Trypanosoma brucei brucei and T. b. gambiense: stumpy bloodstream forms express more CB1 epitope in endosomes and lysosomes than slender forms

CB1-glycoprotein is a component of flagellar pocket, endosome, and lysosome membranes of long, slender bloodstream forms of the Trypanosoma brucei subgroup of African trypanosomes. We have used immunoblotting, immunofluorescence, and cryoimmunoelectron microscopy to study CB1-glycoprotein expression as long, slender bloodstream forms of pleomorphic T. b. brucei and T. b. gambiense transform through intermediate stages into short, stumpy forms. Intermediate and stumpy forms express more CB1-glycoprotein than long, slender forms. These results, coupled with previous work showing that procyclic forms do not express CB1-glycoprotein, show that the expression of lysosomal membrane glycoproteins is regulated coordinately with other aspects of lysosome and endosome function as these trypanosomes go through their life cycle.

Characterization of human serum-resistant and serum-sensitive clones from a single Trypanosoma brucei gambiense parental clone

A protocol was developed to select clones of Trypanosoma brucei gambiense having different levels of resistance to normal human serum. Human serum-resistant clones were selected from a single parental clone by continuous serum treatment of infected immunosuppressed mice. Human serum-sensitive revertant clones were also obtained by continuous passage of resistant clones in immunosuppressed mice but without human serum pressure. It has been demonstrated that our trypanosome clones express distinct but stable levels of resistance. The variant antigenic type of each clone was characterized serologically and by 1-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. After selective pressure with human serum, variant antigen-type differences always occurred among clones in which different human serum susceptibilities were found. The work reported here demonstrates that in our T. brucei gambiense immunosuppressed mouse model there is a predictable association between variant antigen type and human serum resistance.

Relationship between human serum trypanocidal activity and host resistance to the African trypanosomes

Results reported here show that humans have various levels of trypanocidal activity in their sera. This difference appeared stable when different samples were taken from the same individuals over time. It was not possible to account for the variability between individuals by obvious differences in health, nutrition, or living habits. In addition, the trypanocidal titers did not vary significantly when stored for various lengths of time at -70 C. To examine the relationship between the titer of trypanocidal activity in a host and the degree of human serum resistance of the challenge trypanosome inoculum, mice (C57BL/6J) were pretreated with various amounts of different human serum and then infected with clones having different degrees of resistance to human serum. It was demonstrated that host susceptibility to an African trypanosome infection depends upon 2 variables: the level of trypanocidal activity in individual human serum and the degree of human serum resistance of individual clones of African trypanosomes. Based upon the animal model presented here, it is hypothesized that this relationship is under selective evolutionary pressure and will influence the susceptibility of animals in endemic areas as well as the transmission of human trypanosomiasis.

Screening for Trypanosoma brucei gambiense antibodies with the Indirect Fluorescent Antibody Test (IFAT). Effect of age and previous treatment

This paper reports on some of the findings of a longitudinal multi-round investigation into the predictive power of early signs and symptoms of human African trypanosomiasis caused by T.b. gambiense, in the Rural Health Zone of Kasongo (Maniema, Zaire). It assesses the importance of the effect of age and a history of previously treated sleeping sickness on serological positivity as measured by the Indirect Fluorescent Antibody Test (IFAT), used as a screening test. The impact of including age and a history of previous sleeping sickness as part of the screening process is discussed in terms of sensitivity and positive predictive value. Including weak serological positivity among the screening criteria does not appear to improve the sensitivity of the IFAT test in this setting.

