Extracellular proteases of Onchocerca

Identification of miRNAs of Strongyloides stercoralis L1 and iL3 larvae isolated from human stool

Strongyloidiasis is a neglected tropical disease caused by the soil-transmitted nematode by Strongyloides stercoralis, that affects approximately 600 million people worldwide. In immunosuppressed individuals disseminated strongyloidiasis can rapidly lead to fatal outcomes. There is no gold standard for diagnosing strongyloidiasis, and infections are frequently misdiagnosed. A better understanding of the molecular biology of this parasite can be useful for example for the discovery of potential new biomarkers. Interestingly, recent evidence showed the presence of small RNAs in Strongyloididae, but no data was provided for S. stercoralis. In this study, we present the first identification of miRNAs of both L1 and iL3 larval stages of S. stercoralis. For our purpose, the aims were: (i) to analyse the miRNome of L1 and iL3 S. stercoralis and to identify potential miRNAs of this nematode, (ii) to obtain the mRNAs profiles in these two larval stages and (iii) to predict potential miRNA target sites in mRNA sequences. Total RNA was isolated from L1 and iL3 collected from the stool of 5 infected individuals. For the miRNAs analysis, we used miRDeep2 software and a pipeline of bio-informatic tools to construct a catalog of a total of 385 sequences. Among these, 53% were common to S. ratti, 19% to S. papillosus, 1% to Caenorhabditis elegans and 44% were novel. Using a differential analysis between the larval stages, we observed 6 suggestive modulated miRNAs (STR-MIR-34A-3P, STR-MIR-8397-3P, STR-MIR-34B-3P and STR-MIR-34C-3P expressed more in iL3, and STR-MIR-7880H-5P and STR-MIR-7880M-5P expressed more in L1). Along with this analysis, we obtained also the mRNAs profiles in the same samples of larvae. Multiple testing found 81 statistically significant mRNAs of the total 1553 obtained (FDR < 0.05; 32 genes expressed more in L1 than iL3; 49 genes expressed more in L3 than iL1). Finally, we found 33 predicted mRNA targets of the modulated miRNAs, providing relevant data for a further validation to better understand the role of these small molecules in the larval stages and their valuein clinical diagnostics.

A putative lysozyme and serine carboxypeptidase from Heterorhabditis bacteriophora show differential virulence capacities in Drosophila melanogaster

Nematode virulence factors are of interest for a variety of applications including biocontrol against insect pests and the alleviation of autoimmune diseases with nematode-derived factors. In silico "omics" techniques have generated a wealth of candidate factors that may be important in the establishment of nematode infections, although the challenge of characterizing these individual factors in vivo remains. Here we provide a fundamental characterization of a putative lysozyme and serine carboxypeptidase from the host-induced transcriptome of Heterorhabditis bacteriophora. Both factors accelerated the mortality rate following Drosophila melanogaster infections with Photorhabdus luminescens, and both factors suppressed phenoloxidase activity in D. melanogaster hemolymph. Furthermore, the serine carboxypeptidase was lethal to a subpopulation of flies and suppressed the upregulation of antimicrobial peptides as well as phagocytosis. Together, our findings suggest that this serine carboxypeptidase possess both toxic and immunomodulatory properties while the lysozyme is likely to confer immunomodulatory, but not toxic effects.

