Lectins discriminate between pathogenic and nonpathogenic South American trypanosomes

Trypanosoma (Herpetosoma) rangeli Tejera, 1920: an updated review

Trypanosoma rangeli, a parasite generally considered non-pathogenic for man, is the second species of human trypanosome to be reported from the New World. The geographical distribution of T. rangeli often overlaps with that of T. cruzi, the same vertebrate and invertebrate hosts being infected. Their differentiation thus becomes of real, practical importance, particularly as they share approximately half the antigenic determinants recognized by the humoral response. Little is known about the life cycle of T. rangeli in the vertebrate host, although thousands of human and wild animal infections have been reported. Recent studies have revealed 2 major phylogenetic lineages in T. rangeli having different characteristics, thus leading to better understanding of the epidemiology and interactions with this parasite's vertebrate hosts and triatomine vectors. Based on further genetic characterization analysis, the authors have proposed 2 alternative hypotheses and consider that T. rangeli could have had clonal evolution or have been subjected to speciation processes.

Characterization of a candidate Trypanosoma rangeli small nucleolar RNA gene and its application in a PCR-based parasite detection

In this study, we report the isolation and characterization of a candidate Trypanosoma rangeli small nucleolar RNA (snoRNA) gene, and the development of a PCR assay for detection of the parasite based on its nucleotide sequence. This gene, isolated from a T. rangeli genomic sub-library, was named snoRNA-cl1 and is encoded by a multi-copy gene of 801bp in length. Computer sequence analysis of snoRNA-cl1 showed the presence of two sequence motifs, box C and box D, as well as of two long stretches that perfectly complement the universal core region of the mature rRNA 28S, suggesting that cl1 encodes for a Box C/D snoRNA from the parasite. Hybridization analysis using cl1 as probe, showed a weak hybridization signal with Trypanosoma cruzi DNA, demonstrating the existence of differences in this locus between these two species. Two oligonucleotide primers from this gene, which specifically amplified a 620-bp fragment in KP1 (+) and KP1 (-) strains of T. rangeli, were used in a PCR assay. The amplification allowed the detection of 1pg of DNA in the presence of heterologous DNA and no amplification was observed with different T. cruzi strains (groups I and II). In addition, the PCR assay reported here is able to detect T. rangeli in the presence of T. cruzi DNA, and is useful for detection of the parasite in samples from infected vectors.

Identification and distribution of carbohydrate moieties on the salivary glands of Rhodnius prolixus and their possible involvement in attachment/invasion by Trypanosoma rangeli

In the present study, FITC-labelled lectins (WGA, Con A, PNA, HPA, and TPA) were utilized to investigate carbohydrate residues on the surface of Rhodnius prolixus salivary glands. The results revealed that the salivary glands are rich in carbohydrate moieties and the diversity in binding pattern of particular lectins showed the presence of specific carbohydrate residues in the basal lamina, muscle, and cell layers of the glands. Subsequently, the sugars detected on the salivary gland surface were employed to investigate the interaction between Trypanosoma rangeli and the R. prolixus salivary glands. In vitro adhesion inhibition assays using long epimastigote forms (the invasion/adhesion forms) showed that some sugars tested were able to block the receptors on both the surfaces of the salivary glands and on T. rangeli. Among the sugars tested, GlcNAc, GalNAc, and galactose showed the highest overall inhibitory effect, following pre-incubation of either the salivary glands or parasites. These results are discussed in relation to previous work on the role of carbohydrates and lectins in insect vector/parasite interactions.

[Review of the biologic and diagnostic aspects of Trypanosoma (Herpetosoma) rangeli]

This review has three objectives: a) To stimulate further research of this prevalent human infection b) to examine the progress of current diagnostic techniques and c) to emphasise the significance of the flagellate parasite Trypanosoma (Herpetosoma) rangeli in Chagas' Disease endemic areas of South and Central America. Both Trypanosoma rangeli and Trypanosoma cruzi overlap in many of the areas of Latin America utilising the same triatomine vectors. Also a vast range of mammalian species have been found naturally infected with T. rangeli. The biology of the parasitism of T. rangeli is revised and emphasis is given regarding its biological cycle. T. cruzi and T. rangeli share common antigens and cross react serologically. Human infection in the chronic phase may be misdiagnosed as T. cruzi infection. Conventional and modern diagnostic and identification methods are discussed. Unfortunately we do not know the real distribution of T. rangeli infections in most areas and epidemiological studies to examine concomitant dual infections deserve further investigation.

