Distribution of epitopes of Trypanosoma cruzi amastigotes during the intracellular life cycle within mammalian cells

In this study we have examined the distribution of epitopes defined by monoclonal antibodies raised against Trypanosoma cruzi amastigotes during the intracellular life cycle of the parasite. We have raised monoclonal antibodies towards amastigote forms and performed preliminary immunochemical characterization of their reactivities. MAB 1D9, 3G8, 2B7, 3B9, and 4B9 react with carbohydrate epitopes of the parasite major surface glycoprotein--Ssp-4 defined by MAB 2C2 [5]; MAB 4B5 reacts with a noncarbohydrate epitope in all developmental stages of the parasite, and MAB 3B2 also detects a noncarbohydrate epitope preferentially in T. cruzi flagellated forms. Vero cells infected with tissue culture-derived trypomastigotes of clone D11 (G strain) were fixed at different times during the intracellular proliferation of parasites, and processed for immuno-electron microscopy and confocal immunofluorescence with the different monoclonal antibodies. We observed that while the surface distribution of MAB 2C2 and 4B9 epitopes was uniform throughout the cycle, MAB 1D9, 3G8, and 2B7 reacted with cytoplasmic membrane-bound compartments of the amastigotes. MAB 3B9 displayed a unique surface dentate pattern in some amastigotes. MAB 4B5 recognized a curved-shaped structure at the flagellar pocket region in some intracellular amastigotes and localized to the membrane in dividing forms. In intracellular trypomastigotes, MAB 4B5 also displayed a punctate pattern near the flagellar pocket.

Release of membrane-bound trails by Trypanosoma cruzi amastigotes onto modified surfaces and mammalian cells

Upon incubation at 37 degrees C onto glass coverslips coated with Concanavalin A, poly-L-lysine, or a monoclonal antibody (1D9) directed to the parasite major surface glycoprotein Ssp-4, extracellular Trypanosoma cruzi amastigotes release trails of material barely visible by light microscopy. This release is not associated with parasite movements. Immunolabeling studies confirmed that the material is derived from the parasite's membrane since thin section through samples labeled with 1D9 revealed that the trails are membrane-bound structures. Scanning electron microscopy showed that the approximately 0.1-micron(s) thick trails of material emerging from the amastigotes can be uniform or beaded, indicating a tendency to vesiculation. The trails are preferentially released from the flagellar pocket region and/or at the opposite posterior end of the parasite body, and seem to be devoid of microtubules. The release is time and temperature-dependent and fixed parasites do not form trails. All attempts to inhibit trail release using drugs (antimycin A, sodium azide, cytochalasin D, nocodazole, genistein, staurosporine, EGTA) failed. The observation of trails associated with intracellular parasites and amastigotes invading Vero cells suggests that this is probably a physiological process.

Polymorphism of the 35- and 50-kilodalton surface glycoconjugates of Trypanosoma cruzi metacyclic trypomastigotes

In this study, we examined the immunochemical properties of the 35- and 50-kDa (35/50-kDa) surface glycoconjugates expressed on the surface of metacyclic trypomastigotes of Trypanosoma cruzi using three different monoclonal antibodies directed to this component. The 35/50-kDa surface antigen was expressed by metacyclic trypomastigotes of 11 different strains of T. cruzi and displayed a significant degree of molecular polymorphism. Results of immunoblotting and complement-mediated lysis were consistent with such diversity. Different monoclonal antibodies reacted with distinct epitopes on the 35/50-kDa antigen, which is resistant to proteases and behaves as an amphiphilic component.

Resistance to acute Trypanosoma cruzi infection resulting from immunization of mice with a 90-kilodalton antigen from metacyclic trypomastigotes

The stage-specific 90-kDa surface antigen of Trypanosoma cruzi metacyclic trypomastigotes was affinity purified and used for immunization studies. Mice immunized with the 90-kDa antigen plus alum as an adjuvant were resistant to challenge with Tulahuen strain metacyclic forms, displaying either reduced or subpatent parasitemias. Mice immunized with the purified antigen without adjuvant or with antigen plus Freund adjuvant or glucan developed high parasitemias, comparable to those of nonimmunized controls, upon metacyclic challenge. Sera of mice immunized with the 90-kDa antigen plus alum showed complement-dependent trypanolytic activity and also greatly inhibited the invasion of Vero cells by metacyclic forms of G and Tulahuen strains in vitro. These sera were found by a competition binding assay to contain antibodies that recognized the same or topographically related sites as the monoclonal antibody 1G7, an antibody previously shown to reduce the infectivity of metacyclic forms in vivo and in vitro. In contrast, 1G7-related antibodies were poorly represented in sera with negative or low trypanolytic activity, such as those from mice immunized with purified antigen without adjuvant.

The stage-specific 90-kilodalton surface antigen of metacyclic trypomastigotes of Trypanosoma cruzi

The 90-kDa antigen, previously identified by the monoclonal antibody 1G7 to be a stage-specific surface protein of metacyclic trypomastigotes of Trypanosoma cruzi, has been further characterized in this study. Experiments of metabolic labeling with [35S]methionine, [2H]mannose and [3H]galactose revealed that the 90-kDa antigen is the main glycoprotein synthesized by metacyclic forms (G strain). Through pulse-chase experiments with [35S]methionine-labeled metacyclic trypomastigotes, it was found that the antigen is synthesized as a 75-kDa precursor polypeptide that is rapidly processed to the mature 90-kDa molecule. When metacyclic trypomastigotes were treated with tunicamycin, the production of 90-kDa antigen was greatly diminished, and the 75-kDa species, which was also expressed on the cell surface, accumulated. Concanavalin A bound strongly to the 90-kDa antigen, but failed to recognize the 75-kDa polypeptide. Treatment of neuraminidase had no effect on the 90-kDa antigen, whereas digestion by endoglycosidase H generated a polypeptide of 82 kDa. Altogether these data indicate that the 90-kDa antigen is a glycoprotein containing N-linked oligosaccharide side chains of the high-mannose type. The 90-kDa glycoprotein may be involved in the process of host cell invasion, since the internalization of metacyclic forms into Vero cells was partially inhibited by monoclonal antibody 1G7.

