Antigenic makeup of subcellular fractions of Trypanosoma cruzi

Cell fractionation of parasitic protozoa: a review

Cell fractionation, a methodological strategy for obtaining purified organelle preparations, has been applied successfully to parasitic protozoa by a number of investigators. Here we present and discuss the work of several groups that have obtained highly purified subcellular fractions from trypanosomatids, Apicomplexa and trichomonads, and whose work have added substantially to our knowledge of the cell biology of these parasites.

Identification of immunodominant antigens in Mexican strains of Trypanosoma cruzi

Chagas disease represents an important public health problem. In Mexico most studies have been performed using Trypanosoma cruzi' antigens extracted from strains of other geographical origins. This work was aimed at developing a reactive antigen to perform serological diagnosis of Chagas' disease, using Mexican T. cruzi strains. We prepared antigenic extracts from epimastigotes, trypomastigotes and sphaeromastigotes of three Mexican strains. Parasites homogenate was obtained by lysis and sonication, solubilized proteins were analyzed by SDS-PAGE, Western-blot assays, and ELISA to determine the reactivity against sera from chagasic reference serum and chagasic and leishmaniasic patients and healthy donors. Western Blot profiles revealed, with the reference serum, eleven main components between 212 to 25 kDa; however, five bands corresponding to 74, 44, 31, 25 and 18 kDa antigens were recognized by the T. cruzi reactive sera from Mexican chagasic patients, which did not cross-react with Leishmania mexicana. Antigens from the Tequesquitengo strain yielded the best reactivity in the enzymatic immunoassay, thus enabling us to propose their use for serodiagnoses of Chagas' disease in Mexico.

Control of Trypanosoma cruzi epimastigote motility through the nitric oxide pathway

Trypanosoma cruzi epimastigote motility can be enhanced by addition of L-arginine, to the culture. This effect is blocked by N-methyl-L-arginine, a competitive inhibitor of the nitric oxide synthase. N-methyl-D-aspartate and L-glutamate, two agonists of the NMDA/L-glutamate receptor, also enhanced motility. This stimulation is blocked by MK-801 a noncompetitive antagonist of the NMDA receptor. In addition, sodium nitroprusside, a guanylyl cyclase stimulator and 8-Br-cyclic GMP, and analog of cyclic GMP, also stimulated epimastigote motility. It is suggested that an increase of intracellular cyclic GMP levels mediated by nitric oxide may be responsible for the increase in epimastigote motility.

Epitopes common to Trypanosoma cruzi and mammalian tissues are recognized by sera from Chagas' disease patients: prognosis value in Chagas disease

Monoclonal antibodies (MoAbs) raised against Trypanosoma cruzi microsomal fraction (Mc) and cross-reactive with mammalian tissues were used to evaluate the ability of cross-reactive T. cruzi antigens to induce an immune response in Chagas' disease. Thus, we studied the ability of sera from Chagas' disease patients (CDP) with different degrees of cardiac dysfunction to block the immune recognition of these MoAb to the target antigen determining for each serum an inhibition index (II). By means of this approach we inferred that blocking of monoclonal antibody binding to T. cruzi microsomes by subjects' serum represents antibodies with the same reactivity. After serological and medical examinations, individuals were separated into the following groups: Chagas' disease patients without manifest cardiac involvement (CDP-0), CDP with suspected or borderline cardiac disease (CDP-1), CDP with moderate myocardial dysfunction (CDP-2), CDP with overt cardiac dysfunction (CDP-3) and controls including healthy subjects (HS) and patients with idiopathic myocarditis (IMP). The reactivity between MoAb 5F2 and its target antigen was significantly (p < 0.05) inhibited by sera from CDP irrespective of the clinical stage [CDP: n = 46, 50 +/- 20, mean II +/- SD: control: n = 16, 18 +/- 8]. Moreover, 5F2 was able to distinguish (p < 0.05) sera from CDP with mild disease (CDP clinical grade 0/1: n = 26, 34 +/- 18) from that of CDP with severe disease (CDP clinical grade 2/3: n = 20, 67 +/- 7). Moreover, the inhibitory capacity of sera from asymptomatic CDP (CDP-0) correlated with patients age (r = 0.66, p < 0.05). CDP-0 below or equal 40 years of age had results (n = 15, 25 +/- 13) comparable (p > 0.05) to that of controls while mean inhibition of CDP-0 over 40 years of age (n = 5, 60 +/- 5) was indistinguishable (p > 0.05) from that of patients with severe disease. Competitive assay with MoAb 5A9B11 also showed significant differences (p < 0.05) between sera from CDP (n = 46, 46 +/- 24) and controls (n = 13, 5 +/- 5). On the contrary, the differences observed between CDP with different cardiac involvement was not significant (mild: n = 26, 31 +/- 22; severe: n = 20, 66 +/- 11). However a thorough study of data from asymptomatic sera revealed the existence of two levels of reactivity, with low and high capacity to inhibit the reaction of 5A9B11 against Mc. On the contrary, CDP sera showed a blocking activity for 1A10C11 comparable to that of controls (CDP: n = 25, 19 +/- 9; control: n = 12, 14 +/- 6). Some cross-reactive MoAbs recognized epitopes partially composed of carbohydrates. Interestingly, 5F2 and 5A9B11 epitopes did not appear to have carbohydrates moieties. In summary, immunoinhibition assays revealed differences in the immune response of chronic chagasic patients against parasite epitopes. These results have opened the possibility to identify a prognosis marker of the disease suggesting the clinical utility of monitoring levels of these anti-Mc antibodies in patients with chronic Chagas' disease.

