MHC class I molecules are an essential cell surface component involved in Theileria parva sporozoite binding to bovine lymphocytes

The major histocompatibility complex (MHC) class I molecules are ubiquitous cell surface molecules involved in the cell-mediated immune response. We show here, using a number of different, independent approaches, that these proteins are an essential component of the host cell surface receptor involved in Theileria parva sporozoite invasion. Monoclonal antibodies (mAbs) reactive with common determinants on MHC class I molecules and with beta-2 microglobulin inhibited sporozoite entry by specifically preventing the initial binding event. However, in experiments using lymphocytes from heterozygous cattle in which at least four MHC class I gene products are expressed, mAbs which reacted with only one of these products did not inhibit entry. Using a series of bovine deletion mutant cell lines from which one or both MHC class I haplotypes had been lost, sporozoite binding and entry clearly correlated with the level of class I surface expression. While the level of sporozoite entry into cells in which one of the MHC class I haplotypes was lost was only slightly lower than into the parent cells, in a double deletion cell line having less than 5% of the class I expression of the parent cells the level of infection was only 4.3% of that into the parent cells. Furthermore, sporozoite entry into cells from a spontaneously arising mutant cell line exhibiting low levels of class I expression was correspondingly low. Treatment of lymphocytes with IL-2 produced a significant increase in host cell susceptibility and sporozoite entry and this increase correlated with either an increase in the number of target molecules per host cell, or in the binding of bovine MHC class I molecules to the mAbs. In particular, a significant increase in the level of reactivity with mAb W6/32 was observed. Lastly, we show that parasite entry can be competitively inhibited with an isolated sporozoite surface protein, p67. However, p67 binds weakly to lymphocyte surface molecules and initial attempts to use p67 to isolate the relevant host cell molecule(s) have not been successful.

Sequence and expression of a 90-kilodalton heat-shock protein family member of Theileria parva

A Theileria parva specific full-length cDNA clone, T7, which encodes a protein with more than 60% homology to heat shock protein 90 (hsp90) of other organisms, has been identified. T7 appears to be a single copy gene. The gene is expressed as a protein of 87 kDa in both the sporozoite and schizont stages of T. parva. The protein was not found in the piroplasm stage, although the corresponding transcript was detected, suggesting post-transcriptional regulation of the gene. In the schizont stage the T7 protein is upregulated upon heat shock and localized in the cytoplasm.

Identification of Babesia bigemina infected erythrocyte surface antigens containing epitopes conserved among strains

The presence of previously uncharacterized antigens (new antigens) on the surface of intact erythrocytes infected with three strains of Babesia bigemina from Kenya and one each from Puerto Rico, Mexico, St. Croix, and Texcoco-Mexico was demonstrated by indirect immunofluorescent antibody (IFA) reactions. These antigens were not strain specific because antibodies in bovine immune serum to either the Mexico or Kenya isolates reacted with all seven strains tested. Homologous and heterologous immune serum antibodies bound a maximum of 83% and 55%, respectively, of intact erythrocytes infected with the Kenya-Ngong strain but not uninfected erythrocytes. Both sera caused agglutination of only infected erythrocytes. Antibodies eluted from the surface of glutaraldehyde (0.25%) fixed infected erythrocytes had IFA reaction patterns among strains similar to those of immune sera before elution. Eluted antibodies were used to determine if these antigens were protein and encoded by B. bigemina. Eluted antibodies bound seven parasite-encoded proteins of 240, 220, 66, 62, 58, 52 and 38 kDa in an erythrocyte surface-specific immunoprecipitation reaction of 35S-methionine labelled proteins. It was concluded that the surface of B. bigemina infected erythrocytes had parasite-encoded proteins and that these proteins had surface exposed epitopes that were conserved among the seven strains examined which were from two continents.

Characterisation of the gene encoding a candidate vaccine antigen of Theileria parva sporozoites

We have cloned and characterised the gene encoding the 67-kilodalton stage-specific surface antigen, p67, of Theileria parva (Muguga) sporozoites. The gene which is present in a single copy, is divided into 2 exons by an intron 29 bp long and is transcribed into mRNA of about 2500 nucleotides. The gene is present in all stocks of T. parva and there is a related gene in Theileria annulata. The deduced amino acid sequence of 709 residues predicts that p67 is a membrane protein and that it lacks tandemly repeated sequences. Recombinant p67 has been expressed in Escherichia coli as a fusion protein with Sj-26, a glutathione-S-transferase of Schistosoma japonicum. Antibodies to purified recombinant proteins containing residues 9-316 or 397-709 of p67 bind to p67 in immunoblots and neutralise sporozoite infectivity in vitro. Recombinant p67 is, therefore, a candidate antigen for development of an anti-sporozoite vaccine for East Coast fever in cattle.

