Molecular characterization and expression of two putative protective excretory secretory proteins of Haemonchus contortus

Divergent humoral responses between males and females against 24 kDa excretory-secretory protein of Haemonchus contortus and influence of ovine β-globin polymorphism

Lambs harboring the Hb-AA β-globin haplotype present improved cell-mediated responses and increased resistance against Haemonchus contortus infection. The aim of the present study was to compare the effect of sex and β-globin haplotypes on specific humoral responses and phenotypes of resistance during H. contortus infection in Morada Nova sheep. As expected, females displayed stronger resistance during the first and second experimental challenges. Differential systemic humoral immune responses were observed comparing sex groups, in which higher levels of specific antibodies targeting 24 kDa excretory-secretory (ES24) protein of H. contortus of IgG and IgM antibodies were respectively observed as predominant isotypes in males and females. The IgM levels were significantly correlated with phenotypes of resistance, evaluated by packed cell volume and fecal egg counts. To our knowledge this is the first study reporting divergent humoral responses profiles to H. contortus infection between male and female sheep. The impact of β-globin haplotypes was less pronounced in females compared to males. Notably, only males showed significant weight differences across haplotypes, with Hb-AA lambs being the heaviest. Additionally, Hb-AA males had significantly higher PCV (indicating better red blood cell health) and lower FEC (indicating lower parasite burden). These findings suggest a more pronounced effect of β-globin polymorphisms on H. contortus infection in males, potentially due to their generally weaker resistance compared to females. This study highlights the importance of sex and β-globin haplotypes in shaping immune responses to H. contortus infection. Specifically, IgM antibodies targeting the ES24 protein appear to play a crucial role in host-parasite interactions and may hold promise for therapeutic development.

Excreted/Secreted 15-kDa Proteins and Serine Protease Peptides from Haemonchus contortus Act as Immune-Response Enhancers in Lambs

This study assessed the immunoprotective effect in lambs of a native excreted/secreted 15-kDa protein and two synthesised S28 peptides derived from the infective transitory larvae (xL3) and adult stages (AS) of Haemonchus contortus. Twenty-two Pelibuey lambs were divided into negative and positive control groups, as well as immunised lamb groups, with 100 µg of the 15-kDa native protein (15kDaNP) and S28 peptides (S28P). The eggs per gram (EPG) and haematocrit were measured, and AS were counted and morphologically measured. To assess the immunoprotection in lambs, indirect enzyme-linked immunosorbent assays and relative expression analyses of immune cytokines were performed using serum and abomasal samples. Our results showed a 72.28% reduction in adult worms (AW) in the 15kDaNP-immunised group, achieving a high clinical response with 41% haematocrit and low EPG values (436 ± 661). Conversely, the S28P group achieved the highest IgG levels (2.125 ± 0.880 OD), with AW exhibiting the greatest body length (p > 0.05) and upregulation of the IL5 and FCεR1A genes associated with nematode control. The 15kDaNP group showed increased expression of genes related to nematode control and anti-inflammatory responses, including IL4, IL5, IL6, and IL13 (p < 0.05). The S28P and 15kDaNP should be explored as potential vaccines against sheep haemonchosis.

A variant of the venom allergen-like protein, DdVAP2, is required for the migratory endoparasitic plant nematode Ditylenchus destructor parasitism of plants

The potato rot nematode, Ditylenchus destructor, poses a serious threat to numerous root and tuber crops, yet the functional characterization of effectors from this migratory endoparasitic plant nematode remains limited. Despite inhabiting distinct habitats, sedentary and migratory plant parasitic nematodes share the structurally conserved effectors, such as venom allergen-like proteins (VAPs). In this study, a variant of DdVAP2 was cloned from D. destructor. The transcription profile analysis revealed that DdVAP2 was higher expressed in D. destructor feeding on either potato or sweet potato compared to on fungus via qRT-PCR. And DdVAP2 was highly expressed at all life stages feeding on sweet potato, except for eggs. DdVAP2 was confirmed to be specifically expressed in the subventral esophageal glands of D. destructor through in situ hybridization assays. Combined with functional validation of the signal peptide of DdVAP2, it suggested that DdVAP2 could be secreted from nematode into host. Heterologous expression of DdVAP2 in Nicotiana benthamiana revealed that the protein localized in both cytosol and nuclei of plant cells. Knocking down DdVAP2 by RNAi in D. destructor resulted in infection and reproduction defects on plants. All the results suggest that DdVAP2 plays a crucial role in the interaction between D. destructor and plants by facilitating the nematode infection.

