Expression of host defense peptides in the intestine of Eimeria-challenged chickens

Avian coccidiosis is caused by the intracellular protozoan Eimeria, which produces intestinal lesions leading to weight gain depression. Current control methods include vaccination and anticoccidial drugs. An alternative approach involves modulating the immune system. The objective of this study was to profile the expression of host defense peptides such as avian beta-defensins (AvBDs) and liver expressed antimicrobial peptide 2 (LEAP2), which are part of the innate immune system. The mRNA expression of AvBD family members 1, 6, 8, 10, 11, 12, and 13 and LEAP2 was examined in chickens challenged with either E. acervulina, E. maxima, or E. tenella. The duodenum, jejunum, ileum, and ceca were collected 7 d post challenge. In study 1, E. acervulina challenge resulted in down-regulation of AvBD1, AvBD6, AvBD10, AvBD11, AvBD12, and AvBD13 in the duodenum. E. maxima challenge caused down-regulation of AvBD6, AvBD10, and AvBD11 in the duodenum, down-regulation of AvBD10 in the jejunum, but up-regulation of AvBD8 and AvBD13 in the ceca. E. tenella challenge showed no change in AvBD expression in any tissue. In study 2, which involved challenge with only E. maxima, there was down-regulation of AvBD1 in the ileum, AvBD11 in the jejunum and ileum, and LEAP2 in all 3 segments of the small intestine. The expression of LEAP2 was further examined by in situ hybridization in the jejunum of chickens from study 2. LEAP2 mRNA was expressed similarly in the enterocytes lining the villi, but not in the crypts of control and Eimeria challenged chickens. The lengths of the villi in the Eimeria challenged chickens were less than those in the control chickens, which may in part account for the observed down-regulation of LEAP2 mRNA quantified by PCR. Overall, the AvBD response to Eimeria challenge was not consistent; whereas LEAP2 was consistently down-regulated, which suggests that LEAP2 plays an important role in modulating an Eimeria infection.

Changes in expression of an antimicrobial peptide, digestive enzymes, and nutrient transporters in the intestine of E. praecox-infected chickens

Coccidiosis is a major intestinal disease of poultry, caused by several species of the protozoan Eimeria. The objective of this study was to examine changes in expression of digestive enzymes, nutrient transporters, and an antimicrobial peptide following an Eimeria praecox challenge of chickens at days 3 and 6 post-infection. Gene expression was determined by real-time PCR and analyzed by one-way ANOVA. In the duodenum, the primary site of E. praecox infection, a number of genes were downregulated at both d3 and d6 post-infection. These genes included liver expressed antimicrobial peptide 2 (LEAP2), the cationic (CAT1), anionic (EAAT3), and L-type (LAT1) amino acid transporters, the peptide transporter PepT1 and the zinc transporter ZnT1. Other transporters were downregulated either at d3 or d6. At both d3 and d6, there was downregulation of B(o)AT and CAT1 in the jejunum and downregulation of LEAP2 and LAT1 in the ileum. LEAP2, EAAT3, and ZnT1 have been found to be downregulated following challenge with other Eimeria species, suggesting a common cellular response to Eimeria.

Expression of digestive enzymes and nutrient transporters in Eimeria-challenged broilers

Avian coccidiosis is a disease caused by the intestinal protozoa Eimeria. The site of invasion and lesions in the intestine is species-specific, for example E. acervulina affects the duodenum, E. maxima the jejunum, and E. tenella the ceca. Lesions in the intestinal mucosa cause reduced feed efficiency and body weight gain. The growth reduction may be due to changes in expression of digestive enzymes and nutrient transporters in the intestine. The objective of this study was to compare the expression of digestive enzymes, nutrient transporters and an antimicrobial peptide in broilers challenged with either E. acervulina, E. maxima or E. tenella. The genes examined included digestive enzymes (APN and SI), peptide and amino acid transporters (PepT1, ASCT1, b(0,+)AT/rBAT, B(0)AT, CAT1, CAT2, EAAT3, LAT1, y(+)LAT1 and y(+)LAT2), sugar transporters (GLUT1, GLUT2, GLUT5 and SGLT1), zinc transporter (ZnT1) and an antimicrobial peptide (LEAP2). Duodenum, jejunum, ileum and ceca were collected 7 days post challenge. E. acervulina challenge resulted in downregulation of various nutrient transporters or LEAP2 in the duodenum and ceca, but not the jejunum or ileum. E. maxima challenge produced both downregulation and upregulation of nutrient transporters and LEAP2 in all three segments of the small intestine and ceca. E. tenella challenge resulted in the downregulation and upregulation of nutrient transporters and LEAP2 in the jejunum, ileum and ceca, but not the duodenum. At the respective target tissue, E. acervulina, E. maxima and E. tenella infection caused common downregulation of APN, b(0,+)AT, rBAT, EAAT3, SI, GLUT2, GLUT5, ZnT1 and LEAP2. The downregulation of nutrient transporters would result in a decrease in the efficiency of protein and polysaccharide digestion and uptake, which may partially explain the weight loss. The downregulation of nutrient transporters may also be a cellular response to reduced expression of the host defense protein LEAP2, which would diminish intracellular pools of nutrients and inhibit pathogen replication.

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.

Expression of digestive enzymes and nutrient transporters in Eimeria acervulina-challenged layers and broilers

Avian coccidiosis is a disease caused by intestinal protozoa in the genus Eimeria. Clinical signs of coccidiosis include intestinal lesions and reduced feed efficiency and BW gain. This growth reduction may be due to changes in expression of digestive enzymes and nutrient transporters in the intestine. The objective of this study was to examine the differential expression of digestive enzymes, transporters of amino acids, peptides, sugars, and minerals, and an antimicrobial peptide in the small intestine of Eimeria acervulina-infected broilers and layers. Uninfected broilers and layers, in general, expressed these genes at comparable levels. Some differences included 3-fold and 2-fold greater expression of the peptide transporter PepT1 and the antimicrobial peptide LEAP2 (liver expressed antimicrobial peptide 2), respectively, in the jejunum of layers compared with broilers and 17-fold greater expression of LEAP2 in the duodenum of broilers compared with layers. In the duodenum of Eimeria-infected broilers and layers, there was downregulation of aminopeptidase N; sucrase-isomaltase; the neutral, cationic, and anionic amino acid transporters b(o,+)AT/rBAT, B(o)AT, CAT2, and EAAT3; the sugar transporter GLUT2; the zinc transporter ZnT1; and LEAP2. In the jejunum of infected layers there was downregulation of many of the same genes as in the duodenum plus downregulation of PepT1, b(o,+)AT/rBAT, and the y(+) L system amino acid transporters y(+) LAT1 and y(+) LAT2. In the ileum of infected layers there was downregulation of CAT2, y(+)LAT1, the L type amino acid transporter LAT1, and the sugar transporter GLUT1, and upregulation of APN, PepT1, the sodium glucose transporter SGLT4, and LEAP2. In E. acervulina-infected broilers, there were no gene expression changes in the jejunum and ileum. These changes in intestinal digestive enzyme and nutrient transporter gene expression may result in a decrease in the efficiency of protein digestion, uptake of important amino acids and sugars, and disruption of mineral balance that may affect intestinal cell metabolism and Eimeria replication.

Molecular characterization and immunological roles of avian IL-22 and its soluble receptor IL-22 binding protein

As a member of the interleukin (IL)-10 family, IL-22 is an important mediator in modulating tissue responses during inflammation. Through activation of STAT3-signaling cascades, IL-22 induces proliferative and anti-apoptotic pathways, as well as antimicrobial peptides (AMPs), that help prevent tissue damage and aid in its repair. This study reports the cloning and expression of recombinant chicken IL-22 (rChIL-22) and its soluble receptor, rChIL22BP, and characterization of biological effects of rChIL-22 during inflammatory responses. Similar to observations with mammalian IL-22, purified rChIL-22 had no effect on either peripheral blood mononuclear cells (PBMCs) or lymphocytes. This was due to the low expression of the receptor ChIL22RA1 chain compared to ChIL10RB chain. rChIL-22 alone did not affect chicken embryo kidney cells (CEKCs); however, co-stimulation of CEKCs with LPS and rChIL-22 enhanced the production of pro-inflammatory cytokines, chemokines and AMPs. Furthermore, rChIL-22 alone stimulated and induced acute phase reactants in chicken embryo liver cells (CELCs). These effects of rChIL-22 were abolished by pre-incubation of rChIL-22 with rChIL22BP. Together, this study indicates an important role of ChIL-22 on epithelial cells and hepatocytes during inflammation.

