Eimeria tenella enolase and pyruvate kinase: A likely role in glycolysis and in others functions

Two cDNA codings for glycolytic enzymes were cloned from a cDNA library constructed from the schizont stage of the avian parasite Eimeria tenella. Enolase and pyruvate kinase cDNA were fully sequenced and compared with sequences of enzymes from other organisms. Although these enzymes were already detected in the sporozoite stage, their expression was enhanced during the first schizogony in accordance with the anaerobic conditions of this part of the life cycle of the parasite. Under activating conditions, microscopic observations suggest that these glycolytic enzymes were relocalised inside sporozoites and moreover were in part secreted. The enzymes were also localised at the apex of the first generation of merozoites. Enolase was partly observed inside the nucleus of sporozoites and schizonts. Taken together, these results suggest that glycolytic enzymes not only have a function in glycolysis during anaerobic intracellular stages but may also participate in the invasion process and, for enolase, in the control of gene regulation.

Study of proteins associated with the Eimeria tenella refractile body by a proteomic approach

Refractile bodies (RB), whose function is still unknown, are specific structures of Eimeriidae parasites. In order to study their proteome, RB were purified from Eimeria tenella sporozoites by a new procedure using a reversible fixation followed by centrifugation. RB proteins were resolved by two-dimensional electrophoresis. Around 76 and 89 spots were detected on RB two-dimensional gels using gradients in the 3-10 and 4-7 range, respectively. RB proteins were located mainly between pH 5 and 7. RB gels were then compared with previously established maps of the entire sporozoite proteome. Proteins appearing in new spots were identified by mass spectrometry. Thirty protein isoforms were located in RB. Added to the already known RB proteins such as Eimepsin and SO7', the new RB proteins were defined as haloacid dehalogenase, hydrolase, subtilase, lactacte dehydrogenase or ubiquitin family proteins. The RB proteome analysis confirmed the hypothesis that this structure is a reservoir for proteins necessary to invasion but also suggests that RB have energetic and metabolic functions.

The heat shock protein 90 of Eimeria tenella is essential for invasion of host cell and schizont growth

The 90-kDa heat shock proteins (Hsp90) are important for stress tolerance, for newly synthesised protein folding and for the growth of various organisms. Participation of Hsp90 in the development of Apicomplexa, notably in Plasmodium falciparum and Toxoplasma gondii, has been proven. In this work, the importance of Hsp90 for Eimeria tenella, which is responsible for avian caecal coccidiosis, was studied. Our results show that E. tenella Hsp90 (EtHsp90) expression increases during infection. Immunofluorescence microscopy studies reveal a dispersed localisation of EtHsp90 during the first schizogony. Moreover, EtHsp90 is secreted by sporozoites as early as 5min after addition of FCS in a temperature-dependent manner. By using staurosporine, we invalidated the hypothesis that EtHsp90 might be a micronemal protein. Then, EtHsp90 was detected in a parasitophorous vacuole membrane. This result suggests the importance of EtHsp90 for intracellular growth of the parasite. Inhibition of EtHsp90 function using specific antibodies and geldanamicin attenuates the capacity of E. tenella to invade and grow in the host cell.

Eimeria tenella microneme protein EtMIC3: identification, localisation and role in host cell infection

The gene coding for Eimeria tenella protein EtMIC3 was cloned by screening a sporozoite cDNA library with two independent monoclonal antibodies raised against the oocyst stage. The deduced sequence of EtMIC3 is 988 amino acids long. The protein presents seven repeats in tandem, with four highly conserved internal repeats and three more divergent external repeats. Each repeat is characterised by a tyrosine kinase phosphorylation site, WRCY, and a reminiscent motif of the thrombospondin1 (TSP1)-type I domain, CXXXCG. The protein EtMIC3 is localised at the apex of free parasite stages. It is not detected in the early intracellular parasite stage but is synthesised in mature schizonts. Secretion of the protein is induced when sporozoites are incubated in complete medium at 41 degrees C. Strangely enough, the two independent mAb that allow cloning of EtMIC3 interfere with parasitic growth in different ways. One is able to inhibit parasite invasion whereas the other inhibits development. Expression and localisation of the protein EtMIC3 are consistent with a protein involved in the invasion process as is expected for a microneme protein.