A Venom Allergen-Like Protein, RsVAP, the First Discovered Effector Protein of Radopholus similis That Inhibits Plant Defense and Facilitates Parasitism

Radopholus similis is a migratory endoparasitic nematode that is extremely harmful to host plants. Venom allergen-like proteins (VAPs) are members of the cysteine-rich secretory protein family that are widely present in plants and animals. In this study, we cloned a VAP gene from R. similis, designated as RsVAP. RsVAP contains an open reading frame of 1089 bp encoding 362 amino acids. RsVAP is specifically expressed in the esophageal gland, and the expression levels of RsVAP are significantly higher in juveniles than in other life stages of R. similis. This expression pattern of RsVAP was consistent with the biological characteristics of juveniles of R. similis, which have the ability of infection and are the main infection stages of R. similis. The pathogenicity and reproduction rate of R. similis in tomato was significantly attenuated after RsVAP was silenced. In tobacco leaves transiently expressing RsVAP, the pathogen-associated molecular pattern-triggered immunity (PTI) induced by a bacterial flagellin fragment (flg22) was inhibited, while the cell death induced by two sets of immune elicitors (BAX and Gpa2/RBP-1) was repressed. The RsVAP-interacting, ras-related protein RABA1d (LeRabA1d) was identified in tomato hosts by yeast two-hybrid and co-immunoprecipitation assays. RsVAP may interact with LeRabA1d to affect the host defense response, which in turn facilitates nematode infection. This study provides the first evidence for the inhibition of plant defense response by a VAP from migratory plant-parasitic nematodes, and, for the first time, the target protein of R. similis in its host was identified.

The immunogenic maturation of goat monocyte-derived dendritic cells and upregulation of toll-like receptors by five antigens of Haemonchus contortus in-vitro

Previously, it was found that several proteins of Haemonchus contortus were involved in the stimulation of the host immune system. However, the information about the selection of superlative antigens with immunogenic efficacies on host DCs is lacking. In the current study, the stimulatory effects of five recombinant proteins (elongation factor-1α, arginine kinase, ES-15, ES-24, and ADP-ribosylation factor 1) of H. contortus on the maturation of goat monocyte-derived dendritic cells (md-DCs) were reported. Recombinant proteins were purified separately in E. coli expression and incubated with isolated goat peripheral blood mononuclear cells (PBMC). Immunofluorescence assay (IFA) results confirmed the binding of these molecules to the md-DC's surface as compared to control groups. In the flow cytometry analysis, recombinant proteins induced md-DC stimulation via the up-regulation of the expression of the costimulatory molecule (CD80) and MHC-II. Quantitative RT-PCR data showed a significant increase in the expression of specific genes of the WNT and toll-like receptor (TLR) signaling pathways. The result of ELISA indicated the higher levels of cytokine (IL-10, IL-12, IFN-γ, and TNF-α) secretion in the md-DC compared to the negative (pET-32a His-Tag) and blank (PBS) control groups. The data gives valuable support in the selection of potential antigens for future studies on the immunomodulation of the host against the infection of H. contortus.

Characterization of Haemonchus contortus Excretory/Secretory Antigen (ES-15) and Its Modulatory Functions on Goat Immune Cells In Vitro

Small size excretory/secretory (ES) antigens of the Haemonchus contortus parasite have intense interest among researchers for understanding the molecular basis of helminths immune regulation in term of control strategies. Immunomodulatory roles of H. contortus ES-15 kDa (HcES-15) on host immune cells during host–parasite interactions are unknown. In this study, the HcES-15 gene was cloned and expression of recombinant protein (rHcES-15) was induced by isopropyl-ß-d-thiogalactopyranoside (IPTG). Binding activity of rHcES-15 to goat peripheral blood mononuclear cells (PBMCs) was confirmed by immunofluorescence assay (IFA) and immunohistochemical analysis showed that H. contortus 15 kDa protein localized in the outer and inner structure of the adult worm, clearly indicated as the parasite’s ES antigen. The immunoregulatory role on cytokines production, cell proliferation, cell migration, nitric oxide (NO) production, apoptosis, and phagocytosis were observed by co-incubation of rHcES-15 with goat PBMCs. The results showed that cytokines IL-4, IL-10, IL-17, the production of nitric oxide (NO), PBMCs apoptosis, and monocytes phagocytosis were all elevated after cells incubated with rHcES-15 at differential protein concentrations. We also found that IFN-γ, TGF-β1, cells proliferation and migration were significantly suppressed with the interaction of rHcES-15 protein. Our findings indicated that low molecular ES antigens of H. contortus possessed discrete immunoregulatory roles, which will help to understand the mechanisms involved in immune evasion by the parasite during host–parasite interactions.