Molecular cloning and functional characterization of the avian macrophage migration inhibitory factor (MIF)

Macrophage migration inhibitory factor (MIF) is recognized as a soluble factor produced by sensitized T lymphocytes and inhibits the random migration of macrophages. Recent studies have revealed a more prominent role for MIF as a multi-functional cytokine mediating both innate and adaptive immune responses. This study describes the cloning and functional characterization of avian MIF in an effort to better understand its role in innate and adaptive immunity, and potential use in poultry health applications. The full-length avian MIF gene was amplified from stimulated chicken lymphocytes and cloned into a prokaryotic expression vector. The confirmed 115 amino acid sequence of avian MIF has 71% identity with human and murine MIF. The bacterially expressed avian recombinant MIF (rChMIF) was purified, followed by endotoxin removal, and then tested by chemotactic assay and quantitative real-time PCR (qRT-PCR). Diff-Quick staining revealed a substantial decrease in migration of macrophages in the presence of 0.01microg/ml rChMIF. qRT-PCR analysis revealed that the presence of rChMIF enhanced levels of IL-1beta and iNOS during PBMCs stimulation with LPS. Additionally, the Con A-stimulated lymphocytes showed enhanced interferon (IFN)-gamma and IL-2 transcripts in the presence of rChMIF. Interestingly, addition of rChMIF to the stimulated PBMCs, in the presence of lymphocytes, showed anti-inflammatory function of rChMIF. To our knowledge, this study represents the first report for the functional characterization of avian MIF, demonstrating the inhibition of macrophage migration, similar to mammalian MIF, and the mediation of inflammatory responses during antigenic stimulation.

Immunostimulatory complexes containing Eimeria tenella antigens and low toxicity plant saponins induce antibody response and provide protection from challenge in broiler chickens

Immunostimulating complexes (ISCOMs) are unique multimolecular structures formed by encapsulating antigens, lipids and triterpene saponins and are one of the most successful antigen delivery systems for microbial antigens. In the current study, both the route of administration and the antigen concentration of ISCOMs, containing Eimeria tenella antigens and saponins from native plants, were evaluated in their ability to stimulate humoral immunity and to protect chickens against a challenge infection with E. tenella. Broiler chickens were immunized with ISCOM preparations containing E. tenella antigens and the purified saponins Gg6, Ah6 and Gp7 isolated from Glycyrrhiza glabra, Aesculus hippocastanum and Gipsophila paniculata, respectively. The effects of the route of administration, dose of antigen and type of saponin used for construction of ISCOMs were evaluated for ability to stimulate serum IgG and IgM and to protect chickens against a homologous challenge. A single intranasal immunization was the most effective route for administering ISCOMs although the in ovo route was also quite effective. Dose titration experiments demonstrated efficacy after single immunization with various ISCOM doses but maximum effects were observed when ISCOMs contain 5-10mug antigen. Immunization of birds by any of the three routes with E. tenella antigens alone or antigens mixed with alum hydroxide adjuvant resulted in lower serum antibody and reduced protection to challenge relative to immunization with ISCOMs. Overall the results of this study confirm that significant immunostimulation and protection to challenge are achieved by immunization of chickens with ISCOMs containing purified saponins and native E. tenella antigens and suggest that ISCOMs may be successfully used to develop a safe and effective vaccine for prevention of avian coccidiosis.

Molecular cloning and functional characterization of avian interleukin-19

The present study describes the cloning and functional characterization of avian interleukin (IL)-19, a cytokine that, in mammals, alters the balance of Th1 and Th2 cells in favor of the Th2 phenotype. The full-length avian IL-19 gene, located on chromosome 26, was amplified from LPS-stimulated chicken monocytes, and cloned into both prokaryotic (pET28a) and eukaryotic (pcDNA3.1) expression vectors. The confirmed avian IL-19 amino acid sequence has 66.5% homology with human and murine IL-19, with a predicted protein sequence of 176 amino acids. Analysis of avian IL-19 amino acid sequence showed six conserved, structurally relevant, cysteine residues as found in mammals, but only one N-glycosylation residue. The recombinant IL-19 (rChIL-19) expressed in the prokaryotic system was purified by Ni(+)-resin column followed by endotoxin removal. Using purified avian rChIL-19, expression of Th2 cytokines was measured in splenocytes using quantitative real-time PCR (qRT-PCR). In the presence of rChIL-19, expression levels of IL-4 and IL-13, as well as IL-10, were significantly increased after 6- and 12 h treatments. This was confirmed by treating splenocytes with supernatants from IL-19 transfected cells. Also, avian monocytes incubated with rChIL-19 displayed increased expression of IL-1beta, IL-6, and IL-19. This study represents the first report for the cloning, expression, and functional characterization of avian IL-19. Taken together, avian IL-19 function seems to be conserved and similar to that of mammals and may play an important role in responses to intracellular poultry pathogens like bacteria and protozoa.

Identification and characterization of a serpin from Eimeria acervulina

Serpins are serine protease inhibitors that are widely distributed in metazoans but have not been previously characterized in Eimeria spp. A serpin from Eimeria acervulina was cloned, expressed and characterized. Random screening of an E.acervulina sporozoite cDNA library identified a single clone (D14) whose coding region shared high similarity to consensus structure of serpins. Clone D14 contained an entire open reading frame (ORF) consisting of 1,245 nts that encode a peptide 413 amino acids in length with a predicted molecular weight of 45.5 kDa and containing a signal peptide 28 residues in length. By Western blot analysis, polyclonal antiserum to the recombinant serpin (rbSp) recognized a major 55 kDa protein band in unsporulated oocysts and in oocysts sporulated up to 24 hr (fully sporulated). The anti-rbSp detected bands of 55 kDa and 48 kDa in sporozoites (SZ) and merozoites (MZ) respectively. Analysis of MZ secretion products revealed a single protein of 48 kDa which may correspond to secreted serpin. By immuno-staining the serpin was located in granules distributed throughout both the SZ and MZ but granules appeared to be concentrated in the parasite's anterior. Analysis of the structure predicts that the E. acervulina serpin should be an active inhibitor. However, rbSp was without inhibitory activity against common serine proteases. By Western blot analysis the endogenous serpin in MZ extracts did not form the expected high molecular weight complex when coincubated with either trypsin or subtilisin. The results demonstrate that E. acervulina contains a serpin gene and expresses a protein with structural properties similar to an active serine protease inhibitor. Although the function of the E. acervulina serpin remains unknown the results further suggest that serpin is secreted by the parasite where it may be involved in cell invasion and other basic developmental processes.

Immunostimulating complexes incorporating Eimeria tenella antigens and plant saponins as effective delivery system for coccidia vaccine immunization

Immunostimulating complexes (ISCOMs) are unique, multimolecular structures formed by encapsulating antigens, lipids, and triterpene saponins of plant origin, and are an effective delivery system for various kinds of antigens. The uses of ISCOMs formulated with saponins from plants collected in Kazakhstan, with antigens from the poultry coccidian parasite Eimeria tenella, were evaluated for their potential use in developing a vaccine for control of avian coccidiosis. Saponins isolated from the plants Aesculus hippocastanum and Glycyrrhiza glabra were partially purified by HPLC. The saponin fractions obtained from HPLC were evaluated for toxicity in chickens and chicken embryos. The HPLC saponin fractions with the least toxicity, compared to a commercial saponin Quil A, were used to assemble ISCOMs. When chicks were immunized with ISCOMs prepared with saponins from Kazakhstan plants and E. tenella antigens, and then challenged with E. tenella oocysts, significant protection was conveyed compared to immunization with antigen alone. The results of this study indicate that ISCOMs formulated with saponins isolated from plants indigenous to Kazakhstan are an effective antigen delivery system which may be successfully used, with low toxicity, for preparation of highly immunogenic coccidia vaccine.