Helminth secretomes reflect different lifestyles and parasitized hosts

Helminths cause a number of medical and agricultural problems and are a major cause of parasitic infections in humans, animals and plants. Comparative analysis of helminth genes and genomes are important to understand the genomic biodiversity and evolution of parasites and their hosts in terms of different selective pressures in their habitats. The interactions between the infective organisms and their hosts are mediated in large part by secreted proteins, known collectively as the "secretome". Proteins secreted by parasites are able to modify a host's environment and modulate their immune system. The composition and function of this set of proteins varies depending on the ecology, lifestyle and environment of an organism. The present study aimed to predict, in silico, the secretome in 44 helminth species including Nematoda (31 species) and Platyhelminthes (13 species) and, understand the diversity and evolution of secretomes. Secretomes from plant helminths range from 7.6% (943 proteins) to 13.9% (2,077 proteins) of the filtered proteome with an average of 10.2% (1,412 proteins) and from free-living helminths range from 4.4% (870 proteins) to 13% (3,121 proteins) with an average of 9.8% (2,126 proteins), respectively, and thus are considerably larger secretomes in relation to animal helminth secretomes which range from 4.2% (431 proteins) to 11.8% (2,419 proteins) of the proteomes, with an average of 7.1% (804 proteins). Across 44 secretomes in different helminth species, we found five conserved domains: (i) PF00014 (Kunitz/Bovine pancreatic trypsin inhibitor domain), (ii) PF00046 (Homeobox domain), (iii) PF00188 (cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins), (iv) PF00085 (Thioredoxin) and (v) PF07679 (Immunoglobulin I-set domain). Our results detected secreted proteins associated with invasion, infection, adhesion and immunoregulation processes as protease inhibitors and cytokines, among other functions. In summary, this study will contribute towards the understanding of host-parasite interactions and possibly identify new molecular targets for the treatment or diagnosis of helminthiases.

Serine proteases of parasitic helminths

Serine proteases form one of the most important families of enzymes and perform significant functions in a broad range of biological processes, such as intra- and extracellular protein metabolism, digestion, blood coagulation, regulation of development, and fertilization. A number of serine proteases have been identified in parasitic helminths that have putative roles in parasite development and nutrition, host tissues and cell invasion, anticoagulation, and immune evasion. In this review, we described the serine proteases that have been identified in parasitic helminths, including nematodes (Trichinella spiralis, T. pseudospiralis, Trichuris muris, Anisakis simplex, Ascaris suum, Onchocerca volvulus, O. lienalis, Brugia malayi, Ancylostoma caninum, and Steinernema carpocapsae), cestodes (Spirometra mansoni, Echinococcus granulosus, and Schistocephalus solidus), and trematodes (Fasciola hepatica, F. gigantica, and Schistosoma mansoni). Moreover, the possible biological functions of these serine proteases in the endogenous biological phenomena of these parasites and in the host-parasite interaction were also discussed.

Isolation, identification and functional profile of excretory-secretory peptides from Onchocerca ochengi

Parasitic helminths excrete or secrete a variety of functional molecules into the internal milieu of their mammalian hosts and arthropod vectors which reveal distinct immunomodulatory and other biological activities. We identified and initially characterized the low molecular weight peptide composition of the secretome from the filarial parasite Onchocerca ochengi. A total of 85 peptides were purified by liquid chromatography and further characterized by mass spectrometry. 72 of these peptides were derived from already described Onchocerca proteins and 13 peptide sequences are included in the sequence of uncharacterized proteins. Three peptides, similar to host defense peptides, revealed antibacterial activity. The present analysis confirms the putative involvement of low molecular weight compounds in the parasite-host cross-talk.

Proteinases in excretory-secretory products of Toxocara canis second-stage larvae: zymography and modeling insights

Components released in excretory-secretory products of Toxocara canis larvae (TES) include phosphatidylethanolamine-binding proteins (TES26), mucins (TES120, MUC2-5), and C-type lectins (TES32, TES70) and their biochemical, immunological, and diagnostic properties have been extensively studied albeit proteinase activities towards physiological substrates are almost unknown. Proteolytic activities in TES samples were first analyzed by gel electrophoresis with gelatin as substrate. Major activities of ~400, 120, and 32 kDa in TES were relatively similar over a broad pH range (5.5–9.0) and all these were of the serine-type as leupeptin abolished gelatinolysis. Further, the ~400 kDa component degraded all physiological substrates tested (laminin, fibronectin, albumin, and goat IgG) and the 120 kDa component degraded albumin and goat IgG while proteinases of lower MW (45, 32, and 26 kDa) only degraded laminin and fibronectin, preferentially at alkaline pH (9.0). By protein modeling approaches using the known sequences of TES components, only TES26 and MUC4 displayed folding patterns significantly related to reference serine proteinases. These data suggest that most of serine proteinase activities secreted in vitro by infective larvae of T. canis have intriguing nature but otherwise help the parasite to affect multiple components of somatic organs and bodily fluids within the infected host.