HcTTR: a novel antagonist against goat interleukin 4 derived from the excretory and secretory products of Haemonchus contortus

Haemonchus contortus (H. contortus) has evolved sophisticated evasion mechanisms to ensure their survival, including generating excretion and secretion products (ESPs) to regulate the secretion of host cytokines. Interleukin 4 (IL4) is a classic T-helper cell type 2 (Th2)-type cytokine that plays an irreplaceable role against nematode infection. In this study, three proteins, glutathione S-transferase domain containing protein (HcGST), transthyretin domain containing protein (HcTTR) and calponin actin-binding domain containing protein (HcCab), were identified to bind to goat IL4 by co-immunoprecipitation (Co-IP) assays and yeast two-hybrid screening. Additionally, cell proliferation analysis showed that HcTTR blocked the IL4-induced proliferation of peripheral blood mononuclear cells in goats, while HcGST and HcCab did not. In addition, HcTTR could also downregulate the transcription of candidate genes in the IL4-induced JAK/STAT pathway. These results indicated that HcTTR is a novel antagonist against goat IL4 from HcESPs, and this information could improve our understanding of the relationship between host cytokines and parasite infections.

Recombinant Haemonchus contortus 24 kDa excretory/secretory protein (rHcES-24) modulate the immune functions of goat PBMCs in vitro

A 24 kDa protein is one of the important components in Haemonchus contortus (barber pole worm) excretory/secretory products (HcESPs), which was shown to have important antigenic function. However, little is known about the immunomodulatory effects of this proteinon host cell. In the present study gene encoding 24kDa excretory/secretory protein (HcES-24) was cloned. The recombinant protein of HcES-24 (rHcES-24) was expressed in a histidine-tagged fusion protein soluble form in Escherichia coli. Binding activity of rHcES-24 to goat PBMCs was confirmed by immunofluorescence assay (IFA) and its immunomudulatory effect on cytokine secretion, cell proliferation, cell migration and nitric oxide production were observed by co-incubation of rHcES-24. IFA results revealed that rHcES-24 could bind to the PBMCs. The interaction of rHcES-24 increased the production of IL4, IL10, IL17 and cell migration in dose dependent manner. However, rHcES-24 treatment significantly suppressed the production of IFNγ, proliferation of the PBMC and Nitric oxide (NO) production. Our findings showed that the rHcES-24 played important regulatory effects on the goat PBMCs.

Progress in the development of subunit vaccines for gastrointestinal nematodes of ruminants

The global increase in anthelmintic resistant nematodes of ruminants, together with consumer concerns about chemicals in food, necessitates the development of alternative methods of control for these pathogens. Subunit recombinant vaccines are ideally placed to fill this gap. Indeed, they are probably the only valid option for the long-term control of ruminant parasitic nematodes given the increasing ubiquity of multidrug resistance in a range of worm species across the world. The development of a subunit multicellular parasite vaccine to the point of practical application would be a groundbreaking step in the control of these important endemic infections of livestock. This review summarizes the current status of subunit vaccine development for a number of important gastrointestinal nematodes of cattle and sheep, with a focus on the limitations and problems encountered thus far, and suggestions as to how these hurdles might be overcome.

Stage and tissue expression patterns of Schistosoma mansoni venom allergen-like proteins SmVAL 4, 13, 16 and 24

Background

Schistosoma mansoni venom allergen-like protein (SmVAL) is a gene family composed of 29 members divided into group 1 encoding proteins potentially secreted, and group 2 encoding intracellular components. Some members were found to be upregulated in the transition of germ ball - cercariae - day 3 schistosomula, suggesting that group 1 SmVAL proteins are associated with the invasion of the human host, although their functions are not completely established. Recently, we have described the localization of SmVAL7 (group 1) and SmVAL6 (group 2) transcripts in the oesophageal gland and in the oral and ventral suckers of adult parasites, respectively. The expression patterns of the two genes suggest that SmVAL7 protein plays a role in the blood-feeding process while SmVAL6 is associated with the parasite attachment and movement in the vasculature. In this way, searching for additional secreted SmVAL proteins that could be involved in key processes from skin penetration to the beginning of blood-feeding, we investigated the tissue localization of SmVAL4, 13, 16 and 24 by whole-mount in situ hybridization (WISH).

Results

We report here the localization of group 1 SmVAL4 and 24 transcripts in the pre-acetabular glands of developing germ balls. Time course experiments of in vitro cultured schistosomula after cercariae transformation demonstrated that SmVAL4 protein is secreted during the first 3 h of in vitro culture, correlating with the emptying of acetabular glands as documented by confocal microscopy. In addition, the localization of SmVAL13 transcripts in adult male anterior oesophageal gland suggests that the respective protein may be involved in the first steps of the blood-feeding process. SmVAL16 was localized close to the neural ganglia and requires further investigation.