Metacyclic neutralizing effect of monoclonal antibody 10D8 directed to the 35- and 50-kilodalton surface glycoconjugates of Trypanosoma cruzi

It was shown in this work that the infectivity of metacyclic forms of Trypanosoma cruzi was affected upon interaction with the monoclonal antibody (10D8), which reacts with a carbohydrate epitope of the 35- and 50-kilodalton (kDa) surface glycoconjugates. The invasion of Vero cells by metacyclic forms of strains Tulahuen and G was inhibited 50 to 67% in the presence of 10D8 (10 micrograms/ml), whereas a nonrelated monoclonal antibody to Plasmodium berghei had no such effect. In mice that were inoculated with metacyclic forms preincubated with 10D8 or that had passively received 10D8 before challenge with metacyclic forms, a considerable decrease in the parasitemia levels was observed. The 35- and 50-kDa antigens were detectable by the galactose oxidase and sodium boro[3H]hydride procedure but not by surface iodination or metabolic labeling with [35S]methionine, suggesting that they may be of glycolipid nature. The finding that the 35- and 50-kDa antigens are major bands recognized by sera of mice immunized with killed metacyclic forms and protected against acute infection, in addition to the results with 10D8, indicate that these glycoconjugates may play an important role in the metacyclic form-host cell association that initiates T. cruzi infection.

Trypanosoma cruzi metacyclic trypomastigotes: neutralization by the stage-specific monoclonal antibody 1G7 and immunogenicity of 90 kD surface antigen

In this study we have investigated the ability of the stage-specific monoclonal antibody (MoAb) 1G7 to neutralize the infectivity of Trypanosoma cruzi metacyclic trypomastigotes (Tulahuen strain). Mice inoculated with metacyclics pre-incubated with 1G7 or the corresponding Fab fragments were found to develop greatly reduced parasitaemias compared with control animals. Similar results were obtained when mice received 1G7 (0.5 mg/mouse) before challenge with metacyclics. The 90 kD surface protein recognized by MoAb 1G7 was affinity purified and analysed for its immunogenic properties. Immunization of mice with 90 kD antigen induced antibodies that reacted with the native metacyclic surface antigen. The purified antigen was also capable of specifically stimulating the 'in-vitro' proliferation of 90 kD-primed T-cells. Furthermore, in a preliminary experiment in which mice were immunized with the purified polypeptide and challenged with Tulahuen metacyclics, low parasitaemia levels were observed in 60% of animals as opposed to non-immunized controls. The iodinated 90 kD antigen, which has previously been shown to be ubiquitous among T. cruzi strains, was precipitated by different immune sera including various chagasic sera.

Reactivity of stage-specific monoclonal antibody 1G7 with metacyclic trypomastigotes of Trypanosoma cruzi strains: lytic property and 90,000 mol. wt surface antigen polymorphism

Eleven strains of Trypanosoma cruzi, originating from a variety of vertebrate and invertebrate hosts in distinct geographical regions, were examined for the reactivity of metacyclic stages with the monoclonal antibody 1G7. Trypomastigotes of five strains were susceptible to complement-dependent 1G7-mediated lysis. Higher levels of 1G7 bound to metacyclics of lysis-susceptible strains as compared to lysis-resistant isolates. Excluding Y and CL strains, 1G7 reacted with metacyclics of all T. cruzi isolates by binding to a 90,000 mol. wt surface polypeptide. A 90,000 mol. wt protein lacking the 1G7-specific epitope but immunologically related to the 90,000 mol. wt antigen of other T. cruzi isolates is present in Y and CL strains. The intensity of the 90,000 mol. wt band, detected by surface iodination of metacyclics or in immunoblots using the monoclonal antibody 1G7 or the monospecific antiserum to 90,000 mol. wt protein, varied among different strains and also a discrete variation was observed in its molecular weight. The overall analysis reveals a polymorphism of the 90,000 mol. wt protein, which is ubiquitous among the different T. cruzi isolates.

Trypanolytic activity and antibodies to metacyclic trypomastigotes of Trypanosoma cruzi in non-Chagasic human sera

Metacyclic trypomastigotes of Trypanosoma cruzi, derived either from triatomid vectors or axenic cultures, were found to be extensively lysed by sera of some non-Chagasic healthy individuals through activation of the alternative complement pathway. Antibodies to T. cruzi metacyclics were detected by direct agglutination test in normal human sera (NHS) containing trypanolytic activity. Absorption of lytic NHS with metacyclic trypomastigotes, but not with non pathogenic Herpetomonas samuelpessoai promastigotes, abolished the trypanolytic effect. Natural antibodies to trypomastigotes were not found in NHS devoid of trypanolytic activity. Precipitation of 131I-labelled metacyclic surface proteins with lytic NHS revealed as the major band a polypeptide with an apparent molecular weight of 75,000.