Towards a reference map of Eimeria tenella sporozoite proteins by two-dimensional electrophoresis and mass spectrometry

Eimeria tenella is a parasite of great importance as a disease causing agent in the poultry industry. Until recently, biological studies have focused on specific proteins, some of which play an important role in the parasite life cycle. Post-genomic studies will make it possible to understand the complexity of the parasites and their interactions with host cells. Here we present a systematic reference map of the proteins from E. tenella sporozoites. The proteins expressed at the sporozoite stage were resolved between isoelectric points 3-10 and 4-7. They were systematically identified using mass spectrometry and 16 known Eimeria sporozoite proteins were identified on two-dimensional maps. Peptide fragmentation data from mass spectrometry were compared to single and consensus expression sequence tags in databases and to the E. tenella genome (not annotated). Among the set of unknown proteins analysed, 12 new assignments were proposed on the basis of similarities with Apicomplexa proteins. In order to define sporozoite proteins as potential targets for coccidiosis therapy, proteins were studied according to their relative abundance and immunogenicity in the sporozoite. Immunoblots of sporozoite 2D maps with chicken sera were performed and approximately 50 proteins were defined as antigens. It was shown that abundance and immunogenicity are not related in the sporozoite stage. Perspectives of gene prediction and completion of the genome annotation by a proteomic approach is discussed.

Production of a functional chicken single-chain variable fragment antibody derived from caecal tonsils B lymphocytes against macrogamonts of Eimeria tenella

Avian coccidiosis is due to a protozoan intracellular parasite belonging to the genus Eimeria which multiplies in the intestine of the host. In order to identify Eimeria antigens which reflect the natural avian humoral immune response, chicken hybridomas were produced by fusion of myeloma MuH1 with B lymphocytes from Eimeria tenella infected chicken. B lymphocytes used for fusions were isolated from tonsils at the basis of caeca where the parasite develops. One of the clones (G1F5) recognised oocyst antigens and the macrogamont stage of the parasite in ELISA and immunofluorescence assay. A single-chain variable fragment (scFv) antibody was cloned from the light chain variant region (VL) and heavy chain variant region (VH) genes of the hybridoma. This recombinant antibody (scFv G1F5) exhibited antigen binding specificity to oocysts and macrogamonts of E. tenella equivalent to the mAb produced by the clone G1F5. Nucleotide sequence analysis of VL genes from scFv G1F5 compared to the germ-line revealed vestiges of gene conversion. scFv derived from chicken B lymphocytes isolated from the gut-associated lymphoid tissue following experimental infection can reveal specific antigens recognised by the avian immune response.

Gene discovery in Eimeria tenella by immunoscreening cDNA expression libraries of sporozoites and schizonts with chicken intestinal antibodies

Specific antibodies were produced ex vivo from intestinal culture of Eimeria tenella infected chickens. The specificity of these intestinal antibodies was tested against different parasite stages. These antibodies were used to immunoscreen first generation schizont and sporozoite cDNA libraries permitting the identification of new E. tenella antigens. We obtained a total of 119 cDNA clones which were subjected to sequence analysis. The sequences coding for the proteins inducing local immune responses were compared with nucleotide or protein databases and with expressed sequence tags (ESTs) databases. We identified new Eimeria genes coding for heat shock proteins, a ribosomal protein, a pyruvate kinase and a pyridoxine kinase. Specific features of other sequences are discussed.

Aspartyl proteinase genes from apicomplexan parasites: evidence for evolution of the gene structure

Aspartyl proteinases are a widely distributed family of enzymes. All vertebrate aspartyl proteinases share a conserved nine-exon gene structure, but in other organisms the structure of aspartyl proteinase genes varies considerably. The exon-intron patterns generally reflect phylogeny based on amino acid sequences. However, close comparison of these gene structures reveals some striking features, such as the conservation of intron positions and intron phases between aspartyl proteinases from nematodes and apicomplexans. Here, we discuss the implications of gene structure for the possible evolution of the aspartyl proteinase family, with particular reference to the plasmepsins of Plasmodium falciparum and eimepsin from Eimeria tenella.