Conclusions

Our findings demonstrate that SmVAL proteins have localizations that place them in strategic positions to be considered as potential vaccine candidates as some members are exposed to interaction with the immune system and may participate in key processes of mammalian invasion and parasitism establishment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2144-2) contains supplementary material, which is available to authorized users.

Immunity to Haemonchus contortus and Vaccine Development

Sheep are capable of developing protective immunity to Haemonchus contortus through repeated exposure to this parasite, although this immune protection is the result of a complex interaction among age, gender, physiological status, pregnancy, lactation, nutrition and innate and adaptive immunity in the host animal. There are multiple effectors of the protective immune response, which differ depending on the developmental stage of the parasite being targeted, and our understanding of the effector mechanisms has developed considerably in the 2000s. The rational design of vaccines based on 'natural' or 'exposed' antigens depends on an understanding of this exposure-induced immunity. However, the most effective current vaccines rely on protection via the induction of high circulating antibody levels to 'hidden' gut antigens of H. contortus. The success of this latter strategy has resulted in the launch of a vaccine, which is based on extracts of the parasite's gut, to aid in the control of Haemonchus in Australia. The development of recombinant subunit vaccines based on the components of the successful native vaccine has not yet been achieved and most of the recent successes with recombinant subunit vaccines have focussed on antigens unrelated to the gut antigens. The future integration of an understanding of the immunobiology of this parasite with advances in antigen identification, expression (or synthesis) and presentation is likely to be pivotal to the further development of these recombinant subunit vaccines. Recent progress in each of the components underpinning this integrated approach is summarized in this review.

A preliminary proteomic characterisation of extracellular vesicles released by the ovine parasitic nematode, Teladorsagia circumcincta

Teladorsagia circumcincta is a major cause of ovine parasitic gastroenteritis in temperate climatic regions. The development of high levels of anthelmintic resistance in this nematode species challenges its future control. Recent research indicates that many parasite species release extracellular vesicles into their environment, many of which have been classified as endocytic in origin, termed exosomes. These vesicles are considered to play important roles in the intercellular communication between parasites and their hosts, and thus represent potentially useful targets for novel control strategies. Here, we demonstrate that exosome-like extracellular vesicles can be isolated from excretory-secretory (ES) products released by T. circumcincta fourth stage larvae (Tci-L4ES). Furthermore, we perform a comparative proteomic analysis of vesicle-enriched and vesicle-free Tci-L4ES. Approximately 73% of the proteins identified in the vesicle-enriched fraction were unique to this fraction, whilst the remaining 27% were present in both vesicle-enriched and vesicle-free fraction. These unique proteins included structural proteins, nuclear proteins, metabolic proteins, proteolytic enzymes and activation-associated secreted proteins. Finally, we demonstrate that molecules present within the vesicles-enriched material are targets of the IgA and IgG response in T. circumcincta infected sheep, and could potentially represent useful targets for future vaccine intervention studies.

The barber's pole worm CAP protein superfamily--A basis for fundamental discovery and biotechnology advances

Parasitic worm proteins that belong to the cysteine-rich secretory proteins, antigen 5 and pathogenesis-related 1 (CAP) superfamily are proposed to play key roles in the infection process and the modulation of immune responses in host animals. However, there is limited information on these proteins for most socio-economically important worms. Here, we review the CAP protein superfamily of Haemonchus contortus (barber's pole worm), a highly significant parasitic roundworm (order Strongylida) of small ruminants. To do this, we mined genome and transcriptomic datasets, predicted and curated full-length amino acid sequences (n=45), undertook systematic phylogenetic analyses of these data and investigated transcription throughout the life cycle of H. contortus. We inferred functions for selected Caenorhabditis elegans orthologs (including vap-1, vap-2, scl-5 and lon-1) based on genetic networking and by integrating data and published information, and were able to infer that a subset of orthologs and their interaction partners play pivotal roles in growth and development via the insulin-like and/or the TGF-beta signalling pathways. The identification of the important and conserved growth regulator LON-1 led us to appraise the three-dimensional structure of this CAP protein by comparative modelling. This model revealed the presence of different topological moieties on the canonical fold of the CAP domain, which coincide with an overall charge separation as indicated by the electrostatic surface potential map. These observations suggest the existence of separate sites for effector binding and receptor interactions, and thus support the proposal that these worm molecules act in similar ways as venoms act as ligands for chemokine receptors or G protein-coupled receptor effectors. In conclusion, this review should guide future molecular studies of these molecules, and could support the development of novel interventions against haemonchosis.

