The ecology of antigenic variation

A detailed molecular analysis using recombinant DNA technologies is extremely important to our understanding of the phenomena of antigenic variation in the African trypanosomes; however, by itself, it may not completely explain antigenic variation as it occurs in vivo. Several laboratories have demonstrated the ability of one variant population to replace another in vivo as well as the presence of heterogeneous populations of trypanosomes within an individual animal. These two phenomena do not permit us to explain antigen variation solely on the basis of the molecular regulation of variant antigen expression. In addition to studies in molecular biology, it will be necessary to define clearly the differences in growth rates of variant populations and the role of competition between these variants in a single anatomical site. It will also be necessary to determine the influence of various physiological environments on growth rates and the competition between the different variants of a single repertoire. It is concluded that the phenomenon of antigenic variation is a complex problem in ecology and population dynamics as well as molecular regulation. This paper is designated to examine a variety of the ecological parameters presumably involved in antigenic variation.

Relevance of autoantigens to autoimmunity in African trypanosomiasis: study of DNA and thyroglobulin antibodies

In order to investigate whether the autoantibody production in the course of African trypanosomiasis is the result of a generalized polyclonal activation or if it is a specific (antigen-dependent) phenomenon we looked for the presence of autoantibodies directed against autoantigens likely to be released (DNA) or unlikely to be released (thyroglobulin) into the circulation during human T. gambiense infection. Sera from 21 patients with African trypanosomiasis were screened for anti-native DNA or anti-denatured DNA antibodies by a Farr DNA binding radioimmunoassay. In addition, antibodies to native DNA were also assessed by indirect immunofluorescent assays using Crithidia luciliae or rat liver sections as substrates. Anti-thyroglobulin antibodies were studied by the passive hemagglutination technique. IgM levels and fluorescent anti-trypanosomal antibodies (FATA) were concomitantly evaluated. The denaturated DNA binding capacity was significantly higher in the sera from trypanosomiasis patients than in sera from healthy blood donors. These capacities were greater in patients with high IgM levels and high FATA titres. Anti-native DNA or anti-thyroglobulin antibodies were not detected. This preferential formation of anti-denatured DNA antibodies suggests a specific antigen-dependent) activation of autoreactive cells rather than a generalized polyclonal activation.

Tropical medicine: recent advances in malaria and other protozoal diseases

Two recent developments in the field of trypanosomiasis and malaria are presented: 1) A novel mode of gene expression has been discovered in trypanosomes which enables the parasite to change its surface antigenicity with each new wave of parasitaemia, thus making an effective host response impossible. 2) The possibility to cultivate Plasmodium falciparum in vitro allows studies on the interaction of parasites and red cells, on drug resistance and on surface antigens.- Research in tropical diseases has given important contributions to biology and medicine in general. Basic research on the other hand is necessary to fight successfully tropical disease which are still common and often fatal.

Antibody responses induced by immunization of inbred mice susceptible and resistant to African trypanosomes

We tested the ability of inbred mice that were either susceptible (strain A/J) or resistant (strain C57BL/6 and A/J X C57BL/6 hybrids) to African trypanosomes to produce specific antibodies to trypanosome antigens in the absence of living parasites. This experiment was carried out to eliminate the influence of trypanosome growth or metabolism on immune responsiveness. Mice were immunized with keyhole limpet hemocyanin or solubilized Trypanosoma brucei gambiense, and serum antibodies were measured in solid-phase radioimmunometric assays after primary and challenge injections. Both susceptible and resistant mice showed increases in keyhole limpet hemocyanin-specific or trypanosome-specific immunoglobulin M and immunoglobulin G after immunization. When immunized with trypanosome antigens, resistant mice made qualitatively and quantitatively superior specific immunoglobulin M responses, particularly to the trypanosome major variable surface glycoprotein. Susceptible A/J mice produced good specific antibody responses, although these were predominantly of the immunoglobulin G isotypes. These results show that A/J and C57BL/6 mice respond differentially in terms of immunoglobulin isotype and repertoire in response to injected antigens. The possibility that this differential antibody response influences susceptibility to African trypanosomes is discussed.