Nitric oxide-mediated cytostatic activity on Trypanosoma brucei gambiense and Trypanosoma brucei brucei

Macrophages collected from BCG-infected mice or exposed in vitro to interferon-gamma plus lipopolysaccharide developed a cytostatic activity on Trypanosoma brucei gambiense and Trypanosoma brucei brucei. This trypanostatic activity of activated macrophages was inhibited by addition of N-monomethyl-L-arginine, an inhibitor of the L-arginine-nitric oxide (NO) metabolic pathway, indicating a role for NO as the effector molecule. Contrary to trypanosomes treated with N2gas, trypanosomes treated with NO gas did not proliferate in vitro on normal macrophages. Compared to mice infected with control parasites, mice infected with NO-treated parasites had decreased parasitemias in the first days postinfection and had a prolonged survival. Addition of excess iron reversed the trypanostatic effect of both activated macrophages and NO gas. These data show that activated macrophages exert an antimicrobial effect on T.b. gambiense and T.b. brucei through the L-arginine-NO metabolic pathway. In trypanosomes, NO could trigger iron loss from critical targets involved in parasite division. The participation of this effector mechanism among the other immune elements involved in the control of African trypanosomes (antibodies, complement, phagocytic events) remains to be defined.

Human African trypanosomiasis: presence of antibodies to galactocerebrosides

Improvements were made in the immunodetection of anti-galactocerebroside (anti-GalC) antibody in sera of patients with human African trypanosomiasis by thin-layer chromatography, enzyme-linked immunosorbent assay, and immunoadsorption. Rabbit anti-GalC antibodies were used to standardize these techniques and demonstrate their specificity. Anti-GalC antibodies were found in the sera of 42.8% of 63 patients with human African trypanosomiasis. Thirty-four control subjects living in the same endemic area were also tested. Anti-GalC levels were higher in human African trypanosomiasis patients with neurologic disturbances compared with patients without such disturbances. These antibodies were distributed mainly between the IgG and IgM classes, but 28% of the patients with human African trypanosomiasis had increased IgA levels without anti-GalC antibody activity.

Inhibition of IgM antibody-mediated aggregation of Trypanosoma gambiense in the presence of complement

This paper deals with the immune reaction between Trypanosoma gambiense and monoclonal IgM mouse antibody at equivalence with or without rabbit complement. Antibody-mediated trypanosome clumps formed in the absence of complement, and were readily dissociated by complement to become free. In the presence of complement, on the other hand, T. gambiense were not aggregated by the antibody. Free parasites adhered readily to cultured peritoneal macrophages. Complement-mediated dissociation of the clumped trypanosomes in the equivalence area released a large number of previously bound surface antigens. These antigens were capable of binding again to fresh IgM antibody. Experimental results further indicated that the complement system caused a functional alteration, changing the multivalent nature of the IgM antibody in the immune complex into a univalent one. This phenomenon is of great advantage to the infected host in clearing pathogens in vivo, as it allows more antibodies to attach to trypanosomes and subsequently initiate complement activity.

Immunological activities of monoclonal IgG1 antibody against Trypanosoma gambiense

The present paper deals with the immune reaction between a monoclonal IgG1 antibody and Trypanosoma gambiense. The aggregation of trypanosomes, immune adherence to macrophages and protection against infection are associated with the antibody. IgG1-mediated clumping of trypanosomes is readily dissociated by the addition of complement. Dissociation of the clumped trypanosomes in the equivalence area released approximately fifty percent of previously bound surface antigens. These antigens were capable of binding again to new IgG1 antibody. Complement deposition rendered bivalent IgG1 antibody in the immune complex functionally univalent. Such an event in the presence of complement is of great advantage to the infected host in killing pathogens in vivo, as it allows more antibodies to attach to surface antigens and subsequently to initiate complement activity.

[Serological evidence of the existence of a wild reservoir of Trypanosoma brucei gambiense in the Pendjari biosphere reservation in the Republic of Benin]

In the national park of Pendjari, situated in the North-West of Benin, 91 wild animals, belonging to seven species, were darted. Thick and thin blood smears were examined for trypanosomes and plasma for trypanolytic antibodies against 6 antigenic variants of Trypanosoma brucei gambiense. Parasites were found in 13.92% and trypanolytic antibodies in 20.88% of the samples. A total of 28.57% of animals were positive by at least one of the two test systems used. Morphologically Trypanosoma congolense, T. vivax and T. brucei were identified. Overall prevalence was 40% in Adenota kob (n: 50), 13.63% in Alcelaphus buselaphus (n: 22), 10% in Hippotragus equinus (n: 10), 33% in Kobus defassa (n: 3), 0% in Phacochoerus aethiopicus (n: 3) and in Syncerus caffer (n: 2). The only lion (Panthera leo) examined was serologically positive. The results indicate that the wild animals are reservoirs of animal trypanosomes and suggest that among them Adenota kob and Panthera leo are carriers of T. brucei gambiense, one of the etiological aspects of human trypanosomiasis.