Vaccination of lambs with the recombinant protein rHc23 elicits significant protection against Haemonchus contortus challenge

Gene encoding a somatic protein of Haemonchus contortus (Hc23) known to confer significant protection against experimental haemonchosis has been cloned and expressed in a prokaryotic system. A cDNA library of H. contortus using the vector λ ZAP II was obtained. Full-length gene was amplified, cloned and expressed in Escherichia coli BL21. The recombinant protein was purified in Ni-NTA column. Recombinant protein (rHc23) had 203 aminoacids and a molecular mass of 24.15 kDa. Recombinant protein (100 μg/dose) with aluminum hydroxide as adjuvant was administered to 5-6 months age female Assaf lambs on days -42, -28 and -14. On day 0 animals were infected with 15,000 L3 of H. contortus. Vaccination with rHc23 elicited a significant protection against challenge, with >80% reductions in both fecal egg counts and average abomasal parasite burdens at the end of the experiment (45 days post challenge) besides lack of variations in packed cell volume. Results support the feasibility of vaccination against lamb haemonchosis with a recombinant product from an exposed antigen.

Transcriptional profiling of the oesophageal gland region of male worms of Schistosoma mansoni

The intestinal tract of schistosomes opens at the mouth and leads into the foregut or oesophageal region that is lined with syncytium continuous with the apical cytoplasm of the tegument. The oesophagus is surrounded by a specialised gland, the oesophageal gland. This gland releases materials into the lumen of the oesophagus and the region is thought to initiate the lysis of erythrocytes and neutralisation of immune effectors of the host. The oesophageal region is present in the early invasive schistosomulum, a stage potentially targetable by anti-schistosome vaccines. We used a 44k oligonucleotide microarray to identify highly up-regulated genes in microdissected frozen sections of the oesophageal gland of male worms of S. mansoni. We show that 122 genes were up-regulated 2-fold or higher in the oesophageal gland compared with a whole male worm tissue control. The enriched genes included several associated with lipid metabolism and transmembrane transport as well as some micro-exon genes. Since the oesophageal gland is important in the initiation of digestion and the fact that it develops early after invasion of the mammalian host, further study of selected highly up-regulated functionally important genes in this tissue may reveal new anti-schistosome intervention targets for schistosomiasis control.

Immune responses associated with resistance to haemonchosis in sheep

This paper examines the known immunological and genetic factors associated with sheep resistance to infection by Haemonchus contortus. Such resistance is an inheritable genetic trait (h², 0.22–0.63) associated with certain sheep breeds. Resistant sheep do not completely reject the disease; they only harbor fewer parasites than susceptible sheep and therefore have a lower fecal egg count. Protective immune response to haemonchosis is an expression of genetic resistance. Genes associated with resistance and susceptibility are described. Genetically resistant sheep have nonspecific mechanisms that block the initial colonization by Haemonchus contortus larvae. These sheep also have an efficacious Th2 type response (e.g., increases in blood and tissue eosinophils, specific IgE class antibodies, mast cells, IL-5, IL-13, and TNFα) that protects them against the infection; in contrast, susceptible sheep do not efficiently establish this type of immune response. Finally, the main reported antigens of H. contortus were reviewed.

An analysis of the transcriptome of Teladorsagia circumcincta: its biological and biotechnological implications

BACKGROUND

Teladorsagia circumcincta (order Strongylida) is an economically important parasitic nematode of small ruminants (including sheep and goats) in temperate climatic regions of the world. Improved insights into the molecular biology of this parasite could underpin alternative methods required to control this and related parasites, in order to circumvent major problems associated with anthelmintic resistance. The aims of the present study were to define the transcriptome of the adult stage of T. circumcincta and to infer the main pathways linked to molecules known to be expressed in this nematode. Since sheep develop acquired immunity against T. circumcincta, there is some potential for the development of a vaccine against this parasite. Hence, we infer excretory/secretory molecules for T. circumcincta as possible immunogens and vaccine candidates.

