Identification of a tryptophan-like epitope borne by the variable surface glycoprotein (VSG) of African trypanosomes

Antibodies (Ab) directed against a tryptophan-like epitope (WE) were previously detected in patients with human African trypanosomiasis (HAT). We investigated whether or not these Ab resulted from immunization against trypanosome antigen(s) expressing a WE. By Western blotting, we identified an antigen having an apparent molecular weight ranging from 60 to 65 kDa, recognized by purified rabbit anti-WE Ab. This antigen, present in trypomastigote forms, was absent in procyclic forms and Trypanosoma cruzi trypomastigotes. Using purified variable surface glycoproteins (VSG) from various trypanosomes, we showed that VSG was the parasite antigen recognized by these rabbit Ab. Anti-WE and anti-VSG Ab were purified from HAT sera by affinity chromatography. Immunoreactivity of purified antibodies eluted from affinity columns and of depleted fractions showed that WE was one of the epitopes borne by VSG. These data underline the existence of an invariant WE in the structure of VSG from several species of African trypanosomes.

Experimental studies on the evolution of antimony-resistant phenotype during the in vitro life cycle of Leishmania infantum: implications for the spread of chemoresistance in endemic areas

Pentavalent antimonial unresponsiveness is an emerging problem in endemic areas and information on factors which could modulate the transmission of drug-resistant phenotypes and parasites during life cycle are warranted. Using axenic amastigotes resistant to potassium antimonyl tartrate (Sb(III)) we investigated the modulation of antimonyl resistance during the in vitro life cycle. We assessed: (i) the stability of the drug-resistant phenotype during the in vitro life cycle; (ii) the transmission of drug-resistant clones when mixed with a wild-type clone at different susceptible/chemoresistant ratios (50/50,90/10,10/90) after one or two in vitro life cycles. We demonstrate that: (i) mutants which were 12,28,35 and 44 fold more resistant to Sb(III)-antimonial than their parental wild-type, were Glucantime Sb(V)-resistant when growing in THP-1 cells; (ii) the drug-resistant phenotype was partially retained during long-term in vitro culture (3 months) in drug free medium; (iii) the antimonyl-resistant phenotype was retained after one or more in vitro life cycles. However, when drug-resistant parasites were mixed with susceptible, mutants could not be detected in the resulting population, after one or two in vitro life cycles, whatever the initial wild-type/chemoresistant ratio. These results could be explained by the lower capacity of drug-resistant amastigotes to undergo the amastigote-promastigote differentiation process, leading probably to their sequential elimination during life cycle. Taken together, these observations demonstrate that different factors could modulate the transmission of Leishmania drug resistance during the parasite's life cycle.

In vitro growth of Leishmania amazonensis promastigotes resistant to pentamidine is dependent on interactions among strains

The in vitro growth of promastigote cells of Leishmania amazonensis was found to strongly depend on interactions among strains that differed in their pentamidine resistance. In particular, the growth of resistant strains was reduced when they shared the same environment with a less-resistant strain.

Antimonial-mediated DNA fragmentation in Leishmania infantum amastigotes

The basic treatment of leishmaniasis consists in the administration of pentavalent antimonials. The mechanisms that contribute to pentavalent antimonial toxicity against the intracellular stage of the parasite (i.e., amastigote) are still unknown. In this study, the combined use of several techniques including DNA fragmentation assay and in situ and cytofluorometry terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling methods and YOPRO-1 staining allowed us to demonstrate that potassium antimonyl tartrate, an Sb(III)-containing drug, was able to induce cell death associated with DNA fragmentation in axenic amastigotes of Leishmania infantum at low concentrations (10 microg/ml). This observation was in close correlation with the toxicity of Sb(III) species against axenic amastigotes (50% inhibitory concentration of 4.75 microg/ml). Despite some similarities to apoptosis, nuclease activation was not a consequence of caspase-1, caspase-3, calpain, cysteine protease, or proteasome activation. Altogether, our results demonstrate that the antileishmanial toxicity of Sb(III) antimonials is associated with parasite oligonucleosomal DNA fragmentation, indicative of the occurrence of late events in the overall process of apoptosis. The elucidation of the biochemical pathways leading to cell death could allow the isolation of new therapeutic targets.

DNA transformation of Leishmania infantum axenic amastigotes and their use in drug screening

Protocols for DNA electroporation in Leishmania promastigote cells are well established. More recently, in vitro culture of axenic Leishmania amastigotes became possible. We have established conditions for DNA transformation of axenically grown Leishmania infantum amastigotes. Parameters for DNA electroporation of Leishmania axenic amastigotes were systematically studied using luciferase-mediated transient transfection. Cell lines expressing stable luciferase activity were then selected, and their ability to be used in an in vitro drug screening procedure was determined. A model was established, using axenic amastigotes expressing luciferase activity, for rapidly determining the activity of drugs directly against both axenic and intracellular amastigotes. For intracellular amastigotes, the 50% effective concentrations of pentamidine, sodium stibogluconate (Pentostam), meglumine (Glucantime), and potassium antimonyl tartrate determined with the luciferase assay were 0.2 microM (0.12 microg/ml), 55 microg/ml, 95 microg/ml, and 0.12 microg/ml, respectively; these values are in agreement with values determined by more labor-intensive staining methods. We also showed the usefulness of luciferase-expressing parasites for analyzing drug resistance. The availability of luciferase-expressing amastigotes for use in high-throughput screening should facilitate the search for new antileishmanial drugs.

