Localization in vivo and in vitro confirms EnApiAP2 protein encoded by ENH_00027130 as a nuclear protein in Eimeria necatrix

Introduction

Apicomplexan AP2 family of proteins (ApiAP2) are transcription factors (TFs) that regulate parasite growth and development, but little is known about the ApiAP2 TFs in Eimeria spp. ENH_00027130 sequence is predicted to encode a Eimeria necatrix ApiAP2 protein (EnApiAP2).

Methods

The cDNAs encoding full-length and truncated EnApiAP2 protein were cloned and sequenced, respectively. Then, the two cDNAs were cloned into the pET28a(+) expression vector and expressed expressed in Escherichia coli BL21. The mouse polyclonal antibody (pAb) and monoclonal antibody (mAb) against recombinant EnApiAP2 (rEnApiAP2) and EnApiAP2tr (rEnApiAP2tr) were prepared and used to localize the native EnApiAP2 protein in E. necatrix, respectively. Finally, the recombinant pEGFP-C1-ΔNLS-EnApiAP2s (knockout of a nuclear localization sequence, NLS) and pEGFP-C1-EnApiAP2 plasmid were constructed and transfected into DF-1 cells, respectively, to further observe subcellular localization of EnApiAP2 protein.

Results

The EnApiAP2 gene had a size of 5019 bp and encoded 1672 amino acids, containing a conserved AP2 domain with a secondary structure consisting of an α-helix and three antiparallel β-strands. The rEnApiAP2 and rEnApiAP2tr were predominantly expressed in the form of inclusion bodies, and could be recognized by the 6×His tag mAb and the serum of convalescent chickens after infection with E. necatrix, respectively. The native EnApiAP2 protein was detected in sporozoites (SZ) and second generation merozoites (MZ-2) extracts, with a size of approximately 210 kDa. A quantitative real-time PCR (qPCR) analysis showed that the transcription level of EnApiAP2 was significantly higher in SZ than in MZ-2, third generation merozoites (MZ-3) and gametocytes (P<0.01). EnApiAP2 protein was localized in the nuclei of SZ, MZ-2 and MZ-3 of E. necatrix. The protein of EnApiAP2 was localized in the nucleus of the DF-1 cells, whereas the ΔNLS-EnApiAP2 was expressed in the cytoplasm, which further confirmed that EnApiAP2 is nucleoprotein.

Discussion

EnApiAP2 protein encoded by ENH_00027130 sequence was localized in the nucleus of E. necatrix parasites, and relied on the NLS for migration to DF-1 cell nucleus. The function of EnApiAP2 need further study.

Novel Insights Into Sterol Uptake and Intracellular Cholesterol Trafficking During Eimeria bovis Macromeront Formation

Apicomplexan parasites are considered as defective in cholesterol synthesis. Consequently, they need to scavenge cholesterol from the host cell by either enhancing the uptake of extracellular cholesterol sources or by upregulating host cellular de-novo biosynthesis. Given that Eimeria bovis macromeront formation in bovine lymphatic endothelial host cells in vivo is a highly cholesterol-demanding process, we here examined host parasite interactions based on host cellular uptake of different low-density lipoprotein (LDL) types, i.e., of non-modified (LDL), oxidized (oxLDL), and acetylated LDL (acLDL). Furthermore, the expression of lipoprotein-oxidized receptor 1 (LOX-1), which mediates acLDL and oxLDL internalization, was monitored throughout first merogony, in vitro and ex vivo. Moreover, the effects of inhibitors blocking exogenous sterol uptake or intracellular transport were studied during E. bovis macromeront formation in vitro. Hence, E. bovis-infected primary bovine umbilical vein endothelial cells (BUVEC) were treated with inhibitors of sterol uptake (ezetimibe, poly-C, poly-I, sucrose) and of intracellular sterol transport and release from endosomes (progesterone, U18666A). As a read-out system, the size and number of macromeronts as well as merozoite I production were estimated. Overall, the internalization of all LDL modifications (LDL, oxLDL, acLDL) was observed in E. bovis-infected BUVEC but to different extents. Supplementation with oxLDL and acLDL at lower concentrations (5 and 10 µg/ml, respectively) resulted in a slight increase of both macromeront numbers and size; however, at higher concentrations (25–50 µg/ml), merozoite I production was diminished. LOX-1 expression was enhanced in E. bovis-infected BUVEC, especially toward the end of merogony. As an interesting finding, ezetimibe treatments led to a highly significant blockage of macromeront development and merozoite I production confirming the relevance of sterol uptake for intracellular parasite development. Less prominent effects were induced by non-specific inhibition of LDL internalization via sucrose, poly-I, and poly-C. In addition, blockage of cholesterol transport via progesterone and U18666A treatments resulted in significant inhibition of parasite development. Overall, current data underline the relevance of exogenous sterol uptake and intracellular cholesterol transport for adequate E. bovis macromeront development, unfolding new perspectives for novel drug targets against E. bovis.

Expression Analysis and Serodiagnostic Potential of Microneme Proteins 1 and 3 in Eimeria stiedai

Eimeria stiedai is an apicomplexan protozoan parasite that invades the liver and bile duct epithelial cells in rabbits and causes severe hepatic coccidiosis, resulting in significant economic losses in the domestic rabbit industry. Hepatic coccidiosis lacks the typical clinical symptoms and there is a lack of effective premortem tools to timely diagnose this disease. Therefore, in the present study we cloned and expressed the two microneme proteins i.e., microneme protein 1 (EsMIC1) and microneme protein 3 (EsMIC3) from E. stiedai and used them as recombinant antigens to develop a serodiagnostic method for an effective diagnosis of hepatic coccidiosis. The cDNAs encoding EsMIC1 and EsMIC3 were cloned and the mRNA expression levels of these two genes at different developmental stages of E. stiedai were determined by quantitative real-time PCR analysis (qRT-PCR). The immunoreactivity of recombinant EsMIC1 (rEsMIC1) and EsMIC3 (rEsMIC3) proteins were detected by Western blotting, and indirect enzyme-linked immunosorbent assays (ELISAs) based on these two recombinant antigens were established to evaluate their serodiagnostic potential. Our results showed that the proteins encoded by the ORFs of EsMIC1 (711 bp) and EsMIC3 (891 bp) were approximately 25.89 and 32.39 kDa in predicted molecular weight, respectively. Both EsMIC1 and EsMIC3 showed the highest mRNA expression levels in the merozoites stage of E. stiedai. Western blotting analysis revealed that both recombinant proteins were recognized by E. stiedai positive sera, and the indirect ELISAs using rEsMIC1 and rEsMIC3 were developed based on their good immunoreactivity, with 100% (48/48) sensitivity and 97.9% (47/48) specificity for rEsMIC1 with 100% (48/48) sensitivity and 100% (48/48) specificity for rEsMIC3, respectively. Moreover, rEsMIC1- and rEsMIC3-based indirect ELISA were able to detect corresponding antibodies in sera at days 6, 8, and 10 post E. stiedai infection, with the highest positive diagnostic rate (62.5% (30/48) for rEsMIC1 and 66.7% (32/48) for rEsMIC3) observed at day 10 post infection. Therefore, both EsMIC1 and EsMIC3 can be used as potential serodiagnostic candidate antigens for hepatic coccidiosis caused by E. stiedai.