An antigenic recombinant serine protease from Trichinella spiralis induces protective immunity in BALB/c mice

In this study, we report the cloning and characterization of a cDNA encoding a Trichinella serine protease gene (TspSP-1.3) from GenBank. The recombinant TspSP-1.3 protein (rTspSP-1.3) was expressed in an Escherichia coli expression system and purified with Ni-affinity chromatography. Real-time quantitative PCR analysis revealed that TspSP-1.3 was expressed at significantly higher levels in muscle larvae and adult worms than in newborn larvae. TspSP-1.3 was detected in excretory-secretory proteins of Trichinella spiralis with western blotting. Immunization with the rTspSP-1.3 antigen induced humoral immune responses, which manifested as elevated specific anti-rTspSP-1.3 IgG and IgE antibodies and a mixed Th1/Th2 response. To determine whether purified rTspSP-1.3 had good antigenicity and could be a vaccine candidate for the control of T. spiralis infection, we immunized BALB/c mice with rTspSP-1.3 and subsequently challenged the mice with T. spiralis larvae. The results showed that mice vaccinated with rTspSP-1.3 exhibited an average reduction in the muscle larvae burden of 39 % relative to the control group. These results suggest that TspSP-1.3 could be a novel vaccine candidate for controlling Trichinella infection.

Screening of different classes of proteases in microfilarial and adult stages of Setaria cervi

Many of the filarial proteases involved in critical physiological functions are expressed in stage-specific manner and belong to various mechanistic classes. Setaria cervi, a bovine filarial parasite express different classes of proteases. This parasite shows strong antigenic cross-reactivity with human filarial parasites Wuchereria bancrofti and Brugia malayi. Somatic extracts of S. cervi microfilariae (mf) and adult stages as well as their excretory-secretory (ES) products were screened for the presence of different classes of proteases using general (casein, bovine hemoglobin) and class specific substrates. Detergent-soluble extracts of male and female worms were also screened. Significant enzyme activity was detected in ES products both at pH 5.0 and 7.0 with casein. Cathepsin B-like activity was found to be much higher in membrane-bound extract than in the crude-soluble extract. However, it was also found to be actively secreted by both mf and adult worms. Cathepsin D-like activity assayed at pH 3.0 was very low both in somatic extract as well as in ES products. Collagenase activity at neutral pH showed higher levels, both in somatic extract and ES products. Cathepsin L-like activity was detected only in crude-soluble extract but was below detectable limit in ES products. Leucine aminopeptidase activity was significant both in crude-soluble extract and ES products. This study, thus, might be helpful for a better understanding of host-parasite interaction and identification of appropriate virulence factors that may be targeted as vaccine and/or drug targets against lymphatic filariasis.

Identification and characterization of onchoastacin, an astacin-like metalloproteinase from the filaria Onchocerca volvulus

The tissue-invasive nematode Onchocerca volvulus causes skin and eye pathology in human onchocerciasis. While the adult females reside sessile in subcutaneous nodules, the microfilariae are abundantly released from the nodules, males and juvenile worms migrate through the host tissue. Matrix-degrading metallo- and serine proteinases have been detected in excretory-secretory worm products that may be essential for migration of the mobile stages. In this study, a 1713bp long cDNA encoding for a putative proteinase of O. volvulus has been isolated. The predicted protein sequence includes a signal peptide indicating secretion to the extracellular space, a propeptide, an astacin-like protease domain, an EGF-like and a CUB-domain, thereby identifying the protein as a member of the astacin family of zinc endopeptidases. Onchoastacin, Ov-AST-1, is most closely related to a subfamily comprising nematode astacins including Caenorhabditis and Ancylostoma. Ov-AST-1 was expressed as a recombinant protein in baculovirus-infected insect cells and exhibited enzymatic activity. The exposure of onchoastacin to the host immune system is indicated by demonstration of IgG reacting with the recombinant Ov-AST-1 and with two peptides of the protein. Since a homologous metalloproteinase is part of a promising hookworm vaccine, Ov-AST-1 may be a candidate for intervention strategies in filarial infections.