Genomic organisation and developmentally regulated expression of an apicomplexan aspartyl proteinase

The cDNA for an aspartyl proteinase, termed eimepsin, was isolated from an Eimeria tenella sporulated oocyst library and the deduced amino acid sequence found to be almost identical to a previously described aspartyl proteinase from E. acervulina (97.4% amino acid identity). An E. tenella cosmid clone covering the entire eimepsin gene was cloned and characterised. Sequencing revealed that the eimepsin gene spans 2.9 kb and consists of 18 exons and 17 introns. The 5' flanking region sequence of the gene contains a putative transcriptional promoter sequence (TATAAA box) and three potential transcription initiator sites (Inr sites). Expression of eimepsin at the mRNA and protein level is developmentally regulated during oocyst sporulation. The eimepsin transcript was detected in unsporulated oocysts and increased in abundance during the early part of sporulation when the oocyst undergoes nuclear division and blast formation. Thereafter, the level of the eimepsin transcript decreases and in the excysted sporozoite, no eimepsin-specific RNA was detected. Expression of eimepsin lags behind transcript expression by some hours, and the protein accumulates in the oocyst during sporocyst and sporozoite formation.

Differential localisation of an Eimeria tenella aspartyl proteinase during the infection process

Aspartyl proteinases are essential for the survival of many pathogens. A single copy gene in species of Eimeria encodes an aspartyl proteinase, which we propose should be called eimepsin to conform to the commonly used names of this family of proteinases. An epitope map, constructed using BIAcore technology, confirmed the specificity of 14 mAbs for eimepsin and defined four antigenic domains, which were conserved between native and recombinant forms of eimepsin. In resting sporozoites, mAb defining antigenic domains I and II stained the refractile body organelles, whereas those defining antigenic domains III and IV stained cytoplasmic granules. During host cell invasion, the staining patterns of mAb defining antigenic domains I, III and IV changed dramatically with the apical tips of invading sporozoites becoming strongly stained. In contrast, mAb defining antigenic domain II continued to stain only the refractile bodies. During early schizogony, mAb to all four domains stained the single fused refractile body, but when schizonts matured, mAb to antigenic domains I, III and IV stained the apical tip of merozoites whereas those to antigenic domain II continued to follow the developmental redistribution of the refractile body. Irrespective of localisation, mAb to three antigenic domains recognised a polypeptide of 49 kDa, which from N-terminal sequencing corresponds to a mature form of eimepsin. Staining with fluorescent pepstatin localised a mature, active form of eimepsin to the refractile bodies of the sporozoite, schizont and first generation merozoite. It remains to be determined whether eimepsin has a catalytic function within the refractile body or whether the activated enzyme is stored in the refractile body so that it can be rapidly redistributed to the apical tip during parasite invasion.

Adjuvant effect of cholera toxin on systemic and mucosal immune responses in chickens infected with E. tenella or given recombinant parasitic antigen per os

We investigated the adjuvant effect of cholera toxin (CT) on the intestinal and systemic immune systems of chickens. The CT was given orally, mixed with a non-replicating antigen, a recombinant Eimeria protein, IPEI, or with a replicating one, Eimeria tenella parasite. There were increases in the specific IgA and IgG responses to the recombinant protein IPEI, with a significant anti-1PE1 IgG response in the duodenum (p < 0.05) and caecum (p < 0.05) 4 weeks after immunization and a specific IgA (p < 0.05) response in the duodenum after 3 weeks. A transient anti-1PE1 IgG (p < 0.05) response was detected in the serum 1 week post-injection and an IgA response (p < 0.05) at 2 weeks. CT given with the replicative parasite caused no change in the intestinal and systemic immune responses with 1 or 3 immunizations although a specific antiparasitic in vitro proliferation of the spleen cells from infected chickens was observed. Nevertheless, 0.05 mg CT given per os to chickens was strongly immunogenic in both experiments. A strong serum IgG (p < 0.01) response was detected as soon as 1 week after the end of the immunization protocol with 1PE1 and 2 weeks after infection with E. tenella. Strong anti-CT IgG responses were also detected by the second week post-immunization in the duodenum and caeca (p < 0.01). Hence, CT can be used as a mucosal adjuvant in chickens to improve the intestinal immune response.