Stable transfection of Eimeria necatrix through nucleofection of second generation merozoites

Eimeria spp., the causative agents of coccidiosis, are the most common protozoan pathogens of chickens. Infection with these parasites can result in poor development or death of animals leading to a devastating economic impact on poultry production. The establishment of transfection protocols for genetic manipulation of Eimeria species and stable expression of genes would help advance the biology of these parasites as well as establish these organisms as novel vaccine delivery vehicles. Here, we report the selection of the first stable transgenic E. necatrix population, EnHA1, consitutively expressing the EYFP reporter following transfection of the 2^nd generation merozoites with a linear DNA fragment harboring the EYFP reporter gene, the HA1 gene from the avian influenza virus H9N2 and the TgDHFR-TS selectable marker, which confers resistance to pyrimethamine. Transfected merozoites were inoculated into chickens via the cloacal route, and feces from 18 h to 72 h post inoculation were collected and subjected to subsequent serial passages, FACS sorting and pyrimethamine selection. A gradual increase in the number of EYFP-expressing sporulated oocysts was noticed with more than 90% EYFP + oocysts obtained after five passages. Immunofluorescence assay confirmed successful expression of the HA1 antigen in the EnHA1 population. The ability to genetically manipulate E. necatrix merozoites and express heterologous genes in this parasite will pave the way for possible use of this organism as a vaccine-delivery vehicle.

Both host and parasite MIF molecules bind to chicken macrophages via CD74 surface receptor

Macrophage migration inhibitory factor (MIF) is recognized as a soluble protein that inhibits the random migration of macrophages and plays a pivotal immunoregulatory function in innate and adaptive immunity. Our group has identified both chicken and Eimeria MIFs, and characterized their function in enhancing innate immune responses during inflammation. In this study, we report that chicken CD74 (ChCD74), a type II transmembrane protein, functions as a macrophage surface receptor that binds to MIF molecules. First, to examine the binding of MIF to chicken monocytes/macrophages, fresh isolated chicken peripheral blood mononuclear cells (PBMCs) were stimulated with rChIFN-γ and then incubated with recombinant chicken MIF (rChMIF). Immunofluorescence staining with anti-ChMIF followed by flow cytometry revealed the binding of MIF to stimulated PBMCs. To verify that ChCD74 acts as a surface receptor for MIF molecules, full-length ChCD74p41 was cloned, expressed and its recombinant protein (rChCD74p41) transiently over-expressed with green fluorescent protein in chicken fibroblast DF-1 cells. Fluorescence analysis revealed a higher population of cells double positive for CD74p41 and rChMIF, indicating the binding of rChMIF to DF-1 cells via rChCD74p41. Using a similar approach, it was found that Eimeria MIF (EMIF), which is secreted by Eimeria sp. during infection, bound to chicken macrophages via ChCD74p41 as a surface receptor. Together, this study provides conclusive evidence that both host and parasite MIF molecules bind to chicken macrophages via the surface receptor ChCD74.

The genome of Eimeria falciformis--reduction and specialization in a single host apicomplexan parasite

BACKGROUND

The phylum Apicomplexa comprises important unicellular human parasites such as Toxoplasma and Plasmodium. Eimeria is the largest and most diverse genus of apicomplexan parasites and some species of the genus are the causative agent of coccidiosis, a disease economically devastating in poultry. We report a complete genome sequence of the mouse parasite Eimeria falciformis. We assembled and annotated the genome sequence to study host-parasite interactions in this understudied genus in a model organism host.

RESULTS

The genome of E. falciformis is 44 Mb in size and contains 5,879 predicted protein coding genes. Comparative analysis of E. falciformis with Toxoplasma gondii shows an emergence and diversification of gene families associated with motility and invasion mainly at the level of the Coccidia. Many rhoptry kinases, among them important virulence factors in T. gondii, are absent from the E. falciformis genome. Surface antigens are divergent between Eimeria species. Comparisons with T. gondii showed differences between genes involved in metabolism, N-glycan and GPI-anchor synthesis. E. falciformis possesses a reduced set of transmembrane transporters and we suggest an altered mode of iron uptake in the genus Eimeria.

CONCLUSIONS

Reduced diversity of genes required for host-parasite interaction and transmembrane transport allow hypotheses on host adaptation and specialization of a single host parasite. The E. falciformis genome sequence sheds light on the evolution of the Coccidia and helps to identify determinants of host-parasite interaction critical for drug and vaccine development.

Characterisation and histopathological observations of a selected Brazilian precocious line of Eimeria acervulina

Precocious lines of Eimeria acervulina "Cu" and "I" strains were obtained after 25 passages of oocysts in chickens that showed a shortening of the prepatent period for first oocyst output from 96 h to 81 and 82 h, respectively. Both precocious lines were evaluated for pathogenicity using as criteria weight gain, lesion score and total oocyst production. Infection of the "Cu" precocious line in chickens showed a high weight gain, low lesion score and low oocyst production, when compared to parent strain infected chickens. However, the results did not show a significant difference in relation to the criteria used above for the E. acervulina "I" precocious line when compared to its parent strain. This suggests a low degree of attenuation for the "I" strain but good attenuation for the precocious "Cu" line. The histopathological observations of chickens infected with the E. acervulina "Cu" parent strain and precocious line, comparing life cycle and intestinal lesions, showed: (1) parasite stages only in the border cells of infected chicken intestinal villi, for the precocious line; (2) parasite stages in the border cells of the intestinal villi and submucosa cells near the Lieberkühn glands of the intestine; and (3) high degree of inflammatory cells around the parasites in chickens infected with the parent strain. The "Cu" strain was also characterized for sensitivity against eight anticoccidial drugs. Sensitivity was observed for four anticoccidial drugs and partial resistance for four other drugs, although the strain had never had previous contact with anticoccidial drugs, suggesting the presence of a natural resistance factor. This Brazilian E. acervulina "Cu" precocious line showed attenuation for pathogenicity in chickens, suggesting that it could be a suitable strain for use as a live vaccine in Brazil.

