Identification and isolation of a variant surface glycoprotein from Trypanosoma vivax

Global distribution, host range and prevalence of Trypanosoma vivax: a systematic review and meta-analysis

BACKGROUND

Trypanosomosis caused by Trypanosoma vivax is one of the diseases threatening the health and productivity of livestock in Africa and Latin America. Trypanosoma vivax is mainly transmitted by tsetse flies; however, the parasite has also acquired the ability to be transmitted mechanically by hematophagous dipterans. Understanding its distribution, host range and prevalence is a key step in local and global efforts to control the disease.

METHODS

The study was conducted according to the methodological recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. A systematic literature search was conducted on three search engines, namely PubMed, Scopus and CAB Direct, to identify all publications reporting natural infection of T. vivax across the world. All the three search engines were screened using the search term Trypanosoma vivax without time and language restrictions. Publications on T. vivax that met our inclusion criteria were considered for systematic review and meta-analysis.

RESULT

The study provides a global database of T. vivax, consisting of 899 records from 245 peer-reviewed articles in 41 countries. A total of 232, 6277 tests were performed on 97 different mammalian hosts, including a wide range of wild animals. Natural infections of T. vivax were recorded in 39 different African and Latin American countries and 47 mammalian host species. All the 245 articles were included into the qualitative analysis, while information from 186 cross-sectional studies was used in the quantitative analysis mainly to estimate the pooled prevalence. Pooled prevalence estimates of T. vivax in domestic buffalo, cattle, dog, dromedary camel, equine, pig, small ruminant and wild animals were 30.6%, 6.4%, 2.6%, 8.4%, 3.7%, 5.5%, 3.8% and 12.9%, respectively. Stratified according to the diagnostic method, the highest pooled prevalences were found with serological techniques in domesticated buffalo (57.6%) followed by equine (50.0%) and wild animals (49.3%).

CONCLUSION

The study provides a comprehensive dataset on the geographical distribution and host range of T. vivax and demonstrates the potential of this parasite to invade other countries out of Africa and Latin America.

The origins of the trypanosome genome strains Trypanosoma brucei brucei TREU 927, T. b. gambiense DAL 972, T. vivax Y486 and T. congolense IL3000

The genomes of several tsetse-transmitted African trypanosomes (Trypanosoma brucei brucei, T. b. gambiense, T. vivax, T. congolense) have been sequenced and are available to search online. The trypanosome strains chosen for the genome sequencing projects were selected because they had been well characterised in the laboratory, but all were isolated several decades ago. The purpose of this short review is to provide some background information on the origins and biological characterisation of these strains as a source of reference for future users of the genome data. With high throughput sequencing of many more trypanosome genomes in prospect, it is important to understand the phylogenetic relationships of the genome strains.

Trypanosoma vivax infections: pushing ahead with mouse models for the study of Nagana. I. Parasitological, hematological and pathological parameters

African trypanosomiasis is a severe parasitic disease that affects both humans and livestock. Several different species may cause animal trypanosomosis and although Trypanosoma vivax (sub-genus Duttonella) is currently responsible for the vast majority of debilitating cases causing great economic hardship in West Africa and South America, little is known about its biology and interaction with its hosts. Relatively speaking, T. vivax has been more than neglected despite an urgent need to develop efficient control strategies. Some pioneering rodent models were developed to circumvent the difficulties of working with livestock, but disappointedly were for the most part discontinued decades ago. To gain more insight into the biology of T. vivax, its interactions with the host and consequently its pathogenesis, we have developed a number of reproducible murine models using a parasite isolate that is infectious for rodents. Firstly, we analyzed the parasitical characteristics of the infection using inbred and outbred mouse strains to compare the impact of host genetic background on the infection and on survival rates. Hematological studies showed that the infection gave rise to severe anemia, and histopathological investigations in various organs showed multifocal inflammatory infiltrates associated with extramedullary hematopoiesis in the liver, and cerebral edema. The models developed are consistent with field observations and pave the way for subsequent in-depth studies into the pathogenesis of T. vivax - trypanosomosis.