Trypanosoma brucei gambiense: cerebral immunopathology in mice

Ninety outbred white adult female mice were infected with Trypanosoma brucei gambiense (GUMS 2, alias LUMP 1237) originating from a Zairian patient and known to produce a low parasitaemia in rodents. The development of cerebral trypanosomiasis was independent upon the number of parasites inoculated per mouse. Trypanosomes appeared in the circulating blood about four months after infection, when some mice started to show the first signs of paresis which subsequently led to cachexia. A clinical test to stage such a development is described. 57 mice were sacrificed at various intervals after infection, starting from one to 22 months. The morphological changes in the brain consisted of a diffuse meningoencephalitis in 45 mice, (78.9%) often associated with parasites, the latter being best visualised in 21 mice (36.8%) by immunofluorescence using a specific antitrypanosome antibody. The trypanosomes showed a predominantly extravascular distribution in the cerebral parenchyma, to a lesser extent in the meninges and only rarely in the choroid plexuses. Deposits of immunoglobulins in the choroid plexuses and cerebral infiltrations by plasma cells were mild. The level of circulating immune complexes was found to be increased. Adequate intravenous Melarsoprol did not prevent the disease from progressing to advanced stages, and there is limited morphological evidence that it did not eradicate the parasite from the host. The immunofluorescent use of an antitrypanosome antibody to demonstrate the persistence of tissue parasites after chemotherapy is recommended. Murine models seem therefore to be suitable for drug screening in cerebral trypanosomiasis since all three trypanosomes of the brucei group can be adapted to mice.

Conservation of a variant-specific surface antigen gene in different trypanosome species and sub-species

In Trypanosoma brucie brucie, T. b. rhodesiense, T. b. gambiense and T. evansi, the variant-specific antigen (VSA) genes are organized in families of related sequences, one of which is duplicated when expressed. Some of these VSA sequences appear to be conserved in the different species and sub-species: restriction mapping of isotypic genes of AnTat 1.8 VSA (from T. b. brucei) reveals extensive homology in T. b. rhodesiense, T. b. gambiense and T. evansi, although the genetic surrounding differs in each case. By contrast, the AnTat 1.1 sequence (also from T. b. brucei) appears to be absent from T. b. gambiense DNA.

[Autoantibodies in human african trypanosomiasis (smooth muscle antibodies during a Trypanosoma gambiense disease) (author's transl)]

The authors report the case of a patient with a T. gambiense african trypanosomiasis who presented up to one year after treatment autoimmune disorders seemingly related to this infection, and especially smooth muscle autoantibodies with high titres, antinuclear antibodies, antibodies to erythrocytes, and rheumatoid factors, with probably production of immune complexes and complement activation by both pathways. The particularity of this case is the production of smooth muscle autoantibodies, which has never been reported before in african trypanosomiasis. It seems that other usual conditions of smooth muscle antibodies production may be eliminated, and no antigenic community between some components of smooth muscles and trypanosomes has been found. So it may be an autoimmune disorder induced by trypanosomiasis and possibly linked with cytotoxicity effects.

Analysis of the DNA and RNA changes associated with the expression of isotypic variant-specific antigens of trypanosomes

Using specific (32P) labelled cDNA probes, we compared the mRNAs and the genomic DNA sequences coding for the synthesis of two pairs of serologically related variant-specific antigens (VSAs) of trypanosomes: AnTat 1.1 and AnTat 1.1b, both from the strain 1125 of T.b.brucei and AnTat 1.8 and LiTat 1.6 from T.b.brucei and T.b. gambiense, respectively. Within each pair, large similarities were observed in the coding sequence, except in the 3' region which appears to be highly variable. However, a low level of cross-hybridization can be detected between all sequences, in the 3' region only. The expression of these VSAs is linked to a similar duplication-transposition mechanism. The insertion locus of the transposition unit is the same both in AnTat 1.1 and AnTat 1.1b DNAs. In both pairs, the transposition unit seems to comprise at least about 200 bp upstream of the 5' extremity of the coding sequence. The significance of these results, regarding the structure and synthesis of the VSAs, is discussed.

