Characterization of proteolytic enzymes from larval and adult Nippostrongylus brasiliensis

Hymenolepis diminuta Infection Affects Apoptosis in the Small and Large Intestine

The rat tapeworm Hymenolepis diminuta has been shown to cause alterations in gastrointestinal tissues. Since hymenolepiasis induces a number of reactions in the host, it is reasonable to assume that it may also be involved in the mechanisms of apoptosis in the intestines. Individual research tasks included an examination of the effect of H. diminuta infection on; (i) the cellular localization of the expression of pro-apoptotic protein Bax and anti-apoptotic protein Bcl-2, as well as caspase-3 and caspase-9, and (ii) the effects of the infection on the expression of Bcl-2, Bax, Cas-3 and Cas-9, at the mRNA and protein levels. Molecular tests (including mRNA (qRT PCR) and the protein (Western blot) expression of Bax, Bcl-2, and caspases-3, -9) and immunohistochemical tests were performed during the experiment. They showed that H. diminuta infection activates the intrinsic apoptosis pathway in the small and large intestine of the host. H. diminuta infection triggered the apoptosis via the activation of the caspase cascade, including Cas-3 and Cas-9. Hymenolepiasis enhanced apoptosis in the small and large intestine of the host by increasing the expression of the pro-apoptotic gene and protein Bax and by decreasing the expression of the anti-apoptotic gene and protein Bcl-2.

The influence of selected gastrointestinal parasites on apoptosis in intestinal epithelial cells

Studies on the parasite–host interaction may provide valuable information concerning the modulation of molecular mechanisms as well as of the host immune system during infection. To date, it has been demonstrated that intestinal parasites may affect, among others, the processes of digestion in the gastrointestinal system of the host, thus limiting the elimination of the parasite, the immune response as well as inflammation. However, the most recent studies suggest that intestinal parasites may also affect modulation of the apoptosis pathway of the host. The present paper presents the latest scientific information on the influence of intestinal parasite species (Blastocystis sp., Giardia sp., Cryptosporidium sp., Trichuris sp., Entamoeba histolytica, Nippostrongylus brasiliensis, Heligmosomoides polygyrus) on the molecular mechanisms of apoptosis in intestinal epithelial cells. This paper stresses that the interdependency between the intestinal parasite and the host results from the direct effect of the parasite and the host’s defense reactions, which lead to modulation of the apoptosis pathways (intrinsic and extrinsic). Moreover, the present paper presents the role of proteins involved in the mechanisms of apoptosis as well as the physiological role of apoptosis in the host’s intestinal epithelial cells.

A core set of venom proteins is released by entomopathogenic nematodes in the genus Steinernema

Parasitic helminths release molecular effectors into their hosts and these effectors can directly damage host tissue and modulate host immunity. Excreted/secreted proteins (ESPs) are one category of parasite molecular effectors that are critical to their success within the host. However, most studies of nematode ESPs rely on in vitro stimulation or culture conditions to collect the ESPs, operating under the assumption that in vitro conditions mimic actual in vivo infection. This assumption is rarely if ever validated. Entomopathogenic nematodes (EPNs) are lethal parasites of insects that produce and release toxins into their insect hosts and are a powerful model parasite system. We compared transcriptional profiles of individual Steinernema feltiae nematodes at different time points of activation under in vitro and in vivo conditions and found that some but not all time points during in vitro parasite activation have similar transcriptional profiles with nematodes from in vivo infections. These findings highlight the importance of experimental validation of ESP collection conditions. Additionally, we found that a suite of genes in the neuropeptide pathway were downregulated as nematodes activated and infection progressed in vivo, suggesting that these genes are involved in host-seeking behavior and are less important during active infection. We then characterized the ESPs of activated S. feltiae infective juveniles (IJs) using mass spectrometry and identified 266 proteins that are released by these nematodes. In comparing these ESPs with those previously identified in activated S. carpocapsae IJs, we identified a core set of 52 proteins that are conserved and present in the ESPs of activated IJs of both species. These core venom proteins include both tissue-damaging and immune-modulating proteins, suggesting that the ESPs of these parasites include both a core set of effectors as well as a specialized set, more adapted to the particular hosts they infect.