Human macrophage tumor necrosis factor (TNF)-alpha production induced by Trypanosoma brucei gambiense and the role of TNF-alpha in parasite control

Trypanosoma brucei gambiense, a causative agent of sleeping sickness, induced a dose-dependent production of tumor necrosis factor (TNF)-alpha by human macrophages in vitro. TNF-alpha was also induced in the Mono Mac 6 cell line, which indicates a direct effect of parasite components on macrophages. Parasite-soluble factors were also potent inducers of TNF-alpha. The addition of anti-TNF-alpha to cocultures of macrophages and parasites increased the number of trypanosomes and their life span, whereas irrelevant antibodies had no effect. TNF-alpha may have a direct role (i.e., direct trypanolytic activity) and/or an indirect one, such as TNF-alpha-mediated induction of cytotoxic molecules. A direct dose-dependent lytic effect of TNF-alpha on purified parasites was observed. This lytic effect was inhibited by anti-TNF-alpha. These data suggest that, as in experimental trypanosomiasis, TNF-alpha is involved in parasite growth control in human African trypanosomiasis.

Efficacy of second line drugs on antimonyl-resistant amastigotes of Leishmania infantum

In a previous paper we have demonstrated that the induction, by direct drug pressure, of a resistance to Sb(III) antimony at physiological concentration in the amastigote stage of the parasite, led to a high cross-resistance to Sb(V) species in the form of Glucantime. In this paper, further chemoresistant clones were characterized. Axenic amastigotes of Leishmania infantum were adapted to survive in culture medium containing 4, 20, 30 and 120 microg/ml of potassium antimonyl tartrate Sb(II). These mutants were 12, 28, 35 and 44-fold more resistant to Sb(III) than the parental wild-type clone. They were able to resist at concentrations of Glucantime Sb(V) as high as 160 microg/ml when growing in THP-1 cells. We have investigated the efficacy of second line drugs in clinical use (pentamidine and amphotericin B) on the antimony-resistant mutants. Amphotericin B was toxic for both wild-type and chemoresistant mutants at concentrations ranging from 0.05 to 0.15 microM. Pentamidine which is extensively used when the first course of antimonial pentavalent compounds is unsuccessful, was more toxic for all the chemoresistant organisms than for the wild-type clone. In the same way, chemoresistant amastigotes growing within THP-1 cells were more susceptible to pentamidine than the wild-type clone. Our results showed that the resistance of the mutants was restricted to the antimony containing drugs and did not led to a cross-resistance against the other clinically relevant drugs. These results confirmed that these two drugs (pentamidine and amphotericin B) are good candidates to treat pentavalent antimonial unresponsiveness.

Cloning of a Leishmania major gene encoding for an antigen with extensive homology to ribosomal protein S3a

Following purification by affinity chromatography, a Leishmania major S-hexylglutathione- binding protein of molecular mass 66kDa was isolated. The immune serum against the parasite 66kDa polypeptide when used to screen a L. major cDNA library could identify clones encoding for the human v-fos transformation effector homologue, namely ribosomal protein S3a, and thus was named LmS3a-related protein (LmS3arp). A 1027bp cDNA fragment was found to contain the entire parasite gene encoding for a highly basic protein of 30kDa calculated molecular mass sharing homology to various ribosomal S3a proteins from different species. Using computer methods for a multiple alignment and sequence motif search, we found that LmS3arp shares a sequence homology to class theta glutathione S-transferase mainly in a segment containing critical residues involved in glutathione binding. These new findings are discussed in the light of recent published data showing multiple function(s) of the ribosomal proteins S3a.

Secreted antigens of the amastigote and promastigote forms of Leishmania infantum inducing a humoral response in humans and dogs

To study the antigens secreted by promastigote and amastigote forms of Leishmania infantum which are able to induce a humoral response in human patients and dogs, we have carried out immunoprecipitation assays with different supernatants of in vitro cultured parasites, metabolically labelled with [35S]methionine, using serum samples from human patients and dogs. In addition, some metabolic labelling experiments were performed daily during the in vitro culture parasite's life cycle to follow the time course excretion-secretion of parasitic antigens. The results demonstrated that the two different hosts developed an antibody response against secreted antigens of both stages of Leishmania infantum. Nevertheless, the humoral response directed against the excreted-secreted antigens of the promastigote forms was qualitatively and quantitatively different when we compare the human and the dog immune responses. On the other hand, when the excreted-secreted antigens of the amastigote forms are immunoprecipitated with either human or canine immune serum, the humoral response is similar. In addition, the time course study showed that excretion-secretion of antigens was qualitatively and quantitatively modulated during the parasitic in vitro life cycle.

Leishmania spp: completely defined medium without serum and macromolecules (CDM/LP) for the continuous in vitro cultivation of infective promastigote forms

The elimination of serum or of serum-derived macromolecules that supplant the fetal calf serum requirement from Leishmania culture media could decrease costs and improve the feasibility of large-scale production of well-defined parasite material. We report a completely defined medium, without serum-derived protein and/or macromolecules as a serum substitute, of common, available, and inexpensive constituents that can be used in place of serum-supplemented media for the continuous in vitro cultivation of promastigote forms of various Leishmania species. Typical promastigote morphology was observed in Giemsa-stained smears, regardless of the strain analyzed. Electrophoretic analysis showed that the proteinase patterns of aserically grown promastigote forms were similar to those obtained in serum-supplemented RPMI 1640 medium for all Leishmania studied. Similar antigenic profiles were recognized in immunoblots by sera from hosts with visceral or cutaneous leishmaniasis after growing promastigotes in the two different culture media. For parasites causing both cutaneous and visceral leishmaniasis, the absence of serum and macromolecules in the culture medium did not markedly change their in vitro infectivity for resident mouse macrophages and their virulence in animals compared with parasites cultivated in nondefined medium. Serum-free technology will be increasingly important in providing stability and reproducibility as research using promastigote moves closer to therapeutic applications.