Eimeria tenella: cloning and characterization of cDNA encoding a S3a ribosomal protein

A lambda Zap II cDNA library was constructed from Eimeria tenella first- generation schizonts mRNA and screened with a mouse serum raised against this parasitic stage. This serum identified a clone encoding a S3a ribosomal protein (EtS3a). The 858-bp cDNA fragment, containing the entire parasitic gene encoded a highly basic protein of 264 amino acids (aa) with a molecular weight of 29.780kDa. Based upon amino acid sequence comparison, EtS3a is highly homologous to v-fos transformation effector (encoded by the fte-1 gene) and cyc-07 (a plant homologue of fte-1) and similar to the yeast MFT1 (encoded by the mitochondrial fusion targeting gene). The expressions of mammalian fte-1, plant cyc-07 and yeast MFT1 have all been shown to be cell-cycle-regulated and involved in protein synthesis at the level of the ribosome. Since EtS3a expression is also developmentally regulated, we suggest that this gene product is a functional homologue of fte-1, cyc-07 and MFT1 and an important molecule regulating the development of Eimeria tenella.

Purification of first-generation Eimeria tenella schizonts

A rapid and simple method for purifying first-generation Eimeria tenella schizonts was developed with infected chicken cecal tissue. The schizonts were harvested from the tissue by treatment with a mixture of 3 enzymes: hyaluronidase, dispase, and collagenase. Subsequent purification of the parasites by filtration through gauze and centrifugation resulted in a clean final preparation compared with the starting material. Microscopical and biochemical examinations, performed to assess the quality of the schizont purification, showed a high degree of purity. This procedure may be used to obtain clean schizonts minimally contaminated with host-cell debris in order to study this parasitic stage.

Purification of a leucine aminopeptidase from Eimeria falciformis

A leucine aminopeptidase was purified from the oocysts of Eimeria falciformis using affinity chromatography and gel filtration techniques. It had a molecular weight of 45-50 kDa. Its maximal activity against leucyl-p-nitro anilide was at pH 8.6. It is a metallo-enzyme highly inhibited by bestatin.

Immune responses and protective effect in mice vaccinated orally with surface sporozoite protein of Eimeria falciformis in ISCOMs

Immunostimulating complexes (ISCOMs) were built after treatment of a purified surface protein from Eimeria falciformis sporozoites with a palmitic acid derivation, leading to a high ratio (33-64%) of P27 incorporation in these cage-like structures. P27 kept its antigenicity after incorporation in ISCOMs, which induced, after iterative intubations by the oral route to groups of mice, a systemic IgG response, a local IgA response, and a local enhanced cellular response as demonstrated by lymphoproliferation of mesenteric lymph node cells upon in vitro stimulation with antigen. This immunization (120 micrograms in six oral doses at 2-day intervals) afforded mice a partial protection (60%) against a subsequent 400 oocyst challenge. The reduction in daily oocyst excretion was corroborated by significantly different weight losses between immunized and control mice on days 9 and 10 postinfection and the subsequent death of these control mice. These observations provide the first application of ISCOMs to parasitic intestinal diseases.

The immunodominant Eimeria acervulina sporozoite antigen previously described as p160/p240 is a 19-kilodalton antigen present in several Eimeria species

A lambda Zap II cDNA expression library, constructed from Eimeria acervulina (PAPa46 strain) sporulated oocyst stage, was screened with sera raised to E. acervulina or Eimeria tenella oocysts in order to isolate clones coding for antigens common to the two species. Most of the clones isolated were derived from the same gene. Antisera raised to a recombinant glutathione-S-transferase fusion protein 1P reacted with an antigen of 19 kDa in immunoblot of E. acervulina sporulated and unsporulated oocysts. Immunofluorescence of E. acervulina sporozoites indicated that the antigen is located in the cytoplasm. The anti-1P antisera reacted on immunoblots of E. tenella with a 19-kDa antigen and by immunofluorescence on E. tenella, Eimeria maxima and Eimeria falciformis sporozoites, indicating that the antigen is conserved in Eimeria species. DNA sequencing indicated that the sequence was almost identical to that of clone cSZ1 previously described by Jenkins et al. using E. acervulina strain #12. The 1P insert hybridized to a 1150-nt mRNA from E. acervulina PAPa46 strain and strain #12, a size consistent with the observed molecular weight of the protein.

