hr and 24 hr of differentiation and metacyclic trypomastigotes) resulted in the isolation of several clones from each time point. Northern blot analysis showed that some genes are transiently expressed (6 hr and 24 hr differentiating cells), while others are present in differentiating cells and in metacyclic trypomastigotes. Nucleotide sequencing of six clones characterized so far showed that they do not display any homology to gene sequences available in the GeneBank.

Representation of Differential Expression: A New Approach to Study Differential Gene Expression in Trypanosomatids

During the past five years, several methods have been described that allow the isolation and cloning of stage-specific or cell-specific genes. The characterization of genes expressed at different stages of parasite development is of the utmost importance for the understanding of the mechanisms involved in the regulation of gene expression. Here, Samuel Goldenberg and Marco Aurelio Krieger describe a method for the amplification and cloning of Trypanosoma cruzi genes expressed specifically at different times of the metacyclogenesis process. This method, representation of differential expression (RDE), should be useful for the isolation and cloning of any trypanosomatid gene transcribing differentially expressed messenger RNA.

Chagas' disease diagnosis: evaluation of several tests in blood bank screening

Blood transfusion is one of the principal routes of transmission of Chagas' disease, a major endemic disease in Latin America. Methods for blood screening are not accurate and may yield false results that lead to high social and economic costs. This study compares two methods of diagnosing Chagas' disease (indirect immunofluorescence and hemagglutination) and several enzyme-linked immunosorbent assays (ELISAs) with regard to specificity and sensitivity, by using human sera with known serologic and parasitologic characteristics, as well as samples with discrepant results on conventional serologic tests. An ELISA using recombinant antigens showed no cross-reactivity with sera that were positive for other diseases. All evaluated ELISAs performed well, and their use may lead to a reduction of more than 50 percent in the number of discordant sera. Further improvements are needed in view of the complexity of the serologic diagnosis of Chagas' disease.

Trypanosoma cruzi flagellar repetitive antigen expression by recombinant baculovirus: towards an improved diagnostic reagent for Chagas' disease

We constructed a recombinant baculovirus that expressed part of a Trypanosoma cruzi flagellar repetitive antigen (FRA). Both cell- associated and secreted forms of recombinant FRA were detected in cultures of virus-infected Spodoptera frugiperda (Sf9) cells. These forms show a complex pattern after polyacrylamide gel electrophoresis and Western blot analysis using either an anti-FRA rabbit serum or human Chagasic sera. Competitive Western-blot experiments revealed that all bands react with the same antibodies as a bacterially-derived FRA. Polymerase chain reaction and Southern blots of the recombinant viral DNA also showed a complex pattern, suggesting the presence of more than one repeat unit in the viral genome. When tested against a panel of human sera from an endemic area for Chagas' disease, FRA recombinant-Sf9 culture supernatant showed the same reactivity as purified FRA produced in bacteria.

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

We tested two Trypanosoma cruzi recombinant antigens in a diagnostic test for Chagas' disease. These antigens were a cytoplasmic repetitive antigen (CRA) and a flagellar repetitive antigen (FRA). The results indicate that the recombinant antigens give better results when used in combination than when used separately, and that the removal of the beta-galactosidase portion of the recombinant fusion proteins increases the specificity of the diagnostic test for Chagas' disease. In addition, a direct enzyme-linked immunosorbent assay (ELISA), which involves the use of peroxidase-labeled antigens to detect the immune-complexes, was developed and compared with a conventional ELISA. The results indicate that the recombinant (CRA+FRA) ELISA is better than the conventional ELISA in the diagnosis of Chagas' disease, providing 100% specificity and sensitivity in all sera tested to date. The recombinant ELISA was compared with conventional serologic tests (hemagglutination and immunofluorescence) for Chagas' disease diagnosis, and the results show that the recombinant ELISA does not give rise to false-positive results that are observed with the two other tests. The use of the recombinant ELISA should be useful in the prevention of transmission of Chagas' disease by blood transfusions.

Expression and polymorphism of a Trypanosoma cruzi gene encoding a cytoplasmic repetitive antigen

The study of the expression of a Trypanosoma cruzi gene encoding a cytoplasmic repetitive antigen (CRA) during the metacyclogenesis process shows that this gene is not expressed in metacyclic trypomastigote forms of the parasite. However, a slight increase in CRA expression was observed following the nutritional stress of epimastigotes which precedes T. cruzi metacyclogenesis in vitro. The comparison of the expression of CRA in different T. cruzi strains shows that this gene is highly polymorphic: some strains display one and others display two polypeptides reacting with a CRA antiserum. The comparison of T. cruzi G-49 strain and Dm 28c clone shows that they display rather different Northern and Southern blot profiles when probed with a clone corresponding to the repetitive region of the CRA gene. A similar polymorphism was also observed for the gene encoding a flagellar repetitive antigen, suggesting that gene polymorphism might be a common feature of many T. cruzi genes.

Structure and expression of two Trypanosoma cruzi genes encoding antigenic proteins bearing repetitive epitopes

Trypanosoma cruzi genes were cloned in lambda gt11 and screened with an anti-trypomastigote antiserum. Two out of twelve clones were selected in view of their reactivity with human chagasic sera. One clone encodes a flagellar antigen (FRA) of more than 300 kDa, whereas the other corresponds to a roughly 225-kDa cytoplasmic antigen (CRA). The flagellar antigen is present in both epimastigotes and trypomastigotes, but the cytoplasmic antigen is not found in trypomastigotes. The CRA clone is entirely composed of at least 23 copies of a 42-bp repeat and the FRA gene contains at least 14 copies of a 204-bp motif. The FRA gene hybridizes to a RNA of about 10 kb, while the CRA gene detects a transcript of 5.2 kb.