Epidemiological studies on the animal reservoir of gambiense sleeping sickness. Part II. Parasitological and immunodiagnostic examination of the human population

The prevalence of the disease was determined in the population (n = 3402) of a highly endemic sleeping sickness area in the Ivory Coast and an area of recent low endemicity in southwestern Upper Volta by using parasitological techniques supplemented by the determination of trypanosome specific antibodies and serum macroglobulins (IgM). 62 cases of trypanosomiasis were diagnosed parasitologically in the sleeping sickness focus in the Ivory Coast. 30 Trypanozoon stocks were established for their behavioural and biochemical characterization. The percentage of specific antibody carriers. 26% and 10% obtained with the enzyme-linked immunosorbent assay (ELISA) in both areas, respectively, was compared to that obtained for raised IgM levels. False negative diagnosis resulted in 24% with the ELISA, 12% with the indirect immunofluorescent test (IFT) and 19% with the radial immunodiffusion (RID). Considering IFT and IgM levels together, the proportion of false negative results fell to 8%. Possible reasons for low sensitivities, especially of the ELISA are discussed.

Immunization of rabbits with zeolite absorbed Trypanosoma gambiense inactive vaccine

T. Gambiense was treated with natural zeolite, a very powdery mineral material which has strong absorptive capacity from the cationic exchangeable properties, and kept at 4 degrees C for 3 days. Rabbits injected with this inactivated vaccine were completely protected from a challenge inoculation of homologous viable parasites. Collected immune sera by weekly intervals from the immunized animals were tested for their ability to agglutinate trypanosomes. Serum antibodies were shown high titers 3 weeks post-inoculation, i.e., 1:512, and plateau of this titer was persistent up 3-4 weeks. For the experiment of passive protective effects of rabbit immune sera, mice were inoculated with 100 viable T. Gambiense by subcutaneous or intracerebral routes and then immediately performed two injection doses of 0.1 ml antiserum at intervals of 24 hours by subcutaneous. The protective ability was remarkable at the first to second weeks after the last immunization and then slightly decreased although a high level of agglutination titer remained in immune serum.

Immune complexes in serum and in cerebrospinal fluid in African trypanosomiasis. Correlation with polyclonal B cell activation and with intracerebral immunoglobulin synthesis

The possible occurrence of immune complexes (IC) in serum and in cerebrospinal fluid (CSF) has been studied in 36 patients with African trypanosomiasis (Trypanosoma brucei gambiense). In serum, very high levels of IC were detectable by the (125)I-C1q-binding and by the conglutinin-binding assays with positive results in 94 and 87%, respectively, of untreated patients. Circulating IC were found in both early and late stages of the disease, without significant quantitative differences; their size was 15-25S. There was a significant negative correlation between C3 values and C1qBA. Our studies suggest that circulating IC occurring during trypanosomiasis may be the expression of a polyclonal B cell activation. Indeed, there was a significant correlation (P < 0.001) between the levels of circulating IC and either the levels of IgM (mean value 12.5+/-7.2 mg/ml) or with the levels of rheumatoid factor-like antiimmunoglobulin antibodies that were detected by solid phase radioimmunoassay in 74% of the patients.IC were detected in 31 of 35 CSF samples, with a marked elevation in patients with definite involvement of the central nervous system as compared with earlier stages of sleeping sickness. The occurrence of IC in CSF was not related to an impairment of the blood-brain barrier as shown by analysis of CSF/serum albumin ratios. The level of IC in CSF did not correlate with the serum level and, therefore, circulating IC do not appear to cross efficiently an unimpaired blood-brain barrier. The analysis of IgG, IgM, and albumin concentrations in serum and CSF demonstrates a marked intracerebral immunoglobulin synthesis in patients with manifestations of meningoencephalitis. There was a correlation between CSF-C1q binding assay and this local IgG synthesis. These data are consistent with a local formation of IC in CSF in patients with active meningoencephalitis. The results obtained in eight patients followed during therapy suggest that the presence of IC in CSF may be an indicator of a continuing central nervous system disease and that the quantitation of CSF-IC may be useful for monitoring patient care.

The use of culture-derived metacyclic trypanosomes in studies on the serological relationships of stocks of Trypanosoma brucei gambiense

Metacyclic trypanosomes of five stocks of Trypanosoma brucei gambiense were produced in vitro in tsetse head-salivary gland explant cultures and used to infect rabbits. Sera were collected from the rabbits and monitored by agglutination tests for antibody production to nine serotype antigens of T. b. gambiense. In the case of a Nigerian stock of T. b. gambiense the sequences of antibody production were found to be similar in animals infected with the stock transmitted by tsetse flies and from culture. Many similarities were also found between the patterns of antibody production in rabbits infected with stocks of T. b. gambiense from Senegal, Nigeria, Zaire and Uganda. The occurrence of similar serotypes in geographically different stocks of T. b. gambiense provides further support for continuing efforts to develop improved serodiagnostic tests for sleeping sickness based on variable trypanosome antigens and to find techniques for immunoprophylaxis.