Molecular characterization and immunogenicity of neutralization-sensitive Babesia bigemina merozoite surface proteins

Monoclonal antibodies binding to the surface of live Mexico isolate Babesia bigemina merozoites have defined 4 parasite-encoded surface antigens (36, 45, 55, and 58 kDa) that are potential targets for immune-mediated neutralization of merozoites. In this study, we have characterized the post-translational modification, antigenic polymorphism, and immunogenicity of these 4 proteins. Monoclonal antibody immunoaffinity-purified 36- and 55-kDa polypeptides were identical in gel electrophoresis to immunoprecipitated radiolabeled proteins, while the purified 45-kDa protein consisted of 2 closely spaced polypeptides with relative molecular weights of 45 and 43 kDa. The 36-, 45-, and 55-kDa proteins were post-translationally modified by incorporation of [3H]glucosamine and [3H]myristic acid, suggesting they are integral membrane proteins secured by a phosphatidylinositol anchor. Cross-reactivity studies with monoclonal and monospecific polyclonal antibodies revealed marked antigenic polymorphism of these 3 glycoproteins among diverse geographic isolates. In contrast, none of the polypeptides bound by anti-p58 monoclonal antibody were glycosylated or myristilated. Both monoclonal and monospecific polyclonal antibodies recognizing p58 bound to similar molecular weight proteins in 4 additional isolates of B. bigemina from Mexico, Puerto Rico, St. Croix, and Kenya, suggesting widespread conservation of p58 immunogenic epitopes among geographic isolates. Calves immunized with immunoaffinity purified gp45, gp55, or p58 antigens were able to neutralize the infectivity of merozoites as indicated by significant reductions in the peak parasitemia after experimental challenge. Precise definition and appropriate presentation of neutralization sensitive epitopes on gp45, gp55, or p58 may enhance the merozoite neutralizing immune response in immunized cattle.

Differences between N'Dama and Boran cattle in the ability of their peripheral blood leucocytes to bind antibody-coated trypanosomes

Investigations were undertaken to evaluate the immune response of trypanotolerant N'Dama (Bos taurus) and susceptible Boran (Bos indicus) cattle to two Trypanosoma congolense variable antigen types (VATs) expressed in both breeds following tsetse-transmitted challenge. The VAT-specific antibodies of both IgM and IgG1 isotypes produced by both breeds had similar neutralizing titres. The interaction between immune sera, trypanosomes and freshly isolated peripheral blood leucocytes (PBL) from uninfected N'Dama and Boran animals was studied. It was found that both N'Dama and Boran immune sera were able to induce adherence of trypanosomes to the N'Dama PBL, but not to Boran PBL. The adherence-inducing activity was exhibited by both IgM and IgG1 antibodies, but IgG1 antibodies were more efficient in this respect. These results suggest that there are qualitative and/or quantitative differences in the immunoglobulin receptor function of PBL between the two breeds of cattle.

The entry of Theileria parva sporozoites into bovine lymphocytes: evidence for MHC class I involvement

We have examined the process of Theileria parva sporozoite entry into susceptible bovine lymphocytes and have begun to identify one of the possible molecular interactions involved in the process. The entry process involves a defined series of events and we have used a number of experimental procedures in combination with a method of quantitation to examine various aspects of this process. T. parva sporozoites are nonmotile organisms and the initial sporozoite-lymphocyte interaction is a chance event which can occur at 0-2 degrees C. All subsequent stages in the process are temperature dependent, require the participation of live intact sporozoites and host cells, and involve some cytochalasin-inhibitable rearrangement of the host cell surface membrane or cytoskeleton. Sporozoite entry can be inhibited by antibodies (mAbs) reactive with major histocompatibility complex (MHC) class I molecules (IL-A 19, IL-A 88) and with beta 2 microglobulin (B1G6), whereas mAbs reactive with MHC class II molecules (IL-A 21, J 11), and a common panleucocyte surface antigen, (IL-A 87; a bovine equivalent of CD 11a) have no effect. These results indicate that MHC class I molecules play a role in the process of T. parva sporozoite entry into bovine lymphocytes although as yet the precise role has not been determined. Once internalized within the lymphocyte, a process that takes less than 3 min at 37 degrees C, the sporozoite rapidly escapes from the encapsulating host cell membrane; a process which occurs concurrently with the discharge of the contents of the sporozoite rhoptries and microspheres. The intracytoplasmic parasite is covered by a layer of sporozoite-derived fuzzy material to which host cell microtubules rapidly become associated.