Immune mechanism facilitating clearance of Trypanosoma gambiense by IgG3 antibody from infected host

The aggregation of trypansomes, immune adherence to macrophage and protection against infection of Trypanosoma gambiense are associated with IgG3 antibody. IgG3-mediated clumping trypanosomes are readily dissociated by the aid of complement to become free. Dissociation of the clumped trypanosomes in the equivalence area released approximately fifty percent of previous bound surface antigens. These antigens were capable of binding again to new IgG3 antibody. Experiments indicated that complement deposition altered functionally bivalent IgG3 antibody in the immune complex into a univalent one. Such event in the presence of complement is of great advantage to the infected host in killing pathogens in vivo, as it allows more antibodies to attach to surface antigens and subsequently initiate complement activity.

An experimental latex agglutination test for antibody detection in human African trypanosomiasis

A latex card agglutination test for detection of antibodies in human African trypanosomiasis is presented. The latex was covalently coated with semipurified surface glycoprotein of Variable Antigen Type LiTat 1.6 of Trypanosoma brucei gambiense. Sera from 100 patients infected with T.b. gambiense, 26 patients infected with T.b. rhodesiense and 707 individuals without trypanosomiasis, including 132 malaria seropositives, have been tested. At serum dilution 1:16, sensitivity of the test was 91% for the T.b. gambiense and 42.3% for the T.b. rhodesiense group. Specificity was over 99%. The reagent remained stable at +/- 6 degrees C for at least 3 months. Reagent kept at 37 degrees C for 3 months retained its sensitivity and showed a slight decrease in specificity.

[Interpretation of the CATT (Card Agglutination Trypanosomiasis Test) in the screening for human trypanosomiasis due to Trypanosoma brucei gambiense]

Mass screening for Gambiense sleeping sickness is usually done with the Card Agglutination Trypanosomiasis Test (CATT) in series (total blood CATT followed by a serum CATT if the first test is positive) and the search for trypanosomes in cervical adenopathies. At present, the double positives (blood CATT and serum CATT) as well as the subjects in whom the trypanosome was found (in the blood or gland juice) are treated. The existence of patients whose gland punction was proved positive whereas the total blood CATT remained negative, has led the authors to make a survey with the CATT in parallel (on blood and serum CATT) on a 2,030 subjects sample in the Boko Songho site (Congo-Bouenza area). Whereas the prevalence of the positive cases to blood CATT and serum CATT (CATT in series) is 6.8%, the prevalence of the positive cases to at least one of both CATT's (CATT in parallel) is 19%. The 12.2% discordant results (blood+/serum- or blood-/serum+) have been reexamined a month later with the CATT and with the indirect Fluorescent Antibody Test (IFAT). Among these, 22.3% had become positive to blood and serum, whereas 30.6% had become negative. The latter group presents the problem of cross-reactions. The authors performed an IFAT with Trypanosoma congolense (T.c.) as antigen on an 18 subjects sample with a discordant CATT. All IFAT performed with T.c. were positive to a 1/50th threshold whereas some of the serum remained negative with IFAT when Trypanosoma brucei gambiense had been used as an antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

African trypanosomes express an immunogenic protein with a repeating epitope of 24 amino acids