Characterization of the antigen SO7 during development of Eimeria tenella

The developmental expression of the antigen SO7, which has been previously shown to protect chickens against infection by several Eimeria species, was investigated. Using RT-PCR, mRNA for SO7 was found to be restricted primarily to unsporulated oocysts (0 hr). Western blot (WB) analysis with an antibody to recombinant SO7 (rbSO7) revealed expression of the protein from 6 to 72 hr (fully sporulated) of sporulation and in sporozoites (SZ). SO7 was absent in host-derived second-stage merozoites (MZ) and was present in culture-derived first-stage MZ but at a level of only 25% of that exhibited by SZ. During invasion of Madin-Darby bovine kidney (MDBK) cells by SZ in vitro, the level of SO7 within cells, as determined by WB analysis, remained relatively constant until 48 hr of development and then decreased by about 40% at the next time point (72 hr). The SO7 secreted into the culture media during in vitro development increased to a relative maximum at 48 hr and then decreased to about 20% of maximum at 72 hr. Immunostaining with anti-rbSO7 indicates that SO7 is highly concentrated in both refractile bodies (RB) of SZ, with some limited distribution in the apical complex. Anti-rbSO7 intensively stained the intracellular parasites and the first-stage schizonts during in vitro development of E. tenella in MDBK cells. Upon release from the schizonts, the first-stage merozoites stained with 1 or 2 bright spots typically at each end. The results suggest that SO7 is closely associated with the SZ RB and is developmentally regulated but may not play a direct role in cellular invasion.

Serine protease activity in developmental stages of Eimeria tenella

A number of complex processes are involved in Eimeria spp. survival, including control of sporulation, intracellular invasion, evasion of host immune responses, successful reproduction, and nutrition. Proteases have been implicated in many of these processes, but the occurrence and functions of serine proteases have not been characterized. Bioinformatic analysis suggests that the Eimeria tenella genome contains several serine proteases that lack homology to trypsin. Using RT-PCR, a gene encoding a subtilisin-like and a rhomboid protease-like serine protease was shown to be developmentally regulated, both being poorly expressed in sporozoites (SZ) and merozoites (MZ). Casein substrate gel electrophoresis of oocyst extracts during sporulation demonstrated bands of proteolytic activity with relative molecular weights (Mr) of 18, 25, and 45 kDa that were eliminated by coincubation with serine protease inhibitors. A protease with Mr of 25 kDa was purified from extracts of unsporulated oocysts by a combination of affinity and anion exchange chromatography. Extracts of SZ contained only a single band of inhibitor-sensitive proteolytic activity at 25 kDa, while the pattern of proteases from extracts of MZ was similar to that of oocysts except for the occurrence of a 90 kDa protease, resistant to protease inhibitors. Excretory-secretory products (ESP) from MZ contained AEBSF (4-[2-Aminoethyl] benzenesulphonyl fluoride)-sensitive protease activity with a specific activity about 10 times greater than that observed in MZ extracts. No protease activity was observed in the ESP from SZ. Pretreatment of SZ with AEBSF significantly reduced SZ invasion and the release of the microneme protein, MIC2. The current results suggest that serine proteases are present in all the developmental stages examined.

Partial purification and characterization of an aminopeptidase from Eimeria tenella

Our previous investigation demonstrated the expression in Eimeria tenella sporulated oocysts of an aminopeptidase (AP) with strong homology to AP N. To further understand the role of proteases during development, we investigated the molecular and biochemical properties of E. tenella AP. Greater than 95% AP activity was present in a soluble extract during sporulation of oocysts with highest activity in fully sporulated oocysts. The AP activity was inhibited by the AP inhibitors bestatin and 1,6-phenanthroline, but not by serine protease inhibitors. The AP had specificity for synthetic endopeptidase substrates that contain arginine, alanine, or glycine at the N terminus. Partial purification of the enzyme yielded a major protein band with an Mr of about 106 kDa and an isoelectric point (Ip) of 5.1. Reverse transcription-polymerase chain reaction indicated that the gene for AP is expressed during sporulation, but expression is absent or greatly reduced in the sporozoites and merozoites. On the basis of the deduced gene structure, the predicted Mr is 110 kDa with a pI of 5.59. Database search indicates that the E. tenella AP shares significant homology with the AP from Apicomplexan taxa: Toxoplasma gondii, Cryptosporidium parvum, and Cryptosporidium hominis. Together, these results confirm the presence of a cytosolic AP related to AP N, which is expressed and active during sporulation of E. tenella oocysts.

HEAT SHOCK PROTEIN 90 GENES OF TWO SPECIES OF POULTRY EIMERIA: EXPRESSION AND EVOLUTIONARY ANALYSIS

Heat shock protein 90 (Hsp90) is 1 of the most abundant and evolutionarily conserved proteins. In most species, Hsp90 is essential for proper cell function. In this study, we present the molecular analysis of Hsp90 from Eimeria species, the causative agents of avian coccidiosis. The full-length Eimeria acervulina Hsp90 complementary DNA was isolated from intestinal intraepithelial lymphocytes of Eimeria-infected chickens. From evolutionary analysis and sequence identity, it is likely that Eimeria Hsp90 sequences described thus far encode the cytosolic versions of the protein. Although at the nucleotide and amino acid levels Eimeria tenella and E. acervulina Hsp90 are highly similar, their expression profiles differ considerably. Although E. tenella transcripts were detected in all developmental stages tested, E. acervulina transcripts were not found in oocysts undergoing sporulation or in fully sporulated oocysts, suggesting that messenger RNA expression may be regulated quite differently between Eimeria species.

Analysis of transcripts expressed by Eimeria tenella oocysts using subtractive hybridization methods

To characterize the genes expressed by Eimeria tenella oocysts, the sequence of 499 expressed sequence tags (ESTs) was obtained from complementary DNA (cDNAs) enriched for transcripts expressed by unsporulated or sporulated oocysts. Of these, 225 clones were isolated from cDNA of sporulated oocysts and 274 from unsporulated oocysts. A total of 163 unique sequences were found, and the majority of these (64%) represent novel genes with no significant homology to the proteins in GenBank. Approximately half of the unique transcripts generated from sporulated oocysts are also expressed by sporozoites and merozoites, whereas the expression of most (79%) of the transcripts from unsporulated oocysts has not yet been detected at other stages of development. The expression of 4 transcripts obtained from the subtracted cDNAs was confirmed by quantitative reverse transcriptase-polymerase chain reaction. The results confirmed that these transcripts are in fact differentially expressed between sporulated and unsporulated oocysts.

A conserved 19-kDa Eimeria tenella antigen is a profilin-like protein

A wide range of recombinant proteins from Eimeria species have been reported to offer some degree of protection against infection and disease, but the specific biological function of these proteins is largely unknown. Previous studies have demonstrated a 19-kDa protein of unknown function designated SZ-1 in sporozoites and merozoites of Eimeria acervulina that can be used to confer partial protection against coccidiosis. Reverse transcriptase-polymerase chain reaction indicated that the gene for SZ-1 is expressed by all the asexual stages of Eimeria tenella. Rabbit antisera to recombinant SZ-1 recognized an approximately 19-kDa protein from extracts of E. tenella sporozoites, merozoites, sporulated oocysts, and oocysts in various stages of sporulation. Immunofluorescence antibody staining indicated specific staining of E. tenella sporozoites and merozoites. Staining was most intense in the cytoplasm of the posterior end of the parasite. The primary amino acid sequence of the gene for E. tenella SZ-1 deduced from the E. tenella genome indicated a conserved domain for the actin-regulatory protein profilin. A conserved binding site for poly-L-proline (PLP), characteristic of profilin was also observed. SZ-1 was separated from soluble extract of E. tenella proteins by affinity chromatography using a PLP ligand, confirming the ability of SZ-1 to bind PLP. SZ-1 also partially inhibited the polymerization of actin. The current results are consistent with the classification of SZ-1 as a profilin-related protein.

The effect of dietary betaine on intestinal and plasma levels of betaine in uninfected and coccidia-infected broiler chicks

Chicks fed betaine supplemented diets and infected with Eimeria acervulina and Eimeria maxima had markedly higher levels of betaine in the duodenum and mid-gut than unsupplemented, infected chicks. Uninfected chicks fed betaine exhibited almost twice the levels of betaine in the gut as infected chicks. Plasma betaine levels were lower in E. maxima-infected chicks than in E. acervulina-or Eimeria tenella-infected chicks. Betaine supplementation reversed the decrease in weight gain in E. maxima- infected chicks but had no effect on the decrease in weight gains in E acervulina- and E. tenella-infected chicks. Coccidia-infected birds on normal diets regularly exhibit increases in plasma NO(2)(+)NO(3). This increase was abolished in E.tenella-infected birds on betaine supplement. Betaine feeding did not alter this effect in E. acervulina- and E. maxima-infected birds. Results indicate that betaine supplementation has a positive effect on gut betaine levels in birds infected with E. acervulina and E. maxima. In all treatment groups, infection lowered the levels of betaine.