Global protein expression analysis in apicomplexan parasites: Current status

Members of the phylum Apicomplexa are important protozoan parasites that cause some of the most serious, and in some cases, deadly diseases in humans and animals. They include species from the genus Plasmodium, Toxoplasma, Eimeria, Neospora, Cryptosporidium, Babesia and Theileria. The medical, veterinary and economic impact of these pathogens on a global scale is enormous. Although chemo- and immuno-prophylactic strategies are available to control some of these parasites, they are inadequate. Currently, there is an urgent need to design new vaccines or chemotherapeutics for apicomplexan diseases. High-throughput global protein expression analyses using gel or non-gel based protein separation technologies coupled with mass spectrometry and bioinformatics provide a means to identify new drug and vaccine targets in these pathogens. Protein identification based proteomic projects in apicomplexan parasites is currently underway, with the most significant progress made in the malaria parasite, Plasmodium falciparum. More recently, preliminary two-dimensional gel electrophoresis maps of Toxoplasma gondii and Neospora caninum tachyzoites and Eimeria tenella sporozoites, have been produced, as well as for micronemes in E. tenella. In this review, the status of proteomics in the analysis of global protein expression in apicomplexan parasites will be compared and the challenges associated with these investigations discussed.

Protein from intestinal Eimeria protozoan stimulates IL-12 release from dendritic cells, exhibits antitumor properties in vivo and is correlated with low intestinal tumorigenicity

The small intestine (SI) of vertebrates exhibits low tumorigenesis and rarely supports metastatic growth from distant tumors. Many theories have been proposed to address this phenomenon, but none has been consistently supported. One candidate mechanism is that the vast immunologic compartment of the SI provides a heightened level of tumor immunosurveillance. Consistent with this, we have identified a molecule of low abundance from bovine SI that has the hallmarks of a potent immunostimulant and may be associated with the natural suppression of cancer in the intestinal tract. The protein originates from an endemic gut protozoan, Eimeria spp., and is homologous to the antigen 3-1E previously isolated from the avian apicomplexan E. acervulina. We show here that it is a very potent stimulator of IL-12 release from dendritic cells, upregulates inflammatory modulators in vivo (IL-12, MCP-1, IL-6, TNF-alpha and INF-gamma) and has antitumor properties in mice. In addition, it is synergistic in vitro with anti-CD40 antibody, IFN-gamma, IL-4 and GM-CSF; is active across species barriers in vivo; and has no observable toxicity. Based on these activities, we speculate that it is an inducer of protozoan-targeted innate immunity, which may explain its potential benefit to the intestinal tract and potency as an agent in cancer immunotherapy.

Eimeria maxima TRAP family protein EmTFP250: subcellular localisation and induction of immune responses by immunisation with a recombinant C-terminal derivative

EmTFP250 is a high molecular mass, asexual stage antigen from Eimeria maxima strongly associated with maternally derived immunity to this protozoan parasite in hatchling chickens. Cloning and sequence analysis has predicted the antigen to be a novel member of the thrombospondin-related anonymous protein (TRAP) family of apicomplexan parasites. Members of the TRAP family are microneme proteins and are associated with host cell invasion and apicomplexan gliding motility. In order to assess the immunogenicity of EmTFP250, a C-terminal derivative encoding a low complex, hydrophilic region and putative transmembrane domain/cytosolic tail was expressed in a bacterial host system. The recombinant protein was used to immunise mice and chickens and found to induce strong IgG responses in both animal models as determined by specific ELISAs. Using Western blotting, protective maternal IgG antibodies previously shown to recognise native EmTFP250 recognised the recombinant protein and, in addition, antibodies raised against the recombinant protein were shown to recognise native EmTFP250. Localisation studies employing immuno-light microscopy and immuno-electron microscopy showed that antibodies to the recombinant protein specifically labeled micronemes within merozoites of E. maxima. Furthermore, antibodies to the recombinant EmTFP250 derivative showed similar labeling of micronemes within merozoites of Eimeria tenella. This study is further suggestive of a functional importance for EmTFP250 and underscores its potential as a candidate for a recombinant vaccine targeting coccidiosis in chickens.

Coccidiosis control by administering toltrazuril in the drinking water for a 2-day period

A 56-day floor pen study was conducted to determine the appropriate time to administer toltrazuril (Baycox) (TOL) for control of coccidiosis in broiler chickens. Litter was seeded with field strains of Eimeria acervulina, Eimeria maxima and Eimeria tenella. On Days 0, 21, 35 and 56, all birds and feed were weighed. Starting on Day 14, weekly lesion scores and oocyst counts were performed. The treatments were 125 ppm nicarb (NIC) in the starter to 66 ppm salinomycin (SAL) in the grower with no TOL (NIC/SAL/no TOL), 66 ppm salinomycin in both the starter and the grower but no TOL (SAL/SAL/no TOL), or no in-feed medication with the following TOL treatment: TOL Days 2-3, TOL Days 6-7, TOL Days 10-11, TOL Days 14-15, TOL Days 18-19, and as control NM/NM/no TOL (NM). The withdrawal feed was nonmedicated. TOL was administered in the drinking water at the rate of 7 mg/kg body weight. Oocysts per gram litter and lesion scores showed a significant infection in the NM birds, which peaked about Day 21. The NIC/SAL gave excellent early protection but only moderate protection during the SAL phase. The final performance for the SAL/SAL was significantly less compared to all TOL and NIC/SAL birds. All TOL treatments but Days 2-3 provided good coccidiosis control with accompanying performance. The absence of clinical coccidiosis relapse during the last third of the growout along with moderate oocyst counts and low lesions was indicative of unimpaired coccidiosis immunity. It can be inferred from the overall results that the use of TOL as the sole anticoccidial for two consecutive days in the drinking water between Days 10 and 14 would be the best time for good coccidiosis control allowing full performance.

World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines for evaluating the efficacy of anticoccidial drugs in chickens and turkeys

These guidelines have been written to aid in the design, implementation and interpretation of studies for the assessment of drug efficacy against Eimeria species in chickens and turkeys. The information provided deals with many aspects of how to conduct controlled studies in battery cages (dose determination), floor pens (dose confirmation), and commercial facilities (field effectiveness studies), the selection of birds, housing, feeding, preparation of medicated rations, record keeping, diagnostic techniques, and methods for the preparation, maintenance and use of parasites. These guidelines are also intended to assist investigators in conducting specific studies, provide specific information for registration authorities involved in the decision-making process, assist in the approval and registration of new anticoccidial drugs, and facilitate the world-wide adoption of standard procedures.