Production and characterization of monoclonal antibodies directed against Eimeria falciformis and cross-reactive with sporozoites from two species of avian coccidia

Monoclonal antibodies (mAbs) were obtained against the surface antigens of the Eimeria falciformis sporozoite by immunizing mice with whole homogenized sporozoite. The hybridomas were selected by their reactivities against oocyst extracts, then against glutaraldehyde-treated sporozoites. Three mAbs recognized both the surface of E. falciformis, E. tenella, and E. acervulina and their refractile bodies, whereas a fourth mAb recognized only one epitope on the refractile bodies. All mAbs bound to the same immunoaffinity-purified antigens in Western-blot analysis (P27 for E. falciformis and P25 for E. tenella and E. acervulina). Thus, the mAbs define at least two shared epitopes between sporozoite antigens from different eimerian species. Two of these mAbs are involved in the in vitro phagocytosis of E. falciformis sporozoites by macrophages and also in their lysis by neutrophils. Altogether, these properties showed that the four mAbs came from different activated B-cells. The P27 antigen recognized by our mAbs represents a major target of the in vitro destructive immune response.

Cloning and characterization of an Eimeria acervulina sporozoite gene homologous to aspartyl proteinases

A lambda ZapII cDNA library was constructed using mRNA from Eimeria acervulina sporulated oocysts and screened with monoclonal antibodies raised against Eimeria tenella sporulated oocytes. Monoclonal antibody N3C8B12 identified a clone (6S2) potentially encoding an aspartyl proteinase since significant homology with cathepsin D, pepsin and renin proteinases was revealed by sequence comparisons. The 1500-bp cDNA fragment containing the coccidial gene was subcloned into pGEX-FA expression vector, leading to the production of an 80-kDa fusion protein (FA6S2) which was used to immunize rabbits. The anti-FA6S2 rabbit sera revealed a single 43-kDa protein present in Eimeria acervulina, Eimeria tenella, Eimeria maxima and Eimeria falciformis sporulated oocyst antigens. Indirect immunofluorescence and electron microscopy with mAb N3C8B12 localized the putative aspartyl proteinase in the refractile bodies of Eimeria tenella sporozoites.

Protective oral immunization of chickens against Eimeria tenella with sporozoite surface antigens

Antigens were extracted from the surface of Eimeria tenella sporozoites with a solution containing Triton X 100 (1%), sodium dodecyl sulphate (0.5%) Na deoxycholate (1%) and EDTA (1 mM). After removal of the detergents, these surface antigen preparations conferred an immunity that protected chickens against a subsequent infection (10(4) sporulated oocysts). The best results were obtained after two 250 micrograms injections of Al(OH)3 adsorbed antigens (oocyst output per g caecal material on Day 7 post infection: 2.39 x 10(7) +/- 0.32 x 10(7) oocysts for controls and 7.37 +/- 10(6) +/- 3.19 x 10(6) oocysts for vaccinated birds) and after four gastric intubations of liposome entrapped antigens (oocysts output on Day 7 postinfection: 2.75 x 10(6) +/- 2.02 x 10(6) g-1 caecal material). These results represented respectively 70 and 88% protection indexes. Studies on the systemic and local antibody response after one or several infections of chickens with the parasite indicated at least 20 different molecules in the detergent antigens which are classified after immunoblotting according to their properties.