Infection with intracellular protozoan parasites such as Plasmodium, Leishmania and Trypanosoma cruzi induces a strong antibody response against proteins containing tandem repeats, suggesting that these repetitive epitopes may camouflage vulnerable parasite antigens from a 'protective' immune response. We tested this theory by immunoscreening a cDNA expression library of African trypanosomes, extracellular parasites that evade their hosts' immune response by antigenic variation, and found that the most frequently detected trypanosome protein contains more than 40 tandem copies of a 24-amino acid repeat with a consensus sequence of A-M-E-D-E-L-D-S-L-R-A-L-N-E-Q-Y-E-A-L-Q-R-T-N-A (net charge = -4). This protein is encoded on an mRNA of more than 20 kb and has slight sequence similarities with cytoskeletal, intermediate filament proteins in other organisms. Thus, protozoan proteins with tandemly repeating epitopes do not exist solely to divert the humoral immune response; they have other specific physiological functions for the parasites and affect the overall parasite-host interaction in unknown and perhaps different ways.

Absence of serological markers of infection with Trypanosoma brucei gambiense in domestic animals in a sleeping sickness focus in south Congo

A total of 33 domestic animals living in close contact with man in a human trypanosomiasis focus in South Congo were examined parasitologically and tested for serological markers of Trypanosoma brucei gambiense infection. 84.8% of the animals presented detectable T. congolense parasitaemia. The high rate of seropositivity observed with CATT (81.8%) contrasted with the low seroprevalence found with ELISA (less than 13%). None of the 33 plasma samples showed lytic antibodies when analysed by immune lysis test against 10 distinct T. b. gambiense predominant variable antigen types (LiTat 1.1 to 1.10). The results demonstrate the lack of specificity of CATT, and to a lesser extent ELISA, in detecting T. b. gambiense infection in animals. The seropositivity may be due to cross-reaction with certain T. congolense antigens. The absence of serological markers specific to T. b. gambiense confirms the parasitological data which estimate the prevalence rate of animals infected with Trypanozoon as less than 1% in the region.

Control of antigenic variation in African trypanosomes

Antigenic variation of African trypanosomes results from the controlled expression of a single variant cell-surface glycoprotein (VSG) gene from a repertoire of about 1,000 genes. The transcription of the VSG genes occurs uniquely at telomeres, where the expressed VSG gene is part of a large polycistronic transcription unit that appears to be transcribed by a specialized RNA polymerase. Recent developments that enhanced our understanding of the control of VSG gene expression and of the mechanisms of antigenic variation are discussed in this review.

Infectivity of Trypanosoma (Trypanozoon) brucei gambiense for baboons (Papio hamadryas, Papio papio)

In order to study sensitivity or resistance of T.b. gambiense to baboon serum, two species of baboons, P. hamadryas and P. papio were inoculated with T.b. gambiense clone LiTat 1.1. Both species were receptive to infection but, parasitological and immunological parameters showed that P. papio was more trypanotolerant than P. hamadryas. The VAT-specific trypanolysis test and the ELISA, using MoAb for circulating antigen detection may be appropriate for the diagnosis of human trypanosomiasis due to T.b. gambiense.

[Evaluation of Testryp CATT applied to blood samples on filter paper and on diluted blood in a focus of trypanosomiasis due to Trypanosoma brucei gambiense in the Ivory Coast]

The Testryp CATT was performed on dried blood samples on filter-paper and on diluted blood using a microtechnique. This method was applied to both sample collection techniques and was evaluated in parallel with the classical Testryp CATT on whole blood, as described in the instructions provided with the reagents by the manufacturer. A total of 2087 people were tested; 453 samples were tested in the laboratory and 1634 during a field survey in 5 villages of a trypanosomiasis focus in Daloa, Côte d'Ivoire. This study has demonstrated that the Testryp CATT micromethod on either type of sample collection gives results comparable to the Testryp CATT on whole blood. The collection of dried blood samples on filter-paper can be performed by non-specialized staff in trypanosomiasis control programmes of the national health services. In addition, a flask of CATT reagent will allow testing of 6 times more people by the micromethod than by the classical whole-blood method. The micromethod is suitable in the implementation of programmes for the serological surveillance of populations at risk.