Secreted proteomes of different developmental stages of the gastrointestinal nematode Nippostrongylus brasiliensis

Hookworms infect more than 700 million people worldwide and cause more morbidity than most other human parasitic infections. Nippostrongylus brasiliensis (the rat hookworm) has been used as an experimental model for human hookworm because of its similar life cycle and ease of maintenance in laboratory rodents. Adult N. brasiliensis, like the human hookworm, lives in the intestine of the host and releases excretory/secretory products (ESP), which represent the major host-parasite interface. We performed a comparative proteomic analysis of infective larval (L3) and adult worm stages of N. brasiliensis to gain insights into the molecular bases of host-parasite relationships and determine whether N. brasiliensis could indeed serve as an appropriate model for studying human hookworm infections. Proteomic data were matched to a transcriptomic database assembled from 245,874,892 Illumina reads from different developmental stages (eggs, L3, L4, and adult) of N. brasiliensis yielding∼18,426 unigenes with 39,063 possible isoform transcripts. From this analysis, 313 proteins were identified from ESPs by LC-MS/MS-52 in the L3 and 261 in the adult worm. Most of the proteins identified in the study were stage-specific (only 13 proteins were shared by both stages); in particular, two families of proteins-astacin metalloproteases and CAP-domain containing SCP/TAPS-were highly represented in both L3 and adult ESP. These protein families are present in most nematode groups, and where studied, appear to play roles in larval migration and evasion of the host's immune response. Phylogenetic analyses of defined protein families and global gene similarity analyses showed that N. brasiliensis has a greater degree of conservation with human hookworm than other model nematodes examined. These findings validate the use of N. brasiliensis as a suitable parasite for the study of human hookworm infections in a tractable animal model.

Exploring the immunology of parasitism--from surface antigens to the hygiene hypothesis

Helminth immunology is a field which has changed beyond recognition in the past 30 years, transformed not only by new technologies from cDNA cloning to flow cytometry, but also conceptually as our definition of host immune pathways has matured. The molecular revolution defined key nematode surface and secreted antigens, and identified candidate immunomodulators that are likely to underpin parasites' success in eluding immune attack. The immunological advances in defining cytokine networks, lymphocyte subsets and innate cell recognition have also made a huge impact on our understanding of helminth infections. Most recently, the ideas of regulatory immune cells, in particular the regulatory T cell, have again overturned older thinking, but also may explain immune hyporesponsiveness observed in chronic helminth diseases, as well as the link to reduced allergic reactions observed in human and animal infections. The review concludes with a forward look to where we may make future advances towards the final eradication of helminth diseases.

Proteinases of females of the phytoparasiteGlobodera pallida(potato cyst nematode)

Sensitive assays capable of detecting proteinases in single females of the phytoparasiteGlobodera pallidahave been developed and used to define the proteinase activity of young adult females. Digestion of the large subunit of the plant protein Rubisco established a pH optimum for the proteinase activity at pH 5·7. The activity was inhibited by the cysteine proteinase inhibitorsp-chloromercuribenzoic acid (PMBA) andp-chloromercurisulphonic acid (PMSA) and stimulated by both cysteine and dithiothreitol (DTT). It was moderately reduced by L-trans-epoxysuccinyl-leucylamido-(4- guanidino) butane (E64) but not by specific inhibitors of serine, aspartate or metallo-proteinases. The activity separated into 3 bands on a non-denaturing gel but only I proteinase of 62 kDa was recovered following a combination of anion-exchange chromatography and affinity chromatography using PMBA. The effect of inhibitors was similar to that reported previously for some of the cysteine proteinase activity recovered fromCaenorhabditis elegansbut is apparently not that for which the corresponding gene has been cloned in this nematode andHaemonchus contortus.The proteinase may have a major role in digestion of dietary protein and so offers an exciting target for future control of this important plant-parasitic nematode.

Classes and crossreactivity of proteinases in the excretory–secretory products of Caenorhabditis elegans

Proteinases released during the in vitro maintenance of asynchronous cultures of the free-living nematode Caenorhabditis elegans were characterized on the basis of subunit composition, fluorogenic substrate specificity, inhibitor sensitivity and pH optima. Cysteine proteinases are present in the excretory–secretory products (ESP) as indicated by the hydrolysis of cathepsin fluorogenic substrates and confirmed by immunoblotting. Serine proteinases were predominant as indicated by substrate gel analysis and inhibitor studies. The presence of metallo-proteinases was also indicated by inhibitor studies. The optimal pH value for cysteine proteinases was 5.5, while serine proteinases were optimal at pH 8.0. As a control, cultures of Escherichia coli, the diet of C. elegans, were extracted separately and gave no evidence of overlap with C. elegans ESP. Cross reactivity between the ESP of C. elegans and antibodies raised against the ESP of the equine parasite Strongylus vulgaris indicated antigenic relatedness of a proteic epitope. This is the first study to characterize the ESP of C. elegans and to display its relatedness with that of S. vulgaris.

Helminth-derived products inhibit the development of allergic responses in mice

RATIONALE

Epidemiological studies suggest that infections with helminths protect from the development of asthma. Supporting this view is our published finding that infection with Nippostrongylus brasiliensis decreased ovalbumin-induced Th2 responses in the lung of mice.

OBJECTIVES

To evaluate if N. brasiliensis excretory-secretory products also prevent the development of asthma.

METHODS

Mice were immunized with ovalbumin/alum intraperitoneally in the absence or presence of helminthic products and then challenged intranasally with ovalbumin. Six days later, we analyzed if the mice developed Th2 responses in the lung.