Characterization of a developmentally regulated oocyst protein from Eimeria tenella

Changes in proteins during sporulation of Eimeria tenella oocysts were investigated. Unsporulated E. tenella oocysts collected from cecal tissue at 7 days postinoculation were sporulated in aerated media at 28 C for 0-48 hr. Gel analysis of soluble protein extracts prepared from oocysts from their respective time points indicated the presence of 2 prominent bands with relative molecular weight (Mr) in the range of 30 kDa and making up 20% of the total protein. These 2 bands, designated as major oocyst proteins (MOPs), were absent or barely detectable by 21 hr of sporulation. MOP bands were weakly reactive with glycoprotein stain but showed no mobility shift on deglycosylation. By gel analysis it was shown that the purified MOPs consisted of 2 bands of Mr 28.7 and 30.1 kDa. However, by matrix-assisted laser deabsorption-time of flight analysis it was shown that masses were about 17% lower. Internal sequence analysis of the 28.7-kDa protein generated 2 peptides of 17 and 14 amino acids in length, consistent with a recently described protein coded by the gam56 gene and expressed in E. maxima gametocytes. Rabbit antibodies made against MOPs were localized to outer portions of sporocysts before excystment and to the apical end of in vitro-derived sporozoites. These same antibodies were found to react with bands of Mr 101 and 65 kDa by Western blot but did not recognize MOPs in soluble or insoluble sporozoite extracts. The data suggest that the MOPs are derived from part of a gametocyte protein similar to that coded by gam56 and are processed during sporulation into sporocyst and sporozoite proteins. Alternatively, the binding of anti-MOP to 101- and 65-kDa proteins may result from alternatively spliced genes as the development of parasite proceeds.

Recent advances in biology and immunobiology of Eimeria species and in diagnosis and control of infection with these coccidian parasites of poultry

Avian coccidiosis, an intestinal disease caused by protozoan parasites of the genus Eimeria, occurs worldwide. It is considered to be one of the most economically important diseases of domestic poultry. For many years, prophylactic use of anticoccidial feed additives has been the primary means of controlling coccidiosis in the broiler industry and has played a major role in the growth of this industry, which now can produce about 7.6 billion chickens annually. However, development of anticoccidial resistance has threatened the economic stability of the broiler industry. Although there has been little effort by the pharmaceutical industry to develop new anticoccidials, the mounting problem of drug resistance of Eimeria species has prompted major research efforts to seek alternative means of control through increased knowledge of parasite biology, host response, and nutritional modulation. As a consequence, important advancements have been made, particularly in defining parasite antigens that have potential use in vaccines, defining the Eimeria genome, understanding the immunology of coccidial infections, and the practical applications of live vaccines. This review describes the progress in these areas, most of which has occurred within the past 10 to 15 years.

Interaction of dietary vitamin E with Eimeria maxima infections in chickens

In two trials, broiler chickens, processed similarly to those placed in commercial operation, were fed, from 1 d of age, a range (13 to 200 ppm) of DL-alpha-tocopheryl acetate (VE-AC) levels, and the effects on the pathology of Eimeria maxima infections were assessed at 6 d postinoculation (PI). In Trial 1, dietary levels of VE-AC had little significant effect on variables characterizing pathology except for the number of oocysts shed, which was significantly increased in chicks treated with higher VE-AC levels. The infection was judged to be mild based on moderate lesion scores (2.2+/-0.2), lack of significant effects on weight gain (7+/-1.6% decrease), moderate reduction in plasma carotenoids (21+/-2%) and small increases in plasma NO2-+NO3- (141+/-12%). In uninfected and infected chickens, plasma alpha-tocopherol (AT) increased with dietary levels of VE-AC; however, E. maxima infection caused a fairly constant decrease in AT of 35.3+/-3.2% across these levels. Plasma gamma-tocopherol (GT) levels were unaffected by dietary VE-AC or E. maxima infection. In Trial 2, pathology, again, was relatively unaffected by dietary VE-AC level. The infection was judged to be severe based on lesion scores (3.5+/-0.1), reduction in weight gain (30.7+/-3%), plasma carotenoids (72.4+/-1.5%), uric acid (16.3+/-3.4), albumin (37.8+/-2.8%), large increases (261+/-8%) in plasma NO2-+NO3-, and high numbers of oocysts shed per chick (4.12+/-0.4 x 10(7)). Plasma AT again increased with increasing dietary VE-AC levels in uninfected and infected chicks, but the mean decrease across VE-AC levels caused by E. maxima infection was 73.14+/-3.3%. GT levels were erratic and unrelated to dietary VEAC or infection. Thus, in processed broiler chickens, high dietary VE-AC did not prevent or lessen the pathology caused by mild or severe infections with E. maxima. The main effect of E. maxima infection appeared to be reduction in plasma AT levels. We postulate that this reduction may be due to malabsorption of AT, which results from physical damage to the absorptive mucosa, reduction in esterases required to hydrolyze the VE-AC, and a generalized lipid malabsorption, preventing movement of the free AT to circulating blood and infected tissues.

Eimeria tenella infection in chickens: effect on plasma and muscle 3-methylhistidine

To assess muscle breakdown during avian coccidiosis, the level of the nonmetabolizable amino acid 3-methylhistidine (3MH) was determined in muscle and plasma from chickens infected with the cecal parasite Eimeria tenella. The change in 3MH level during infection was determined in birds, each inoculated with 0 to 200,000 sporulated oocysts. The effect of levels of parasitism was evaluated at 6 d postinoculation. The 3MH levels of plasma and muscle were determined by HPLC after derivatization with fluorescamine. Weight gains, packed cell volumes, and gross lesion scores were also determined. E. tenella infected birds with lesion scores of 3 or 4 had significantly elevated plasma and muscle 3MH, whereas infected birds with lesion scores of 0, 1, or 2 did not have elevated plasma and muscle 3MH; however, there was a linear inverse relationship between weight gain and both plasma and muscle 3MH. The results suggested that muscle breakdown, as assessed by plasma and muscle levels of 3MH, was elevated during the acute stage of E. tenella infection and was most likely associated with anorexia caused by infection. However, the correlation of 3MH levels with severity of infection was not as strong as that previously observed for E. acervulina infection, most likely due to the differences in pathology caused by the two species.

Cuticular collagen synthesis by Ascaris suum during development from the third to fourth larval stage: identification of a potential chemotherapeutic agent with a novel mechanism of action

The dominant proteins released by Ascaris suum during development in vitro from the L3 to L4 stage were identified as collagenous cuticular proteins by sequence analysis and susceptibility to digestion by collagenase. Under reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the collagen proteins separated into 3 groups with molecular weights estimated at 32 kDa, 54-60 kDa, and 71-91 kDa. The 32-kDa protein represents monomeric collagen; the 54-60- and 71-91-kDa components represent dimeric and trimeric forms, respectively, polymerized by nonreducible cross-links. Furthermore, the release of these forms of collagen was developmentally regulated, as exemplified by a sequential temporal progression from monomeric to dimeric to trimeric forms in association with the in vitro transition from L3 to L4. The data suggest that collagen released in vitro during development of A. suum L3 to L4 reflects the increased translation of collagen gene products and their initial assembly into higher molecular weight molecules associated with the synthesis of the L4 cuticle. A biotinylated dipeptidyl fluoromethylketone cysteine protease inhibitor (Bio-phe-ala-FMK) bound specifically to the 32-kDa collagen and, to a lesser extent, to a 30-kDa protein; binding was dependent on the presence of dithiothreitol (DTT) and was prevented by iodoacetamide. Because cysteine residues play an essential role in the initial assembly of the collagen monomers into the higher molecular weight oligomers present in the mature nematode cuticle, inhibition of molting of A. suum L3 to L4 by the cysteine protease inhibitor Z-phe-ala-FMK might be due to its binding to thiol groups of collagen monomers during a critical phase of collagen assembly. Prevention of cystine cross-links during this critical period of cuticle assembly by peptide-FMK inhibitors may represent a potential control mechanism having a novel mechanism of action.