[First evidence of Trypanosoma rangeli in the southeast of Brazil, an endemic region for Chagas' disease]

This short communication informs the discovery of Trypanosoma rangeli for the first time at Triângulo Mineiro region, South-east of Brazil, a highly endemic area of Chagas' disease and also the natural infection of Didelphis albiventris with the same trypanosome. Both the findings were demonstrated through blood smears, xenodiagnosis, microhematocrit technics and PCR. The last one was realized in faeces and hemolymph of Triatoma infestans utilizing as controls strains of T. rangeli from Colombia.

Trans-sialidase and sialidase activities discriminate between morphologically indistinguishable trypanosomatids

The expression of trans-sialidase and sialidase activities in the kinetoplastid protozoa was explored as a potential marker to discriminate between the morphologically indistinguishable flagellates isolated from human, insects and vertebrate reservoir hosts. By virtue of the differences observed in the ratios of these enzyme activities, a collection of 52 species and strains comprising the major taxa of these parasites could be separated into four expression types. Type-I parasites express comparable levels of both trans-sialidase and sialidase activities (Endotrypanum species and Trypanosoma lewisi). Type-II parasites express predominantly trans-sialidase activity (Trypanosoma cruzi and Trypanosoma conorhini). Type-III parasites express sialidase activity exclusively (Trypanosoma rangeli and Trypanosoma leeuwenhoeki). Type-IV parasites do not express either activity (Leishmania species and Trypanoplasma borreli). The measurement of trans-sialidase and sialidase activities thus permits the differentiation of parasites frequently found in the same insect vectors that are difficult to distinguish, such as T. cruzi and T. rangeli, or in the same sylvatic vertebrate and invertebrate hosts, such as Leishmania and Endotrypanum.

Direct lysis of Trypanosoma cruzi: a novel effector mechanism of protection mediated by human anti-gal antibodies

Anti-gal antibodies directed against a carbohydrate epitope present in mouse laminin (galactosyl alpha 1-3 galactose) and detected in high levels in sera from patients in the acute phase of Chagas disease are responsible for the direct lysis (DL) of Trypanosoma cruzi blood forms independent of either the classic or alternative complement pathways. Furthermore, the lectins Euonymus europaeus (EE) specific for the carbohydrates gal alpha 1-3 gal present a similar lytic activity against T. cruzi at the same concentrations of purified anti-gal antibodies. The DL activity was tested with several other lectins but Concanavalin A (Con A) specific for alpha-D-mannose and alpha-D-glucose was the only one also presenting lytic activity. The lectins and anti-gal antibodies lytic activity can be inhibited by specific carbohydrates suggesting that this phenomenon is related to the capability of these lectins or anti-gal antibodies to bind to a crucial surface component of T. cruzi. Moreover, the infectivity of T. cruzi blood forms to mice was clearly inactivated by incubation with acute chagasic sera (ACS) but not by ACS absorbed by immunoaffinity chromatography with mouse laminin, a strong evidence that high levels of anti-gal antibodies participate in the decline of the parasitaemia from the acute to the chronic phase in Chagas disease.

Lectins and their application to clinical microbiology

Lectins are generally associated with plant or animal components, selectively bind carbohydrates, and interact with procaryotic and eucaryotic cells. Lectins have various specificities that are associated with their ability to interact with acetylaminocarbohydrates, aminocarbohydrates, sialic acids, hexoses, pentoses, and as other carbohydrates. Microbial surfaces generally contain many of the sugar residues that react with lectins. Lectins are presently used in the clinical laboratory to type blood cells and are used in a wide spectrum of applications, including, in part, as carriers of chemotherapeutic agents, as mitogens, for fractionation of animal cells, and for investigations of cellular surfaces. Numerous studies have shown that lectins can be used to identify rapidly certain microorganisms isolated from a clinical specimen or directly in a clinical specimen. Lectins have been demonstrated to be important diagnostic reagents in the major realms of clinical microbiology. Thus, they have been applied in bacteriology, mycology, mycobacteriology, and virology for the identification and/or differentiation of various microorganisms. Lectins have been used successfully as epidemiologic as well as taxonomic markers of specific microorganisms. Lectins provide the clinical microbiologist with cost-effective and potential diagnostic reagents. This review describes the applications of lectins in clinical microbiology.