Trypanosoma cruzi and mammalian heart cross-reactive antigens

Monoclonal antibodies produced against T. cruzi microsomal fraction (Mc) were used to investigate the presence of molecular mimicry between the parasite and mammalian tissues. A total of 42 cell lines secreting anti-Mc antibodies were characterized and selected by ELISA, dot blotting and Western blotting assays. Twenty seven supernatants reactive with Mc and/or parasite cytosol (CS) also reacted with human myocardial and/or skeletal muscle antigens by dot blotting assay. Twelve among those cross-reactive hybridomes, which happen to be all of the IgM isotype and to recognize structures on the surface and/or flagellum of the parasite, were selected for cell cloning. Western blotting analysis of these 12 monoclonal antibodies revealed that they mainly recognized bands of 65, 45, 34 and 27 kDa on myocardium and bands of 71, 59, 44 and 30-27 kDa on skeletal muscle. Moreover, seven among them, when assayed by immuno-histochemistry on human and hamster myocardium and skeletal muscle, recognized cytoplasmic antigens, although the monoclonal antibodies 5F2 and 5A9B11 did also bind to the vessel muscle layer. Competitive assays proved the specificity of tissue structures recognition by these monoclonal antibodies. Moreover, this reactivity resulted to be organ specific as they failed to react on lung, stomach and kidney samples. These results demonstrate the cross-reactivity of mammalian and parasite antigens, thus supporting the possibility that molecular mimicry plays a central role in the development of chagasic cardiomyopathy.

Trypanosoma cruzi: T-cell-dependent mechanisms of resistance during chronic infection

Effector mechanisms of resistance exerted by T cells from BALB/c mice chronically infected with Trypanosoma cruzi, Tulahuén strain, were studied. Spleen cells from chronically infected mice (Chro-SC) prestimulated with heat-killed trypomastigotes (HKT) and/or IL-2 destroyed PHA-labeled p-815 mastocytoma cells, HKT-pulsed macrophages, and normal peritoneal macrophages. However, HKT-stimulated Chro-SC did not affect the infectivity of free bloodstream forms of the parasite. Upon HKT stimulation, Chro-SC or their culture supernatant activated peritoneal macrophages for the destruction of intracellular amastigotes. The effect was abolished after Thy 1.2+ cell depletion. The addition of Cyclosporin A (CyA), which blocks T-cell activation, during HKT-stimulation of Chro-SC, diminished their ability to activate the trypanocidal activity of macrophages. CyA also inhibited the production of both macrophage-activating factors and interferon-gamma by HKT-stimulated Chro-SC. CyA administration to recipients of nylon-wool nonadherent spleen cells from chronically infected mice inhibited their adoptively acquired resistance against T. cruzi, suggesting that the conferred resistance depended on the effect of specifically activated cells. When administered during the chronic stage of the infection, CyA abrogated the antigen-specific delayed type hypersensitivity response but increased the levels of anti-T. cruzi IgG antibodies. Neither parasitemia, tissular parasitism in myocardium or skeletal muscle, nor mortality were detected after CyA treatment, suggesting the presence of a CyA nonsensitive mechanism(s) in the control of T. cruzi during the chronic phase of the infection.