Clone-specific immune colostrum induces increased resistance in goat kids challenged with Trypanosoma congolense

The course of infection and the humoral immune response to Trypanosoma congolense clone ILNat 3.1 were studied in test goat kids receiving colostrum from dams immunized with the surface coat of ILNat 3.1 and control kids that received colostrum from nonimmunized dams. At 24-48 h after birth, all test kids had detectable serum antibodies to the trypanosome clone. There was no difference in the prepatent period between the test and control kids following challenge with 10(3) T. congolense ILNat 3.1 trypanosomes 8 days after birth. After the first 7 days of the experimental period, significantly lower parasitemia was recorded in test kids than in control kids. The mean packed red cell volume of test kids was not significantly different from that of control kids 7 days after infection. The test kids gained as much weight as noninfected control kids; both groups gained twice as much weight as infected control kids. Following infection, all kids developed antibodies against the infecting trypanosome clone. Fifteen test kids had titers equal to or greater than 1280 compared to only two control kids. The test kids survived longer after infection compared to control kids. The results suggest that colostrum from does immunized with the surface of a T. congolense clone did not prevent infection, but decreased parasitemia and prolonged survival of kids challenged with the same clone.

Identification of antigens for use in immunodiagnosis of Taenia saginata cysticercosis

Fifteen metacestode antigens from Taenia saginata were defined by Laurell crossed immunoelectrophoresis and investigated for their potential use in immunodiagnosis of bovine cysticercosis. Several antigens cross reacted with those of some common cattle parasites. Three of the antigens, designated as numbers 4, 8 and 11, were selected on the basis of their restricted cross reactions and were isolated by affinity chromatography. These antigens showed high sensitivity and specificity values in the enzyme-linked immunosorbent assay (ELISA) for serodiagnosis of bovine cysticercosis.

Characterization of a polymorphic immunodominant molecule in sporozoites and schizonts of Theileria parva

This study examines several aspects of a polymorphic, immunodominant molecule (PIM) found in the protozoan parasite, Theileria parva. The antigen is present in all T.p. parva stocks examined, and in the related subspecies, T.p.bovis and T.p.lawrencei. It is the predominant antigen recognized by antisera from immune cattle on Western blot analysis of schizont-infected lymphocytes, and is the only antigen which has been shown to react with anti-schizont monoclonal antibodies (MoAbs) on Western blots or in immunoprecipitations. The antigen shows polymorphism in both size and expression of antibody epitopes among the different stocks of T. parva. The antigen is present in sporozoites as well as schizonts.

A single exon codes for the enzyme domain of a protozoan cysteine protease

Theileria parva is an intracellular protozoan parasite of cattle. We have determined the nucleotide sequence of a gene and cDNA coding for a cysteine protease of T. parva. The gene is divided into two exons. The first exon codes for a signal sequence and for part of the "pro" region of the zymogen. The second exon codes for the remainder of the pro region, including residues thought to be involved in zymogen processing, and for the entire enzyme domain. Part of this exon cross-hybridizes, at high stringency, with DNA isolated from Plasmodium falciparum. It is likely that the T. parva gene is functionally active. Parasite extracts contain hydrolytic activity against benzyloxycarbonyl-Phe-Arg-7-amido-4-methylcoumarin. This activity is optimal at pH 6.0 and is inhibited by the cysteine protease inhibitor L-trans-epoxysuccinyl-leucylamido(4-guanidino)butane (E-64). This is, to our knowledge, the first description of a gene coding for a eukaryotic cysteine protease which lacks an intron in DNA coding for the enzyme domain.