RESULTS

A total of 407,357 ESTs were assembled yielding 39,852 putative gene sequences. Conceptual translation predicted 24,013 proteins, which were then subjected to detailed annotation which included pathway mapping of predicted proteins (including 112 excreted/secreted [ES] and 226 transmembrane peptides), domain analysis and GO annotation was carried out using InterProScan along with BLAST2GO. Further analysis was carried out for secretory signal peptides using SignalP and non-classical sec pathway using SecretomeP tools. For ES proteins, key pathways, including Fc epsilon RI, T cell receptor, and chemokine signalling as well as leukocyte transendothelial migration were inferred to be linked to immune responses, along with other pathways related to neurodegenerative diseases and infectious diseases, which warrant detailed future studies. KAAS could identify new and updated pathways like phagosome and protein processing in endoplasmic reticulum. Domain analysis for the assembled dataset revealed families of serine, cysteine and proteinase inhibitors which might represent targets for parasite intervention. InterProScan could identify GO terms pertaining to the extracellular region. Some of the important domain families identified included the SCP-like extracellular proteins which belong to the pathogenesis-related proteins (PRPs) superfamily along with C-type lectin, saposin-like proteins. The 'extracellular region' that corresponds to allergen V5/Tpx-1 related, considered important in parasite-host interactions, was also identified. Six cysteine motif (SXC1) proteins, transthyretin proteins, C-type lectins, activation-associated secreted proteins (ASPs), which could represent potential candidates for developing novel anthelmintics or vaccines were few other important findings. Of these, SXC1, protein kinase domain-containing protein, trypsin family protein, trypsin-like protease family member (TRY-1), putative major allergen and putative lipid binding protein were identified which have not been reported in the published T. circumcincta proteomics analysis. Detailed analysis of 6,058 raw EST sequences from dbEST revealed 315 putatively secreted proteins. Amongst them, C-type single domain activation associated secreted protein ASP3 precursor, activation-associated secreted proteins (ASP-like protein), cathepsin B-like cysteine protease, cathepsin L cysteine protease, cysteine protease, TransThyretin-Related and Venom-Allergen-like proteins were the key findings.

CONCLUSIONS

We have annotated a large dataset ESTs of T. circumcincta and undertaken detailed comparative bioinformatics analyses. The results provide a comprehensive insight into the molecular biology of this parasite and disease manifestation which provides potential focal point for future research. We identified a number of pathways responsible for immune response. This type of large-scale computational scanning could be coupled with proteomic and metabolomic studies of this parasite leading to novel therapeutic intervention and disease control strategies. We have also successfully affirmed the use of bioinformatics tools, for the study of ESTs, which could now serve as a benchmark for the development of new computational EST analysis pipelines.

Molecular cloning, expression, and characterization of a putative activation-associated secreted protein from Angiostrongylus cantonensis

Activation-associated secreted protein (ASP) had been found in many helminthes, which was associated with pathogenesis and stage transition. A complementary DNA (cDNA) sequence encoding a putative two-domain ASP was obtained from an Angiostrongylus cantonensis fourth-stage larvae cDNA library, which we designated as AgASP. The cDNA of AgASP contains an open reading frame encoding 424 amino acids, the first 19 residues being a putative secretion signal. The expression pattern of this protein was investigated by real-time polymerase chain reaction and Western blot. We found that this protein expressed most highly in the brain-stage larvae (Lbr) of this parasite and existed in the excretory/secretory products of this stage. Immunofluorescence showed it existed in the lumen of the Lbr. The recombinant protein can be recognized by the infection sera from mice (nonpermissive host), while it cannot be recognized by infection sera from rats (permissive host). The infiltration of neutrophils in infected nonpermissive host can be lessened by immunizing this host with this protein (immunized vs control group, 13.7 ± 10.2 vs 65.5 ± 19.2). These findings suggest that this protein plays a role in the pathogenesis of human angiostrongyliasis and is worthy of further study.

SCP/TAPS proteins in helminths--where to from now?

A diverse array of proteins belonging to the SCP/TAPS 'family' has been described for various eukaryotic organisms, including parasites. Although SCP/TAPS proteins have been hypothesized to play key roles in various fundamental biological processes, such as host-pathogen interactions and defence mechanisms, there is still a limited understanding of the precise roles of these proteins. Here, we review current knowledge of key SCP/TAPS proteins of helminths and their proposed roles in parasite-host interactions. Molecular investigations of these molecules in parasites and the integration of structural and functional data could lead to new and innovative approaches for the treatment and control of parasitic diseases, with important biotechnological outcomes.

Cloning and characterization of a venom allergen-like protein gene cluster from the pinewood nematode Bursaphelenchus xylophilus

Pinewood nematode (PWN) is the causal agent of the pine wilt disease. Previous studies have suggested that secretions from the esophageal glands of PWN play an important role in pathogenicity. A cluster of three venom allergen-like protein genes and one pseudogene, Bx-vap-1, Bx-vap-2, Bx-vap-3 and Bx-vap-P, were identified within a 3.7-kb region. Additionally, three putative modification, transport and regulatory protein genes were also detected in the same flanking region of the Bx-vap gene cluster. Genes vap-1, -2 and -3 are functional and encode three major allelic variants of PWN venom allergen-like proteins. But Bx-vap-P is an untranscribed pseudogene. Genes vap-1, -2 and -3 produce predicted products of 204, 206 and 203 amino acid residues, respectively, including the putative signal peptide sequence at the amino termini. In situ mRNA hybridization analysis showed that the transcripts of genes vap-1, -2 and -3 accumulated exclusively within the esophageal gland cells of Bursaphelenchus xylophilus.