Protective effect of zeolite absorbed Trypanosoma gambiense inactive vaccines on mice

Inactive T. gambiense vaccines treated with strong absorbent natural zeolite and kept at 4 degrees C for 3 days were injected into mice. After 2 weeks, 75% of the white mice which had received single injection survived, 85% of double injections survived challenge with 100 parasites separated from T. gambiense-infected mouse blood. However, the survival rats of the inoculated mice challenged after 3 weeks were 55% (one injection) and 80% (two injections) respectively. The mice were challenged 2 weeks after they were inoculated with vaccines made in the same way as mentioned above except that the prepared time was lengthened to 6 days. The total survival rates were 67.4% (one injection) and 85% (two injections) and these challenged 3 weeks after inoculation were 50% (one injection) and 80% (two injections). Mice not surviving in the experimental groups lived longer by 3--4 days than those in the controlled ones which had no survivors at all. Inactive vaccines prepared with artificial zeolite showed little protective effect on mice.

Antigenic variation in trypanosomes: a computer analysis of variant order

African trypanosomes can undergo antigenic variation and evade the host immune response. Whether the antigenic variants arise in an ordered sequence or randomly has been in dispute but has not been statistically tested. The coefficient of concordance (W), a statistic designed to detect similarities between sequences of objects, was applied to the literature data. The tendency towards a reproducible order of variants was strong, although in several of the studies the number of experimental animals was so low that no conclusions could be drawn. A computer model was used to determine whether this degree of order could arise with random generation of variants followed by selection. The model simulated a trypanosome clone with 90 possible variants, widely differing variant-specific growth rates, random variant origin and variant eradication by an anamnestic host immune response. Parameters varied were maximum parasitaemia, growth rate differential between 'fast' and 'slow' variants, and parasitologist ability to detect minor variants. Random generation and selection by growth rate alone could not produce the degree of variant orderliness reported in the literature. However, experiments with larger numbers of host animals and direct investigation of variant growth rates and competitive interactions are necessary before the random generation-selection hypothesis can be proven or disproven.

Experimental infections of laboratory rodents with recently isolated stocks of Trypanosoma brucei gambiense. 1. Parasitological investigations

Albino rats and white mice were infected with populations of Trypanosoma brucei gambiense isolated from patients in four different areas in Central Africa. Differences in virulence as shown by the level of parasitaemia, number of relapses, and length of survival time, were observed amongst the stocks according to their geographical origin and secondarily to the degree of adaptation to the rodents. All the stocks are pathogenic for the laboratory rodents, and the presence of extravascular trypanosomes in the brain was confirmed in all infected animals. Spleen, liver, and kidneys were less constantly found to be positive. The morphology of the extravascular parasites was highly variable, ranging from long slender trypomastigotes to spheromastigotes and even amastigotes.

[Immunoenzymatic diagnosis (ELISA) of human African trypanosomiasis. (A comparative study of several antigens) (author's transl)]

A comparative study, by ELISA, of purified exoantigen and of five crude antigenic extracts from several strains of T.b. gambiense and T.b. brucei has shown a wide range of results. The best sensitivity is obtained with virulent strains from human origin. For more accuracy, an association of such antigens would be preferable.

Protective immune response in mice immunized with antigens from Trypanosoma gambiense-infected mouse blood