Proteolytic activity in Caenorhabditis elegans : soluble and insoluble fractions

Proteolytic activities of soluble and insoluble fractions of the free-living soil nematode Caenorhabditis elegans were measured across a range of substrates, temperatures and pH conditions. Several protease inhibitors were also tested under these conditions. Results of these studies indicate that proteolytic activity is present in cytosolic (CF) and non-cytosolic (NCF) fractions of C. elegans extracts at every condition of pH, temperature and buffer assayed. On the other hand, the use of different protease inhibitors demonstrated the existence of exo and endoproteases types in CF as well as NCF. Moreover our results show that the use of two protease inhibitor mixed types proposed by several authors are not enough to avoid this lytic activity when homogenates of this nematode are employed in biochemical assays.

Characterization of a Novel Filarial Serine Protease Inhibitor, Ov-SPI-1, from Onchocerca volvulus, with Potential Multifunctional Roles during Development of the Parasite

A novel filarial serine protease inhibitor (SPI) from the human parasitic nematode Onchocerca volvulus, Ov-SPI-1, was identified through the analysis of a molting third-stage larvae expressed sequence tag dataset. Subsequent analysis of the expressed sequence tag datasets of O. volvulus and other filariae identified four other members of this family. These proteins are related to the low molecular weight SPIs originally isolated from Ascaris suum where they are believed to protect the parasite from host intestinal proteases. The two Ov-spi transcripts are up-regulated in the molting larvae and adult stages of the development of the parasite. Recombinant Ov-SPI-1 is an active inhibitor of serine proteases, specifically elastase, chymotrypsin, and cathepsin G. Immunolocalization of the Ov-SPI proteins demonstrates that the endogenous proteins are localized to the basal layer of the cuticle of third-stage, molting third-stage, and fourth-stage larvae, the body channels and multivesicular bodies of third-stage larvae and the processed material found between the two cuticles during molting. In O. volvulus adult worms the Ov-SPI proteins are localized to the sperm and to eggshells surrounding the developing embryos. RNA interference targeting the Ov-spi genes resulted in the specific knockdown of the transcript levels of both Ov-spi-1 and Ov-spi-2, a loss of native proteins, and a significant reduction in both molting and viability of third-stage larvae. We suggest the Ov-SPI proteins play a vital role in nematode molting by controlling the activity of an endogenous serine protease(s). The localization data in adults also indicate that these inhibitors may be involved in other processes such as embryogenesis and spermatogenesis.

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.

Proteolytic enzymes secreted by larval stage of the parasitic nematode Trichinella spiralis

Excretory/secretory products (ES), collected from in vitro cultures of muscle larvae (L1) of Trichinella spiralis (Owen, 1835) were examined for the presence of proteolytic enzymes. Several discrete proteinases in the size range of 25-55 kDa were identified by substrate gel electrophoresis and were characterised according to pH optima, substrate specificity and inhibitor sensitivity using azocasein assay. Serine, cysteine and metalloproteinases active at pH 5-7 were identified. The serine proteinases were found to predominate and some of them were found to be specific for the larval stage of the parasite. The results from the substrate analysis indicated the presence of collagenolytic and elastolytic activities. The proteinase activity was inhibited by IgG isolated from T. spiralis-infected mice, an observation of relevance to understanding host/parasite interactions and, ultimately, the development of anti-Trichinella vaccine.

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.

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.

Characterization of intestinally active proteinases of cyst-nematodes

Cryostat sections of juvenile and adult female stages of the soybean cyst-nematode, Heterodera glycines, were incubated with 4 different naphthylamide-linked peptide substrates to localize and characterize proteinase activity within the animal. Detected activity was restricted to the intestine and 2 distinct classes of proteinase were identified on the basis of substrate specificity and sensitivity to plant proteinase inhibitors. A cathepsin L-like cysteine proteinase activity capable of hydrolysing the synthetic substrates Z-Ala-Arg-Arg-MNA and Z-Phe-Arg-MNA but not Z-Arg-Arg-MNA or L-Arg-NA was inhibited by an engineered variant of a cysteine proteinase inhibitor from rice (Oc-I delta D86). The cleavage of Z-Phe-Arg-MNA was sensitive to inhibition by a combination of Oc-I delta D86 and cowpea trypsin inhibitor (CpTI). Degenerate oligonucleotide primers were used to amplify fragments of cysteine proteinase genes from 2 cyst-nematodes, H. glycines and Globodera pallida. Comparison of the H. glycines fragment with known genes established highest homology to cathepsin L-like genes. In contrast, the amplified G. pallida fragment displayed greatest homology to cathepsin B-like genes from Caenorhabditis elegans.