Release of hyaluronidase during in vitro development of Ascaris suum from the third to fourth larval stage

An enzyme that degraded glycosaminoglycan hyaluronic acid was released during in vitro development of Ascaris suum L3 to L4. The enzyme did not hydrolyze glycosaminoglycan chondroitin sulfate A. One molecular form of hyaluronidase was detected, with a molecular weight estimated at 47.8 +/- 8.6 kDa by sucrose density gradient centrifugation and at 55.0 +/- 1.3 kDa by substrate SDS-PAGE zymography. Activity of the enzyme was optimal between pH 5.0 and 6.0, and was present at neutral pH. Hyaluronidase activity was not affected by 5 mM concentrations of cupric sulfate, zinc chloride, calcium chloride, manganese chloride or EDTA. In addition, NaCl had no effect on enzyme activity at concentrations of 0.2-1.0 M. The highest level of hyaluronidase was present in culture fluid collected between days 4 and 6 of in vitro culture, and this period corresponded with that of the highest rate of increase in the percentage of L4. The presence or absence of hyaluronic acid plays a key role in basic developmental processes of vertebrates and is regulated, in part, by hyaluronidases. Developmental processes occurring during the transition of A. suum L3 to L4 may likewise depend on hyaluronidase. In addition, the infection process of a number of organisms, including some nematodes, depends on hyaluronidase. A. suum may likewise utilize hyaluronidase to facilitate larval migration within the host.

Elevation of muscle and plasma 3-methylhistidine as a result of turkey coccidiosis

To assess muscle breakdown during avian coccidiosis, the level of the non-metabolizable amino acid 3-methylhistidine (3MH) was determined in muscle and plasma from turkey poults that received an infection with a field isolate containing a mixture of Eimeria species. The effect of increased levels of parasitism was evaluated at 6 days postinoculation (DPI) in birds receiving 2.5 x 10(4), 1 x 10(5), or 2 x 10(5) oocysts each. The changes in 3MH levels during recovery from acute infection were assessed at 6-29 DPI in animals given 1.9 x 10(5) oocysts per bird. In some experiments, uninoculated birds given the same amount of feed as infected birds (pair fed) were used to determine the impact of feed deprivation on weight loss and 3MH levels. Infected birds had significantly elevated plasma and muscle 3MH at 6 DPI after a single dose of Eimeria oocysts. The plasma and muscle 3MH returned to control levels after 14 DPI. The 3MH levels increased with increased dose of oocysts. Plasma and muscle 3MH levels were well correlated, and an inverse curvilinear relationship between weight gain and plasma 3MH concentrations levels was observed. Plasma and muscle 3MH levels were significantly elevated in pair-fed birds, but 3MH levels in infected birds were increased by 30% over pair-fed birds. The results suggested that muscle breakdown, as assessed by plasma and muscle levels of 3MH, increased during the acute stage of Eimeria infection in turkey poults.

A developmentally regulated hyaluronidase of Haemonchus contortus

The trichostrongylid nematode Haemonchus contortus released a hyaluronic acid-degrading enzyme during in vitro development from the third (L3) to fourth (L4) larval stage. The enzyme did not degrade chondroitin sulfate A. Enzyme activity was optimal between pH 4.0 and 6.0, and the enzyme was inhibited by high concentrations of NaCl; the divalent cations Cu2+, Zn2+, Ca2+, and Mn2+ were not inhibitory. The hyaluronidase had a molecular mass estimated at 57 kDa by sucrose density gradient centrifugation and at 111 kDa by substrate sodium dodecyl sulfate polyacrylamide gel electrophoresis (reducing and nonreducing conditions), suggesting the formation of a dimer during the electrophoretic separation conditions. The level of hyaluronidase released during in vitro development peaked between 24 and 48 hr in culture and then gradually decreased, with little or no activity present in the 168-hr culture fluid. The enzyme was not detected in culture fluid from 24-hr incubations of either the mid-L4 stage (obtained from sheep 7 days postinfection) or the adult stage (obtained from sheep 30-35 days postinfection). The temporal expression of the hyaluronidase suggested a role for this enzyme in the early stages of the L3-L4 developmental process.

Effect of Eimeria acervulina infections on plasma L-arginine

As part of a program to study the pathological effects of coccidia infections on growth, we have examined the relationship of plasma L-arginine (ARG) levels to infective doses of Eimeria acervulina and infection-associated changes in weight gain, plasma carotenoids, and plasma NO2- + NO3-. Chickens consuming a starter ration containing 1.68% ARG were infected with a range of doses of E. acervulina. At 6 d postinoculation (PI), weight gains were significantly reduced by infections with 5 x 10(5) and 1 x 10(6) oocysts per chick (OPC). Gross lesion scores of chickens infected with 5 x 10(4) through 1 x 10(6) OPC were significantly greater than scores of chicks infected with 1 x 10(3) OPC. Compared with levels from uninfected controls, plasma NO2- + NO3- concentrations were significantly increased by infection with 5 x 10(5) and 1 x 10(6) OPC, plasma concentrations of ARG were significantly decreased by infection with 5 x 10(4) through 1 x 10(6) OPC, and plasma carotenoids were significantly decreased by all infection doses. Plasma arginine was significantly correlated with plasma carotenoids (P > 0.0187), but not with infection dose or weight gain; plasma NO2- + NO3- was positively correlated (P > 0.0043) with infection dose and negatively correlated (P > 0.0158) with weight gain. Regression analysis of the measured variables indicated that the strongest relationship existed between plasma ARG and carotenoids. This finding suggests that in this infection model, reduction in plasma ARG is most likely associated with nutrient malabsorption that accompanies infection and is likely not significantly impacted by synthesis of nitric oxide that is associated with the immune response.

Eimeria acervulina infection elevates plasma and muscle 3-methylhistidine levels in chickens

To assess muscle breakdown during avian coccidiosis, the level of the nonmetabolizable amino acid 3-methylhistidine (3MH) was determined in muscle, plasma and excreta from chickens infected with Eimeria acervulina. The changes in 3MH levels during infection were assessed at 1-29 days postinoculation (DPI) in animals given 5 x 10(5) oocysts per bird. The effect of levels of parasitism were evaluated at 8 DPI in birds receiving 5 x 10(3), 5 x 10(4), 5 x 10(5) or 1 x 10(6) oocysts each. The 3MH levels of plasma, muscle, and excreta samples were determined by high-pressure liquid chromatography after derivatization with fluorescamine. Weight gains, breast muscle weight, eviscerated weight, plasma carotenoid levels, dry weight of muscle, and gross lesion scores were also determined. Infected birds had significantly elevated plasma and muscle 3MH at 4 and 8 DPI following a single dose of E. acervulina. The increase in 3MH levels had an inverse relationship with the time course of weight gain and plasma carotenoid levels. Plasma and muscle 3MH levels returned to control values by 15 DPI and remained unchanged from control values through the remainder of the experiment (29 DPI). Breast weight was decreased in infected birds, but the ratio of breast weight to eviscerated body weight was unchanged. Excretion of 3MH decreased relative to controls at 4 and 8 DPI and returned to control levels on 15 DPI. The plasma and muscle levels of 3MH were related to severity of infection; however, levels of excreted 3MH were not. The results suggested that muscle breakdown, as assessed by plasma and muscle levels of 3MH, increased during the acute stage of E. acervulina infection. The underlying causes for this muscle breakdown was unclear but could involve a physiological response to anorexia and decreased food intake during the acute phase of infection. Levels of excreted 3MH did not increase during infection and this may be the result of decreased excreta output during infection. Plasma and muscle levels of 3MH were correlated with severity of E. acervulina infections but may not be as sensitive an indicator of infection as plasma carotenoid levels or other physiological parameters.