MAIN RESULTS

The application of the helminthic products together with ovalbumin/alum during the sensitization period totally inhibited the development of eosinophilia and goblet cell metaplasia in the airways and also strongly reduced the development of airway hyperreactivity. Allergen-specific IgG1 and IgE serum levels were also strongly reduced. These findings correlated with decreased levels of IL-4 and IL-5 in the airways in product-treated animals. The suppressive effects on the development of allergic responses were independent of the presence of Toll-like receptors 2 and 4, IFN-gamma, and most important, IL-10. Interestingly, suppression was still observed when the helminthic products were heated or treated with proteinase K. Paradoxically, we found that strong helminth product-specific Th2 responses were induced in parallel with the inhibition of ovalbumin-specific responses.

CONCLUSION

Our results suggest that helminths suppress the development of asthma by secreting substances that modulate allergic responses without affecting the generation of helminth-specific Th2 immunity. The identification of these products may lead to the design of novel therapeutic intervention strategies for the treatment of asthma.

Detection of enzymes dehydrogenases and proteases inBrugia malayi filarial parasites

Lymphatic filariasis caused mainly by infection fromW. bancrofti andB. malayi remains a major cause of clinical morbidity in tropical and subtropical countries. Analysis ofB. malayi mf, infective larval and adult worm lysates for the activity of enzymes led to the demonstration of activities of three key enzymes of carbohydrate metabolism viz., Malate dehydrogenase (MDH), Malic enzyme (ME) and Glucose-6-phosphate dehydrogenase (G6PDH) in all the three stages of the parasite. The specific activity of all the three dehydrogenases was significantly high in mf lysate compared to their activity in lysates of the other two stages (P<0.001). Analysis by native polyacrylamide gel to their activity inlysates of the other two stages (P<0.001). Analysis by native polyacrylamide gel electrophoresis (PAGE) using 7.5% non-gradient gel showed the presence of two isoforms of each of the three enzymes (MDH, ME & G6PDH) in mf lysate, while only one form of each enzyme was present in L(3) larval and adult worm lysates. Further proteolytic enzyme activity was demonstrated both in microfilarial and infective larval lysates ofB. malayi. While both mf and L(3) larval lysates showed optimal protease activity at alkaline pH of 9.0, the mf lysate showed increased activity also at pH 3.0. The infective larval lysate was markedly inhibited by Tosylamide-L-Phenylalanine chloromethyl ketone (TPCK), a thiol protease inhibitor, while the protease activity in mf lysate was significantly inhibited by both TPCK and a serine protease inhibitor Phenyl Methyl Sulphonyl Flouride (PMSF). In sodium do-decyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), using gelatin copolymerized gel, the microfilarial lysate showed 3 protease molecules of 40 kDa, 180 kDa and 200 kDa and the L(3) larval lysate had 6 protease molecules of 18, 25, 37, 49, 70 and 200 kDa size.

Matrix metalloproteinases activity demonstrated in the infective stage of the nematodes, Angiostrongylus cantonensis

Ingestion of the larval nematode Angiostrongylus cantonensis can cause the human eosinophilic meningitis known as angiostrongyliasis. Analysis of the extracts and excretory-secretory (ES) products of A. cantonensis larvae and adult stages on gelatin substrate zymography demonstrated the presence of distinct gelatinolytic enzymes. In worm extracts, inhibitor studies showed that the metalloproteinases revealed in L(1) (23 kDa), L(3) (66, 42 and 30 kDa), young adult worm (72 and 94 kDa) and adult worm (72 and 94 kDa). In ES products, the L(1) revealed one low (42 kDa) and two high (105 and 94 kDa) molecular weight proteolytic bands that degraded gelatin in substrate gels. The L(3) revealed three low (66, 50, and 30 kDa) and one high (105 kDa) molecular weight proteolytic bands. Inhibitor studies confirmed that the 105 and 94 proteolytic bands of the L(1), and the 50 and 30 kDa proteolytic bands of the L(3) classification were metalloproteinases. These metalloproteinases secreted in the infective larvae may be associated with the parasite dissemination or pathogenesis.

Th2 induction by Nippostrongylus secreted antigens in mice deficient in B cells, eosinophils or MHC Class I-related receptors

The populations of immune system cells necessary for induction of the Th2 response have yet to be fully defined. Among the most consistent natural stimuli for Th2 responses are helminth parasites, such as the gastrointestinal nematode Nippostrongylus brasiliensis. Strong Th2 bias in immune responsiveness to live parasite infection can be reproduced by injection of a soluble Nippostrongylus excretory/secretory product (NES) collected from adult worm parasites in vitro. Injection of soluble NES induces a residual type-2 response (IL-13) even in IL-4-deficient mice, and drives a fully polar Th2 response in IL-5-deficient animals. A potent IL-10 response is observed irrespective of IL-4 or IL-5 gene status. While MHC Class II knockout animals fail to mount any IL-4 or IL-10 response, the Th2 bias is intact in Class I knockouts, indicating that CD8+ or NK-like T cells restricted to classical or non-classical Class I molecules do not play an essential role in Th2 induction. B cell-deficient microMT animals also show responses, which are strongly skewed to IL-4 production. Thus, Th2 induction by Nippostrongylus antigens is independent of B cells, or MHC class I presentation, and does not require a sufficiency of eosinophils in vivo.