Binding of lectins to culture and vector forms of Trypanosoma rangeli Tejera, 1920 (Protozoa, Kinetoplastida) and to structures of the vector gut

Culture forms of Trypanosoma rangeli could be agglutinated with Canavalia ensiformis (Con A) lectin and, less effectively with Pisum sativum agglutinin (PEA), at a concentration of 200 micrograms/ml. Ricinus communis agglutinin I (RCA I) agglutinated trypanosomes only if they were not previously washed with physiological Ringer's solution. Three other lectins did not react with the same parasite forms. Direct or indirect lectin-gold labeling techniques were applied to LR-White embedded thin sections of T. rangeli culture forms and to forms in the gut, hemolymph, and salivary glands of Rhodnius prolixus. Under these conditions, Con A was the only lectin out of 9 that bound to the surface of trypanosomes from culture and from the bug hemolymph. Con A did not react with any midgut or salivary gland forms. The preservation of the biological activity of the lectin-gold complexes that did not bind to the parasite surface was confirmed by reactions with structures of the invertebrate host.

Trypanosoma cruzi: studies on the interactions of lectins with glycoconjugates of different zymodemes

Detergent extracts were made of eight strains of Trypanosoma cruzi which were representative of the principal zymodemes. The extracts were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the glycoproteins were reacted with 21 different 125I-labeled lectins and autoradiographed. The staining patterns with particular lectins varied considerably between strains. Concanavalin A stained up to 17 distinct bands in some strains. Other lectins such as peanut lectin only stained two bands in zymodeme 1 strains and none in the other zymodemes. The reaction of N-acetylgalactosamine-specific lectins with some bands indicated the presence of this sugar and this was confirmed by analysis of the extracts. The lectin staining patterns provided an insight into the glycoprotein composition of the bands and should indicate whether combinations of lectins can be used in affinity chromatography systems to purify the glycoproteins.

Detection of surface carbohydrates on Pneumocystis carinii by fluorescein-conjugated lectins

Lectins react with a wide range of different carbohydrates (Table 1). Even so-called monospecific anti-H(O) lectins from Lotus tetragonolobus, Ulex europaeus, and Anguilla anguilla react not only with the anti-H determinant but also with several fucosylated carbohydrates. Consequently, the type of lectin receptor existing on the surface of Pneumocystis carinii should be determined, because only a carbohydrate analysis can demonstrate the kind of carbohydrates which exist on the cell surface of this parasite. For the purpose of this study we used fluorescent isothiocyanata (FITC)-conjugated lectins. Concanavalin A (Con A) and Maclura pomifera (MPA) agglutinin reacted to P. carinii at low concentrations, and the fluorescence intensity was gradually increased with the concentration of the lectins. With lectins from Bauhinia purpurea (BPA), Dolichos biflorus (DBA), Glycine max (SBA), Griffonia simplicifolia (GS-I, GS-II), and Triticum vulgaris (WGA), fluorescence was emitted at high concentrations, while Arachis hypogaea (PNA) and Ulex europaeus (UEA-I) agglutinins did not show fluorescence. The results suggest that P. carinii has abundant Con A- and MPA-specific carbohydrates on the surface.

Identification of chitin as a structural component of Giardia cysts

The intestinal parasite Giardia lamblia is a significant cause of diarrheal disease, which is perpetuated by the infective cyst form of the parasite. Although a rational approach to the control of giardiasis would be to inhibit cyst formation, nothing is known of the chemical composition of the cyst wall or of its biosynthesis. In these studies, we have shown that chitin is a major structural component of G. lamblia and G. muris cyst walls. This conclusion is based on the finding that chitinase specifically destroys the cyst wall, as revealed by electron microscopy. The presence of chitin was also shown directly by lectin binding studies. Of 12 lectins with diverse carbohydrate recognition specificity, only the N-acetylglucosamine-specific lectins wheat germ agglutinin, succinylated wheat germ agglutinin, and tomato lectin bound to cyst walls, as shown by fluorescence microscopy and cytochemistry. Wheat germ agglutinin binding was completely abolished by treatment of the cysts with purified chitinase. This effect was specific since it could be prevented by incubating the enzyme with chitin before treatment of the cysts. Treatment of cysts with N-acetyl-beta-glucosaminidase partially inhibited wheat germ agglutinin binding, whereas other glycosidases and proteases had no effect. These findings indicate that chitin is a major structural component of Giardia cyst walls and raise the possibility that inhibitors of chitin synthesis may be of use in preventing encystation and thus controlling spread of the disease.