Immunogenicity and property of antigens obtained from Trypanosoma gambiense-infected mouse blood (IMP) were examined. A strong vaccine effect against intravenous challenges with 3 x10(3) parasites given on study day 3, 5, or 14 (day 0 = immunization) was observed in mice immunized with a combination of IMP (2 mg protein/mouse) and Freund's complete adjuvant (FCA). But when the challenge was given on day 21 or 30, per cent survival in mice dropped to the 20- and 40-per cent level, respectively. Among fractioned components of IMP, IMP-1, IMP-2, and imp-3, by gel filtration with Sephadex G-200, all of the mice immunized with IMP-1 antigen alone or together with FCA and challenged on day 5 were able to conquer intraperitoneal challenges with 1 x10(2) parasites. Mice immunized with IMP-2 or IMP-3 died within 6 days after challenge. Moreover, protection efficacy shown by IMP-1p (144,000 xg sediment of IMP-1) antigen in mice was similar to that by IMP and IMP-1 antigens. IMP-3 yielded a single precipitin line against mouse anti-IMP serum by Ouchterlony double diffusion method but this response was eliminated when the antiserum was absorbed by IMP-1p. No precipitin line was identified between mouse anti-IMP serum and IMP-1 or IMP-2. From electron microscopic observations, elements of IMP-1 and IMP-1p are possibly corresponded to the fragments of filopodia of the parasites.

The natural occurrence of Trypanozoon in domestic chicken in the Ivory Coast

From a natural infected chicken (Gallus gallus var. domesticus) in the Ivory Coast trypanosomes were isolated using Mastomys natalensis as recipient animal. Trypanosomes were diagnosed as belonging to the subgenus Trypanozoon from its morphology and its infectivity for rodents. The stabilated stock was able to infect a laboratory chicken. The stock proved to be human plasma subresistant and showed electrophoretic patterns of three enzymes (ALAT III, ME I, PEP III) so far only seen in pig and dog originated Trypanozoon stocks from the same region surveyed. The discovery for the first time of chicken harbouring Trypanozoon has to be considered in epizootiology and epidemiology of trypanosomiases.

[Comparative study of immunoenzyme technics, ELISA and on formed antigens, in the immunologic diagnosis of African trypanosomiasis]

The enzyme linked immunosorbent assay (ELISA) for the serodiagnosis of human african trypanosomiasis is described, comparatively with the immunoperoxidase technique using blood streamforms of Trypanosoma brucei as antigen. Practical aspects for measuring the amount of antibody in serum samples from infected rabbits and from patients with african sleeping sickness are discussed. ELISA does offer important advantages over the other method used namely: -- quantitative estimates are possible, -- it bends itself readily to large scale series, owing the fact that it can be fully automatic. These qualities will be turned to full account when the different classes of antibodies present in trypanosomiasis suffers can be examined by means of specific antigenic fractions.

The identification of Trypanosoma brucei gambiense in Liberian pigs and dogs by isoenzymes and by resistance to human plasma

29 Trypanozoon stocks from Liberian pigs and dogs were screened for human plasma resistance and electrophoretic isoenzyme patterns of eleven enzymes. Two stocks from pigs were found both to be resistant to human plasma and to have an isoenzyme marker, a slow alanine aminotransferase (ALAT) pattern, previously found only in Trypanosoma brucei gambiense from man. This constitutes evidence that the pig is a reservoir of human trypanosomiasis in West Africa. The T.b.gambiense ALAT was also found in stocks from 5 other pigs and a dog, but none of these stocks was resistant to human plasma; conversely, 9 further isolations from pigs and 2 from dogs were plasma resistant but did not have the T.b.gambiense ALAT. The lack of correspondence between the two characteristics is discussed. A T.b.gambiense stock from man in Zaire had the ALAT pattern characteristic of T.b.gambiense from Senegal and Nigeria, together with the ASAT triplet found in most T.b.gambiense stocks. Peptidase polymorphism was shown in trypanosomes for the first time.

[Reliability of the indirect immunofluorescence test in the diagnosis of African human trypanosomiasis (author's transl)]

The reliability of an immunodiagnosis depends on its efficiency, i.e. the possibility of sorting out infected people from uninfected thanks to a good sensibility and a good specificity, and to its reproductibility. The authors have studied the reliability of the Indirect Immunofluorescence Antibody Test (IFAT) for trypanosomiasis diagnosis on 90 sera (30 sera from patients with proven trypanosomiasis and 60 sera from patients free of trypanosome infection). Reproductibility is considered as good when the reading has been done by the same reader. Sensibility approaches 100 p. 100 and specificity varies according to readers: the reader taking the "brillance" into account obtains a specificity of more than 85 p. 100 and the reader reading the immunofluorescence extinction obtains a specificity between 65 p. 100 and 77 p. 100. The IFAT may be taken as a reference to evaluate new immunodiagnosis.