Signal sequence analysis of expressed sequence tags from the nematode Nippostrongylus brasiliensis and the evolution of secreted proteins in parasites

BACKGROUND

Parasitism is a highly successful mode of life and one that requires suites of gene adaptations to permit survival within a potentially hostile host. Among such adaptations is the secretion of proteins capable of modifying or manipulating the host environment. Nippostrongylus brasiliensis is a well-studied model nematode parasite of rodents, which secretes products known to modulate host immunity.

RESULTS

Taking a genomic approach to characterize potential secreted products, we analyzed expressed sequence tag (EST) sequences for putative amino-terminal secretory signals. We sequenced ESTs from a cDNA library constructed by oligo-capping to select full-length cDNAs, as well as from conventional cDNA libraries. SignalP analysis was applied to predicted open reading frames, to identify potential signal peptides and anchors. Among 1,234 ESTs, 197 (~16%) contain predicted 5' signal sequences, with 176 classified as conventional signal peptides and 21 as signal anchors. ESTs cluster into 742 distinct genes, of which 135 (18%) bear predicted signal-sequence coding regions. Comparisons of clusters with homologs from Caenorhabditis elegans and more distantly related organisms reveal that the majority (65% at P < e-10) of signal peptide-bearing sequences from N. brasiliensis show no similarity to previously reported genes, and less than 10% align to conserved genes recorded outside the phylum Nematoda. Of all novel sequences identified, 32% contained predicted signal peptides, whereas this was the case for only 3.4% of conserved genes with sequence homologies beyond the Nematoda.

CONCLUSIONS

These results indicate that secreted proteins may be undergoing accelerated evolution, either because of relaxed functional constraints, or in response to stronger selective pressure from host immunity.

Comprehensive analysis of the secreted proteins of the parasite Haemonchus contortus reveals extensive sequence variation and differential immune recognition

Haemonchus contortus is a nematode that infects small ruminants. It releases a variety of molecules, designated excretory/secretory products (ESP), into the host. Although the composition of ESP is largely unknown, it is a source of potential vaccine components because ESP are able to induce up to 90% protection in sheep. We used proteomic tools to analyze ESP proteins and determined the recognition of these individual proteins by hyperimmune sera. Following two-dimensional electrophoresis of ESP, matrix-assisted laser desorption ionization time-of-flight and liquid chromatography-tandem mass spectrometry were used for protein identification. Few sequences of H. contortus have been determined. Therefore, the data base of expressed sequence tags (dbEST) and a data base consisting of contigs from Haemonchus ESTs were also consulted for identification. Approximately 200 individual spots were observed in the two-dimensional gel. Comprehensive proteomics analysis, combined with bioinformatic search tools, identified 107 proteins in 102 spots. The data include known as well as novel proteins such as serine, metallo- and aspartyl proteases, in addition to H. contortus ESP components like Hc24, Hc40, Hc15, and apical gut GA1 proteins. Novel proteins were identified from matches with H. contortus ESTs displaying high similarity with proteins like cyclophilins, nucleoside diphosphate kinase, OV39 antigen, and undescribed homologues of Caenorhabditis elegans. Of special note is the finding of microsomal peptidase H11, a vaccine candidate previously regarded as a "hidden antigen" because it was not found in ESP. Extensive sequence variation is present in the abundant Hc15 proteins. The Hc15 isoforms are differentially recognized by hyperimmune sera, pointing to a possible specific role of Hc15 in the infectious process and/or in immune evasion. This concept and the identification of multiple novel immune-recognized components in ESP should assist future vaccine development strategies.

Up-regulation of Fas (CD95) and induction of apoptosis in intestinal epithelial cells by nematode-derived molecules

Infection by the intestinal nematode Nippostrongylus brasiliensis induces acceleration of apoptosis in the small intestinal villus epithelial cells in vivo. In the present study, we examined whether worm extract or excretory-secretory product induces apoptosis in the rat intestinal epithelial cell line IEC-6 in vitro. In the presence of worm extract or excretory-secretory product (> or =6 microg/ml), IEC-6 cell growth was significantly suppressed, and there was a concomitant increase in the number of detached cells in culture dishes. Detached cells showed nuclear fragmentation, activation of caspase-3, and specific cleavage of poly(ADP-ribose) polymerase, suggesting that apoptosis was induced in these cells. Semiquantitative reverse transcription-PCR showed that expression of Fas (CD95) mRNA was up-regulated as early as 6 h after addition of excretory-secretory product, while Fas ligand expression and p53 expression were not up-regulated. Fluorescence-activated cell sorter analyses revealed a significant increase in Fas expression and a slight increase in FasL expression in IEC-6 cells cultured in the presence of excretory-secretory product, while control IEC-6 cells expressed neither Fas or FasL. These results indicated that N. brasiliensis worms produce and secrete biologically active molecules that trigger apoptosis in intestinal epithelial cells together with up-regulation of Fas expression, although the mechanism of induction of apoptosis remains to be elucidated.

