B-Cell Responses in Chronic Chagas Disease: Waning of Trypanosoma cruzi-Specific Antibody-Secreting Cells Following Successful Etiological Treatment.

BACKGROUND: A drawback in the treatment of chronic Chagas disease (American trypanosomiasis) is the long time required to achieve complete loss of serological reactivity, the standard for determining treatment efficacy. METHODS: Antibody-secreting cells and memory B cells specific for Trypanosoma cruzi and their degree of differentiation were evaluated in adult and pediatric study participants with chronic Chagas disease before and after etiological treatment. RESULTS: T. cruzi-specific antibody-secreting cells disappeared from the circulation in benznidazole or nifurtimox-treated participants with declining parasite-specific antibody levels after treatment, whereas B cells in most participants with unaltered antibody levels were low before treatment and did not change after treatment. The timing of the decay in parasite-specific antibody-secreting B cells was similar to that in parasite-specific antibodies, as measured by a Luminex-based assay, but preceded the decay in antibody levels detected by conventional serology. The phenotype of total B cells returned to a noninfection profile after successful treatment. CONCLUSIONS: T. cruzi-specific antibodies in the circulation of chronically T. cruzi-infected study participants likely derive from both antigen-driven plasmablasts, which disappear after successful treatment, and long-lived plasma cells, which persist and account for the low frequency and long course to complete seronegative conversion in successfully treated participants.

Sequential combined treatment with allopurinol and benznidazole in the chronic phase of Trypanosoma cruzi infection: a pilot study.

OBJECTIVES: Even though the use of combined drugs has been proved to be effective in other chronic infections, assessment of combined treatment of antiparasitic drugs in human Chagas' disease has not been performed. Herein, a pilot study was conducted to evaluate the tolerance and side effects of a sequential combined treatment of two antiparasitic drugs, allopurinol and benznidazole, in the chronic phase of Trypanosoma cruzi infection. PATIENTS AND METHODS: Changes in total and T. cruzi-specific T and B cells were monitored during a median follow-up of 36 months. Allopurinol was administered for 3 months (600 mg/day) followed by 30 days of benznidazole (5 mg/kg/day) in 11 T. cruzi-infected subjects. RESULTS: The combined sequential treatment of allopurinol and benznidazole was well tolerated. The levels of T. cruzi-specific antibodies significantly decreased after sequential combined treatment, as determined by conventional serology and by a multiplex assay using recombinant proteins. The frequency of T. cruzi-specific interferon-γ-producing T cells significantly increased after allopurinol treatment and decreased to background levels following benznidazole administration in a substantial proportion of subjects evaluated. The levels of total naive (CD45RA + CCR7 + CD62L+) CD4 + and CD8 + T cells were restored after allopurinol administration and maintained after completion of the combined drug protocol, along with a decrease in T cell activation in total peripheral CD4 + and CD8 + T cells. CONCLUSIONS: This pilot study shows that the combination of allopurinol and benznidazole induces significant modifications in T and B cell responses indicative of a reduction in parasite burden, and sustains the feasibility of administration of two antiparasitic drugs in the chronic phase of Chagas' disease.

Parasite genomics: current status and future prospects.

The past year has brought great progress in the genome-sequencing efforts on a large number of protozoan and metazoan parasites. Whereas many of these projects are in their initial stages, at least one (for Plasmodium falciparum) is nearing completion. The information released to date has been most revealing with respect to immune evasion mechanisms.

Measurement of parasite-specific antibody responses using a tritiated avidin-solid phase radioimmunoassay.

A solid phase radioimmunoassay (RIA) to measure parasite-specific antibody responses has been developed. The assay utilizes 3H-labeled avidin as the indicator molecule and represents a marked improvement in detection of specific antibodies to Trypanosoma cruzi over previously used RIA. Avidin is easily labeled to high efficiency (3.6 X 10(5) cpm/micrograms) under very mild conditions using N-succinimidyl-[2,3-3H]propionate, and the high efficiency of avidin-biotin binding coupled with the increased safety and longer half-life of the labeled reagent give this method advantage over currently used 125I-labeled Ab RIAs.