Identification of a Theileria mutans-specific antigen for use in an antibody and antigen detection ELISA

Purified piroplasms of Theileria mutans were used to immunize BALB/c mice to generate monoclonal antibodies (MoAbs). The MoAbs recognized an antigen of a relative molecular mass of 32 kDa in Western blots. This antigen was also recognized by sera from cattle which had recovered naturally from experimental tick-transmission or infections induced by the blood stages of T. mutans. The MoAbs did not react, in indirect immunofluorescence or enzyme-linked immunosorbent assays (ELISA), with the common haemoparasites of cattle, namely, T. parva, T. annulata, Babesia bigemina, B. bovis, Anaplasma marginale, Trypanosoma congolense, T. vivax or T. brucei. An antigen capture ELISA was established with two of the MoAbs which recognized different epitopes on the 32 kDa molecule. Using this test it was possible to detect circulating antigens or immune complexes in sera collected from cattle during the acute or chronic phases of infection. When the purified 32 kDa protein was used as antigen in a micro-ELISA to detect circulating antibodies in both experimental and field cattle sera, it was found that the titres of antibodies ranged between 1:20 and 1:10,240. Results of this study indicate that the antigen and immune complex capture assays and the antibody detection ELISA can be complementary in the immunodiagnosis of acute and chronic T. mutans infections. Moreover, the tests are useful in the differential diagnosis of the disease and for epidemiological studies.

Identification of lambda gt11 clones encoding the major antigenic determinants expressed by Theileria parva sporozoites

An antiserum, C16, was raised in cattle against freeze-thawed extracts of sporozoites of Theileria parva (Muguga). This antiserum, which neutralizes sporozoite infectivity in vitro, identified theileria-specific antigens having approximate molecular masses of 105, 90, 85, 69, 67, 52, 47, and 43 kilodaltons (kDa) on Western blots (immunoblots) of infected tick salivary gland extracts. The antiserum was used to screen an expression library of T. parva (Muguga) genomic DNA fragments. Three recombinant bacteriophage clones carrying different theileria DNA inserts were studied. The expressed gene product from each clone was used to affinity purify antibodies from C16 antiserum for use in probing Western blots of uninfected and infected tick salivary gland extracts. The population of antibodies selected by each clone specifically recognized a subset of the antigens identified by C16 antiserum. The antigens fell into three distinct groups as defined by their reactivity with each set of selected antibodies. One group included antigens of 105, 90, 85, and 35 kDa, a second group included antigens of 69, 67, 52, 47, and 43 kDa, and the third group included an apparently distinct pair of antigens of 47 and 43 kDa. Thus, antibodies that reacted with determinants encoded by the three recombinant phage clones recognized all of the major antigens seen on Western blots probed with whole C16 antiserum. These results suggest that there may be only three immunodominant antigens expressed in T. parva (Muguga) sporozoites. Additionally, monoclonal antibodies have been raised which neutralize sporozoite infectivity in vitro. These antibodies react with epitopes of the antigens with Mrs of 69,000, 67,000, 52,000, 47,000, and 43,000 which are encoded in clone pgT-42 and have been used to localize these epitopes on the sporozoite surface.

SfiI and NotI polymorphisms in Theileria stocks detected by pulsed field gel electrophoresis

DNAs of Theileria parva parva, T. p. lawrencei, T. p. bovis and Theileria mutans stocks, from Kenya, Uganda, Zanzibar and Zimbabwe were digested with either SfiI or NotI and analysed using contour-clamped homogeneous electric field (CHEF) and field-inversion gel electrophoresis (FIGE). The SfiI-digested T. parva genomic DNA resolved into approximately 30 fragments while the NotI digestion produced between 4-7 bands. The summation of the sizes of SfiI fragments gave an estimate of 9-10 X 10(6) base pairs for the size of the T. parva genome. Heterogeneity within T. p. parva Muguga, Pemba/Mnarani and Mariakani stocks was detected. All the T. parva stocks analysed showed SfiI and NotI restriction fragment length polymorphisms (RFLP). Hybridisation of 5 SfiI-digested T. parva DNAs with a Plasmodium berghei telomeric repeat probe suggested that most of the polymorphisms and heterogeneity occurred in the telomeric or sub-telomeric regions of the genome. The recognition by the Plasmodium telomeric probe of 7-8 strongly hybridising SfiI bands indicates that the T. parva genome may possess at least 4 chromosomes. The T. mutans genome was cut frequently with the above enzymes resulting in large numbers of fragments predominantly below 50 kb, thus suggesting either a much higher G + C content than T. parva or the presence of highly reiterated G + C-rich regions.