Previous infection with the nematode Nippostrongylus brasiliensis alters the immune specific response against Chlamydophila abortus infection

An experimental mouse model to analyze the interaction between the immune responses elicited following infection with Nippostrongylus brasiliensis and Chlamydophila abortus has been established. Mice infected with C. abortus 7 days after N. brasiliensis showed an increased bacterial multiplication in spleen and liver compared to bacteria-alone infected mice. However the morbidity of these mice, expressed as weight loss, was significantly lower. Analysis of the immune responses elicited showed that spleen from co-infected mice had reduced IFN-gamma production in response to C. abortus antigen. The bias towards a type 2 response in co-infected mice was confirmed by an increase in the production of IL-4 and in the lower ratio IgG2a/IgG1. In pregnant mice co-infection caused a delay in the time of abortion and an increased systemic susceptibility to C. abortus infection.

Identification of abundantly expressed novel and conserved genes from the infective larval stage of Toxocara canis by an expressed sequence tag strategy

Larvae of Toxocara canis, a nematode parasite of dogs, infect humans, causing visceral and ocular larva migrans. In noncanid hosts, larvae neither grow nor differentiate but endure in a state of arrested development. Reasoning that parasite protein production is orientated to immune evasion, we undertook a random sequencing project from a larval cDNA library to characterize the most highly expressed transcripts. In all, 266 clones were sequenced, most from both 3' and 5' ends, and similarity searches against GenBank protein and dbEST nucleotide databases were conducted. Cluster analyses showed that 128 distinct gene products had been found, all but 3 of which represented newly identified genes. Ninety-five genes were represented by a single clone, but seven transcripts were present at high frequencies, each composing >2% of all clones sequenced. These high-abundance transcripts include a mucin and a C-type lectin, which are both major excretory-secretory antigens released by parasites. Four highly expressed novel gene transcripts, termed ant (abundant novel transcript) genes, were found. Together, these four genes comprised 18% of all cDNA clones isolated, but no similar sequences occur in the Caenorhabditis elegans genome. While the coding regions of the four genes are dissimilar, their 3' untranslated tracts have significant homology in nucleotide sequence. The discovery of these abundant, parasite-specific genes of newly identified lectins and mucins, as well as a range of conserved and novel proteins, provides defined candidates for future analysis of the molecular basis of immune evasion by T. canis.

Proteinases and associated genes of parasitic helminths

Many parasites have deployed proteinases to accomplish some of the tasks imposed by a parasitic life style, including tissue penetration, digestion of host tissue for nutrition and evasion of host immune responses. Information on proteinases from trematodes, cestodes and nematode parasites is reviewed, concentrating on those worms of major medical and economical importance. Their biochemical characterization is discussed, along with their putative biological roles and, where available, their associated genes. For example, proteinases expressed by the various stages of the schistosome life-cycle, in particular the well-characterized cercarial elastase which is involved in the penetration of the host skin and the variety of proteinases, such as cathepsin B (Sm31), cathepsin L1, cathepsin L2, cathepsin D, cathepsin C and legumain (Sm32), which are believed to be involved in the catabolism of host haemoglobin. The various endo- and exoproteinases of Fasciola hepatica, the causative agent of liver fluke disease, are reviewed, and recent reports of how these enzymes have been successfully employed in cocktail vaccines are discussed. The various proteinases of cestodes and of the diverse superfamilies of parasitic nematodes are detailed, with special attention being given to those parasites for which most is known, including species of Taenia, Echinococcus, Spirometra, Necator, Acylostoma and Haemonchus. By far the largest number of papers in the literature and entries to the sequence data bases dealing with proteinases of parasitic helminths report on enzymes belonging to the papain superfamily of cysteine proteinases. Accordingly, the final section of the review is devoted to a phylogenetic analysis of this superfamily using over 150 published sequences. This analysis shows that the papain superfamily can be divided into two major branches. Branch A contains the cathepin Bs, the cathepsin Cs and a novel family termed cathepsin Xs, while Branch B contains the cruzipains, cathepsin Ls, papain-like and aleurain/cathepsin H-like proteinases. The relationships of the helminth proteinases, and similar proteinases from protozoan parasites and other organisms, within these groups are discussed.