Trypanosoma cruzi: cellular and antibody response against the parasite in mice immunized with a 19-amino acid synthetic peptide

Several monoclonal antibodies were prepared against the flagellar fraction of Trypanosoma cruzi epimastigotes (Tulahuén strain, stock Tul 2). One of them, FCH-F8-4, has previously shown biologic activity against the parasite (complement-mediated lysis and neutralization of the trypomastigote infectivity). Immunopurified antigens using this monoclonal antibody elicited a protective immune response in mice. Two recombinant cDNA clones were detected with this anti-flagellar fraction monoclonal antibody on a lambda gt11 expression library prepared from T. cruzi epimastigote mRNA. The insert of one of these cDNA clones, lambda(FCH-F8-4)1 (150 bp) coded for a 19-amino acid peptide (PAFLGCSSRFSGSFSGVEP). This insert hybridized with a 5.0-kb mRNA from epimastigotes. The beta-galactosidase fusion protein was produced in lysogenic bacteria. The monoclonal antibody recognized the epitope present in the fusion protein after western blotting of the crude lysate. A synthetic peptide (SP4) containing the complete sequence of lambda(FCH-F8-4)1 was constructed on solid phase. This peptide was able to inhibit the ELISA reactivity (in a range from 13 to 52%) of flagellar fraction immunized mouse sera and when administered (coupled to KLH or alone) to BALB/c mice with Bordetella pertussis as adjuvant, it induced a humoral and cellular immune response which was detected by ELISA, immunofluorescence, blotting, and DTH reactions against T. cruzi antigens. The immune response obtained indicates that this synthetic peptide resembles the parasite antigen conformation and could be useful for diagnosis purposes or be able to elicit immunoprotection against T. cruzi infection.

Isolation of a Trypanosoma cruzi antigen by affinity chromatography with a monoclonal antibody. Preliminary evaluation of its possible applications in serological tests

By affinity chromatography with a monoclonal antibody (163B6), obtained in our laboratory, we have isolated a T. cruzi antigen which could be useful for differential diagnosis of Chagas' disease from leishmaniasis. This antigen, a 52-kD protein, reacted with all sera from Chagas' disease patients tested but not with sera from patients with leishmania, in ELISA. The 52-kD antigen is widely distributed in the Trypanosoma genus since the 163B6 monoclonal antibody reacts with T. rangeli and 8 strains and a clone of T. cruzi epimastigotes.

Role of T helper/inducer cells as well as natural killer cells in resistance to Trypanosoma cruzi infection

T lymphocytes provide a major line of defence against many protozoan parasites. The aim of this work was to determine the role of T-cell helper/inducer subset (T h/i) in the resistance to Trypanosoma cruzi in a murine model. The importance of natural killer (NK) cells in the resistance to the parasite was also evaluated. BALB/c and C57BL/6 mice were injected with either monoclonal antibodies against L3T4, Thy 1.2, NK1.1, or with a polyclonal rabbit antiserum against NK cells (anti-asialo GM-1). The effect of in vivo administration of these antibodies was tested in separate functional assays. After antibody treatment, mice were infected with a low dose of T. cruzi in the bloodstream form. Mice depleted of, or reduced in T, T h/i, or NK cell activity all developed higher parasitaemia and had higher mortality than their control counterparts. Mice injected with anti-L3T4 monoclonal antibodies were unable to generate a specific antibody response to the parasite. Treatment of mice with alpha/beta interferon, which is known to boost NK cell activity, resulted in an enhanced resistance to the parasite. Our data indicate that T h/i cells as well as NK cells are of vital importance in controlling parasitaemia and reducing mortality in T. cruzi-infected mice. Finally, we also demonstrate that the production of antibodies specific for T. cruzi is strictly T helper cell-dependent.