Axenically grown amastigotes of Leishmania infantum used as an in vitro model to investigate the pentavalent antimony mode of action

The mechanism(s) of activity of pentavalent antimony [Sb(V)] is poorly understood. In a recent study, we have shown that potassium antimonyl tartrate, a trivalent antimonial [Sb(III)], was substantially more potent than Sb(V) against both promastigotes and axenically grown amastigotes of three Leishmania species, supporting the idea of an in vivo metabolic conversion of Sb(V) into Sb(III). We report that amastigotes of Leishmania infantum cultured under axenic conditions were poorly susceptible to meglumine [Glucantime; an Sb(V)], unlike those growing inside THP-1 cells (50% inhibitory concentrations [IC50s], about 1.8 mg/ml and 22 microg/ml, respectively). In order to define more precisely the mode of action of Sb(V) agents in vivo, we first induced in vitro Sb(III) resistance by direct drug pressure on axenically grown amastigotes of L. infantum. Then we determined the susceptibilities of both extracellular and intracellular chemoresistant amastigotes to the Sb(V)-containing drugs meglumine and sodium stibogluconate plus m-chlorocresol (Pentostam). The chemoresistant amastigotes LdiR2, LdiR10, and LdiR20 were 14, 26, and 32 times more resistant to Sb(III), respectively, than the wild-type one (LdiWT). In accordance with the hypothesis described above, we found that intracellular chemoresistant amastigotes were resistant to meglumine [Sb(V)] in proportion to the initial level of Sb(III)-induced resistance. By contrast, Sb(III)-resistant cells were very susceptible to sodium stibogluconate. This lack of cross-resistance is probably due to the presence in this reagent of m-chlorocresol, which we found to be more toxic than Sb(III) to L. infantum amastigotes (IC50s, of 0.54 and 1.32 microg/ml, respectively). Collectively, these results were consistent with the hypothesis of an intramacrophagic metabolic conversion of Sb(V) into trivalent compounds, which in turn became readily toxic to the Leishmania amastigote stage.

Leishmania major: cell type dependent distribution of a 43 kDa antigen related to silent information regulatory-2 protein family

In previous studies we have characterized several Leishmania major polypeptides and showed that one member of this group (LmSIR2rp) shared significant homology to silent information regulator 2 (SIR2) of Saccharomyces cerevisiae, a protein playing a role in both telomeric and mating type loci repression in these organisms. In the present study, by using molecular and immunological approaches, we could identify LmSIR2rp homologues in different Leishmania species and developmental stages (e.g. logarithmic (LP) and stationary phase promastigotes (SP) and amastigotes). The reactive antigen was also detected in Trypanosoma cruzi extracts. Surprisingly, immunofluorescence assays revealed that LmSIR2rp is associated mainly with cytoplasmic granules of different sizes and numbers depending on the life stage of the parasite used. No reactivity was observed in the nucleus, in agreement with the Western blot showing an absence of immunoreactivity of anti-LmSIR2rp immune serum against parasite nuclear extracts. Furthermore, immunoprecipitation of [35S]methionine-labeled promastigote antigens after pulse chase experiments, using anti-LmSIR2rp fusion protein antibodies, showed that the protein is among parasite excreted-secreted antigens (ESA). Moreover, immunofluorescence assays conducted with short time incubations of either purified LmSIR2rp or viable promastigotes with murine macrophages, revealed that LmSIR2rp could be bound to the macrophage surface. The unexpected cytoplasmic localization of LmSIR2rp and its presence in ESA may suggest a new mode of action for silent information regulatory factor homologues.

Phenotypic characterization of Leishmania mexicana pentamidine-resistant promastigotes. Modulation of the resistance during in-vitro developmental life cycle

Two clones of Leishmania mexicana resistant to 5 microM (LmR5CL2) and 20 microM (LmR20CL1) pentamidine, derived from a parental wild-type clone (LmWTCL3) were selected in vitro using a continuous drug pressure protocol. Both resistant clones expressed a cross-resistance to diminazene aceturate. No differences in their in-vitro infectivity for mouse peritoneal macrophages between wild-type and pentamidine-resistant promastigotes were observed. During these experiments, promastigotes of LmR20CL1 derived from intramacrophagic amastigote forms reverted to the pentamidine-sensitive phenotype, unlike the lower resistant ones. In the same way, when a complete developmental sequence of L. mexicana was achieved in axenic cultures, LmR20CL1 promastigotes derived from axenically growing amastigotes expressed an IC50 value close to the wild-type one, whereas resulting LmR5CL2 promastigotes remained pentamidine resistant. This modulation of the chemoresistance during the developmental life cycle could be significant in the transmission of drug-resistant strains by Phlebotominae as well as in basic research to follow drug resistance during the in-vitro and in-vivo life cycle of Leishmania.