Trichuris suis: a secretory chymotrypsin/elastase inhibitor with potential as an immunomodulator

A serine protease inhibitor, termed TsCEI, was purified from adult-stage Trichuris suis by acid precipitation, affinity chromatography (elastase-agarose), and reverse-phase HPLC. The molecular weight of TsCEI was estimated at 6.437 kDa by laser desorption mass spectrometry. TsCEI potently inhibited both chymotrypsin (K(i) = 33.4 pM) and pancreatic elastase (K(i) = 8.32 nM). Neutrophil elastase, chymase (mouse mast cell protease-1, mMCP-1), and cathepsin G were also inhibited by TsCEI, whereas trypsin, thrombin, and factor Xa were not. The cDNA-derived amino acid sequence of the mature TsCEI consisted of 58 residues including 9 cysteine residues with a molecular mass of 6.196 kDa. TsCEI displayed 48% sequence identity to a previously characterized trypsin/chymotrypsin inhibitor of T. suis, TsTCI. TsCEI showed 36% sequence identity to a protease inhibitor from the hemolymph of the honeybee Apis mellifera. Sequence similarity was also detected with the trypsin/thrombin inhibitor of the European frog Bombina bombina, the elastase isoinhibitors of the nematode Anisakis simplex, and the chymotrypsin/elastase and trypsin inhibitors of the nematode Ascaris suum. The inhibitors of T. suis, an intestinal parasite of swine, may function as components of a parasite defense mechanism by modulating intestinal mucosal mast cell-associated, protease-mediated, host immune responses.

Characterization of acid phosphatase and phosphorylcholine hydrolase in adult Haemonchus contortus

An acid phosphatase (AP) and a phosphorylcholine hydrolase (PCH) were detected in excretory-secretory (ESP) products from adult Haemonchus contortus. The AP had a pH optimum of 4.5 and was inhibited by tartaric acid and sodium fluoride, but not by o-phenanthroline. The AP hydrolyzed paranitrophenol (pnp)-phosphate and to a lesser extent pnp-phenyl-phosphonate but did not hydrolyze diester substrates. Purified AP consisted of heterodimers with relative molecular weight (Mr) of 41.9 and 48.7 kDa and had a native molecular weight of 98 kDa by size-exclusion chromatography (SEC). The PCH had a pH optimum of about 9.5 and was inhibited by EDTA and o-phenanthroline but not by the specific phospholipase inhibitor D609. The specific activity of PCH in the ESP was approximately 25-fold less than that of AP. PCH also hydrolyzed 5'-thymidine monophosphate-pnp at a rate about 40% lower than pnp-phosphorylcholine but did not hydrolyze 3'-thymidine monophosphate-pnp. Partial purification of PCH suggests an Mr of 50.2 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an Mr of 102 kDa by SEC. Both AP and PHC were secreted in vitro in a time-dependent manner and had their highest concentrations in the intestine. The results indicate that H. contortus adults secrete significant amounts of AP that might be a digestive enzyme. PCH is also an intestinal enzyme and is secreted in lesser amounts than AP. The PCH is probably not a phospholipase C but has some characteristics of a type I phosphodiesterase.

Trichuris suis: A secretory serine protease inhibitor

A trypsin inhibitor was identified in extracts of adult Trichuris suis and culture fluids from 24-h in vitro cultivation of adult parasites. The inhibitor was isolated by acid precipitation, affinity chromatography (trypsin-agarose), and reverse phase HPLC as a single polypeptide with a molecular weight estimated at 6.6 kDa by laser desorption mass spectrometry. The purified inhibitor associated strongly with trypsin (equilibrium dissociation inhibitory constant (K(j)) of 3.07 nM) and chymotrypsin (K(j) = 24.5 nM) and was termed TsTCI. Elastase, thrombin, and factor Xa were not inhibited. The cDNA-derived amino acid sequence of the mature TsTCI consisted of 61 residues including 8 cysteine residues with a molecular mass of 6.687 kDa. The N-terminal region of TsTCI (46 residues) showed limited homology (36%) to a protease inhibitor from the hemolymph of the honeybee Apis mellifera, which is considered to be a member of the Ascaris inhibitor family. However, TsTCI did not display sequence homology with other members of this family or the distinctive cysteine residue pattern which distinguishes this family. However, similarity of a region of TsTCI (11 residues) with the reactive site regions of inhibitors from the nematodes Ascaris suum, Anisakis simplex, and Ancylostoma caninum was apparent.

Characterization of a hemoglobin-like protein from adult Haemonchus contortus

A hemoglobin-like protein was purified from supernatants of adult Haemonchus contortus extracts by high-pressure liquid chromatography. The purified protein had an M(r) of 33 kDa as determined by size-exclusion chromatography under non-denaturing conditions and an M(r) of 19 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting the hemoglobin may exist as a dimer. The sequences of 3 peptides resulting from proteolytic digest of the purified protein were determined and demonstrated greater than 50% identity to the globin from Trichostrongylus colubriformis. Adult H. contortus incubated overnight in [3H]leucine, incorporated radioactivity into a peak that coeluted with parasite hemoglobin, indicating the adults synthesize hemoglobin in vitro. The L3-stage lacked hemoglobin, but the L4-stage contained a hemoglobin with an M(r) of 19.6 kDa.

A hemolytic factor from Haemonchus contortus alters erythrocyte morphology

A hemolytic factor from adult Haemonchus contortus caused distinct morphological changes in the surface of sheep red blood cells (RBCs). After a 15 min exposure to the hemolytic factor, hemolysis was not detected in incubation media, but RBCs were spherical in shape with numerous surface projections compared to control cells that were smooth-surfaced biconcave disks. After 30 min, a time at which significant hemolysis occurred, echinocytes were formed, and after 90 min, cells were severely disrupted with many visible holes in membranes. No RBC ghosts were observed. RBCs from four other mammalian species were lysed by the H. contortus hemolytic factor. However, the rate of hemolysis varied with a relative order of sheep approximately rabbit>goat>pig>calf. The morphology of RBCs from all four species was significantly altered after 30 min incubation with the degree of morphological changes related to the degree of hemolysis. These results support the hypothesis that the hemolytic factor acts as a pore-forming agent, although a phospholipase or other enzyme might play a role in solubilization of cell membranes.

Purification and characterisation of a secreted aminopeptidase from adult Ascaris suum

A metalloaminopeptidase was identified in culture fluids collected during in vitro cultivation of adult Ascaris suum. The enzyme was purified by anion-exchange and size-exclusion HPLC. The M(r) of the enzyme was estimated at 293 kDa and consisted of subunits with M(r)s of 153 and 142kDa. The isoelectric point of the aminopeptidase was 4.7. The aminopeptidase displayed a substrate preference for terminal arginyl residues. Aminopeptidase activity was also present in muscle, female reproductive tissue, pharynx, pseudocoelomic fluid and intestine. Among the various tissues, aminopeptidase activity was highest in the intestines; the highest activity was found in culture fluids (three-fold higher than intestinal tissue). The aminopeptidase released by adult A. suum was enzymatically and biochemically identical to an aminopeptidase released during in vitro development of A. suum third- to fourth-stage larvae.

Effect of protease class-specific inhibitors on in vitro development of the third- to fourth-stage larvae of Ascaris suum

Third-stage larvae (L3) of Ascaris suum develop and molt to fourth-stage larvae (L4) during in vitro cultivation; consistently greater than 80% of the larvae develop to L4 during 7 days in culture (DIC). To assess the role of proteases in this process, the effect of protease class-specific inhibitors was studied. The presence of either a serine protease inhibitor (AEBSF, 100 microM) or an aspartic protease inhibitor (pepstatin A, 100 microM) had no effect on the percentage of L4 after 7 DIC. However, the presence of either a cysteine protease inhibitor (Z-Phe-Ala-FMK, 100 microM) or an aminopeptidase inhibitor (amastatin, 100 microM) resulted in 77% and 34% reductions, respectively, in the percentage of L4 compared to untreated cultures; viability of the larvae was not affected. The effect of Z-Phe-Ala-FMK on molting was time and dose dependent. In contrast to Z-Phe-Ala-FMK, E-64, another specific inhibitor of cysteine proteases, had no effect on molting. The data support a role for an aminopeptidase and suggest a role for a cysteine protease in the development of the L3 to L4 stage of A. suum.