Profiling local gene expression changes associated with Eimeria maxima and Eimeria acervulina using cDNA microarray

Eimeria parasites show preferential sites of invasion in the avian intestine and produce a species-specific host immune response. Two economically important species, Eimeria acervulina and Eimeria maxima, preferentially invade and develop in the avian duodenum and jejunum/ileum, respectively. To investigate local host immune responses induced by parasite infection, global transcriptional changes in intestinal intraepithelial lymphocytes (IELs) induced by oral inoculation of chickens with E. acervulina or E. maxima were monitored using cDNA microarrays containing 400 unique chicken genes. Multiple gene transcripts were significantly up- or down-regulated following primary or secondary infection with E. acervulina or E. maxima. In general, infection by either parasite resulted in the expression changes of more genes following primary infection than following secondary infection, and E. acervulina caused more changes than did E. maxima. Although different regions of the small intestine were infected, similar changes in the levels of several cytokine mRNAs were observed in both Eimeria species following primary infection. Also identified was a set of transcripts whose expression was commonly enhanced or repressed in intestinal IELs of chickens infected with either parasite. Microarray analysis of chicken genes induced or repressed following Eimeria infection offers a powerful tool to enhance our understanding of host-parasite interactions leading to protective immunity.

Roles of tyrosine-rich precursor glycoproteins and dityrosine- and 3,4-dihydroxyphenylalanine-mediated protein cross-linking in development of the oocyst wall in the coccidian parasite Eimeria maxima

The oocyst wall of apicomplexan parasites protects them from the harsh external environment, preserving their survival prior to transmission to the next host. If oocyst wall formation could be disrupted, then logically, the cycle of disease transmission could be stopped, and strategies to control infection by several organisms of medical and veterinary importance such as Eimeria, Plasmodium, Toxoplasma, Cyclospora, and Neospora could be developed. Here, we show that two tyrosine-rich precursor glycoproteins, gam56 and gam82, found in specialized organelles (wall-forming bodies) in the sexual stage (macrogamete) of Eimeria maxima are proteolytically processed into smaller glycoproteins, which are then incorporated into the developing oocyst wall. The identification of high concentrations of dityrosine and 3,4-dihydroxyphenylalanine (DOPA) in oocyst extracts by high-pressure liquid chromatography, together with the detection of a UV autofluorescence in intact oocysts, implicates dityrosine- and possibly DOPA-protein cross-links in oocyst wall hardening. In addition, the identification of peroxidase activity in the wall-forming bodies of macrogametes supports the hypothesis that dityrosine- and DOPA-mediated cross-linking might be an enzyme-catalyzed event. As such, the mechanism of oocyst wall formation in Eimeria, is analogous to the underlying mechanisms involved in the stabilization of extracellular matrices in a number of organisms, widely distributed in nature, including insect resilin, nematode cuticles, yeast cell walls, mussel byssal threads, and sea urchin fertilization membranes.

Cloning and characterization of the 82 kDa tyrosine-rich sexual stage glycoprotein, GAM82, and its role in oocyst wall formation in the apicomplexan parasite, Eimeria maxima

The sexual (macrogamete/macrogametocyte) stage antigen, GAM82, in the apicomplexan parasite Eimeria maxima, has an apparent molecular mass of 82 kDa, and has been implicated in protective immunity against coccidiosis in poultry. The gene encoding this protein, gam82, was cloned and sequenced. It is a single-copy, intronless gene, which localizes to a 2145 bp transcript, and is first detected at 130 h post-infection. The gene predicts two distinct domains rich in the residues tyrosine and serine, amino acids that have been implicated in oocyst wall formation in other Eimeria spp., and in the extraorganismic sclerotization of structural proteins throughout the animal kingdom. A high number of small amino acids, predominantly alanine and proline, were detected in the intervening sequence between these two domains. The inference that GAM82 is involved in oocyst wall formation in Eimeria was confirmed when it was shown that a specific antibody to a recombinant version of GAM82 recognized the wall forming bodies in macrogametes, and the walls of oocysts in E. maxima. A closer biochemical analysis of the role of GAM82 in oocyst wall formation by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting showed that the antibodies to the recombinant version of GAM82 recognized an 82 kDa protein in macrogametocyte extracts, and a 30 kDa protein in unsporulated and sporulated oocyst extracts, as well as in purified oocyst wall fragments. Together, these findings indicate that the 82 kDa macrogametocyte antigen, GAM82, is a tyrosine and serine rich precursor protein that is proteolytically processed during development to give rise to a 30 kDa protein, that is incorporated into the oocyst wall. In addition, these findings provide evidence that the oocyst wall of Eimeria species is composed of a family of tyrosine rich proteins, that arise from precursor proteins found in the wall forming bodies of macrogametes.

NMR structure of PW2 bound to SDS micelles. A tryptophan-rich anticoccidial peptide selected from phage display libraries

PW2 (HPLKQYWWRPSI) was selected from phage display libraries through an alternative panning method using living sporozoites of Eimeria acervulina as target. Synthetic PW2 shows anticoccidial activity against E. acervulina and Eimeria tenella with very low hemolytic activity. It also displays antifungal activity but no activity against bacteria. We present the solution structure of the PW2 bound to SDS micelles. In the absence of an interface, PW2 is in random coil conformation. In micelles, structural calculation shows that Trp-7 forms the hydrophobic core that is important for the peptide folding. Lys-4, Tyr-6, Trp-8, and Arg-9 are in the same surface, possibly facing the micelle interface. This possibility was supported by the fact that chemical shift differences for these residues were more pronounced when compared with PW2 in water and in SDS. PW2 gains structure upon binding to SDS micelles. Lys-4, Tyr-6, Trp-8, and Arg-9 were found to bind to the micelle. Trp-7, Trp-8, and Arg-9 composed the WW+ consensus found in the sequence of the peptides selected with the phage display technique against E. acervulina sporozoites. This suggested that Trp-7, Trp-8, and Arg-9 are probably key residues not only for the peptide interaction with SDS micelles but also for the interaction with E. acervulina sporozoites surface.

Eimeria organisms develop in the epithelial cells of equine small intestine

Histopathologic and immunohistochemical examinations were performed to determine the origin of host cells parasitized by Eimeria in the small intestines collected from five foals. Eimeria organisms at various stages (mainly microgametes and macrogametes) were frequently found in the cytoplasm of hypertrophied host cells in the lamina propria at the tips of villi of the jejunum and ileum. The cytoplasm of the host cell was immunohistochemically positive for cytokeratin AE1/AE3 and cytokeratin 13 and was negative for vimentin, desmin, alpha-smooth muscle actin, chromogranin A, neuron-specific enolase, and factor VIII. The host cells parasitized by Eimeria species had the immunostaining characteristics of epithelial cells but not of mesenchymal cells, endothelial cells of lacteals or capillaries, smooth muscle cells or neuroendocrine cells. These results suggest that the host cell of Eimeria species is possibly derived from intestinal epithelial cells and then displaced into the lamina propria of the small intestine.