In vitro life cycle of pentamidine-resistant amastigotes: stability of the chemoresistant phenotypes is dependent on the level of resistance induced

Using a continuous drug pressure protocol, we induced pentamidine resistance in an active and dividing population of amastigote forms of Leishmania mexicana. We selected in vitro two clones with different levels of resistance to pentamidine, with clone LmPENT5 being resistant to 5 microM pentamidine, while clone LmPENT20 was resistant to 20 microM pentamidine. Resistance indexes (50% inhibitory concentration [IC50] after drug presure/IC50 before drug pressure) of 2 (LmPENT5) and 6 (LmPENT20) were determined after drug selection. Both resistant clones expressed significant cross-resistance to diminazene aceturate and primaquine. Pentamidine resistance was not reversed by verapamil, a calcium channel blocker known to reverse multidrug resistance (A. J. Bitonti, et al., Science 242:1301-1303, 1988; A. R. C. Safa et al., J. Biol. Chem. 262:7884-7888, 1987). No difference in the in vitro infectivity for resident mouse macrophages was observed between the wild-type clone (clone LmWT) and pentamidine-resistant clones. During in vitro infectivity experiments, when the life cycle was performed starting from the intramacrophagic amastigote stage, the drug resistance of the resulting LmPENT20 amastigotes was preserved even if the intermediate promastigote stage could not be considered resistant to 20 microM pentamidine. In the same way, when a complete developmental sequence of L. mexicana was achieved axenically by manipulation of appropriate culture conditions, the resulting axenically grown LmPENT20 amastigotes remained pentamidine resistant, whereas LmPENT5 amastigotes lost their ability to resist pentamidine, with IC50s and index of resistance values close to those for the LmWT clone. These results strongly indicate that the level of pentamidine tolerated by resistant amastigotes after the life cycle was dependent on the induced level of resistance. This fact could be significant in the in vivo transmission of drug-resistant parasites by Phlebotominae. Particular attention should be given to the finding that the emergence of parasite resistance is a potential risk of the use of inadequate doses as therapy in humans.

Continuous in vitro culture of Babesia divergens in a serum-free medium

Babesia divergens was cultivated in RPMI 1640 (25 mM HEPES) supplemented with 10% human serum (RPMI-10% HS) with a high percentage of parasitized erythrocytes (PPE) (> or = 40%). Standardization of in vitro tests, purification of exoantigens, biochemical studies and the safety of the culture handler motivated the development of a serum-free defined medium. Removal of serum greatly reduced the PPE but, after a period of adaptation, the culture was continuous and the parasite was able to develop a 3% routine PPE. Addition of vitamins or reduced glutathione in basal medium (RPMI) did not improve the PPE. The supplementation of basal medium with lipidic carrier (Albumax I or bovine serum albumin-Cohn's fraction V) promoted the growth of B. divergens with high PPE (> 30%) close to those obtained in RPMI-10% HS. Neither protein nor lipid fractions alone were able to restore the growth of B. divergens. Nevertheless, the whole lipid fraction from serum or Albumax I added to delipidated albumin partially restored the growth (7% PPE), indicating that the presentation of specific lipids by a carrier is crucial for the parasite. All the data indicate that Albumax I can replace human serum offering the advantages of safety, standardization for chemosensitivity tests, and exoantigen purification.

Leishmania spp.: nitric oxide-mediated metabolic inhibition of promastigote and axenically grown amastigote forms

The antimicrobial effect of activated macrophages on parasites involves nitric oxide (NO). NO induces intracellular parasite killing in murine leishmaniasis. Nevertheless, the mechanisms of action of NO as a final effector molecule on intracellular forms of Leishmania are unknown. The recent development of axenically grown amastigote forms of different Leishmania species allowed direct investigation of NO activity on active and dividing populations of the mammalian stage of various Leishmania species, which normally are only found intracellularly. Authentic NO gas, which reproduced the antimicrobial effect elaborated by activated macrophages, was flushed on promastigote and axenically cultured amastigote forms of L. mexicana, L. amazonensis, and L. chagasi suspended in degassed phosphate-buffered saline (PBS). After NO treatment, the viability of parasites gradually decreased as a function of time postflushing when compared to controls. Interestingly NO killing was more effective on promastigote forms than on amastigote forms. After 12-hr postflushing incubation in PBS, cultures of NO-treated parasites, contrary to controls (N2-treated), failed to proliferate whatever the species and the developmental stage considered. Addition of both FeSO4 and L-cysteine to PBS immediately after NO treatment reversed the capacity of authentic NO gas to inhibit the multiplication of both parasite stages of Leishmania. Supplementation of PBS with alpha-ketoglutarate and cis-aconitate (citric acid cycle substrates) also reversed the leishmanicidal activity of NO, whereas addition of citrate was less effective. The course of the developmental life cycle in vitro was also inhibited by NO gas treatment. Enzymatic analysis showed that aconitase activity was dramatically reduced by NO gas, whereas glucose phosphate isomerase, aspartate transferase, and phosphoglucomutase activities were unchanged. In accordance, promastigote and amastigote forms of Leishmania were shown to be killed by antimycin A, an inhibitor of mitrochondrial respiration. All these data demonstrated that NO action led to lethal metabolic inhibition in both developmental parasite stages by, at least in part, triggering iron loss from enzyme(s) with iron-sulfur prosthetic groups, in particular aconitase.