In vitro interactions between murine neutrophils and Eimeria falciformis sporozoites

The in vitro interactions between elicited mouse peritoneal neutrophils, antibodies and newly excysted sporozoites of Eimeria falciformis resulted in lysis of the parasite. This lysis required the presence of a heat-labile component of normal mouse serum, and was antibody- and cell-concentration-dependent. Under optimal conditions (serum dilution = 1/192, effector cell/sporozoite = 10/1) this lysis, which began after incubation at 37 degrees C for 4 h, was nearly complete after 18 h. It began by opsonization of the sporozoites by antibodies and complement. Inhibition studies performed with inhibitors of neutrophil function did not enable us to determine the mechanism of this extracellular lysis (oxidative respiratory burst or enzyme release), since only metal chelators, lysosomotropic reagents and compounds known to interfere with adenylate cyclase activity were truly inhibitory.

A method of purifying sheep sIg+ lymphocytes as a tool for class II MHC antigen analysis

A method is described for the purification of sheep lymphocytes carrying class II MHC antigens. After incubation of purified blood lymphocytes on anti-IgM-coated petri dishes, the adherent fraction contained 95% sIg-positive cells determined by immunofluorescence. When tested with cross-reacting anti-class II (bovine and human) monoclonal antibodies, more than 95% of these cells were positive either by immunofluorescence or cytotoxicity. This technique will permit studies of the polymorphism of sheep class II antigens.

Phosphorylcholine antigens from Nippostrongylus brasiliensis. II.--Isolation and partial characterization of phosphorylcholine antigens from adult worm

The phosphorylcholine antigens (C substance) were specifically isolated from Nippostrongglus brasiliensis adult worms. They formed a gorup of fairly closely related molecules, but it was not possible to evidence that the carrier molecule was unique. An indirect immunoenzymatic test using immobilized lectins (concanavalin A, phytohaemagglutinin Els, wheat germ agglutinin, recin types I and II, peanut agglutinin) gave some light on the carbohydrate composition of the carrier molecules, whereas the amino acid part of these molecules seemed to indicate an unique oligopeptide, the composition of which would be: Asx (4), Thr (2), Ser (4), Glux (6), Gly (6) Ala (3), Val (2), Ile (1), Leu (2), Phe (8), Lys (2), Arg (1). An epitope of the carrier molecules was demonstrated with anti-N. brasiliensis egg antisera. It was shared with various pathogens including Haemonchus contortus, Schistosoma mansoni and Dipetalonema vitae. It was also found on the purified pneumococcal C. polysaccharide. The C. substance from a variety of parasites can now be isolated by a combination of specific reactions using both anti-phosphorylcholine and anti-carrier molecule antibodies.

Phosphorylcholine antigens from Nippostrongylus brasiliensis. I.--Anti-phosphorylcholine antibodies in infected rats and location of phosphorylcholine antigens

The anti-phosphorylcholine (PC) antibody synthesis was investigated in the rat after infection with the nematode Nippostrongylus brasiliensis. Serum IgM and IgG antibodies were demonstrated from day 2 or 3 post-infection. Intestinal IgA-antibody synthesis began shortly after the worms reached the intestine. Antigens containing PC were located with the fluorescent antibody technique in L3 infective larvae, adult worms and eggs of the parasites. They were always found to internal structures such as intestinal tract or gonads. It seems, therefore, that the anti-PC antibody synthesis resulted from the release of PC antigens by the parasite (moulting fluids, excretion, secretion or breakage products).

Cytidine-5'-diphospho-choline conjugates. I.--Synthesis and fixation to phosphorylcholine-binding proteins

The oxidation of the ribose ring of cytidine-5'-diphospho-choline (CDPC) by periodate to produce reactive dialdehydes was used to couple this activated reagent onto various proteins, onto Ficoll 400 and onto Sepharose 4B. Careful control of parameters of the different steps of the reaction enabled us to synthesize conjugates with a graded number of nucleotide residues. Human serum albumin conjugates with a relatively high degree of substitution were used to demonstrate and to measure anti-phosphorylcholine antibodies and the acute phase reactant, C-reactive protein by precipitation or passive haemagglutination techniques. These methods for measuring C-reactive protein in serum of patient suffering from acute inflammation may be useful for clinicians. CDPC-AH Sepharose was used to purify the phosphorylcholine-binding myeloma protein HOPC8 and to separate C-reactive protein from the bulk of serum proteins. Improvements of this technique will certainly lead to the complete purification of C-reactive protein.