While most research efforts have focused on T. b. brucei trypanosomosis, infections caused by T. vivax and T. congolense which predominate in livestock and small ruminants have been subject to little study. In order to circumvent the major constraints inherent to studying T. vivax/host interactions in the field, we developed in vivo murine models of T. vivax trypanosomosis. We show here that the mouse experimental model reproduce most features of the infection in cattle. More than reflecting only the main parasitological parameters of the animal infection, the mouse model can be used to elucidate the immunopathological mechanisms involved in parasite evasion and persistence, and the tissue damage seen during infection and disease. Studies planned for the future will allow us to further investigate T. vivax–induced immunopathology in an experimental context for which all the necessary tools are now available.

Characterization of a small variable surface glycoprotein from Trypanosoma vivax

Several biochemical properties of a variant surface glycoprotein (VSG) from the parasite Trypanosoma (Duttonella) vivax have been determined. ILDat 2.1 VSG is approximately 40 kDa in size making this the smallest trypanosome VSG described to date. The glycolipid anchor of ILDat 2.1 VSG is resistant to treatment with T. brucei-derived phospholipase C and data based on lectin affinity chromatography, incorporation of radiolabelled sugar and treatment with endoglycosidase H suggest that the T. vivax VSG bears little carbohydrate. cDNA to ILDat 2.1 VSG mRNA has been cloned and the encoded protein sequence includes the N-terminal amino acid peptide sequence derived from native VSG. The molecular weight of the VSG predicted from the translated cDNA sequence is similar to that of the native molecule and in support of the biochemical data it is devoid of sites for N-linked glycosylation. Examination of the deduced ILDat 2.1 VSG protein sequence reveals that it is most similar to T. congolense VSGs in the distribution of Cys residues and like the former it does not contain any of the defined VSG C-terminal domain types. However, unlike T. congolense VSGs it does not readily fit into the currently described VSG N-terminal domain types. Our studies suggest that ILDat 2.1 VSG is distinct from any of the previously characterized VSGs.

Surface-associated serine-threonine kinase in Schistosoma mansoni

Existing evidence suggests that parasites of the genus Schistosoma are responsive to external stimuli derived from the host and from parasites of the opposite sex. We hypothesize that these interactions are mediated by receptors at the parasite surface. To begin to address this issue, we have employed surface labelling by biotinylation to identify and isolate the surface molecules of adult S. mansoni. Isolated surface molecules were subsequently analyzed for the presence of protein kinases, since protein kinase activity is frequently associated with signal-transducing receptors. Our results demonstrate that serine-threonine kinase activity is associated with the parasite surface and that surface proteins of 145, 125, 95 and 57 kDa became phosphorylated on serine and threonine residues under in vitro conditions. No significant tyrosine phosphorylation of surface molecules was detected, despite the presence of many tyrosine-phosphorylated proteins in tegumental extracts. An additional unexpected finding of these studies was that adult schistosomes express considerably more surface molecules than previously indicated by radioiodination studies, and that the majority of these molecules are of parasite rather than host origin.

Biotinylation of proteins on the surface of zona-free mouse oocytes

In this study, we have labelled proteins on the surface of unfertilized, zona-free mouse oocytes using a nonisotopic biotinylation procedure. The zona pellucida was weakened by brief incubation in chymotrypsin and removed by mechanical pipetting through a narrow-bore glass pipette. Surface proteins were labelled using sulfo-NHS-biotin (sulfosuccinimidobiotin), a water-soluble, membrane-impermeable biotinylation reagent. The distribution of biotinylated proteins on the oocyte surface was assessed by fluorescence microscopy using streptavidin-FITC. Bright fluorescence was noted on the surface of the oocyte, except in a circular region overlying the meiotic spindle where the fluorescence was weak or absent. The intensity of fluorescence was markedly reduced by incubation of biotinylated oocytes in trypsin (1 mg/ml) or chymotrypsin (2 mg/ml), and in vitro fertilization experiments showed that biotinylation did not compromise the fertilizability of the oocytes. The biotinylated proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and analyzed by Western blotting using streptavidin-HRP and enhanced chemiluminescence (ECL) detection. The most prominent biotinylated proteins were of M(r) 82 and 69 kD, but other major proteins of M(r) 93, 78, 61, 52, 49, 40, 28, and 22 kD were detected, as well as 14 minor proteins of M(r) 18-100 kD. The major bands could be detected in fewer than 50 oocytes. This biotinylation procedure is fast, versatile and sensitive, and it is therefore an excellent tool for studying proteins exposed on the surface of mammalian oocytes and embryos.