Trypanosoma cruzi: immune response in mice immunized with parasite antigens

The humoral and cellular immune responses were studied in mice immunized with flagellar fraction (F), F plus Bordetella pertussis as adjuvant (F-Bp), and microsomal (Mc) subcellular fractions from the epimastigote forms of Trypanosoma cruzi. The immune response was studied before and after the challenge with 50 bloodstream forms of T. cruzi, Tulahuén strain. The immunization with F-Bp, but not with Mc or F and Bp separately, protected mice, in terms of parasitemia and mortality, from the challenge with the parasite. Before the challenge, levels of specific antibodies in mice immunized with F-Bp were higher than in mice immunized with F or Mc. Antibody levels 17 days after the infection were similar in the three groups of mice while nonimmunized mice reached lower levels. Early during the infection nonimmunized infected mice lacked delayed-type hypersensitivity (DTH) responses to parasite antigens and to concanavalin A (Con A). Mice immunized with F-Bp, however, presented positive DTH responses to parasite antigens and Con A both, before and after the challenge with T. cruzi. DTH reaction was transferred with spleen cells. Mice immunized with Mc behaved similarly to infected nonimmunized animals in their reactivity to parasite antigens. These results indicated striking differences between protected and nonprotected mice in humoral and cellular immune responses during experimental T. cruzi infection.

Differences in resistance to reinfection with low and high inocula of Trypanosoma cruzi in chagasic mice treated with nifurtimox and relation to immune response

Reinfection of chronic chagasic mice after treatment with nifurtimox resulted in different outcomes according to the number of parasites used for inoculation. Nifurtimox-treated chagasic animals injected with 2,500 trypomastigotes developed higher parasitemia and increased mortality compared with nontreated chagasic mice. When reinfection was done with 25 trypomastigotes, treated and nontreated animals showed similar parasitemias and mortalities, which were significantly higher in nonchagasic controls infected for the first time. Immunological studies showed that treatment with nifurtimox led to a decrease in anti-Trypanosoma cruzi antibodies engaged in parasite destruction, inducing either complement-dependent lysis or antibody-dependent cytotoxicity, but no difference in anti-T. cruzi cell-mediated immunity was found between treated and nontreated chagasic animals. It is concluded that treatment with nifurtimox leads to a loss of resistance to reinfection with a large number of trypanosomes, which is maintained with challenge with a few parasites, and that these two thresholds of premunition are probably associated with humoral and cell-mediated anti-T. cruzi immune responses, respectively.

Immunoprotection of mice against Trypanosoma cruzi with a lyophilized flagellar fraction of the parasite plus adjuvant

The immunization with the flagellar (F) fraction from epimastigotes of Trypanosoma cruzi has been shown to protect mice against a challenge of bloodstream trypomastigotes of the parasite, both in terms of mortality and decrease in parasitemia. We have compared the immunoprotective properties of the fresh F fraction with those of a lyophilized F (LF) fraction, alone or together with Bordetella pertussis (Bp) as adjuvant. The best results were obtained with LF + Bp: after challenge with 1 X 10(3) metacyclic trypomastigotes, 100% of the mice immunized with LF + Bp survived, and 60% of them showed no signs of parasitemia. Only the animals in which patent parasitemia was demonstrated presented heart and muscle infiltrates.

Cell-mediated reactivity against human and Trypanosoma cruzi antigens according to clinical status in Chagas' disease patients

The presence of cellular reactivity against homologous tissues and subcellular fractions of Trypanosoma cruzi was investigated in Chagas' disease patients (CDP). CDP were grouped in asymptomatic (CDP-1) and with probable (CDP-2) and overt (CDP-3) cardiomyopathy. Healthy and non-Chagasic cardiomyopathic subjects were studied as controls. Lymphoproliferative reactions against heart tissue extracts were detected in 42% of 72 CDP studied, with similar prevalence of positive reactions in all groups, and correlated with reactivity to both liver and kidney homologous tissues (P less than 0.001). These results confirm the existence of cellular immune reactivity against tissues in CDP, and indicate the lack of organ specificity of this reaction as well as the absence of relation with the clinical state of patients. Cellular reactivity to subcellular fractions of T. cruzi showed a definite pattern according to the clinical status of CDP. Although prevalence of T. cruzi stimulation appeared similar in all groups (70% in CDP-1, 82% in CDP-2 and 75% in CDP-3), CDP-3 showed a significantly higher reactivity to flagellar (69%) and cytosol (63%) fractions than CDP-1 (38 and 27%, respectively). These findings suggest a variable modulation of immune response according to the clinical state of T. cruzi infected subjects.