Construction and use of a multi-competitor gene for quantitative RT-PCR using existing primer sets.

We describe a simple and inexpensive method for the construction of multi-competitor molecules for use as internal standards in quantitative RT-PCR. The construction involves the linking and annealing of 20mer PCR primers with complementary 40mers using either a step-wise or bulk process. The entire construct is then ligated and amplified by PCR prior to cloning. Using this approach, we have constructed a gene containing priming sites for 18 different products of immunological interest, including murine cytokines and cell surface markers, as well as murine beta-actin and T. cruzi rRNA. The cost of production of the competitor is minimized by use of a high-throughput multi-oligonucleotide synthesizer for production of the individual components of the synthetic gene, and by use of the same oligonucleotides in gene construction and as primers for the RT-PCR reactions. This procedure can be applied to the production of other polycompetitor molecules as well as to the construction of other types of synthetic genes.

Molecular cloning of the gene encoding the 83 kDa amastigote surface protein and its identification as a member of the Trypanosoma cruzi sialidase superfamily.

Amastigote surface proteins of Trypanosoma cruzi are likely targets of both humoral and cell-mediated immune responses, however, few such molecules have been well studied. In this study, we have used modified RACE (rapid amplification of cDNA ends) and SOE (gene splicing by overlap extension) polymerase chain reaction strategies to clone the gene for the previously described 83 kDa amastigote surface protein of T. cruzi. Of the several clones obtained, only one clone, clone 4, was found to encode the 20 amino acid sequence originally reported by Pan and McMahon-Pratt (J Immunol 1989;143:1001-1008). The identity of the cloned gene with the 83 kDa amastigote surface protein was further confirmed by the reactivity of polyclonal antisera against the purified 83 kDa protein with the gene product expressed in E. coli. Sequence analyses revealed that this amastigote surface protein (ASP-2) has two conserved aspartic acid box motifs and the highly conserved VTVxNVxLYNR motif characteristic of bacterial and viral sialidases and the type III module of fibronectin, respectively. ASP-2 thus joins ASP-1 as a member of the amastigote surface expressed family of sialidase-like molecules having strong homology with family 2 of the sialidase/trans-sialidase gene superfamily of T. cruzi.

The identification and molecular characterization of Trypanosoma cruzi amastigote surface protein-1, a member of the trans-sialidase gene super-family.

An accumulating body of evidence suggests that T. cruzi-infected host cells are recognized and destroyed by class I major histocompatibility complex (MHC) restricted CD8+ T-cells thus contributing to immune control of the infection [1-6]. However, to date, only a few amastigote proteins which could be the target of this response have been described and gene sequence information is available only for the amastins [7]. In order to identify amastigote proteins which could contribute to immune detection of infected host cells, a panel of monoclonal antibodies specific for amastigote proteins was produced and screened. Three mAbs (IIIC4, VIIC1 and IIID4) were identified which recognized amastigote surface proteins of 78, 26 and 53 kDa, respectively. Screening of an amastigote cDNA expression library with mAb IIIC4 resulted in the isolation of a 2.8 Kb clone. pSI2. The derived amino acid sequence indicates that the pSI2 clone encodes an amastigote surface protein belonging to the T. cruzi trans-sialidase super-family. Based on its preferential expression in the amastigote stage we have named this protein amastigote surface protein-1 (ASP-1). ASP-1 contains the third and fourth Asp block motifs, SxDxGxTW and the fibronectin type III-like domain, VTVxNVxLYNR, thus placing it in family II of the T. cruzi trans-sialidases [8]. ASP-1 is the first trans-sialidase family member shown to be preferentially expressed in the amastigote stage of the T. cruzi life cycle. This expression of ASP-1 on parasites in infected cells and its apparent membrane attachment by a glycosylphosphatidylinositol (GP1)-anchor makes it a prime candidate to enter the class I MHC processing and presentation pathway.

Medium-scale production and purification of monoclonal antibodies in protein-free medium.