Axenically cultured amastigote forms as an in vitro model for investigation of antileishmanial agents

Using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide microassay, previously described as a means of quantifying Leishmania amazonensis in vitro at the amastigote stage (D. Sereno and J. L. Lemesre, Parisitol. Res., in press), we have compared the activities of seven drugs, including those currently used to treat leishmaniasis, against axenically grown amastigote and promastigote forms of three Leishmania species (L. amazonensis, L. mexicana, and L. infantum, responsible for diffuse cutaneous, cutaneous, and visceral leishmaniasis, respectively). The ability of axenically cultured amastigote organisms to be used in an investigation of antileishmanial agents was first evaluated. We have confirmed the toxicities of sodium stibogluconate (Pentostam), pentamidine, and amphotericin B to active and dividing populations of axenically cultured amastigotes. The toxicity of potassium antimonyl tartrate trihydrate, which is generally higher than that of Pentostam, seemed to indicate that pentavalent antimony can be metabolized in vivo to compounds, possibly trivalent in nature, which are more active against the amastigote organisms. When the drug susceptibilities of parasites at both stages were compared, great variations were found for all the drugs studied. These major differences, which show the specific chemosusceptibility of the parasite at the mammalian stage, demonstrate the potential of using cultured amastigotes instead of promastigotes in a drug-screening procedure for early detection. This in vitro model may help in the isolation of active compounds, particularly those with low-grade activities, against the mammalian stage of the parasite.

Correlation of high serum levels of tumor necrosis factor-alpha with disease severity in human African trypanosomiasis

The levels of tumor necrosis factor-alpha (TNF-alpha) in sera from Trypanosoma brucei gambiense-infected patients from the endemic region of Boko Songho (Bouenza focus in Congo) were measured. An increase was observed in sera from patients (geometric mean = 53.75 pg/ml, n = 69) compared with control subjects from the same endemic area (6.72 pg/ml, n = 31). The patients were classified as being in the early (blood lymphatic) stage and late (meningo-encephalitic) stage of disease according to the presence of parasites and cells in cerebrospinal fluid (CSF). An increase in TNF-alpha was noted in late stage patients (68.42 pg/ml, n = 28) compared with early stage patients (43.68 pg/ml, n = 41). Those patients with fever, asthenia, and edema and those with neurologic signs had higher levels of TNF-alpha (89.36 pg/ml, n = 26) than others (38.07 pg/ml, n = 43). No differences in TNF-alpha levels were seen when trypanosomes were detected in one location (blood, lymph nodes, or CSF) or two or three locations. These data show that the levels of TNF-alpha in serum of T. b. gambiense-infected patients were correlated with disease severity (presence of signs of inflammation or presence of major neurologic signs) and indicate that TNF-alpha could be involved in some aspects of human African trypanosomiasis physiopathology.

Circulating antibodies directed against tryptophan-like epitopes in sera of patients with human African trypanosomiasis

Human African trypanosomiasis is often associated with an intense proliferation of B lymphocytes, leading to polyclonal antibody synthesis. Using a modified enzyme-linked immunosorbent assay method, we have found highly significant levels of circulating anti-conjugated tryptophan-like epitope antibodies in sera of patients with sleeping sickness. These antibodies were immunoglobulins (Ig) of the M isotype. There was no correlation between immunologic binding and the Ig levels found in sera of patients with human African trypanosomiasis. Higher antibody levels in stage II of the disease than in stage I may be related to damage to the central nervous system. The specificity of this immunologic binding was evaluated by 1) comparison with that obtained with other related conjugates and 2) serum titration. Anti-conjugated tryptophan-like epitope antibodies were not found in other neurologic diseases tested. Their involvement in this pathology remains unknown.

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.

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.

Serum lipid and lipoprotein abnormalities in human African trypanosomiasis

We have studied the serum lipoprotein system in human African trypanosomiasis (Trypanosoma brucei gambiense infection). The study was carried out on 74 Congolense patients suffering from sleeping sickness and 34 Congolense control subjects living in the endemic region of Boko Songho. We have determined the serum concentrations of lipids (triglycerides, cholesterol, phospholipids) and apolipoproteins (apolipoprotein A-I and B), and the separation of serum lipoproteins by electrophoresis. For the patients infected with T. b. gambiense, in comparison with control subjects, the results have shown (i) a significant increase in triglyceride concentration and a decrease in cholesterol concentration; (ii) a significant rise in apolipoprotein B concentration and a significant reduction in apolipoprotein A-I concentration; and (iii) an increase in low density lipoproteins and a decrease in high density lipoproteins. We conclude, therefore, that human African trypanosomiasis is associated with marked alterations in the composition and levels of host lipoproteins.

Gonadotropic axis and Trypanosoma brucei gambiense infection

A gonad endocrine survey on 46 Congolese patients (15 women and 31 men) with parasitologically confirmed trypanosomiasis found amenorrhoea in 60% of the women and impotence in 70% of the men. The basic gonad endocrine examination showed a decrease in oestradiol levels in about 65% of the women. Both amenorrhoea and low oestrogen levels were observed in the second phase (P2) of the disease, but low oestrogen levels were sometimes noted in the first phase of the disease (P1). In the men, about 50% of the cases (P2) showed a decrease in testosterone. However, as in the women, the variation of testosterone was also observed in the first phase (P1). A static and dynamic examination of the hypothalamic-pituitary-gonadal axis was undertaken in order to investigate the origin of these hypogonadisms. A supra - or extra-hypophyseal origin is discussed.