The in vitro uptake of albumin by adult Haemonchus contortus is altered by extracorporeal digestion

FITC (fluorescein isothiocyanate)-labeled albumin was used as a substrate to further characterize the digestion of host blood proteins by adult Haemonchus contortus. Isolated H. contortus intestine degraded FITC-albumin; degradation was completely inhibited by E-64, a specific inhibitor of cysteine proteases. The in vitro uptake and degradation of FITC-albumin by parasites was also evaluated. Uptake of fluorescence was demonstrated; greater than 50% of the fluorescence was associated with degraded FITC-albumin. However, both the uptake and degradation of FITC-albumin were reduced by about 85%. Additionally, when parasites were incubated in the presence of specific inhibitors of cysteine proteases, degradation of FITC-albumin was shown to occur rapidly in the media during in vitro incubation. This degradation was blocked completely by the presence of cysteine protease inhibitors. These results indicate that the rapid extracorporeal digestion of FITC-albumin (mediated by secreted cysteine proteases) produce relatively high concentrations of low molecular weight FITC-labeled fragments and alters the kinetics of uptake of fluorescence by the parasite. These fragments rather than FITC-albumin are rapidly taken up by the parasites. Thus in vitro demonstration of a definitive role for the cysteine proteases as intestinal digestive enzymes in H. contortus is compromised by the enzyme's extracorporeal activity. This extracorporeal cysteine protease activity may represent the enzyme's predominant activity.

Secretion of an aminopeptidase during transition of third- to fourth-stage larvae of Ascaris suum

Protease activity was identified in culture fluids collected during in vitro development of L3 to L4 larval stages of Ascaris suum. Fluorogenic peptide substrates with unblocked N-termini were specifically hydrolyzed indicating aminopeptidase activity; a terminal arginyl residue was preferred. Culture fluids did not hydrolyze fluorogenic peptide substrates with blocked N-termini (endopeptidase substrates). The aminopeptidase activity was inhibited by 1,10-phenanthroline (metalloprotease inhibitor) and by amastatin and bestatin (aminopeptidase inhibitors); AEBSF (serine protease inhibitor), Z-phe-ala-FMK and E-64 (cysteine protease inhibitors), and pepstatin A (aspartyl protease inhibitor) had little effect on activity. The apparent molecular weight of the aminopeptidase was estimated by sucrose density gradient centrifugation at 293 kDa. The aminopeptidase displayed an acidic isoelectric point of 4.7. The peak secretion of the aminopeptidase was temporally associated with molting and suggests a function for the protease in this complex process.

The effect of disulfiram on egg shell formation in adult Trichuris muris

The effect of disulfiram on egg shell morphology in the parasitic nematode Trichuris muris was studied in vitro and in vivo. Daily disulfiram treatment of mice infected with T. muris beginning 25 days after infection and continuing for 26 days resulted in the production of malformed eggs by adult female worms in all treated groups. In addition, significantly fewer adult worms were found at necropsy in mice treated with 5.0 or 7.5 mg/kg/day of disulfiram as compared with mice treated with 2.5 mg/kg/day or control mice. Adult worms collected from infected, untreated mice and placed in aerobic culture for 5 days in media containing 4 or 8 micrograms/ml of disulfiram released malformed eggs into the culture medium after 30 hr in culture. Oral inoculation of naive mice with malformed eggs did not result in T. muris infections in the mice. The results of these studies suggest that inhibition of phenol oxidase results in disruption of normal egg production by T. muris females and that the enzyme might be a useful target in the development of control strategies aimed at nematode parasites that rely on phenol oxidase for egg shell hardening.

Characterization of haemolytic activity from adult Haemonchus contortus

Adult Haemonchus contortus contain a detergent-soluble factor that haemolyses sheep red blood cells in a time- and concentration-dependent manner. This factor had comparable haemolytic activity at pH 5.0 and 8.0; activity was lower at pH 6.0 and 7.0. The activity was heat-stable, unaffected by proteolytic inhibitors, and inhibited by 20 mM polyethyleneglycol. Haemolytic activity was associated with the particulate fraction of the isolated intestine, suggesting an essential role for this activity in the acquisition of nutrients by disrupting host red blood cells. The data are consistent with the hypothesis that the mechanism of action of the haemolytic factor is as a pore-forming agent.

The in vitro uptake and incorporation of hemoglobin by adult Haemonchus-contortus

The incorporation of radioactivity from [3H]leucine-labeled hemoglobin (Hb) into adult Haemonchus contortus proteins was investigated. Further, the role of previously described cysteine proteases present in intestinal tissue and excretory/secretory products of H. contortus was assessed in the breakdown of Hb. A cell lysate preparation (predominantly Hb) was obtained from reticulocytes metabolically labeled, in vitro, with [3H]leucine. Following 24-h incubation in the presence of [3H]Hb, adult H. contortus incorporated radioactivity. The presence of the protein synthesis inhibitor puromycin (200 micrograms ml-1) reduced incorporation by 72%, indicating that this process was dependent on protein synthesis. The specific cysteine protease inhibitor Z-phe-ala-FMK (PAF) at 0.1 mM had no effect on incorporation of radioactivity; however, the breakdown of Hbg in the culture medium was reduced by 50%. In contrast, PAF at 1.0 mM caused a 78% reduction in incorporated radioactivity. Parasite viability was also decreased by 1.0 mM PAF, and thus the reduction of incorporation of radioactivity may not be due to specific enzyme inhibition. The serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF) at 1.0 mM caused a 40% reduction in incorporation of radioactivity; the aspartic protease inhibitor pepstatin (1 mM) was without effect. Adult H. contortus also incorporated radioactivity from [3H]leucine-labeled intact reticulocytes. This incorporation was inhibited-by 1.0 mM PAF and AEBSF in a manner similar to that for the cell lysate preparation. These data indicate that adult H. contortus degrade Hbg and incorporate the radioactivity into their macromolecules. The specific action of the endogenous cysteine protease in the digestion of Hbg could not be demonstrated unequivocally. However, the hypothesis that the secreted cysteine protease functions in extracorporeal digestion was supported.

Extracellular matrix: A tool for defining the extracorporeal function of parasite proteases

The significance of cysteine protease activity present in excretory/secretory products of the feeding stages of Haemonchus contortus is discussed here by Marcia Rhoads and Raymond Fetterer. Based, in part, on the in vitro degradation and uptake of extracellular matrix components by live parasites, they argue that the cysteine proteases have an essential extracorporeal function in the digestion of host tissues. They also outline the merits of the extracellular matrix model, which mimics the in vivo structure of connective tissue and basement membranes, in analyzing host-parasite interactions and (possibly) parasite developmental processes.

Growth and cuticular synthesis in Ascaris suum larvae during development from third to fourth stage in vitro

Growth, molting and cuticular protein synthesis were determined during the development of Ascaris suum grown in vitro from the third (L3) to the fourth (L4) larval stage. The larvae remained highly viable (90%) and 70% reached the L4 by 7 days in culture (DIC). Analysis of growth and development indicated that ecdysis was asynchronous. The synthesis of noncuticular and cuticular proteins was monitored using 35S-methionine as a metabolic label. Synthesis of noncuticular, cuticular and collagenous cuticular proteins increased in a constant manner, reaching maximal values at about 6 DIC. Synthesis of noncollagenous cuticular proteins (cuticlin) remained relatively constant during most of the culture period, but increased from 6 to 7 DIC. The increase in cuticlin synthesis and the corresponding decrease in cuticular collagen synthesis noted at 7 DIC might represent the synthesis of the outer portions of the adult cuticle in preparation for the fourth molt. The results of this study suggest that this in vitro development system for A. suum, while not suitable to study events regulating the precise timing of molting and cuticular synthesis, might be useful for the analysis of potential growth regulators.

The role of the sheath in resistance of Haemonchus contortus infective-stage larvae to proteolytic digestion

Surface iodinated larvae of Haemonchus contortus were incubated in the presence of the fungal protease, proteinase K, and proteolysis quantified by scintillation counting of released radioactivity. No radioactivity was released from live ensheathed infective-stage larvae (L3(2M)). In contrast, 58% of the radioactivity was released from ecdysed, second molt (2M) cuticles (sheaths) of L3(2M) and 48% from live exsheathed third-stage larvae (L3). When L3(2M) larvae were killed by heat (80 degrees C for 10 min) prior to proteinase K incubation, 61% of the radioactivity was released, whereas less than 7% was released from larvae killed by the metabolic inhibitors NaN3 or KCN. Proteinase K released 44% of the radioactivity from live L3(2M) larvae which had been preincubated with 1% sodium dodecylsulfate (SDS), whereas no radioactivity was released from L3(2M) larvae preincubated with either 1% Triton X-100, 0.2% CTAB, 50% methanol, 50% ethanol, or water. Following incubation with proteinase K, only L3(2M) larvae which had been heat-killed or preincubated with SDS showed visible damage to the sheath. Material released from L3(2M) larvae by exposure to either heat or SDS contained a 98,000 M(r) protein by SDS-PAGE autoradiography. These results indicate that viable L3(2M) larvae are resistant to attack by proteinase K and that this resistance is dependent on structural properties of the sheath.