Development of recombinant antigen vaccines for the control of theileriosis

Immunization against Theileria parva involves infection with sporozoites and simultaneous treatment with a long-acting tetracycline. For T. annulata, immunization is achieved by inoculation of attenuated schizont-infected lymphocytes. The two methods are inadequate because of the use of live organisms and the methods are also bedevilled by the multiplicity of strains, particularly of T. parva. For these reasons, alternative methods of control are being sought. In this review an attempt is made to highlight advances towards subunit vaccines against T. parva and T. annulata. Several candidate antigens which are thought to induce protective responses have been identified and recombinant DNA technology is being employed to produce these antigens in bulk. Relevant antigens may be delivered as subunit vaccines by using recombinant vaccinia virus or attenuated Salmonella spp. as carriers of the genes expressing these antigens. It is likely that effective vaccines against T. parva and T. annulata will have to elaborate immune responses against both the sporozoite and schizont stages of the parasite.

Characterisation of the gene encoding a 104-kilodalton microneme-rhoptry protein of Theileria parva

A neutralizing antiserum, C16, raised against sporozoites of Theileria parva parva was used to screen a lambda gt11 expression library of T. parva parva (Muguga) genomic DNA fragments. Proteins encoded by one phage clone, lambda TpS-17, were reactive with the C16 antiserum. Detailed characterisation of the DNA insert showed it to encode determinants found on four theilerial antigens of approximately 104, 90, 85 and 35 kDa. The sequence encoded by the clone is expressed during sporogony as a single RNA transcript of about 3000 nucleotides. On sequencing a portion of the 5000-bp insert, an open reading frame of 2772 bp was revealed that encoded a 104-kDa protein. Immunoscreening a library of subfragments of the DNA insert with the original antiserum localised sequences encoding the dominant antigenic determinants to an 800-bp stretch of DNA at the 3' end of the open reading frame. Sequence data from three subclones spanning this region show portions of the antigenic domains to be unusually rich in proline residues which are repeated every three amino acids. These repeats often take the form X-S(T)-P or X-K(R)-P. Antibodies directed against each of the three subclones recognize the 104- and 35-kDa antigens and different combinations of the 90- and 85-kDa kDa antigens, suggesting that the smaller proteins are derived from the 104-kDa antigen by limited proteolysis occurring at the carboxyl terminus end of the protein. In immunoelectron micrographs the antigen is associated with the microneme/rhoptry complexes of the sporozoite.

The chromosome profiles of Trypanosoma congolense isolates from Kilifi, Kenya and their relationship to serodeme identity

Chromosomal DNA from 117 Trypanosoma congolense clones from 54 stocks, isolated from cattle introduced onto a ranch in Kilifi in the coastal area of Kenya, was fractionated by the orthogonal field alternation gel electrophoresis technique. The technique resolved chromosomes in the size range of 100 kb-1 Mb. The chromosome profile for cloned trypanosome populations was relatively stable with regard to number and size of the chromosome bands following transmission in mice, cattle, goats or tsetse flies. Only in one clone was a shift observed in the position of one medium-sized chromosome band following cyclical development in tsetse. On the basis of their chromosome profiles, the 117 clones could be divided into 18 distinct groups. Representative clones, randomly selected from 7 of the 18 chromosome profile groups were inoculated into steers and goats in order to raise variable antigen type (VAT) repertoire-specific infection sera. Cross-neutralization assays demonstrated that recovery sera from animals infected with a clone neutralized all the clones with an identical chromosome profile. This suggests that clones having an identical chromosome profile also express an identical VAT-repertoire (serodeme).

Differentiation of F38 mycoplasmas causing contagious caprine pleuropneumonia with a growth-inhibiting monoclonal antibody

Monoclonal antibody WM-25 inhibited the in vitro growth of 13 F38 isolates from goats with contagious caprine pleuropneumonia but not 7 heterologous mycoplasma isolates representing four different species. In contrast to results with polyclonal antisera, growth inhibition by monoclonal antibody WM-25 was specific for F38 mycoplasma isolates and constituted a reliable means of distinguishing F38 from other mycoplasmas.