Development of metacyclic Leishmania promastigotes is associated with the increasing expression of GP65, the major surface antigen

Using immunofluorescence techniques and flow microfluorometry analysis, we have demonstrated that the binding of a monoclonal antibody (VD5/25) produced against GP65, the major surface antigen of Leishmania braziliensis, increased on the surface of stationary-phase promastigotes from all the New World Leishmania species causing mucocutaneous or cutaneous disease as compared with the log-phase parasites. In addition, a sequential development of Leishmania amazonensis promastigotes from a non-infective to an infective stage was demonstrated. Indeed, promastigotes in the stationary phase (days 6-7) were found to be far more infective than those in the logarithmic phase of growth (day 3) both in vitro for mouse peritoneal macrophages and in vivo for BALB/c mice. The intracellular survival and multiplication of L. amazonensis were significantly inhibited when infective promastigotes were treated with the VD5/25 monoclonal antibody. The increasing expression of GP65 on the promastigote surface may thus contribute to Leishmania infectivity. This seems to represent a characteristic mechanism applicable to all New World Leishmania species studied.

The epidemiological importance of the animal reservoir of Trypanosoma brucei gambiense in the Congo. 2. Characterization of the Trypanosoma brucei complex

Biological and biochemical characterization of 36 human and 5 animal congolese stocks of Trypanosoma brucei were performed. One human and all the animal stocks showed a quick adaptation to rodent host whereas the other 35 human stocks were characterized by a low virulence degree (Group 1 of T. gambiense). The virulent stocks showed hybridization patterns specific to the gambiense subspecies. Our results confirm the absence of the T. b. brucei subspecies in the Congo and the low prevalence of domestic animals infected with T. b. gambiense (0.5%). Two cycles of human trypanosomiasis may thus occur in Central Africa: a predominant man-to-man cycle with group 1 trypanosomes and a minor cycle involving an animal reservoir.

Requirements of defined cultivation conditions for standard growth of Leishmania promastigotes in vitro

The growth characteristics of L. chagasi (MHOM/BR/79/LI01) and L. braziliensis (MHOM/BR/72/1670), the causative agents of visceral and muco-cutaneous leishmaniases, respectively, were compared. Inoculum size clearly influences the growth course of both Leishmania species, whatever the culture medium used (serum-supplemented media: GLSH or RPMI, and a chemically defined medium: LITR9). Cultures initiated with low concentrations failed to promote cell growth, while typical growth curves were obtained when higher promastigote inocula were used. For all the species tested, the higher the initial density of flagellates in the medium, the shorter were the periods covered by the latent and particularly by the logarithmic growth phases. In contrast, using constant inocula, variations in the volume of the incubation medium did not change the time-course of the different culture phases of either Leishmania species, provided that the ratio of incubation medium to total flask volume was comparable. Only cell division time significantly increased with the culture volume. We also determined whether or not the growth characteristics of the promastigotes of L. chagasi or L. braziliensis could be generalized to other members of the genus. Our results show that, whatever the culture medium used, L. infantum behaves in the same way as does L. chagasi, whereas L. panamensis, L. guyanensis, L. mexicana and L. amazonensis display growth patterns similar to that of L. braziliensis.

Serodiagnosis of sleeping sickness in the Republic of the Congo: comparison of indirect immunofluorescent antibody test and card agglutination test

The card agglutination test for trypanosomiasis (CATT) was evaluated and compared to the classical immunofluorescent antibody test (IFAT) in the immunological diagnosis of Gambian trypanosomiasis. Tests were performed on serum and whole blood. Cross-reactions were found in the CATT with sera from patients suffering from parasitic infections other than sleeping sickness, but could be largely overcome by selecting 1/10 as the specific threshold dilution. At 1/40 dilution no false positive result was observed in the IFAT. At the specific threshold dilution, the sensitivity of IFAT was 94.7%, compared with 91.6% for the CATT. On whole blood, a more convenient sample in the field, IFAT specificity (100%) was greater than that of the CATT (94.3%), as was its sensitivity (92% compared with 82.5%). In view of its simplicity and rapidity of execution, the CATT is an efficient serological test to detect new foci. When greater sensitivity is required, IFAT should be preferred to CATT.

Specific immunodiagnosis of Chagas disease: immunodiffusion test using a specific serum anti-Trypanosoma cruzi component 5

A micro double diffusion test (MD), allowing the identification of precipitation brand 5 by identity reaction, using a rabbit specific anti-component 5 serum, was evaluated for the immunological diagnosis of Chagas' disease. The previous studies on the Trypanosoma cruzi specificity of component 5[g] were completed, showing it to be absent in Leishmania brazilienis, but present in different strains of T. cruzi. 200 sera from Bolivian patients were studied. (88 with a positive xenodiagnosis, 45 with mucocutaneous leishmaniasis but without Chagas' disease, and 67 controls). Band 5 was found in 74 (84.1%) of the sera with positive xenodiagnosis but was never found either in the leishmaniasis or in the control groups. MD, allowing an easy detection of T. cruzi specific band 5, cheap and simple to perform, can be recommended in association with other serological tests, when highly specific immunodiagnosis of Chagas' disease is required.