An integral membrane glycoprotein associated with an endocytic compartment of Trypanosoma vivax: identification and partial characterization

A 65-kD glycoprotein (gp65) of Trypanosoma (Duttonella) vivax was identified using a murine monoclonal antibody (mAb 4E1) that had been raised against formalin-fixed, in vitro-propagated, uncoated forms. Intracellular localization studies utilizing the mAb in immunofluorescence on fixed, permeabilized T. vivax bloodstream forms and immunoelectron microscopy on thin sections of Lowicryl K4M-embedded cells revealed labeling of vesicles and tubules in the posterior portion of the parasite. Some mAb-labeled vesicles contained endocytosed 10 nm BSA-gold after incubation of the parasites with the marker for 5-30 min at 37 degrees C, and the greatest degree of colocalization was observed after 5 min. Double labeling experiments using the mAb and a polyclonal anti-variant surface glycoprotein (VSG) antibody to simultaneously localize both gp65 and VSG demonstrated that there was little overlap in the distribution of these antigens. Thus, gp65 is associated with tubules and vesicles that are involved in endocytosis but which appear to be distinct from VSG processing pathways within the cell. Using the mAb for immunoblot analyses, gp65 was shown to be enriched in a fraction of solubilized membrane proteins eluted from either immobilized Con A or Ricinus communis agglutinin and was found to possess carbohydrate linkages cleaved by both endoglycosidase H and O-glycosidase, suggesting the presence of N- and O-linked glycans. Protease protection and crosslinking experiments suggest that gp65 is a transmembrane protein with trypsin cleavage and NH2-crosslinking sites on the lumenal face of the vesicles.

Identification of the surface components of Trypanosoma evansi

125I-labelling was used to characterise the surface components of five stocks of Trypanosoma evansi. Two components of 67 and 60.5 kD were labelled in two of the stocks, a single 60.5 kD component in two other stocks and no components in the remaining stock. These differences are probably related to the labelling method and biochemical differences between the stocks.

Trypanosoma brucei rhodesiense bloodstream forms: surface ricin-binding glycoproteins are localized exclusively in the flagellar pocket and the flagellar adhesion zone

Specific binding of fluoresceinated succinyl-concanavalin A, wheat germ agglutinin, and ricin to untreated and trypsinized bloodstream forms of Trypanosoma brucei rhodesiense was quantitated by flow cytofluorimetry, and sites of lectin binding were identified by fluorescence microscopy. All three lectins only bound to the flagellar pocket of untreated parasites. When parasites were trypsinized to remove the variant surface glycoprotein coat, new lectin binding sites were exposed, and specific binding of all three lectins increased significantly. New specific binding sites for succinyl-concanavalin A and wheat germ agglutinin were present along both the free flagellum and flagellar adhesion zone and were uniformly distributed on the parasite surface. However, ricin did not bind uniformly on the surface and did not stain the free flagellum of trypsinized cells. Ricin only bound to the flagellar adhesion zone of trypsinized cells and of cells that had been treated with formaldehyde prior to staining. Electron microscopy of cells exposed to ricin-colloidal gold complexes revealed that that ricin binding was restricted to the anterior membrane of the flagellar pocket of untrypsinized cells and to this portion of the flagellar pocket and the cell body membrane in the flagellar adhesion zone of trypsinized cells. Evidence that these membranes constitute a functionally important membrane microdomain is reviewed.

Parasite-specific antibody responses of ruminants infected with Trypanosoma vivax