Onchocerca volvulus: microfilariae secrete elastinolytic and males nonelastinolytic matrix-degrading serine and metalloproteases

Host tissue penetration by parasitic nematodes may be mediated by both mechanical processes and proteolytic enzymes released by the parasites. Analysis of excretory-secretory (ES) products of Onchocerca volvulus microfilariae and adult stages on substrate gels demonstrated that they contain several distinct proteolytic enzymes. The analysis of the ES products of the microfilariae revealed one low and two high molecular weight proteolytic bands that degraded gelatin in substrate gels. The low molecular weight protein was found to be an elastinolytic protease cleaving soluble and insoluble elastin. ES products of males contained several high molecular weight proteases in the range of >/= 100-kDa degrading gelatin but lacked the low elastinolytic protease. The ES proteases of both developmental stages degraded the extracellular matrix proteins fibronectin, laminin, and collagen type IV, but not intact immunoglobulin G. The optimal protease activity for each of the proteases was found to be at a neutral pH. Inhibitor studies demonstrated their classification as serine and metalloproteases. Female and male extracts were able to hydrolyze azocasein but not gelatin in substrate gels. Protease activity could not be detected in ES products of females and microfilariae extract.

Characterization of protease(s) in adults of Trichuris globulosa (Nematoda: Trichuridae)

The activity of protease(s) has been observed separately in male and female Trichuris globulosa. Different fractions showed optimum protease activity at 37 degrees C, pH 9.5 and 1.5 mg casein concentration. Excretory/secretory (E/S) products showed maximum protease activity, which might be helpful in the degradation of mucosal tissue of the host gut. Male parasites appear to feed extensively on connective tissue collagen/elastin, while females feed on both connective tissue and body/cellular fluids. Inhibition/activation studies revealed the presence of four kinds of protease in the E/S products, cytosolic- and membrane-bound fractions performing different functions.

Viability of eggs, filariform larvae and adults of Strongyloides venezuelensis (Nematoda: Strongyloidea) maintained in vitro

The present study was performed to check the viability of eggs, filariform larvae and adults of Strongyloides venezuelensis exposed to various conditions for an in vitro maintenance. The eggs in the feces remained viable for about 25 days at 4 degrees C and 15 days at room temperature. However, the isolated eggs in sterile saline lost their viability within 24 hr at 4 degrees C. The eggs in morula stage were very sensitive to air drying and rapidly lost their viability (< or = 12 hr). Filariform larvae survived for a maximum period of 45 days in fecal suspension and 28 days in 0.12% nutrient broth in polyvinyl culture bags maintained at 20 degrees C. On the other hand, those isolated from nutrient broth cultures survived for a maximum period of 32 days in tap water and 22 days in sterile saline at 20 degrees C. The mature adult worms obtained from experimentally infected rats survived maximally for 9 days in serum supplemented (10% rat-serum) 0.12% nutrient broth and 4 days in serum free nutrient broth at 37 degrees C while the culture media were changed at an alternate day. The adult female worms deposited fertile eggs in serum supplemented and serum free nutrient broth cultures, however, the hatched larvae (L1) were not able to develop to the filariform stage in the culture media and found to die within 24 hr of maintenance. The present findings on an in vitro maintenance of different stages of S. venezuelensis may provide useful information for biological and biochemical studies with Strongyloides species.

Purification and properties of monomeric (G1) forms of acetylcholinesterase secreted by Nippostrongylus brasiliensis

Acetylcholinesterase (AChE) activity secreted by Nippostrongylus brasiliensis was resolved by sucrose density centrifugation and gel permeation chromatography in single peaks estimated at 4.3 S and 60-85 kDa, respectively. Sedimentation was unaffected by the inclusion of detergent. AChE was purified by affinity chromatography on 9-[Nbeta-(epsilon-aminocaproyl)-beta-aminopropylamino]-acridinium bromide hydrobromide-coupled sepharose 4B. Three forms of the enzyme (A, B and C) were distinguished by non-denaturating polyacrylamide gel electrophoresis, and displayed apparent masses of 74, 69 and 71 kDa respectively when resolved by SDS-PAGE. All three isoforms showed a preference for acetylthiocholine (ASCh) as substrate. They were highly sensitive to inhibition by the AChE-specific inhibitor bis(4-allyldimethylammoniumphenyl)pentan-3-one dibromide, with inhibitor concentration reducing initial activity by 50% (IC50) between 0.1 and 0.8 microM, but activity was unaffected by tetramonoisopropylpyrophosphortetramide (iso-OMPA) at concentrations up to 10 mM. We conclude that the secreted enzymes are authentic AChEs of hydrophilic monomeric (G1) form and broadly similar properties, but which can be distinguished by molecular mass, inhibitor sensitivities and the degree of excess substrate inhibition.