Purification and preliminary characterization of a protease from the excretion-secretion products of Trichinella spiralis muscle-stage larvae

A protease from excretion-secretion products of Trichinella spiralis muscle-stage larvae was purified by continuous elution electrophoresis. The state of purification was analyzed electrophoretically using one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified enzyme was shown to be a single polypeptide with an estimated molecular mass of 35 kDa and isoelectric point of 6.2. Following purification, the enzyme activity was measured by hydrolysis of gelatin, azocoll, azoalbumin, azocasein and collagen as substrates. Maximal azocollytic activity was at pH 5 and a temperature of 37 degrees C. Finally, the proteolytic activity was partially inhibited by N-alpha-p-tosyl-lysine chloromethyl ketone, chymostatin and E-64.

Mechanisms of resistance to Onchocerca infection in blackflies

In this article Peter Ham, Hans Hagen, Andrea Baxter and Jorg Grunewald focus on the susceptibility of blackflies to parasitic filarial infection (particularly Onchocera spp, most of the vectors of which belong to the genus Simulium). They outline what is known about, as well as speculating on, the various defence mechanisms of these insects. Investigations have involved the use of natural and surrogate vectors of bovine onchocerciasis as models for the human vector-parasite relationship.

Partial characterization of proteolytic enzymes in different developmental stages of Ostertagia ostertagi

Proteolytic enzymes present in extracts of third (L3) and fourth (L4) stage larvae and adults of the cattle nematode Ostertagia ostertagi were defined on the basis of pH optima and proteinase inhibitor sensitivity in spectrophotometric assays using azocasein and elastin-orcein as protein substrates. Evidence that different classes of proteinases are expressed in a stage specific manner was provided by the contrasting pH optima and inhibitor sensitivities shown by the enzymes in the different parasite stages. Stage specificity was confirmed by gelatin-substrate analysis. In addition, proteolytic activity was sought in the excretory/secretory products (ES) of the L4 following simple in vitro culture. Contrasting pH and inhibitor sensitivities as well as gelatin-substrate analysis showed that different proteinases were present in somatic L4 extracts and L4 ES products. The secreted proteinases may be useful targets for serodiagnosis or vaccination.

Proteolytic enzymes from Trichinella spiralis larvae

Trichinella spiralis larvae infect their hosts by the penetration of small intestine enterocytes. The exact mechanism of penetration is unknown, but the presence of proteolytic enzymes is suspected. In this study, whole worm extracts and excretory-secretory (ES) components were obtained and their proteolytic enzymes examined. Enzymes from worm extracts were capable of hydrolysing azocoll, a general protease substrate in a wide range of pH (2-8), with maximal activity at pH 5. Trichinella spiralis larval enzymes were sensitive to metalloprotease and serine protease inhibitors. Three proteases were identified in worm extracts at molecular weight (MW) 48, 54 and 62 kDa by incorporating a gelatine substrate into a standard or a modified sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) set-up, in which we used low SDS concentration in gel and electrophoresis buffer (0.01%). Intact larvae incubated in a medium containing azocoll showed azocollytic activity. Subsequent analysis of ES products by modified SDS-PAGE in gels containing gelatine demonstrated the presence of three protease of apparent MW 33, 62 and 230 kDa.

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.

Characterization of proteolytic enzymes from larval and adult Nippostrongylus brasiliensis

Proteases from infective larval (L3) and adult stages of Nippostrongylus brasiliensis were investigated with a combination of techniques involving gelatin degradation and cleavage of fluorogenic substrates. Analysis of L3 excretory-secretory (ES) products revealed enzymes of Mr 51, 58, 79, approximately 150 and approximately 250 kDa. Inhibition profiles indicate that the major 51 kDa protease is a metallo-enzyme. Significantly, little activity was present in larval somatic extracts, suggesting the synthesis of zymogens or precursor forms prior to secretion. Adult ES contained a distinct enzyme, of 50 kDa, and a number of other proteases were detected in somatic extracts of this stage, ranging from 51 to greater than 300 kDa. The largest of these adult somatic enzymes is also a putative metallo-protease. While nearly all enzymes from both L3 and adult are heat labile, incubation at 100 degrees C generated a previously unobserved activity at 20 kDa. Furthermore, a protease of similar size may be found in uninfected rat intestinal tissue, suggesting specific uptake of a host-associated enzyme by the parasite in the form of an inactive, heat-labile complex.