Dissociation of IgG antibody-mediated clumps of Trypanosoma brucei gambiense by complement

Aggregated trypanosome masses that had formed in the region of equivalence in the absence of complement were readily dissociated by complement. Complement-mediated dissociation of the clumped trypanosomes in the area of equivalence released approximately 50% of the previously bound surface antigens. These antigens were capable of rebinding to new IgG antibody. Experiments indicated that complement deposition altered the bivalent IgG antibody in the immune complex into a univalent form. The occurrence of such an event in the presence of complement provides a great advantage to the infected host in the killing of pathogens in vivo, as it enables a greater number of antibodies to attach to surface antigens and subsequently initiate complement activity.

Diagnosing multiple parasitic infections: trypanosomiasis, loiasis and schistosomiasis in a single case

A case is reported of a 32-year-old traveller with loiasis, schistosomiasis and African trypanosomiasis. The patient had been working in oil exploration in Nigeria and Gabon and presented with Calabar swellings and carpal tunnel syndrome. Serology for all 3 diseases was positive but microfilariae of Loa loa and ova of schistosomiasis were not found. Treatment with diethylcarbamazine and praziquantel was given for loiasis and schistosomiasis respectively. Trypanosomes were isolated from a lymph node aspirate only after repetition of the procedure 2 months later and the patient was treated with suramin. He developed a drug induced nephritis and was then treated successfully with alpha-difluoromethylornithine. There is a discussion of the difficulties encountered making these diagnoses in Europeans particularly where there are atypical clinical features. The risks of rural work in West Africa are noted and the importance of considering all parasitic diseases relevant to the travel/occupational history is emphasised.

An expression-site-associated gene family of trypanosomes is expressed in vivo and shows homology to a variant surface glycoprotein gene

Utilizing first-strand cDNA from different stages, a gene family was identified that is expressed in bloodstream form trypanosomes but not in cultured procyclic forms. This family of 50-100 genes, termed bloodstream-specific 1 (BS1), shares a chromosomal distribution pattern similar to the variant surface glycoprotein (VSG) genes and the expression-site-associated genes (ESAGs). The BS1 genes are expressed in several variants of Trypanosoma brucei brucei and in Trypanosoma brucei gambiense. Sequence analysis of five members of this gene family reveals the recently described ESAG 6 and ESAG 7 genes as well as the ESAG X gene to be members of this family. We have been unable to localize the BS1 gene product in the cell but show that chronically infected rabbit serum recognizes recombinant BS1 protein arguing for expression in vivo. Finally we note that the derived protein sequence for the BS1 genes suggests an evolutionary relationship with at least one variant surface glycoprotein gene, and hence these studies may provide clues to understanding the molecular origins of antigenic variation in trypanosomes.

Ordered appearance of antigenic variants of African trypanosomes explained in a mathematical model based on a stochastic switch process and immune-selection against putative switch intermediates

Antigenic variation of African trypanosomes results from the periodic activation of a single new variant cell surface glycoprotein (VSG) gene out of a repertoire of about a 1000 VSG genes. In spite of the apparently random genetic basis of the process of antigenic variation, the relapsing parasitemias are characterized by an as yet unexplained order of appearance of major VSG variants. Here we mathematically test hypotheses concerning the blood-based parasitemia. In our model the antigenic switches occur at random at the DNA level. A variable proportion of the switches has a short intermediate phase in which two different VSGs simultaneously occur on the cell surface. We show that, in a theoretical population of 230 single expressor variants in an immunocompetent or in an immunodeficient host, it is not possible to explain the ordered appearance of variants by affecting the growth coefficients of single expressors or double expressors or by affecting the antigen switch probabilities. Rather, a realistic parasitemia can be obtained if the majority of switches has a double expressor switch-intermediate phase and if the double expressors have a differential susceptibility to the immune control. This study is significant in providing a theoretical basis for the ordered appearance of variants and in explaining previously unresolved discrepancies between the rate of appearance of new variants in culture and in vivo. In addition, testable predictions as to the development of the infections, switch rate of variants, fraction of double expressors, and parasite mortality coefficients are generated.