Ostertagia circumcincta: isolation of a partial cDNA encoding an unusual member of the mitochondrial processing peptidase subfamily of M16 metallopeptidases

A reverse-transcriptase polymerase chain reaction (PCR) procedure was used to isolate an Ostertagia circumcincta partial cDNA encoding a protein with general primary sequence features characteristic of members of the mitochondrial processing peptidase (MPP) subfamily of M16 metallopeptidases. The structural relationships of the predicted protein (Oc MPPX) with MPP subfamily proteins from other species (including the model free-living nematode Caenorhabditis elegans) were examined, and Northern analysis confirmed the expression of the Oc mppx gene in adult nematodes.

Cysteine protease of the nematode Nippostrongylus brasiliensis preferentially evokes an IgE/IgG1 antibody response in rats

Some cysteine proteases such as papain and those of mites and schistosomes have potent allergenic properties. To clarify the allergenicity of nematode cysteine proteases, the enzyme was purified from the intestinal nematode Nippostrongylus brasiliensis using cation exchange chromatography and gel filtration chromatography. The purified protease, of 16 kD and pI 8.5, showed maximum enzyme activity at pH 5.5 and substrate preference for Z-Phe-Arg-MCA. The specific inhibitors of cysteine protease leupeptin, iodoacetic acid, and E-64, completely suppressed the activity, indicating that the purified enzyme belongs to the cysteine protease family. Cysteine protease activity was found not only in somatic extract, but also in the excretory-secretory (ES) product of the nematode. When anti-cysteine protease immunoglobulin isotypes were examined in sera from rats infected with N. brasiliensis, a high level of IgG1 and a lower level of IgE antibody were detected. Depletion of IgG antibodies from the sera using protein G affinity columns resulted in a marked increase in reactivity of anti-cysteine protease IgE with the antigen, possibly due to the removal of competing IgG antibodies. In contrast to IgE and IgG1, production of anti-cysteine protease IgG2a was negligible. These results indicate that the nematode cysteine protease preferentially evokes an IgE/IgG1 antibody response.

Proteinases in the excretory/secretory products (ES) of adult Trichinella spiralis

Adult Trichinella spiralis were maintained in vitro using defined media and the material excreted/secreted (ES) during this time examined for proteolytic enzyme (proteinase) activity using an azocasein assay and gelatin-substrate gels. Several discrete proteinases in the size range 14-100 kDa were observed with optimal activity at pH 7.5. The use of a class-differentiating panel of proteinase inhibitors indicated that serine proteinases were predominant although some inhibition was evident in the presence of cysteine and metalloproteinase inhibitors. Of a panel of potential natural protein substrates tested, ES proteinases only degraded fibrinogen and plasminogen and degradation was, in part, susceptible to the action of serine, cysteine and aspartyl proteinase inhibitors. In addition, antibody harvested from immune but not normal mice inhibited ES proteinase activity, an observation of relevance to the immunobiology of Trichinosis.

Proteinases released in vitro by the parasitic stages of Teladorsagia circumcincta, an ovine abomasal nematode

Proteinases released during in vitro maintenance of third (L3) and fourth larval stage (L4) and adult Teladorsagia circumcincta (formerly Ostertagia circumcincta), an ovine abomasal nematode parasite, were characterized on the basis of pH optima, molecular size and specific proteinase inhibitor sensitivity. Enzyme activity was maximal at alkaline pH and stage-specific release was demonstrated. Proteinases released by the adult parasite degraded a variety of protein substrates including plasminogen, albumin and haemoglobin, in a pH-dependent manner. At alkaline pH fibrinogen degradation was restricted to the alpha and beta peptide chains although the gamma peptide chain was also degraded at acidic pH. Inhibitor sensitivity studies indicated that degradation was predominantly due to metalloproteinases although aspartyl proteinase activity was indicated at acidic pH.

Parasite enzymes and the control of roundworm and fluke infestation in domestic animals

The potential application of parasite enzymes to the serodiagnosis and control of veterinary helminthiases is reviewed. Consideration is given to the use of secreted enzymes as potential antihelminth vaccine components, in the search for novel anthelmintic agents and as serodiagnostic targets. The discussion focuses on recent advances in the definition of the molecular and functional properties of helminth enzymes and the application of this information to the development of novel anthelmintics as well as vaccines. Enzymes included are acetylcholinesterases, enzymes of polyamine and carbohydrate metabolism, proteases and detoxifying activities such as superoxide dismutases and glutathione S-transferases.