Cellular immunity in Chagas' disease patients. Lymphoproliferative response to subcellular fractions of Trypanosoma cruzi

The ability of peripheral mononuclear cells from Chagas' disease patients (CDP) to generate specific proliferative responses in vitro to whole homogenate (WH) and subcellular fractions of T. cruzi was investigated. Flagellar (F), microsomal (Mc) and cell sap (CS) fractions were isolated from a WH obtained by disruption by pressure-depressure. Parasite-free human peripheral mononuclear cells were isolated by centrifugation of leukocyte-rich plasma over discontinuous gradients of Ficoll-Hypaque and cultured for 6 days in the presence of the different fractions of T. cruzi. Eighty-six percent (54/63) of the CDP showed good capacity to respond to at least one of the fractions assayed while only 18% (4/22) of the controls reacted. The Mc fraction showed the best specificity as well as the maximal stimulating effect in CDP (37/55 vs 0/18 in controls) while WH (62% vs 10%), F (54% vs 16%) and CS (52% vs 6%) showed a lesser antigenic capacity. These results suggest that recognition mechanisms and proliferative responses are functional in CDP. No correlation was found between the stimulating capacity of fractions in vitro and their immunogenic capacity previously observed in vivo.

Density gradient purification of human lymphocytes from contaminating trypomastigotes of Trypanosoma cruzi

Mixtures of normal human lymphocytes and T. cruzi trypomastigotes obtained from infected mice were centrifuged over Ficoll-Hypaque (FH) continuous and discontinuous gradients. Trypomastigotes were confined to the range 1.051-1.057 g/ml while lymphocytes ranged between 1.046 and 1.080 g/ml. Over 80% of the lymphocytes were found at 1.060 g/ml or higher densities. A discontinuous gradient of FH with 2 layers of 1.060 and 1.077 g/ml of density respectively was selected to obtain trypomastigotes-free white blood cells from blood samples. The functional capacity of lymphocytes recovered from the lower interface, where no parasites were found, was assessed. The response to phytohaemagglutinin of these high density lymphocytes was as good as to total lymphocytes, suggesting that low density lymphocytes are not necessary for proliferative responses. It is postulated that high density lymphoid populations, free from T. cruzi forms, may be used to study the presence of T cell-mediated immune response in Chagas' disease patients.

Purification and properties of anti-Trypanosoma cruzi antibodies isolated from patients with chronic Chagas' disease

Three purified human IgG antibodies against Trypanosoma cruzi (anti-F, anti-Mc and anti-Cs) showed different reactivities in vitro. While all of them agglutinated specifically sensitized sheep red cells the complement-fixing capacity of anti-Fc and anti-Cs was higher than that of anti-Mc antibody. This one also showed a minimal precipitating activity. When the ability to neutralize mice bloodstream trypomastigotes was analyzed, the results obtained indicated that anti-F antibody was the most effective.

The glycoconjugates from Trypanosoma Cruzi, purification and composition of a glycoprotein

1. The complex of glycoconjugates extracted with phenol-water from culture epimastigotes of a non-infective line (To) of Trypanosoma cruzi, derived from the Tulahuén strain showed only two components by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. 2. The slower migrating glycoconjugate, a glycoprotein of molecular weight 45, 000 was purified to apparent homogeneity. 3. A content of 76% protein, 17% neutral sugars and 6% glucosamine was analysed. Galactose and mannose occur in a ratio of 3:1 as determined by gas-liquid chromatography. A trace of glucose was detected in some samples.

Trypanosoma cruzi: avirulence of the PF strain to Callithrix marmosets

Callithrix jacchus geoffroy marmosets (HumBol. 1812) were injected once subcutaneously with 10.000 parasites/g body weight and followed for a period of six months. The PF strain of Trypanosoma cruzi was used. Follow-up was done through blood cultures, xenodiagnosis, serological tests, and ECG. A small number of normaI animais served as control.

Antigens of subcellular fractions of Trypanosoma cruzi. III. Humoral immune response and histopathology of immunized mice

The relation of humoral antibody response to protection was evaluated in mice immunized with whole homogenates of Trypanosoma cruzi or with its flagellar fraction by direct agglutination and indirect fluorescent antibody test as well as by lytic and neutralizing activity against blood trypomastigotes. The results indicated that lytic antibodies were not implicated directly in protection against these trypanosomes. It was evident from histopathologic examination that the higher the degree of protection achieved, the lower the tissue damage observed in the challenged mice. Serum-neutralizing activity was highest in the groups protected most effectively.