Granulocyte-macrophage colony-stimulating activity in the serum of mice stimulated with homogenates of Trypanosoma gambiense

Infection of mice with Trypanosoma gambiense induced a rapid and transient increase in levels of serum granulocyte-macrophage colony-stimulating activity (GM-CSA) followed by an increase in the numbers of circulating neutrophils and large mononuclear cells. Similar phenomena were observed in mice injected with a trypanosomal homogenate. In such mice, levels of GM-CSA were markedly elevated as early as 1-2 days after administration of the homogenate and then rapidly decreased. Numbers of circulating neutrophils and large mononuclear cells increased within 2 and 3 days after injection of the homogenate, respectively. Induction of GM-CSA by the trypanosomal homogenate promoted colony formation by normal spleen cells, but did not support colony formation by spleen cells from mice treated with 5-fluorouracil. Serum levels of GM-CSA were elevated by injection of crude trypanosomal membrane fractions, but not by soluble components found in supernatants from centrifuged trypanosomal homogenates. GM-CSA-inducing ability of the crude membrane fraction was sensitive to heating at 60 degrees C for 30 min, treatment at pH 2.0, pronase digestion, periodate oxidation, and exposure to 0.1% sodium dodecyl sulphate. This biological activity was also reduced by trypsinization of living trypanosomes before preparation of membrane fractions. These findings suggest that the active component of parasites to induce GM-CSA is associated with a glycoprotein in the surface coat of T. gambiense. GM-CSA may be related to the haematological and immunopathological alterations that occur in African trypanosomiasis.

Immunodiagnosis of sleeping sickness due to Trypanosoma brucei gambiense by detection of antiprocyclic antibodies and trypanosome antigens in patients' sera

Documented sera from 39 Trypanosoma brucei gambiense sleeping sickness patients from Ivory Coast (Côte d'Ivoire) were tested using the Procyclic Agglutination Trypanosomiasis Test (PATT) for the presence of anti-trypanosome antibodies and using an antigen-capture double antibody enzyme-linked immunosorbent assay (ELISA) for the presence of trypanosomal antigens. All 39 sera contained antiprocyclic antibodies and trypanosome antigens whereas 5 control sera did not. The results show that the PATT (for antibody detection) and the double antibody ELISA (for antigen detection) are useful for immunodiagnosis of African sleeping sickness due to T.b. gambiense and that these assays should be simplified for further testing and evaluation in the field.

Human African trypanosomiasis (sleeping sickness): new endemic foci in Bendel State, Nigeria

Human African Trypanosomiasis (Sleeping Sickness) surveys were conducted in five communities in Ethiope and Ndokwa Local Government Areas of Bendel State, Southern Nigeria. Of 670 individuals screened for the disease with the Card Agglutination Test for Trypanosomiasis (CATT), 84 (12.53%) were positive while 45 (6.72%) had traces of antibodies against Trypanosoma brucei gambiense in their blood. Trypanosomes were also demonstrated in the gland juices of 22 individuals following gland punctures and microscopic examination of the aspirates. Analysis of 86 serum samples obtained from the blood randomly collected from individuals in the localities, using the qualitative methods of CATT and Cellognost (Indirect Haemagglutination - IHA) showed that 58 (67.44%) and 57 (66.28%), were seropositive for sleeping sickness, respectively. Further titration of 72 of these serum samples using the Cellognost quantitative method showed 50 samples with antibody titres above 1:20. The clinical manifestations of sleeping sickness recorded in positive individuals included cervical lymphadenopathy, somnolence, psychosis, unsteady gait and tremors, and reproductive abnormalities reflected by secondary amenorrhea and poor obstetric histories. Our observations indicate that the parts of Bendel State surveyed are probably endemic foci of sleeping sickness hitherto unreported. The effectiveness of the CATT in mass screening of populations at risk from the disease is also highlighted.