Biochemical characterisation of the 56 and 82 kDa immunodominant gametocyte antigens from Eimeria maxima

Two immunodominant gametocyte antigens from Eimeria maxima with M(r) 56 kDa and M(r) 82 kDa have been identified previously as potential candidates for inclusion in a recombinant subunit vaccine against coccidiosis in poultry. Here, these proteins have been biochemically characterised, immunolocalised within the parasite, and sequences for their amino termini determined. These antigens co-purify by affinity chromatography suggesting an interaction with each other. However, separation of the proteins by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) in the absence of beta-mercaptoethanol did not reveal the presence of inter-chain disulphide bonds. The true masses of the 56 and 82 kDa antigens are 52450 and 62450 Da, respectively, as determined by mass spectrometry. TX-114 separations suggested that they exist, in part, as soluble proteins within the parasite, and immunolocalisation studies indicated that they were found in the wall forming bodies of macrogametocytes. Separation of the proteins by 2D SDS-PAGE revealed that they are acidic in nature and heterogeneous in charge. Cleavage by neuraminidase and O-glycosidase indicated that the presence of O-linked glycans contributed to some of the charge microheterogeneity of both proteins. The absence of these O-glycans however, did not abolish antibody recognition, suggesting that the development of a recombinant subunit vaccine is possible. A more extensive investigation of the carbohydrate moieties of these proteins revealed that they also possess glucose, fucose, mannose and galactose. There was no evidence for the presence of N-linked glycans. The 56 and 82 kDa antigens were separated from a mixture of proteins in a crude gametocyte lysate by 2D SDS-PAGE, the proteins isolated, and the N-terminus amino acid sequence determined. They showed no homology to each other at the N-terminus, or to any other previously characterised protein. Characterisation of these novel proteins has provided further insights into the molecular mechanisms of gametocyte differentiation in E. maxima.

Nutrient acquisition by intracellular apicomplexan parasites: staying in for dinner

The intracellular forms of the apicomplexan parasites Plasmodium, Toxoplasma and Eimeria reside within a parasitophorous vacuole. The nutrients required by these intracellular parasites to support their high rate of growth and replication originate from the host cell which, in turn, takes up such compounds from the extracellular milieu. Solutes moving from the external medium to the interior of the parasite, are confronted by a series of three membranes --the host cell membrane, the parasitophorous vacuole membrane and the parasite plasma membrane. Each constitutes a potential permeability barrier which must be either crossed or bypassed. It is the mechanisms by which this occurs that are the subject of this review.

Evaluation of surrogate measures of cadmium, lead, and zinc bioavailability to Eisenia fetida

We evaluated weak-electrolyte (0.1 M Ca(NO3)2) soil extractions and ion-exchange membranes coated with a metal chelator as measures of Cd, Pb, and Zn bioavailability in spiked artificial soil by comparing their metal availability estimates to acute lethal toxicity in the earthworm Eisenia fetida. Ca(NO3)2 extractions were precisely related to toxicity in all toxicity tests, and enabled the development of time-independent LC50S (incipient lethal-levels, ILLs) calculated using exposure levels based on extraction data. ILLs with 95% CIs for the Cd, Pb, and Zn toxicity tests were 9.8 (9.4-10.3), 1.16 (1.11-1.22), and 6.33 (6.18-6.49) Ca(NO3)2-extractable mmol metal/kg soil, respectively. Mixture toxicity of Cd, Pb, and Zn, assessed using the toxic unit (TU) approach, was 1.35 TU, suggesting additivity. Chelating ion-exchange membrane uptake was variable, and not well related to toxicity. Weak-electrolyte extractions show promise as precise, inexpensive surrogate measures of Cd, Pb, and Zn bioavailability in soil.

Identification of carbohydrates on Eimeria stiedai sporozoites and their role in invasion of cultured cells in vitro

Invasion specificity of Eimeria stiedai sporozoites in cultured cells was examined. Intracellular sporozoites were observed in hepatobiliary epithelial cells, as early as 3 hours post inoculation (p.i.) but the infection rate was monitored for 6 hours. No intracellular parasites were found in rabbit parenchymal hepatocytes and rabbit kidney cells, even on prolonged culturing. In the hepatobiliary epithelial cells inoculated with fixed sporozoites, no intracellular parasite were found. Sporozoites attached on the cell surface of the hepatobiliary epithelial cells fixed with paraformaldehyde but did not penetrate. The carbohydrates present on Eimeria stiedai sporozoites and their functional role in the process of invasion of host cells were also examined. Lectin binding sites on the surface of sporozoites were detected by means of peroxidase-conjugated lectins. Sporozoites showed specific binding with UEA-I and PNA lectins, which bind L-fucose and D-galactose, respectively. Exposure of sporozoites to 100 microg/ml UEA-I significantly reduced their ability to invade primary rabbit hepatobiliary epithelial cells, but similar treatment with PNA had no such effect. Preincubation of these cells in Dulbecco's minimum essential medium containing 10% fetal bovine serum and 1% L-fucose suppressed the invasion activity of the sporozoites, but preincubation of the sporozoites in the same medium without L-fucose had no effect on cell penetration. D-galactose added to the medium had no effect on the invasion activity of sporozoites. These results indicate that L-fucose residues on E. stiedai sporozoites and L-fucose binding sites on host cells both are associated with recognition and/or invasion process.

A merozoite-specific 22-kDa rhoptry protein of the coccidium Eimeria nieschulzi (Sporozoa, Coccidia) is exocytosed in the parasitophorous vacuole upon host cell invasion

A monoclonal antibody (Mab D12A4) was used to follow the genesis and fate of rhoptries from early first-generation merogony through second-generation merozoites of the rat coccidium Eimeria nieschulzi. The epitope recognized by Mab D12A4 belongs to a 22-kDa protein which can be localized first in developing meronts 25 h post-infection. Early rhoptries appear as distinct granules in the cytoplasm of developing meronts and elongate into mature organelles before merozoite release. The 22-kDa protein is found in the parasitophorous vacuole after host cell invasion. Western blotting and immunofluorescence showed that the 22-kDa rhoptry protein is expressed in schizonts and merozoites but not in sporozoites.