Purification of an adenylyl cyclase-containing plasma membrane fraction from Trypanosoma cruzi

A fraction containing plasma membrane fragments has been purified from epimastigote forms of Trypanosoma cruzi. Cells were broken by sonic vibration under well defined conditions and membranes were isolated by differential centrifugation and equilibrium centrifugation in sucrose gradients. The co-purification (approximately 10-fold) of adenylyl cyclase and plasma membrane-bound radioactive iodine is highly suggestive of the localization of this enzyme in the plasma membrane of T. cruzi. Determination of succinate cytochrome c reductase and glucose-6-phosphatase activities, as well as of total amounts of DNA and RNA in the purified fraction, indicates a negligible contamination from other cellular organelles. The co-purification of acid phosphatase activity with bound labeled iodine and adenylyl cyclase was taken as circumstantial evidence that part of this enzyme also belongs to the plasma membrane of T. cruzi. Conventional electron miscroscopy and freeze-fracture images of this fraction are consistent with a highly enriched plasma membrane preparation.

NAD-linked glutamate dehydrogenase in Trypanosoma cruzi

1. Epimastigotes of Trypanosoma cruzi, Tulahuén strain, contained a NAD-linked glutamate dehydrogenase (EC 1.4.1.3), in addition to the already known NADP-linked enzyme enzyme (EC 1.4.1.4). 2. The partially purified NAD-linked enzyme had a higher molecular weight and was much more labile than the NADP-linked enzyme, and was inhibited by purine nucleotides. 3. These results further emphasize the difference in glutamate metabolism between the parasite and its mammalian host.

Adenosine triphosphatase activities in Trypanosoma cruzi

1. Subcellular fractions obtained from epimastigotes of Trypanosoma cruzi, disrupted by three different procedures, contained in addition to the already known Mg2+-activated adenosine triphosphatase (ATPase; E.C.3.6.1.4), a Ca2+-ATPase activity. 2. The Ca2+-ATPase (a) was activated by low concentrations of CaCl2 (apparent Ka, 80 microM); (b) had a Km for ATP of 0.6 mM (at 1 mM CaCl2, pH 8.0); (c) presented a broad pH curve (optimum 7.1-8.6); and (d) was insensitive to oligomycin concentrations which inhibited the Mg2+-ATPase present in the same preparations. 3. All attempts to find a (Na+-K+)-activated, ouabain-inhibited, ATPase have been unsuccessful, in spite of the fact that living epimastigoes of T. cruzi are able to concentrate K+ and exclude Na+ from the medium.

Isolation and properties of flagella of trypanosomatids

A procedufe is described for the isolation of flagella of Crithidia fasciculata, Herpetomonas samuelpessoai and Leishmania tarentolae in a highly purified state and giving reasonably good yield. The 3 types of flagella give a similar electrophoretic pattern of proteins. It is shown that H. samuelpessoai and, to a lesser extent, C. fasciculata flagella confer protection against Trypanosoma cruzi infection.

Antigens of the subcellular fractions of Trypanosoma cruzi. II. Flagellar and membrane fraction

A method for isolation of membrane and flagellar fractions from Trypanosoma cruzi epimastigotes, and descriptions of their ultrastructural characteristics and antigenic activity are presented. Electron-microscopic observation revealed that the membrane fraction resembled vesicles, as occurs frequently when the pressure-depressure method is used for cell disruption. The flagellar fraction revealed flagella and some membranes, both related and unrelated to the flagellar structure. Flagellar and membrane fractions had 5 and 3 precipitin lines respectively against anti-whole homogenate of T. cruzi, in double diffusion tests. One of the precipitin bands common to both fractions gave a reaction of identiy with one precipitin line of the microsomal fractions, that was not present in the mitochondrial, nuclear and cell sap fractions. Data from tests of protective activity activity obtained during a period of 3 years with whole homogenate and F and M fraction are also presented Protective activity against lethal challenge doses of trypomastigotes is strongly associated with the flagellar fraction.