Identification of a major 72 kilodalton surface antigen in twelve isolates of Leishmania braziliensis braziliensis

The study of the surface antigens of Leishmania braziliensis braziliensis revealed a great homogeneity among ten strains isolated from Bolivia and two reference strains from Brazil and Belize. A 72 kDa major protein, present in all L. b. braziliensis strains, was recognized by both cutaneous and mucocutaneous human sera, but was not recognized by Kala-azar and chagasic sera. No cross-reactive antigens were found among strains of Leishmania braziliensis guyanensis, Leishmania braziliensis panamensis, Leishmania mexicana amazonensis and Leishmania donovani chagasi testing these strains with hamster and human anti-L. b. braziliensis sera. Moreover, these strains possessed major antigens with molecular weights different from those of L. b. braziliensis strains. A microheterogeneity of L. b. braziliensis surface antigens was detected for the high molecular weight antigens and seemed to be related to the isoenzymic microheterogeneity.

Infectivity of Leishmania braziliensis promastigotes is dependent on the increasing expression of a 65,000-dalton surface antigen

Sequential development of Leishmania braziliensis promastigotes from a noninfective to an infective stage was demonstrated. The generation of infective forms was related to their growth cycle and restricted to stationary stage organisms. Using immunofluorescence techniques, we have noticed that the binding of a monoclonal antibody (mAb) against L. braziliensis (VD5/25) increased progressively as the promastigotes developed in culture and was maximal with the infective forms. This antigenic differentiation was not detected with an anti-L. braziliensis polyclonal rabbit antiserum, suggesting that only a few epitopes, including that recognized by VD5/25, have their expression effectively increased on the surface of infective promastigotes. Immunoprecipitation of lysates of surface-iodinated L. braziliensis promastigotes with this mAb revealed two proteins of apparent 65,000 and 50,000 Mr, the 50,000 Mr protein probably representing the unreduced form of the major surface glycoprotein described in several species of Leishmania (GP65). The increasing expression of this epitope was not found with L. chagasi promastigotes, but seems to occur with the parasites from the L. mexicana complex. Intracellular survival of L. braziliensis was completely inhibited when the infective promastigotes were treated with VD5/25. It appears, therefore, that the increasing expression of GP65 on the promastigote surface represents an essential mechanism of leishmania survival in the macrophage.

Infectivity of Leishmania braziliensis promastigotes is dependent on the increasing expression of a 65,000-dalton surface antigen

Sequential development of Leishmania braziliensis promastigotes from a noninfective to an infective stage was demonstrated. The generation of infective forms was related to their growth cycle and restricted to stationary stage organisms. Using immunofluorescence techniques, we have noticed that the binding of a monoclonal antibody (mAb) against L. braziliensis (VD5/25) increased progressively as the promastigotes developed in culture and was maximal with the infective forms. This antigenic differentiation was not detected with an anti-L. braziliensis polyclonal rabbit antiserum, suggesting that only a few epitopes, including that recognized by VD5/25, have their expression effectively increased on the surface of infective promastigotes. Immunoprecipitation of lysates of surface-iodinated L. braziliensis promastigotes with this mAb revealed two proteins of apparent 65,000 and 50,000 Mr, the 50,000 Mr protein probably representing the unreduced form of the major surface glycoprotein described in several species of Leishmania (GP65). The increasing expression of this epitope was not found with L. chagasi promastigotes, but seems to occur with the parasites from the L. mexicana complex. Intracellular survival of L. braziliensis was completely inhibited when the infective promastigotes were treated with VD5/25. It appears, therefore, that the increasing expression of GP65 on the promastigote surface represents an essential mechanism of leishmania survival in the macrophage.

Bioenergetic and cardiovascular responses to exercise in residents at 2.850 m, with asymptomatic Chagas' disease

Cardiovascular and energetic responses at rest, during 30 min of exercise (mechanical output: 125 watts) and for a subsequent recovery period of 5 min were compared in two groups, each comprising 21 residents at an altitude of 2.850 m. One group was in the asymptomatic phase of Chagas' disease with positive serological tests for T. cruzi, whereas the other was without Chagas' disease (negative serological tests). The two groups were similar as regards age, weight-for-height, blood parameters, nutritional status and heart and lung functions, including heart rate and frontal plane QRS axis determinations. At rest, they differed in that maximal and minimal arterial blood pressures were slightly but significantly lower in the group with Chagas' positive serological tests than in the controls. During exercise and recovery, the only differences between them and the controls were that their minimal diastolic arterial blood pressure was significantly lower. In absolute values, the rises in arterial pressure due to exercise were exactly the same in the two groups. Maximal O2 uptake was identical in both groups, as was exercise steady state VO2. These findings indicate that the asymptomatic subjects with Chagas' disease had a normal work capacity and were not affected by high altitude.

Additional data on Trypanosoma cruzi isozymic strains encountered in Bolivian domestic transmission cycles

We have collected in Bolivia 212 stocks of Trypanosoma cruzi from domestic transmission cycles and have assayed for nine enzyme systems (11 gene loci). Only a few different isozyme profiles exist, without recombination between them, a situation also encountered in previous Bolivian samples. The 212 stocks, combined with 207 stocks previously studied, have been analysed to uncover any spatial patterns. The frequency of heterozygous strains (2 and 2a) decreases westwards and with increasing altitude. Given that longitude and altitude are correlated with each other, it is not possible to decide which of these two geographic variables is the relevant one, or if both are. These associations might be due to climatic factors. Studies by other authors have shown, however, that heterozygous strains are rare or absent in the Amazon Basin, which is at low altitude.