Prevention of Eimeria alabamensis coccidiosis by a long-acting baquiloprim/sulphadimidine bolus

Twelve calves aged 6-10 months, and 12 calves aged 10-16 months were turned out onto a permanent pasture known to have been contaminated with oocysts of Eimeria alabamensis during the previous year. Two days after turnout, six of the older calves and six of the younger were each treated with one bolus per 200 kg bodyweight containing 1.6 g baquiloprim and 14.4 g sulphadimidine. The other 12 calves were left untreated. The excretion of Eimeria oocysts, the faecal dry matter and the weight gain of treated and untreated calves within each age group were compared during the first 3 weeks on pasture to assess the efficacy of the bolus in preventing E. alabamensis coccidiosis. All the older of the untreated calves and four of the younger developed gruel-like to watery diarrhoea 4-7 days after turnout. The faecal consistency of the treated calves remained firm and they lost significantly less weight than the control calves during the first 13 days on pasture. The treated calves also excreted significantly fewer oocysts during the first 20 days of grazing; their oocyst excretion remained low during days 8-10 when all but one of the diarrhoeic control calves excreted more than 850,000 oocysts per gram faeces (OPG). Starting on days 12 to 14 the oocyst excretion of 8 of the treated calves increased to 20,000-65,000 OPG and of 2 calves to 210,000-240,000 OPG. There was no difference in oocyst output between treated and untreated calves from the fourth week of grazing and no difference in weight gain among the younger calves. In the older calves there was a tendency for the untreated calves to gain more weight than treated calves.

The mannitol cycle in Eimeria

A metabolic pathway known as the mannitol cycle has been identified in Eimerian parasites. The pathway is a shunt off of the glycolytic pathway at fructose-6-phosphate (F6P). Two enzymes convert F6P to mannitol and two other enzymes are responsible for converting mannitol back to F6P when it is utilized. Although the pathway is present in various stages of the parasite the most apparent role of this pathway is in the sexual portion of the life cycle, particularly in the formation of oocysts. Extremely high concentrations of mannitol, approaching 0.3 M, are present in unsporulated oocysts. Mannitol functions as the endogenous energy source for oocysts to sporulate in the environment outside of the host. An inhibitory protein which inactivates the first enzyme of the mannitol cycle has been isolated from an oocyst derived inhibited enzyme complex and is believed to prevent the futile cycling of F6P during the maturation of oocysts. Evidence of the vital role of mannitol in the development and maturation of Eimeria tenella oocysts has been facilitated through the use of the drug Nitrophenide, a known anticoccidial which has now been found to be an inhibitor of one of the enzymes responsible for the biosynthesis of mannitol in the parasite. This compound prevents the formation of oocysts and at lower doses reduces mannitol levels in shed oocysts. In addition, oocysts with reduced mannitol levels fail to complete the sporulation process lending further evidence for this polyol's role in the parasite.

Diffusion of microinjected markers across the parasitophorous vacuole membrane in cells infected with Eimeria nieschulzi (Coccidia, Apicomplexa)

Cells infected with the intracellular parasite Eimeria nieschulzi were microinjected with lucifer yellow (457 Da), biocytin lucifer yellow (850 Da) and dextranrhodamine (10,000 Da). Immediately after injection of a mixture of the markers into the host cell cytoplasm, a differential diffusion pattern was observed in trophozoites and schizonts. Lucifer yellow and biotin lucifer yellow were seen to enter the parasitophorous vacuole, whereas the dextran was excluded. Since these markers cannot permeate cell membranes, this suggests that the Eimerian parasitophorous vacuole acts as a molecular sieve. This method allows the visualization and further characterization of the parasitophorous vacuole in living cells.

Identification of Eimeria bovis merozoite cDNAs using differential mRNA display

Differences in gene expression between Eimeria bovis sporozoites and first-generation merozoites were analyzed using the technique of differential mRNA display. Approx. 5% of the sequences detected in first-generation merozoites appear to be unique relative to sporozoites. Several of the bands corresponding to merozoite-specific gene expression were isolated and cloned. Northern blot analysis revealed that the cDNA fragments DMZ-7, DMZ-8 and NMZ-6 hybridized to mRNAs expressed at > 50-fold higher levels in merozoites relative to sporozoites. A fourth cDNA fragment, NMZ-4, hybridized to a mRNA expressed at 3-fold higher levels in merozoites. Further characterization demonstrated that expression of DMZ-8 in E. bovis-infected bovine cells begins as early as 12 h after sporozoite invasion and continues throughout the entire 14 days of first-generation schizogony. Sequence analysis of each of the four merozoite cDNAs failed to identify any significant similarity to any entries in the GenBank database, suggesting that these developmentally regulated genes may be unique to coccidian parasites.

Developmentally regulated lectins in Eimeria species and their role in avian coccidiosis

Avian coccidiosis caused by Eimeria species is characterized by rather specific site infections of the intestine. We used hemagglutination and hemagglutination inhibition assays on various developmental stages of Eimeria tenella and on sporozoites of Eimeria acervulina and Eimeria maxima to assay for parasite lectins. Various monosaccharides, polysaccharides, and glycoproteins were used to demonstrate differences in sugar specificity of the lectins between these species. Surface lectins were found on the primary infective stage, i.e., sporozoites, but not on merozoites or unsporulated oocysts. Also, there were differences in the specificities of the various sugar lectins among the different parasite species. Furthermore, there was a dose-dependent reduction of infection of tissue culture cells by sporozoites of E. tenella that were continuously exposed to fetuin, 1 of the specific inhibitors of the lectin. The results of our study are unique in that in 3 species of avian Eimeria all have a lectin on their sporozoites, but the lectins for each species have different sugar specificities. We hypothesize that these lectins found on the surface of the sporozoites may play a role in determining the site of infection within the intestine of the host.

Eimeria refractile body proteins contain two potentially functional characteristics: transhydrogenase and carbohydrate transport

cDNA encoding an immunogenic protein from partially sporulated oocysts of Eimeria acervulina was cloned and used to search for the homologous counterpart in Eimeria tenella. Monospecific antibodies were raised against the recombinant expression product. Using these antibodies, the parasite proteins were found to be localised in the refractile bodies. The derived amino-acid sequences were compared by computer using the SWISSPROT protein database. In addition to high homology between the Eimeria species, extensive similarity was found with pyridine nucleotide transhydrogenase from Escherichia coli. Comparison with the sugar signature database also resulted in a possible sugar binding domain present only in the Eimeria proteins. It is possible that the corresponding parasite proteins play a role in the recently discovered mannitol cycle of Eimeria.

Developmental gene expression of a 230-kilodalton macrogamete-specific protein of the avian coccidial parasite, Eimeria maxima

We prepared a cDNA library from gametocytes of Eimeria maxima and screened it using antibodies raised against an 82-kDa gametocyte antigen. One cDNA clone designated pEM230 was isolated and characterized. It encodes a portion of a 230-kDa gametocyte protein and its DNA sequence shows the presence of several tandem repeats of 42 bp. In order to determine the stage and sex specificity of the mRNA for the 230-kDa protein, Northern blotting and in situ hybridization studies were performed. The 230-kDa protein is encoded for by a 7 kb mRNA, which is expressed exclusively during the macrogamete stage with no detectable expression seen in any other stage of parasite development.