Sera from goats and cattle that were infected with two Trypanosoma vivax clones (ILDat 1.2 and ILDat 2.1) derived from different stocks were analysed for antibody activity against the variable surface glycoproteins (VSGs) of the infecting clones by enzyme-linked immune assays (ELISA) and immune lysis. To obtain purified VSG, lysed trypanosomes were separated on dodecyl sulphate-polyacrylamide gels. The gels were copper stained and the VSG protein band was excised from the gel. After destaining, the proteins were electroeluted from the gel slices and used as antigens in ELISA. High titres of IgM and IgG1 antibodies and lytic antibodies against the VSG of the infecting clone were detected. The IgG1 response appeared about 4 days later than the IgM response. IgG2 antibodies were only detected in goats and cattle that were infected with ILDat 1.2. Two goats and two calves that were infected with ILDat 1.2 showed recurrent peaks in lytic activity and of IgM and IgG1 antibody activity to the VSG of the infecting variable antigenic type (VAT). Two goats that were infected with ILDat 2.1 showed a similar pattern, but in two other goats there was a recurrent peak only in the IgM class. Recurrent peaks of antibody activity to the VSG of ILDat 1.2 and ILDat 2.1 were not detected in the sera of goats that had been inoculated with irradiated trypanosomes or that had been infected with an unrelated T. vivax clone. The recurrence of antibody peaks against the VSG of infecting VATs suggests that trypanosomes with completely or partially identical surface determinants reappear during T. vivax infection of ruminants.

Hybridisation with a repetitive DNA probe reveals the presence of small chromosomes in Trypanosoma vivax

We have isolated and cloned a tandemly repeating element from trypanosoma vivax for use as a species-specific DNA probe. The repeat hybridises only with DNA from T. vivax, not with DNA from other Salivarian trypanosome species (T. brucei spp., T. congolense, T. simiae). The monomer of the repeat is approximately 180 bp long and is 64% GC rich. Hybridisation of the cloned fragment with size-fractionated large DNA molecules of 3 T. vivax stocks revealed a band in the position expected for minichromosomes, although these were believed absent in T. vivax. This band migrated to the 100-250 kb area of the gel at 4 different pulse frequencies and also hybridised with a telomeric repeat probe from T. brucei. The band is unlikely to be simply degraded material, since it failed to hybridise with another highly repetitive sequence from T. vivax and was consistently present in different trypanosome preparations. We conclude that T. vivax does possess mini-chromosomes, although possibly only 1 or 2 per cell.

Use of Iodogen and sulfosuccinimidobiotin to identify and isolate cuticular proteins of the filarial parasite Brugia malayi

The cuticle of filarial nematodes is a dynamic structure which may be an important target for protective host immune responses. Prior studies have employed radioiodination of intact parasites to demonstrate that the collagenous cuticle of filariids contains relatively few exposed proteins, some of which are stage and/or species-specific. In the present study, we have used sulfo-NHS-biotin to label and affinity purify cuticular components of living adult Brugia malayi. Results obtained by this method were compared with the widely used Iodogen method of surface radioiodination by SDS-PAGE analysis of detergent-solubilized worms and by ultrastructural analysis. Both labeling methods produced very similar electrophoretic patterns with major doublets at 70 and 100 kDa, a major band at 25 kDa, and minor bands between 60-200 kDa. Ultrastructural analysis showed that both methods labeled components throughout all levels of the parasite cuticle; underlying somatic tissues were not labeled. The biotinylated components were isolated from the total parasite extract by affinity chromatography on an avidin matrix. Further characterization of these surface-associated proteins may lead to improved methods for the control of filariasis.

Recent studies of the biology of Trypanosoma vivax

Recent biological investigations of the African trypanosomes have been moving away from their previous preoccupation with the phenomenon of antigenic variation. The feeling has arisen that antigenic variation, as demonstrated by the Trypanozoon and Nannomonas subgenera of trypanosomes, is too extensive, the number of serodemes too large and the coexistence of different species in many areas too complicated, to allow any immunoprophylaxis based on antibodies to variable antigens. This is, of course, not to rule out possible biochemical intervention in the biosynthesis or export of VSG molecules by trypanosomes. However, in the case of T. vivax, more information is required concerning antigenic variation and coat structure in this organism before these avenues of investigation are discarded. Ways of improving the yield of mature metacyclic trypanosomes in vitro must be found, so that the contribution of metacyclic variable antigens to the induction of immunity in T. vivax infection can be elucidated. The number of bloodstream VATs must be determined (perhaps by genetic rather than serological means), as there is evidence both for VAT exhaustion contributing to the self-cure of infected hosts, and for a possible limit to the number of VATs which can be expressed in infections in Africa. In South America nothing is known of the number of serodemes of T. vivax which exist, although such knowledge is obviously required, especially if immunity to bloodstream variants is the more important mechanism of inducing immunity to this trypanosome and true cyclical transmission is rare in, or absent from, that subcontinent. Further, in a fragile organism, with a coat of suspect integrity, the method of VSG packing and the relative exposure of underlying surface molecules seems to hold out even more hope for an immunological intervention based on cell surface but invariant molecules than is the case with T. brucei or T. congolense, although this is being attempted with the latter species. In T. brucei infections the appearance of the non-dividing stumpy population acts as a stimulus to the induction of humoral immune responses. In ruminants, antibody responses to T. vivax, at least as judged from lysis tests, lag behind the appearance of the different VATs by some days. It would be important to determine, therefore, whether, if late bloodstream forms could be induced more frequently in the ruminant, the speed of anti-VAT responses could be enhanced. Whilst self-cure appears to be relatively common in T. vivax infections, it is unlikely that it results in sterile immunity.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular size variations in an immunoprotective protein complex among isolates of Anaplasma marginale