Hybridoma cell lines can be adapted to grow in a totally protein-free tissue culture medium and cultured in spinner flasks to generate moderate-to-high quantities of monoclonal antibodies. Such antibodies are easily purified by ammonium sulfate precipitation. This system was shown to be useful for growth of 23 different hybridoma cell lines from different sources to yield an average of 40 mg of highly purified antibody per liter of tissue culture medium.

Interleukin 2 production in patients with Chagas' disease: correlation with anti-parasite antibody responses.

Peripheral blood mononuclear cells (PBMC) isolated from chronic chagasic patients and control individuals in Recife, Brazil were examined for the ability to produce IL-2 in response to concanavalin A (Con A) stimulation. Overall, there was little difference in the range of the response (IL-2 production) between the chagasic and control groups. Within the chagasic group, however, there was a high negative correlation between IL-2 production and the level of anti-parasite antibody. This correlation is thought to be a reflection of the fact that individuals with more recent or more vigorous infections exhibit higher anti-parasite antibody responses but also display a greater degree of immunosuppression, as reflected in depressed IL-2 production.

Parasite persistence in the aetiology of Chagas disease.

Two primary hypotheses are proposed to account for pathogenesis in chronic Trypanosoma cruzi infections: that the persistence of T. cruzi at specific sites in the infected host results in chronic inflammatory reactivity and that T. cruzi infection induces immune responses which are targetted at self tissues. The data supporting parasite persistence as the primary cause of disease in T. cruzi infection have been recently reviewed and the reader is referred to this review for extensive documentation of most of the arguments outlined herein. This manuscript will briefly reiterate the main points of this previous review, adding additional data that have been presented since its publication. Then, philosophical and practical arguments on why Chagas disease should be investigated and treated as a parasitic infection and not as an autoimmune disease are presented. This is admittedly an 'opinion piece' and not a balanced review of the literature on Chagas disease. There are substantial data other than those reviewed here, which have been presented in support of the autoimmunity hypothesis. It is left to others to review that body of literature.

Predominance of CD8+ T lymphocytes in the inflammatory lesions of mice with acute Trypanosoma cruzi infection.

Using glycol methacrylate in conjunction with avidin-biotin-peroxidase complex techniques, we studied the contribution of T cell subsets to tissue inflammation during acute Trypanosoma cruzi infection. Two mouse/parasite model systems whose parasitology and pathology behaved differently were used. In C57Bl/6J mice infected with the T. cruzi Brazil strain, the levels of parasitism in blood and tissue (myocardial and skeletal muscle) reached a maximum at week 6 and decreased rapidly thereafter. Inflammatory responses in tissue corresponded with the parasitism, but decreased in intensity more gradually than that of parasitism. The T lymphocytes (Thy 1.2+) were found to be the major lymphocyte population in inflammatory cardiac and skeletal muscles (64.6-81.2%) at both three and six weeks postinfection. Among T cells, CD8+ cells (47.0-58.9%) significantly outnumbered CD4+ cells (9.3-18.6%). The number of B cells (0-1.0%) and macrophages was low. Experiments using C3H/HeSnJ mice infected with the Sylvio X10/4 clone of T. cruzi at 30 days postinfection resulted in similar findings except for a higher CD8+:CD4+ ratio. The primary finding of this study is that Thy 1.2+CD8+CD4- T lymphocytes are the major cell population in both heart and skeletal muscle in acute murine T. cruzi infection. The predominance of CD8+ T cells coincident with the decrease in the tissue parasite burden suggests a role for CD8+ T cells in the control of T. cruzi at the level of the infected cell.

Diagnosis of Chagas' disease in humans using a biotin-3H-avidin radioimmunoassay.

A radioimmunoassay (RIA) originally designed to measure antibody responses to Trypanosoma cruzi in mice was adapted for use in the immunodiagnosis of Chagas' disease in humans. The assay utilizes biotinylated antibodies and 3H-avidin as the tracer molecules, and has proven to be both safe and sensitive. Results using the RIA and those from direct agglutination and indirect fluorescent antibody tests were comparable in most cases. Using the RIA, we were able to discriminate between mice infected with T. cruzi and Trypanosoma rangeli. Also, sera from Leishmania-infected individuals do not have detectable levels of antibodies capable of binding to T. cruzi. Intact, fixed epimastigotes of T. cruzi are used as the detecting antigen in the RIA and give results comparable to those obtained with intact trypomastigotes.