Extracellular matrix degradation by Haemonchus contortus

To better understand the in vivo function of secreted cysteine proteases of Haemonchus contortus, the ability of live parasites to degrade connective tissue was investigated using [3H]proline-labeled extracellular matrix produced by smooth-muscle cells (R22). The matrix was composed of glycoprotein(s) (34%), elastin (49%), and collagen (15%) in an insoluble, multilayered, cross-linked structure. No degradation of the extracellular matrix by third-stage larvae (L3) (10,000/ml) occurred during 24-hr in vitro incubation. In contrast, fourth-stage larvae (L4) (1,000/ml) degraded 42% of the matrix, whereas adults (100/ml) degraded the entire matrix. The presence of Z-phe-ala-FMK (100 microM), a specific cysteine protease inhibitor, during incubation of adults, reduced matrix degradation to 30% without affecting parasite motility. Isolated adult excretory/secretory products (ESP) (0.1 mg protein/ml) degraded 64% of the total matrix; specific degradation consisted of 80.3% of the glycoprotein, 67.1% of the elastin, and 27.6% of the collagen matrix components. Degradation of the matrix by ESP was stimulated by dithiothreitol (2 mM) and inhibited by Z-phe-ala-FMK. Thus, the secretory cysteine proteases of H. contortus are active under physiological conditions and able to degrade the major components of connective tissue in an in vitro model system that simulates their structure in vivo. These data strengthen the proposed role of these enzymes in the breakdown of host tissue.

Developmentally regulated zinc metalloproteinases from third- and fourth-stage larvae of the ovine nematode Haemonchus contortus

Parasitic third-stage larvae of the sheep abomasal nematode Haemonchus contortus develop and molt in vitro to the fourth stage (L4) in 48-72 hr, at which time they begin feeding. Coincident with the third molt, larvae begin to secrete significant amounts of protein into culture fluids, including a zinc metalloproteinase. This culture-derived zinc metalloproteinase differs from a previously described metalloproteinase from infective third-stage larvae (L3[2M]), which mediates the ecdysis process. These differences include time of expression, molecular mass, and substrate specificity. The purified proteinase, from cultures of L4, has a molecular weight of approximately 46 kDa, functions as an endopeptidase, and digests several native proteins of host origin including fibrinogen and fibronectin.

Developmentally regulated secretion of cathepsin L-like cysteine proteases by Haemonchus contortus

Cysteine protease activity was present in media collected after 24 hr in vitro culture of adult Haemonchus contortus. The released cysteine protease hydrolyzed the fluorogenic 7-amino-4-trifluoromethyl coumarin (AFC)-substituted synthetic peptides Z-phe-arg-AFC and Z-ala-arg-arg-AFC, but not Z-arg-arg-AFC or Z-arg-AFC, characterizing this activity as cathepsin L-like. Within the parasite, cysteine protease activity was highest in extracts of intestinal tissue. Secreted cysteine protease inhibited the clotting of sheep blood and hydrolyzed hemoglobin, fibrinogen, collagen, and IgG; the IgG hydrolysis site was within the hinge region. Four proteases with M(r) values of 30, 34, 37, and 41 kDa were identified with biotinylated-phenylalanine-arginine-fluoromethyl ketone, a specific probe that binds to active cysteine proteases. Adult parasites cultivated in the presence of 0.1 mM levamisole released 50% less protease activity compared to control cultures; in the presence of rafoxanide (0.1 mM), protease was not detected. Cathepsin L-like cysteine protease activity was released also by L4, but not the L3 larval stage. The active and developmentally regulated release of cysteine proteases by H. contortus may have a critical function in worm nutrition, immune evasion, or both.

Localization of phenol oxidase in female Trichuris suis

A phenol oxidase (E.C. 1.10.3.1) preparation from adult female Trichuris suis was assayed by both polarographic and spectrophotometric techniques. The T. suis enzyme oxidized most diphenols including 4-methylcatechol (4MC) and dihydroxyphenylalanine but did not oxidize tyrosine. The pH and temperature optima were 6.8 and 36 C, respectively. The Km measured using 4MC as a substrate ranged from 0.12 to 0.4 mM. The highest phenol oxidase activity was isolated in fractions from the adult females that were enriched in eggs relative to the activity in somatic tissue from females and all male tissues that were assayed. Phenol oxidase activity was localized on sodium dodecyl sulfate-polyacrylamide gel electrophoresis substrate gels into 2 bands with M(r)'s of 44,000 and 53,000. An antibody to the 44,000 band recognized 2 bands of 40,000 and 45,000 M(r) on western blot analysis of the enzyme preparation. Immunocytochemical localization of anti-phenol oxidase antibody in serial cross sections of adult female worms indicates that the enzyme is found exclusively in the anterior part of the parasite in the proximal part of the uterus that is posterior to the junction with the stichosome. Eggs located in more distal parts of the reproductive system did not react with the antibody. The results indicate that a phenol oxidase is located in the fertilized eggs of adult female T. suis. It is likely that phenol oxidase contributes significantly to the chemical hardening process in the eggs when they pass out into the external environment. Inhibition of phenol oxidase may reduce the survivability of the eggs and thus minimize contamination of livestock facilities.

Purification and characterization of surface-associated proteins from adult Haemonchus contortus

Extrinsic radioiodination experiments have shown that male and female adults of Haemonchus contortus (BPL strain) express a stage-specific set of surface-associated proteins with apparent molecular mass values of 30, 58, 81, and 143 kDa. A quantitatively different pattern of iodinated surface proteins is expressed by adults of the PPR strain of H. contortus, whereas the pattern of iodinated proteins expressed by Haemonchus similis is qualitatively distinct (38, 68, and 121 kDa). The 58-, 81-, and 143-kDa proteins of the BPL strain are glycosylated, whereas the 30-kDa protein is not. The binding of wheat germ agglutinin to the surface glycoproteins was inhibited by the trimer of N-acetylglucosamine (N,N,N-triacetylchitotroise) but not by the monosaccharide, indicating the presence of chitin-like homopolymers. The carbohydrate portion of the 58-kDa protein is N-linked and accounts for 30% of its apparent mass. Under nonreducing conditions, the 58-kDa glycoprotein forms a high molecular mass polymer that is unable to penetrate a 10% acrylamide gel. The 143- and 81-kDa surface glycoproteins were not hydrolyzed by either N- or O-glycanase, indicating unusual modifications to the saccharide-linkage and rendering it resistant to glycosidase digestion. The 30-, 58-, and 143-kDa purified surface proteins produced distinct peptide maps with Staphylococcus aureus V8 protease.

The effect of immunization of pigs with Ascaris suum cuticle components on the development of resistance to parenteral migration during a challenge infection

The development of immunity to Ascaris suum was studied in pigs immunized with isolated cuticle fragments from A. suum second and third stage larvae (L2/L3) and adult worms, and compared with other methods that stimulate a strong protective response in pigs. A significant protective response was seen in animals immunized with isolated cuticle fragments from A. suum L2/L3 and adults, but it was less than that seen in animals inoculated with UV-irradiated eggs or naturally exposed to eggs on a dirt lot. Significant IgG responses to 2-mercaptoethanol (2ME)-soluble cuticle components were seen in all groups, but the level of the antibody response did not relate to protection. Group differences in antibody and lymphocyte blastogenic responses to cuticle proteins indicated quantitative and qualitative stage specific differences in 2ME-soluble and insoluble cuticular proteins. Intestinal immunity was notably absent from cuticle immunized pigs because a marked liver white spot response was observed following the challenge inoculation. Thus, cuticle fragments from larval and adult A. suum are capable of inducing a protective response to larval migration; however, the development of intestinal immunity is not a direct function of exposure to these antigens.