Monoclonal antibodies that distinguish Trypanosoma congolense, T. vivax and T. brucei

Monoclonal antibodies (MoAbs) were derived against in-vitro-propagated procyclic forms of Trypanosoma congolense, T. vivax, T. brucei brucei and T.b. rhodesiense in order to identify antigens for use in immunodiagnosis of African trypanosomiasis. The antibodies have been tested against procyclic and bloodstream form trypanosomes of 13 T. congolense, six T. vivax six T.b. brucei, four T.b. rhodesiense, five T.b. gambiense and three T. simiae isolates from different geographical areas by indirect immunofluorescent antibody test (IFAT) and enzyme-linked immunosorbent assay (ELISA). The MoAbs raised against T.b. brucei reacted with all the brucei group of trypanosomes but not with T. congolense, T. simiae or T. vivax. Likewise, MoAbs against T. congolense reacted with T. congolense and T. simiae but not with any of the other species, while those against T. vivax reacted with T. vivax only. The antigens recognized by these MoAbs were present in lysates of bloodstream trypanosomes as well as midgut (for T. congolense and T. brucei) and epimastigote forms from infected Glossina morsitans centralis. There was no reactivity of the MoAbs with Theileria parva, Anaplasma marginale, Babesia bigemina or Plasmodium falciparum. These antibodies and the antigens they recognize should, therefore, prove useful in the development of assay systems for immunodiagnosis of African trypanosomiasis.

Comparison between bloodstream and procyclic form trypanosomes for serological diagnosis of African human trypanosomiasis

Trypanosoma brucei brucei MiTat 1.2 bloodstream and corresponding procyclic forms, as well as procyclics of T. b. gambiense and T. b. rhodesiense, were fixed, in suspension, using a mixture of 80% acetone and 0.25% (v/v) formalin in saline and used as antigens for diagnosis of African human trypanosomiasis by the indirect immunofluorescent antibody test. T. b. brucei bloodstream forms detected 41/42 and 37/41 parasitologically diagnosed cases of T. b. rhodesiense and T. b. gambiense trypanosomiasis, respectively, while the procyclic stages detected the same number (41/42) of T. b. rhodesiense, but fewer (29/41) T. b. gambiense infections.

Characterization of Trypanosoma congolense serodemes in stocks isolated from cattle introduced onto a ranch in Kilifi, Kenya

A herd of 20 cattle was introduced on a ranch in Kilifi, Coast Province of Kenya, where they were in contact with Glossina austeni for 6 months. In total, 65 trypanosome isolates were made from these animals. Examination of the isolates revealed that 61 were Trypanosoma congolense and 4 were T. theileri. Out of the 61 T. congolense isolates, 55 were successfully passaged and cloned in mice to provide trypanosome populations for further analyses. The stocks and their clones were inoculated into goats on which teneral G. morsitans centralis were later fed in order to provide metacyclics for use in serodeme analysis. Identification of serodemes was carried out by indirect immunofluorescence and neutralization using antimetacyclic hyperimmune sera prepared in mice against metacyclics of cloned trypanosome populations. So far 4 serodemes have been identified in 8 stocks and 7 clones. Each of the 9 stocks contained a mixture of at least 2 of the 4 serodemes identified. Furthermore, stocks isolated sequentially from individual animals contained the same serodemes despite repeated treatment with a curative dose (6 mg/kg body weight) of Berenil between isolations. From the latter finding, it can be inferred that the 4 serodemes were present on the ranch throughout the study period.

A new method for fixation and preservation of trypanosomal antigens for use in the indirect immunofluorescence antibody test for diagnosis of bovine trypanosomiasis

A new method for fixation of trypanosomes for use in the indirect immunofluorescent antibody test (IFAT) is described. The method involves fixation of live trypanosomes, in suspension, using a mixture of 80% cold acetone and 0.25% formalin in saline. The fixed trypanosomes were stored in suspension at -60 degrees C, 4 degrees C or at room temperature for at least one year without loss of antigenicity. Using trypanosomes prepared this way as antigens in IFAT, species-specific antibodies were detected within 2 weeks of infection in sera of cattle infected with T. brucei or T. vivax. Thereafter, antibodies recognizing antigens common to the two species as well as T. congolense were detected. The antibody levels to common antigens of the three species declined 2-3 months post-infection, leaving only the species-specific antibodies. The sera obtained from T. congolense infected animals, did not react with T. vivax or T. brucei antigens. The non-specific fluorescence commonly associated with this assay was eliminated by prior absorption of the test sera with normal bovine lymphocyte lysate. This treatment of serum did not affect the specific antibodies to trypanosomal antigens. Analysis of bovine sera prepared from cattle in Kisiwani and Muhaka, along the Kenya coast, using the fixed trypanosomes revealed that some animals had antibodies to one trypanosome species only while others had antibodies to 2 or all 3 trypanosome species.