A suite of genes expressed during transition to parasitic lifestyle in the trichostrongylid nematode Haemonchus contortus encode potentially secreted proteins conserved in Teladorsagia circumcincta

The control of gastro-intestinal nematodes remains largely based on anthelminthic treatments, however spreading of anthelmintic resistance has reduced their efficacy. The genes involved in the transition to parasitic lifestyle could constitute targets of interest to develop alternative control strategies. In the trichostrongylid nematode Haemonchus contortus, we have used a SSH (Suppressive Subtractive Hybridization) based approach to generate two distinct subtracted cDNA libraries specifically enriched in cDNA expressed during the early parasitic fourth stage larvae L4 (5 days post-infection). A total of 200 clones were subjected to dot-blot experiments and 46 clones were selected for further characterization. The 46 corresponding expressed sequence tags (EST) were found to cluster into nine contigs. The corresponding full-length cDNA was obtained for all candidates. The genes encoding potentially secreted proteins were investigated in more detail. RT-PCR experiments confirmed their specific expression or over expression from the early L4 larvae to the adult stages and search for homologs in the trichostrongylid species T. circumcincta was performed in order to investigate whether they may be novel cross-specific targets.

Immunization against Lamb Haemonchosis with a Recombinant Somatic Antigen of Haemonchus contortus (rHcp26/23)

Haemonchosis, caused by the abomasal nematode Haemonchus contortus, is a common parasitic disease of sheep. Our previous results showed that a soluble fraction from adult stages of the nematode (p26/23) induced partial protection against challenge. Recombinant DNA technology was applied to obtain a synthetic protein (rHcp26/23). Immunological assays (ELISA, Western blotting, and immunolocalization), using sera from lambs immunized with p26/23, confirmed the identity of the recombinant protein and demonstrated that the synthetic protein is equivalent to the purified protein employed in the previous immunoprophylaxis studies. Vaccination of lambs with 300 mug of rHcp26/23 and Freund's adjuvant elicited a notable specific antibody response. Immunization did not induce any significant protection after challenge with 16000 infective larvae of H. contortus, and comparable values for parasite faecal egg output, packed cell volume, and abomasal parasite burdens were found in vaccinated and control animals.

Helminth immunoregulation: the role of parasite secreted proteins in modulating host immunity

Helminths are masterful immunoregulators. A characteristic feature of helminth infection is a Th2-dominated immune response, but stimulation of immunoregulatory cell populations, such as regulatory T cells and alternatively activated macrophages, is equally common. Typically, Th1/17 immunity is blocked and productive effector responses are muted, allowing survival of the parasite in a "modified Th2" environment. Drug treatment to clear the worms reverses the immunoregulatory effects, indicating that a state of active suppression is maintained by the parasite. Hence, research has focussed on "excretory-secretory" products released by live parasites, which can interfere with every aspect of host immunity from initial recognition to end-stage effector mechanisms. In this review, we survey our knowledge of helminth secreted molecules, and summarise current understanding of the growing number of individual helminth mediators that have been shown to target key receptors or pathways in the mammalian immune system.

A portrait of the "SCP/TAPS" proteins of eukaryotes--developing a framework for fundamental research and biotechnological outcomes

A wide range of proteins belonging to the SCP/TAPS "family" has been described for various eukaryotic organisms, including plants and animals (vertebrates and invertebrates, such as helminths). Although SCP/TAPS proteins have been proposed to play key roles in a number of fundamental biological processes, such as host-pathogen interactions and defence mechanisms, there is a paucity of information on their genetic relationships, structures and functions, and there is no standardised nomenclature for these proteins. A detailed analysis of the relationships of members of the SCP/TAPS family of proteins, based on key protein signatures, could provide a foundation for investigating these areas. In this article, we review the current state of knowledge of key SCP/TAPS proteins of eukaryotes, with an emphasis on those from parasitic helminths, and undertake a comprehensive, systematic phylogenetic analysis of currently available full-length protein sequence data (considering characteristic protein signatures or motifs) to infer relationships and provide a framework (based on statistical support) for the naming of these proteins. This framework is intended to guide genomic and molecular biological explorations of key SCP/TAPS molecules associated with infectious diseases of plants and animals. In particular, fundamental investigations of these molecules in parasites and the integration of structural and functional data could lead to new and innovative approaches for the control of parasitic diseases, with important biotechnological outcomes.