Trypanosomes and microfilariae in feral owl and squirrel monkeys maintained in research colonies.

A group of 358 owl and squirrel monkeys imported from Colombia, Peru, and Bolivia for the U.S. Agency for International Development Malaria Vaccine Development Program was examined for trypanosomes and microfilariae. Trypanosoma rangeli, isolated by hemoculture from Aotus nancymai, Saimiri b. boliviensis, and S. b. peruviensis, accounted for 76.6% of all trypanosome infections. Trypanosoma cruzi was isolated from 25 of 194 S. b. boliviensis, including two mixed infections with T. rangeli. Identifications of trypanosomes were confirmed by blinded tests with a panel of five rRNA probes on a subsample of cultures identified morphologically. Although no trypanosomes were isolated from Aotus vociferans or A. lemurinus griseimembra, positive serologic responses to T. cruzi were observed by indirect immunofluorescence assay in all species of monkeys examined and ranged from 42.1% among S. b. peruviensis to 92.3% among A. vociferans. Among T. rangeli-infected monkeys, 43.7% were seronegative for T. cruzi. No microfilariae were found in S. b. boliviensis or A. l. griseimembra. Mansonella barbascalensis and Dipetalonema caudispina were observed in A. vociferans, M. panamensis in A. nancymai, and M. saimiri and D. caudispina in S. b. peruviensis. Such naturally occurring infections in imported animal models are potential sources of accidental transmission to animal handlers and uninfected laboratory animals and can introduce confounding variables into otherwise well-planned and well-executed studies.

Loss of suppressor activity in the serum of mice infected with Trypanosoma cruzi.

Previous work from this laboratory documented the presence of a suppressor substance in the serum of mice infected with Trypanosoma cruzi. Currently, however, we have been unable to demonstrate the presence of this suppressor factor, although infected mice were still profoundly suppressed in their ability to respond to SRBC, and suppressor cells were present in the spleens of these animals. Strains of T. cruzi other than the one presently in use in our laboratory gave similar results. Several possible explanations for our inability to demonstrate the presence of the suppressor factor in sera are discussed.

Diagnosis of recent Toxoplasma gondii infection in cats by use of an enzyme-linked immunosorbent assay for immunoglobulin M.

Subclinical Toxoplasma gondii infection was induced in young and adult cats by oral administration of tissue cysts. An antibody-capture ELISA to detect anti-Toxoplasma IgM-class antibodies in the serum of cats was developed. The serologic response to experimental infection was followed in the 2 groups of cats by use of anti-Toxoplasma IgM and IgG detection. This study shows that anti-Toxoplasma IgM-class antibody titers develop early in the course of experimental infection in cats and that the combination of IgM- and IgG-class antibody titer measurement can aid in the detection of recent subclinical toxoplasmosis.

Enzyme-linked immunosorbent assay for the detection of circulating antigens of Toxoplasma gondii in the serum of cats.

An ELISA was developed to detect circulating antigens of Toxoplasma gondii in the serum of cats. For the experiment, toxoplasmosis was induced in a group of cats by oral administration of bradyzoites. An ELISA that detects anti-Toxoplasma IgG, an ELISA to detect circulating antigens, and fecal examinations were performed on samples from each cat for 1 year after inoculation. When coupled with IgG-class antibody measurement, antigen detection can aid in the diagnosis of some cases of subclinical feline toxoplasmosis.

Analysis of the Trypanosoma cruzi cyclophilin gene family and identification of Cyclosporin A binding proteins.