Specific and sensitive immunological diagnosis of Chagas' disease by competitive antibody enzyme immunoassay using a Trypanosoma cruzi-specific monoclonal antibody

Coexistence of Chagas' disease with leishmaniasis and T. rangeli infection in endemic areas and cross-reactivity between corresponding etiological agents can confuse the immunodiagnosis of Chagas' disease. A discriminative serological test could therefore represent a major advance in specific immunodiagnosis. A competitive antibody enzyme immunoassay against a component 5-enriched preparation, using a T. cruzi species-specific monoclonal antibody has allowed development of a specific serodiagnosis of Chagas' disease with high sensitivity (96.6% in undetermined and chronic phases of infection). This test can differentiate Chagas' disease from other cross-reacting parasitic diseases in areas where concomitant infections are unknown or suspected.

Subspecies-specific surface antigens of promastigotes of the Leishmania donovani complex

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of proteins and externally exposed labeled surface constituents were analyzed in promastigotes of three etiological agents of kala azar (Leishmania donovani, HS70 strain from India; L. chagasi, Imperatriz strain from Brazil; L. infantum, ITMPA K263 strain from Morocco and MO strain from France). Coomassie blue-stained gels showed similar protein patterns for L. donovani and L. chagasi and a more distinct one for L. infantum. Surface radioiodination with two different methods, lactoperoxidase and IODO-GEN, gave identical autoradiographic patterns for each parasite. Four major labeled proteins with apparent Mr values of 65,000, 60,000, 50,000, and 26,000 were detected in both L. chagasi and L. donovani. However, the radioiodinated polypeptide pattern of L. infantum only showed two major bands with an apparent Mr of 62,000 and a doublet of 26,000 to 23,000. Immunoprecipitation of detergent extracts of labeled promastigote subspecies with immune sera from rabbits immunized with either L. chagasi or L. infantum and from patients and mice infected with these two parasites, as well as with a monoclonal antibody against the surface of L. donovani promastigotes, demonstrated that the surface antigenic expression of L. infantum is different from that noticed in the two other subspecies, which are similar. Immunofluorescence experiments with some of these antibodies confirmed these results. The present findings should be considered in taxonomic and immunological studies in visceral leishmaniasis.

Comparisons of immunological tests for serodiagnosis of Chagas disease in Bolivian patients

Enzyme linked immunosorbent assay (ELISA) and immunoelectrophoresis (IEP) were evaluated and compared to the classical immunofluorescence (IF) and complement fixation test (CFT) in the immunological diagnosis of Chagas' disease, using 407 sera from Bolivian patients. 72.7 to 79.5% of randomised sera, coming from patients living in endemic areas for Chagas' disease were considered as positive, according to the test limits, previously determined. The techniques could be classified according to their percentage detection as ELISA greater than IF greater than CFT greater than IEP. The quantitative correlations between the tests were excellent (p less than 0.001). 92.8% of the sera were positive or negative for the four tests, 6.1% for three tests and 1.1% for only two tests. The agreement between the tests ranged from 94.6 to 99.2%, co-positivity from 95.5 to 100% and co-negativity from 88.5 to 100%. IF gave the best results, and could be considered as the reference test since it was easy and rapid to perform. However to avoid errors or discrepancies between laboratories, two tests, such as IF and CFT, might be associated. ELISA can be used if higher sensitivity is required. IEP showed 1 to 14 precipitation bands in 96% of the sera from infected patients. The precipitation band 5, previously demonstrated as Trypanosoma cruzi specific, was present in 73% of these sera, indicating the interest to use immunoprecipitation test, if more specificity is required for the immunodiagnosis of Chagas' disease.

Specific humoral depression in chronic patients infected by Trypanosoma cruzi

Realizamos um estudo comparativo entre o xenodiagnóstico e os testes sorológicos para a doença de Chagas. Cento e cincoenta pacientes de algumas áreas endêmicas foram estudados. Quatro deles pareceram revelar um estado particular com um xenodiagnóstico positivo e uma sorologia negativa, esta realizada com quatro diferentes técnicas clássicas (teste de immunofluorescência, ELISA: Enzyme Linked Immunosorbent Assay, teste de fixação do complemento e teste de immuno-eletroforese). O soro de um dos pacientes que apresentou depressão humoral específica mostra elevada quantidade de antígenos circulantes comprovada pela técnica da immuno-eletroforese. Os Autores sugerem o uso de um teste sorológico para detectar a presença de antígenos circulantes de T. cruzi, além da utilização de testes sorológicos clássicos. Isto permitiria o diagnóstico da doença de Chagas em pacientes com uma baixa (ou mesmo inexistente) produção de anticorpos específicos.

Different monoclonal antibodies against the component 5 specific for Trypanosoma cruzi

Three murine monoclonal antibodies (I-35/67, II-190/30, III-160/18) produced by immunization against total epimastigote extract or component 5-enriched fractions of Trypanosoma cruzi (Tehuantepec strain) have been demonstrated to recognize the component 5 specific for T. cruzi. By immunofluorescence studies, one of these monoclonal antibodies (I-35/67) was shown to bind to the epimastigote cell surface, and the two others (II-190/30 III-160/18) were preferentially directed against internal subcellular organelles. Immunoprecipitation using these monoclonal antibodies followed by SDS-PAGE analysis, has led to identification of four molecules with apparent molecular weights of 72 Kd, 51 Kd, 43 Kd, and 24 Kd in T. cruzi epimastigotes. Potential uses of these monoclonal antibodies in serological tests and immunochemical analysis of target antigens are discussed.