Characterization of three neutral proteases of Spirometra mansoni plerocercoid

In the pathogenesis of sparganosis, proteases have been considered to play important roles in tissue migration and parasite feeding. Several bands of proteolysis were observed when crude extracts of Spirometra mansoni plerocercoid (sparganum) were examined using gelatin substrate gel at neutral pH, of which two proteases of 198 and 104 kDa were purified by two chromatographic steps, and a 36 kDa protease was purified by gelatin-affinity and DEAE-anion exchange chromatography. All the purified proteases exhibited optimal activity at pH 7.5 and 0.1 M Tris-HCl. Proteolytic activities at 198 and 104 kDa were inhibited specifically by serine protease inhibitors and 4-(amidinophenyl)methanesulfonyl fluoride (APMSF, 0.5 mM) and N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK, 1 mM), which strongly suggested that these two proteases were trypsin-like proteases. The activity of the 36 kDa protease was inhibited by N-tosyl-L-phenylalanine chloromethyl ketone (TPCK, 1 mM) and chymostatin (0.1 mM), and was potentiated in 10 mM Ca2+ which showed that the protease had a chymotrypsin-like property. All the proteases were Schiff (PAS) positive. Proteases of 198 and 104 kDa degraded collagen completely within 24 h. The 36 kDa enzyme cleaved human recombinant interferon-gamma (rIFN gamma) and bovine myelin basic protein. In addition, all the purified proteins elicited strong antibody responses in the infected patients.

Differential secretion of acetylcholinesterase and proteases during the development of Heligmosomoides polygyrus

The development of the gastrointestinal nematode Heligmosomoides polygyrus was studied in the mouse. Levels of production of acetylcholinesterase and proteases were measured in excretory/secretory products of various stages of the parasite. The production of acetylcholinesterase was found to be maximal between days 4 and 6 post-infection, corresponding to the fourth larval stage of the parasite's life-cycle. Analysis of proteolytic activity revealed both quantitative and qualitative differences between the stages. Quantitative examination showed a maximal concentration of proteolytic enzymes in the early third larval stage (L3). Qualitative analysis revealed L3-associated molecules at 96, 15 and 8 kDa, L4-associated molecules at 58 and 33 kDa and adult-associated molecules at 116, 102, 39 and 25 kDa. A number appeared to be shared by all stages (18, 16 and 13 kDa), whilst others (76 and 42 kDa) appeared to be associated with the late L4/early adult parasite. The biological and immunological implications of variation in the production of proteases and acetylcholinesterase during the development of H. polygyrus are discussed.

Expression and partial characterization of a cathepsin B-like enzyme (Sm31) and a proposed 'haemoglobinase' (Sm32) from Schistosoma mansoni

Schistosoma mansoni protein Sm31 is a cysteine proteinase similar to mammalian lysosomal cathepsin B, proposed to be a key enzyme in schistosome metabolism. Protein Sm32 has been identified as a putative cysteine proteinase termed a 'haemoglobinase'. Since neither Sm31 nor Sm32 have been completely purified, some controversy of the nature of the 'true' digestive enzyme still exists. By incubating a radiolabelled cysteine-proteinase active-site-directed synthetic inhibitor with total S. mansoni proteins, the target of inhibition was Sm31 and not Sm32. The selectivity and irreversibility of inactivation make affinity labelling an invaluable tool for exploring key differences among closely related enzymes and also for studying proteinase activity in a cellular environment. In order to confirm these results, we expressed the complete cDNA sequences of Sm31 and Sm32 in insect cells and analysed the recombinant gene products for proteolytic activities. Cell extracts containing S. mansoni cathepsin B, but not those expressing 'haemoglobinase', were demonstrated to cleave a synthetic substrate benzyloxycarbonyl-arginylarginylaminomethylcoumarin in fluorescence assays. Our findings confirm previous assertions that a cysteine proteinase resembling cathepsin B is the haemoglobinase involved in digestion of host proteins. Thus, the original proposal that Sm32 is a cysteine proteinase has not been verified, and its function remains unknown.

Dirofilaria immitis: proteases produced by third- and fourth-stage larvae

A model of cutaneous extracellular matrix was used to determine if live Dirofilaria immitis larvae secrete proteases which are active at physiological pH and capable of degrading macromolecules found in cutaneous tissue. After 72 hr, 100 third-stage larvae (L3) degraded 24% of the total matrix, while fourth-stage larvae (L4) degraded 10%. A sharp increase in the amount of matrix degraded by L3 corresponded with the onset of the molting process. L3 and L4 degraded comparable amounts of the glycoprotein and elastin components of the matrix, but molting L3 degraded nearly twice the amount of the collagen component (62% vs 35%). Characterization of proteases present in larval-soluble extracts and excretory-secretory products using synthetic substrates and protease inhibitors demonstrated cysteine-protease and metalloprotease activity. Cysteine protease activity was found in whole worm extracts of both L3 and L4. Metalloprotease was secreted at higher levels by molting L3, but was also secreted by L4. Partial separation of the metalloprotease by size-exclusion chromatography indicated that the molecular weight of the native enzyme was in the 49-54 kDa range. The cysteine protease activity was demonstrated in fractions corresponding to 34-39 kDa. The biological function of the D. immitis larval proteases remains to be conclusively determined; however, these data suggest that they are involved in degradation of components of cutaneous tissue and in the molting process.