The Trypanosoma cruzi cyclophilin gene family comprises 15 paralogues whose nominal masses vary from 19 to 110 kDa, namely TcCyP19, TcCyP20, TcCyP21, TcCyP22, TcCyP24, TcCyP25, TcCyP26, TcCyP28, TcCyP29, TcCyP30, TcCyP34, TcCyP35, TcCyP40, TcCyP42 and TcCyP110. Under the conditions used, only some of the T. cruzi cyclophilin paralogue products could be isolated by affinity chromatography. The 15 paralogues were aligned with 495 cyclophilins from diverse organisms. Analyses of clusters formed by the T. cruzi cyclophilins with others encoded in various genomes revealed that 8 of them (TcCyP19, TcCyP21, TcCyP22, TcCyP24, TcCyP35, TcCyP40, TcCyP42 and TcCyP110) have orthologues in many different genomes whereas the other 7 display less-defined patterns of their sequence attributes and their classification to a specific group of cyclophilin's orthologues remains uncertain. Seven epimastigote cDNA clones encoding cyclophilin isoforms were further studied. These genes were found dispersed throughout the genome of the parasite. Amastigote and trypomastigote mRNAs encoding these 7 genes were also detected. We isolated 4 cyclosporin A-binding proteins in T. cruzi epimastigote extracts, which were identified by mass spectrometry as TcCyP19, TcCyP22, TcCyP28 and TcCyP40. Cyclosporin A-binding to these cyclophilins might be of importance to the mechanism of action of Cyclosporin A and its non-immunosuppressive analogues, whose trypanocidal effects were previously reported, and therefore, of potential interest in the chemotherapy of Chagas' disease.

The Trypanosoma cruzi proteome.

To complement the sequencing of the three kinetoplastid genomes reported in this issue, we have undertaken a whole-organism, proteomic analysis of the four life-cycle stages of Trypanosoma cruzi. Peptides mapping to 2784 proteins in 1168 protein groups from the annotated T. cruzi genome were identified across the four life-cycle stages. Protein products were identified from >1000 genes annotated as "hypothetical" in the sequenced genome, including members of a newly defined gene family annotated as mucin-associated surface proteins. The four parasite stages appear to use distinct energy sources, including histidine for stages present in the insect vectors and fatty acids by intracellular amastigotes.

Depletion of CD8+ T cells increases susceptibility and reverses vaccine-induced immunity in mice infected with Trypanosoma cruzi.

The role of CD8+ T cells in immune control of Trypanosoma cruzi infection in mice was examined by using in vivo depletion of CD8+ T cells with antibodies. Both the resistant C57BL/6J and the highly susceptible C3H/HeSnJ developed higher parasitemias and increased or earlier mortality when depleted of CD8+ T cells before infection with the Brazil strain of T. cruzi. CD8 depletion also affected the induction and expression of immunity to T. cruzi after vaccination with the avirulent Corpus Christi strain of T. cruzi. C57BL/6J mice depleted of CD8+ T cells either before or after vaccination showed a near total loss of vaccine induced protection. C3H mice were only partially protected by the vaccination procedure but the protection was totally reversed by anti-CD8 treatment. Chronically infected mice that had survived the acute infection were unaffected by CD8 depletion and showed neither a recrudescence of parasitemia nor an increased susceptibility to reinfection. These results suggest that CD8+ T cells play a role in immunity to T. cruzi in the acute phase but possibly not during the chronic phase of infection. Also, immunization with Corpus Christi strain T. cruzi induces an immunity that is distinct from that induced by survival of the acute phase of infection. The mechanism by which CD8+ T cells contribute to control of T. cruzi infection is not known. However, CD8 depletion had no effect on suppressed immune responses, suggesting their function in T. cruzi-infected mice is related more to the cytotoxic activity or cytokine-producing capacity of this subpopulation of T cells.

Regulation of immunity in Trypanosoma cruzi infection.

Immunity to T. cruzi is complex, involving among other components, antibody production, CD4+ helper cells, CD8+ T cells as both regulators and effectors of immunity, and possibly, double-negative T cells. In addition, several of these components have been implicated in pathogenesis in the chronic infection. Although the immunosuppression observed in the infection seems quite severe, it also appears to provide for a sufficient level of immune responsiveness to control the infection in most hosts. At the same time, immunosuppression may provide the regulatory control necessary to prevent massive chronic pathogenesis in all hosts. Continued study of the relative roles of lymphocyte populations and the products they secrete in immunity and pathogenesis may provide the understanding necessary to enhance immunity to T. cruzi without the feared consequence of increased pathogenesis.