Eimeria tenella sporozoites: the method of excystation affects the surface membrane proteins

Eimerian sporozoites can be recovered from intestinal washings after oral administration of oocysts to chickens but suspensions of sporozoites are usually prepared in the laboratory by incubation of sporocysts or fractured oocysts in vitro, at body temperatures, with relatively high concentrations of trypsin and bile salts. Since these agents affect membrane structure, the surface membrane of proteins of Eimeria tenella sporozoites excysted in vivo and in vitro have been compared. Surface radio-iodination followed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that more 125I was incorporated into polypeptides on sporozoites excysted in vivo than on sporozoites excysted in vitro. The 125I-polypeptide profile of sporozoites excysted in vivo was more resistant to subsequent incubation with pure trypsin than that of sporozoites excysted in vitro, but incubation with bile salts resulted in the loss of some iodinated polypeptides from both preparations of iodinated sporozoites. Reaction with combinations of crude trypsin and bile salts led to the lysis of sporozoites. The method of excystation had no effect on the reaction of convalescent chicken serum with Western blots of sporozoites but the results of immunofluorescent staining carried out with mouse monoclonal antibodies indicated that the structure of the cell surface was altered and some antigenic determinants were lost from sporozoites excysted in vitro. In contrast, neither the infectivity of sporozoites determined in vivo, nor their invasion of cultured cells was changed by the method of excystation.

[Amino acids and their metabolites in Eimeria tenella (Coccidiida) oocysts]

The amino acid composition of protein in the oocysts of Eimeria tenella has been studied in detail by using the new method of purification of the coccidial oocysts. 35 amino acids and their metabolites have been established for the first time at the exogenous stages of development of E. tenella. The oocyst sporulation is noted to be followed by quantitative changes of the majority of free amino acids and their metabolites.

Monosaccharide transport by Eimeria tenella sporozoites

Eimeria tenella sporozoites were incubated in the presence of 3 different [14C]-labeled sugars; D-glucose, 2-deoxy-D-glucose and 3-O-methyl-D-glucose. The initial velocity, Vi, of uptake of D-glucose and 2-deoxy-D-glucose was similar, 41 micrograms/10(10) sporozoites/min and 46 micrograms/10(10) sporozoites/min, respectively; whereas that for 3-O-methyl-D-glucose was significantly lower, 17 micrograms/10(10) sporozoites/min. Initial velocity studies also revealed that glucose uptake was a saturable event, with an apparent KT of 20 mM and an apparent Vmax of 312 micrograms/10(10) sporozoites/min. Uptake was unaffected by exogenous sodium levels or the presence of ouabain. However, 0.1 mM phloretin significantly inhibited glucose uptake. Thus, it would appear that E. tenella sporozoites possess a Na-independent, phloretin-sensitive, carrier-mediated monosaccharide-transport system.

Eimeria tenella: parasite-specific incorporation of 3H-uracil as a quantitative measure of intracellular development

An assay has been developed using parasite-specific incorporation of 3H-uracil to assess the intracellular growth of Eimeria tenella in vitro. As shown by both scintillation counts and autoradiography, 3H-uracil was incorporated specifically into intracellular parasites from the onset of infection and continued throughout development of the first generation schizonts. Mature schizonts and first generation merozoites did not continue to incorporate additional 3H-uracil, indicating that RNA synthesis had halted in these stages. Based on these findings, a semi-automated microscale uracil incorporation assay was developed to determine parasite viability. This method should be useful for biochemical studies with intracellular parasites and for screening compounds for anticoccidial activity. The ease, rapidity, and quantitative nature of this assay contrasts favorably with standard morphometric approaches of determining parasite development. In addition, parallel studies using host cell incorporation of 3H-uridine have been introduced as a method of determining whether antiparasitic activity is direct or indirect in relation to effects on the host cell.

Purine metabolism in the intact sporozoites and merozoites of Eimeria tenella

Intact Eimeria tenella sporozoites and merozoites did not incorporate radiolabeled formate or glycine into their purine nucleotides suggesting a lack of de novo purine synthesis. However, [U-14C]glucose was incorporated into the cellular purine and pyrimidine nucleotide pools of both forms probably via conversion to radiolabeled ribose-1-phosphate and/or 5'-phosphoribosyl-1-alpha-pyrophosphate and the resulting action of various purine and pyrimidine salvage enzymes. Both forms of the parasite salvaged radiolabeled purine bases and nucleosides in a similar fashion. These purines were incorporated into ribonucleotides and into RNA and DNA. Adenine and inosine were transformed to hypoxanthine. Adenosine was converted to both inosine and hypoxanthine. Hypoxanthine and xanthine were not oxidized to uric acid but were metabolized to nucleotides. Guanosine was cleaved to guanine; guanine was deaminated to xanthine. The results demonstrate the presence of several purine salvage pathways. Purine phosphoribosylating and nucleoside phosphorylating activities as well as purine nucleoside cleaving and adenosine, adenine and guanine deaminating activities were evident. The metabolic evidence suggests the enzymes required to convert the newly formed nucleoside monophosphates to ATP and GTP were present also.

Potent and selective hydroxynaphthoquinone inhibitors of mitochondrial electron transport in Eimeria tenella (Apicomplexa: Coccidia)

Novel hydroxynaphthoquinones have been shown to be potent and selective inhibitors of mitochondrial electron transport in the protozoan Eimeria tenella, inhibiting at concentrations of 10(-10) to 10(-11)M. The primary site of electron transport inhibition has been localized to the ubiquinol-cytochrome c reductase span of the respiratory chain, whereas a secondary site of inhibition occurs in the NADH- and succinate-ubiquinone reductase complexes. Inhibition at the primary site is selective for the E. tenella enzyme; inhibition at the secondary sites is comparable in both E. tenella and chick (Gallus gallus) liver mitochondria. Hydroxynaphthoquinone inhibition of chick liver succinate-cyto-chrome c reductase was fully reversible by addition of the exogenous ubiquinone-2 analogue, 6-decyl-2,3-dimethoxy-5-methyl-1,4-benzoquinone; inhibition of the corresponding E. tenella enzyme was not reversed by this ubiquinone. E. tenella lines made resistant to the anticoccidial agents decoquinate or clopidol showed no cross-resistance to the hydroxynaphthoquinones, either at the level of electron transport or in vivo.