Acanthocheilonema viteae: vaccination of jirds with irradiation-attenuated stage-3 larvae and with exported larval antigens

Jirds (Meriones unguiculatus) were immunized with irradiated (35 krad) stage-3 larvae (L3) of Acanthocheilonema viteae. The induced resistance against homologous challenge infection and the antibody response of the animals were studied. Immunization with 3, 2, or 1 dose of 50 irradiated L3 induced approximately 90% resistance. Immunization with a single dose of only 5 irradiated L3 resulted in 60.8% protection while immunization with a single dose of 25 L3 induced 94.1% protection. The protection induced with 3 doses of 50 irradiated L3 did not decrease significantly during a period of 6 months. Sera of a proportion, but not all resistant jirds, contained antibodies against the surface of vector derived L3 as defined by IFAT. No surface antigens of microfilariae or adult worms were recognized by the sera. Vaccinated animals had antibody responses against antigens in the inner organs of L3 and in the cuticle and reproductive organs of adult worms as shown by IFAT. Immunoblotting with SDS-PAGE-separated L3 antigens and L3-CSN revealed that all sera contained antibodies against two exported antigens of 205 and 68 kDa, and against a nonexported antigen of 18 kDa. The 205-kDa antigen easily degraded into fragments of 165, 140, 125, and 105 kDa which were recognized by resistant jird sera. Various antigens of adult worms, but relatively few antigens of microfilariae, were also recognized. To test the relevance of exported antigens of L3 to resistance, jirds were immunized with L3-CSN together with a mild adjuvant. This immunization induced 67.7% resistance against challenge infection and sera of the immunized animals recognized the 205- and 68-kDa antigens of L3.

Morphological demonstration of essential functional changes after in vitro and in vivo transition of infective Onchocerca volvulus to the post-infective stage

Transmission electron microscopic investigation of the morphogenesis of Onchocerca volvulus through the third moult to the post-infective stage revealed essential alterations in various larval organs. Complete rebuilding of surface structures, the reduction of secretory granules in the glandular oesophagus, the unfolding of the intestine, an increase in the number of nerve fibres in the nerve ring and novel sensory papillae were significant findings. Transition from third- to fourth-stage larvae (L4) started as early as 48 h after transfer to vertebrate conditions in vivo in surrogate hosts and in vitro. After a resting period of about 60 h to enable a reduction in gland size and the loosening of the old cuticle and formation of the new one, the larvae started to cast the infective-stage cuticle. Young L4 exhibited a thin, monolayered cuticle and did not rebuild a glandular oesophagus. The body cavity widened, the intestine unfolded and the increased number of microvilli indicated the resumption of metabolic activity.

Anisakis — from the platter to the microfuge

Anisakiasis is a disease caused by the ingestion of anisakid nematodes in raw or improperly prepared fish dishes. Invading larvae penetrate the mucosa and submucosa of the gastrointestinal tract and produce lesions characterized by a marked inflammatory response. Judy Sakanari describes the biochemical and molecular studies on the proteins excreted and/or secreted by Anisakis larvae that are currently underway to help elucidate the role these proteins may play in the invasion process and the pathogenesis of anisakiasis.

Strongyloides stercoralis: identification of a protease that facilitates penetration of skin by the infective larvae

Host invasion and tissue migration of several helminths have been linked to the expression and release of parasite-derived proteases. One of the most remarkable examples of tissue migration is that of larvae of the nematode parasite Strongyloides stercoralis, which can move through tissue at speeds of up to 10 cm per hour. We have shown the Strongyloides L3 larvae secrete a potent histolytic metalloprotease to facilitate their rapid migration. This protease has elastase activity and catalyzes the degradation of a model of dermal extracellular matrix. The importance of this enzyme in the pathogenesis of strongyloidiasis is underscored by the observation that invasion by larvae of skin in vitro is prevented by metalloprotease inhibitors. These results substantiate the role of proteases as virulence factors in strongyloidiasis, as well as other related parasitic infections, and suggest new approaches to therapy.