A major surface protein complex from the Florida isolate of Anaplasma marginale has been previously shown to induce protection in immunized cattle and has been proposed as the basis of a subunit vaccine against anaplasmosis. This complex in the Florida isolate is composed of two noncovalently associated polypeptides with molecular masses of 105 and 100 kilodaltons (kDa). The analogous protein complex from four geographically different isolates of A. marginale was immunoprecipitated and compared with the protein complex of the Florida isolate. The polypeptides of the complex varied in apparent molecular mass among the isolates. By using antibodies recognizing epitopes on each polypeptide of the Florida isolate, the antigenic identity of the polypeptides in the analogous complexes was determined. The polypeptides recognized by the neutralizing monoclonal antibody 22B1, which recognizes a 105-kDa polypeptide in the Florida isolate, ranged from 70 to 100 kDa in the other isolates. Those polypeptides recognized by rabbit antiserum R911, which recognizes a 100-kDa polypeptide in the Florida isolate, ranged from 97 to 100 kDa. The surface-exposed peptides in the complexes were compared by limited enzymatic digestion to assess structural homology among isolates. Despite the marked variations in molecular weight, there were conserved peptides between the 22B1-reactive polypeptides and between the R911-reactive peptides. Determination of the role of the conserved peptides in inducing immunity will be critical in the application of these polypeptides as the basis of a subunit vaccine for bovine anaplasmosis.

Surface protein composition of Aeromonas hydrophila strains virulent for fish: identification of a surface array protein

The surface protein composition of members of a serogroup of Aeromonas hydrophila which exhibit high virulence for fish was examined. Treatment of whole cells of representative strain A. hydrophila TF7 with 0.2 M glycine buffer (pH 4.0) resulted in the release of sheets of a tetragonal surface protein array. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis analysis showed that this sheet material was composed primarily of a protein of apparent molecular weight 52,000 (52K protein). A 52K protein was also the predominant protein in glycine extracts of other members of the high-virulence serogroup. Immunoblotting with antiserum raised against formalinized whole cells of A. hydrophila TF7 showed the 52K S-layer protein to be the major surface protein antigen, and impermeant Sulfo-NHS-Biotin cell surface labeling showed that the 52K S-layer protein was the only protein accessible to the Sulfo-NHS-Biotin label and effectively masked underlying outer membrane (OM) proteins. In its native surface conformation the 52K S-layer protein was only weakly reactive with a lactoperoxidase 125I surface iodination procedure. A UV-induced rough lipopolysaccharide (LPS) mutant of TF7 was found to produce an intact S layer, but a deep rough LPS mutant was unable to maintain an array on the cell surface and excreted the S-layer protein into the growth medium, indicating that a minimum LPS oligosaccharide size was required for A. hydrophila S-layer anchoring. The 52K S-layer protein exhibited hear-dependent SDS-solubilization behavior when associated with OM, but was fully solubilized at all temperatures after removal from the OM, indicating a strong interaction of the S layer with the underlying OM. The native S layer was permeable to 125I in the lactoperoxidase radiolabeling procedure, and two major OM proteins of molecular weights 30,000 and 48,000 were iodinated. The 48K species was a peptidoglycan-associated, transmembrane protein which exhibited heat-modifiable SDS solubilization behaviour characteristic of a porin protein. A 50K major peptidoglycan-associated OM protein which was not radiolabeled exhibited similar SDS heat modification characteristics and possibly represents a second porin protein.