Effects of decoquinate and clopidol on electron transport in mitochondria of Eimeria tenella (Apicomplexa: Coccidia)

Resistance of the chicken coccidium Eimeria tenella to the anticoccidial agents decoquinate and clopidol, and the synergistic activity of mixtures of these compounds have been confirmed in vivo. Inhibition of electron transport by decoquinate and clopidol has been studied in mitochondria isolated from unsporulated oocysts of the same lines of E. tenella as those used in the in vivo studies. Electron transport in mitochondria of a drug sensitive line was susceptible to inhibition by both decoquinate and clopidol, and mitochondria isolated from lines made resistant to one or the other of these compounds showed a corresponding resistance at the level of electron transport. Combinations of low concentrations of decoquinate and clopidol caused a greater inhibition of electron transport than expected from summation of their individual actions. Isobolograms showed that decoquinate and clopidol in fact potentiated each other's effect on electron transport. Induced resistance to either decoquinate or clopidol resulted in an increased sensitivity of electron transport to inhibition by the other drug. Cytochrome spectra of E. tenella mitochondria and a biphasic response of NADH-oxidase and terminal oxidase activity to inhibition by cyanide or azide suggest the presence of two functional terminal oxidases. There is a correlation between the resistance of electron transport to inhibition by decoquinate or clopidol and the susceptibility to inhibition by cyanide or azide. Mitochondrial electron transport that is more resistant to inhibition by decoquinate exhibits greater sensitivity to cyanide and azide; electron transport that is more resistant to inhibition by clopidol exhibits a decreased sensitivity to cyanide and azide. Resistance to decoquinate and clopidol is discussed in view of a possibly branched electron transport chain in mitochondria of E. tenella.

Influence of monensin on cation influx and glycolysis of Eimeria tenella sporozoites in vitro

Extracellular Eimeria tenella sporozoites exposed to 1.0 microgram/ml monensin at 40 C had an accelerated rate of sodium influx as well as an increased rubidium uptake that was inhibited by the cardiac glycoside, ouabain. These results suggested the presence of a functional (Na+-K+)-ATPase and its stimulation by monensin. Under the same conditions, sporozoite ATP concentrations declined, lactate production increased and the rate of amylopectin utilization was enhanced. Exposure to monensin also appeared to stimulate the rate of sporozoite glycolysis. The results of this study demonstrated that the cidal effect of monensin on extracellular sporozoites was caused by the capability of the ionophore to act as a transmembrane sodium carrier.

[Life cycle and cytochemical study of the endogenous developmental stages of Eimeria akeriana (coccidiida, Eimeriidae) from the Asia Minor gerbil]

Three generations of schisonts in the life cycle of Eimeria akeriana, the intestinal parasite of Meriones blackleri, were determined. Gametogony begins in 94 hours, the first oocysts discharge in 5.5--6 days and lasts 14.5 to 15 days after the oocyst administration. A cytochemical study of the distribution of the nucleic acids, proteins and amylopectin at the stages of endogenous development of E. akeriana has revealed a considerable similarity among the parasites of Eimeria though each type is characterized by some cytochemical peculiarities.

Purine metabolism in the protozoan parasite Eimeria tenella

Crude extracts of the oocysts of Eimeria tenella, a protozoan parasite of the coccidium family that develops inside the caecal epithelial cells of infected chickens, do not incorporate glycine or formate into purine nucleotides; this suggests lack of capability for de novo purine synthesis by the parasite. The extracts, however, contain high levels of activity of the purine salvage enzymes: hypoxanthine, guanine, xanthine, and adenine phosphoribosyltransferases and adenosine kinase. The absence of AMP deaminase from the parasite indicates that E. tenella cannot convert AMP to GMP; the latter thus has to be supplied by the hypoxanthine, xanthine, or guanine phosphoribosyltransferase of the parasite. These three activities are associated with one enzyme (HXGPRTase), which has been purified to near homogeneity in high yield (71-80%) in a single step by GMP-agarose affinity column chromatography. The size of the enzyme subunit is estimated to be 23,000 daltons by NaDodSO4 gel electrophoresis. Kinetic studies suggest differences in purine substrate specificity between E. tenella HXGPRTase and chicken liver HGPRTase. Allopurinol preferentially inhibits the parasite enzyme by competing with hypoxanthine; a Ki approximately 22 microM.

Thymidine uptake by chicken kidney cells parasitized by Eimeria tenella: evidence for a diffusable mediating substance

The pattern of DNA synthesis in chicken kidney (CK) cells parasitized by Eimeria tenella was altered; a 2-fold increase in the uptake of [3-H]-thymidine occurred in these cells compared with that shown by the controls. This difference was significantly different at 16 h post-inoculation (p.i.) and reached a peak at 20 h p.i. Non-parasitized cells in co-culture with parasitized cells showed a level of incorporation intermediate between that of the parasitized and non-parasitized monocultures. It was shown that this stimulation was due to a factor released into the medium by the parasite or the parasitized cell. A possible course of events leading to induced and prolonged DNA synthesis by the host cell and the significance of this change in the life-cycle of the parasite is discussed.

Effects of storage time and temperature on amylopectin levels and oocyst production of Eimeria meleagrimitis oocysts

Eimeria meleagrimitis oocysts were stored at 4, 22, 32, or 41.5 degrees C for up to 1 year. Decreases in amylopectin levels (measured as glucose) and viability (measured as oocyst production and mortality in turkeys) of the oocysts were generally related to the length of time in storage and the storage temperature. Oocysts assayed immediately after harvest contained 58.29 +/- 0.75 micrograms of glucose/10(6) oocysts. When the oocysts were stored at 4 degree C for 162 days, the amylopectin level decreased to 65% of the original level. In oocysts stored at 22, 32 and 41.5 degrees C, amylopectin declined to approximately 20% within 162, 76, and 41 days, respectively. Oocysts stored at 4 degree C for 1 year produced more oocysts in turkeys than the original fresh isolate, but caused no mortality. Oocyst production from oocysts stored at 22 and 32 degrees C decreased gradually until, after 9 and 7 months respectively, no patent infections were produced. Oocyst production from oocysts stored at 41.5 degree C markedly reduced within 1 month and was not detected after 4 months.

Thiamine uptake in isolated schizonts of Eimeria tenella and the inhibitory effects of amprolium

The uptake of thiamine by isolated second-generation schizonts of Eimeria tenella and by host intestinal cells was found to consist of two components. One was passive and the other apparently an active process. The kinetic constants of the latter were compared in host (Km = 0.36 microM) and parasite (Km = 0.07 microM) and found to be significantly different. Both systems were competitively inhibited by amprolium but showed different affinities for the drug. (Host Ki = 323 microM; parasite Ki = 7.6 microM). Further differences were observed in schizonts of a drug-resistant line of E. tenella. These findings are discussed in terms of the inhibition of thiamine uptake being the basis of the anticoccidial activity of amprolium.