Proteomic analysis of excretory/secretory products released by Teladorsagia circumcincta larvae early post-infection

Teladorsagia circumcincta is an important parasitic nematode of domestic small ruminants. Drug resistance in this species is common so alternative methods of control are required. As animals develop immunity to T. circumcincta, vaccination is a valid option. Little is known about the antigens that play a role in stimulating immunity at this host/parasite interface. As responses generated between 1 and 5 dpi are known to affect development of these nematodes in their gastric niche, we focused on proteins released during the early stages of infection. To identify molecules potentially involved in immunity, we undertook a proteomics analysis of proteins released from larvae harvested at 1-, 3- and 5-days post-infection (dpi). This analysis produced peptide sequence data that was used to search information available in T. circumcincta expressed sequence tag (EST) databases and enabled identification of a number of excretory/secretory (ES) proteins. Immunoblots were performed to assess the relative molecular weight of ES antigens that were targets of local IgA responses in mucus from sheep rendered immune to infection. ELISA was performed to assess antigen-specific mucus IgA levels in individual sheep. These experiments provided preliminary evidence that the proteins identified in the larval secretome were subject to these antibody responses.

Improved insights into the transcriptomes of the human hookworm Necator americanus--fundamental and biotechnological implications

Hookworms of humans are blood-feeding parasitic nematodes of major socio-economic significance in a wide range of countries. They cause a neglected tropical disease (NTD) called "hookworm disease" (=necatoriasis and/or ancylostomiasis). Necator americanus is the most widely distributed hookworm of humans and is a leading cause of iron deficiency anaemia, which can cause physical and mental retardation and deaths in children as well as adverse maternal-foetal outcomes. Currently, there is a significant focus on the development of new approaches for the prevention and control of hookworms in humans. Technological advances are underpinning the discovery of drug and vaccine targets through insights into the molecular biology and genomics of these parasites and their relationship with the human host. In spite of the widespread socio-economic impacts of human necatoriasis, molecular datasets for N. americanus are scant, limiting progress in molecular research. The present article explores all currently available EST datasets for adult and larval stages of N. americanus using a semi-automated bioinformatic pipeline. In the current repertoire of molecules now available, some have been or are being considered as candidate vaccines against N. americanus. Among others, the most abundant sets of molecules relate to the pathogenesis-related protein (PRP) superfamily, comprising various members, such as the Ancylostoma-secreted or activation-associated proteins (ASPs) and the kunitz-type proteins, both of which are inferred to play key roles in the interplay between N. americanus and the human host. Understanding the molecular biology of these and other novel molecules discovered could have important implications for finding new ways of disrupting the pathways that they are involved in, and should facilitate the identification of new drug and vaccine targets. Also, the bioinformatic prediction of the essentiality of genes and gene products as well as molecular network connectivity of nematode-specific genes, together with sequencing by 454 technology, are likely to assist in the genomic discovery efforts in the very near future, to also underpin fundamental, molecular research of hookworms.

Isolation and immunolocalization of a putative protective antigen (p26/23) from adult Haemonchus contortus

The putative protective antigen, p26/23, from adult Haemonchus contortus was isolated. A soluble extract from adult helminths obtained from the abomasa of hyperinfected (12,000 infective larvae) female Manchego lambs and treated with a mixture of protease inhibitors was subjected to affinity chromatography (hexylgluthatione) to eliminate the enzyme gluthatione S-transferase. The eluate was analyzed by electrophoresis under denaturing and reducing conditions (sodium dodecyl sulfate polyacrylamide gel electrophoresis), electrotransferred to nylon membranes, and assayed by Western blot with sera from immunized lambs. The bands recognized by the lambs' sera corresponding to proteins with a molecular weight of 23-26 kDa (p26/23) were excised, eluted, and separated by reverse-phase chromatography. This allowed the isolation of a single protein, which was expressed in both infective larvae (L3) and the adult stage of the parasite. The first 20 amino acids of the N-terminal end of the purified protein were determined. The partial amino acid sequence revealed a 100% identity with the N terminus of one of the peptides present in the p26/23 immunoprotective fraction previously tested by us against sheep haemonchosis. No significant homology with any reported sequence was found except for the deduced sequence of a hypothetic H.contortus protein (HCC00515). Immunolocalization studies showed that the protein was expressed in the hypodermic chords of the nematode.

Haemonchus contortus: evaluation of two signal sequence trapping systems for detection of secreted molecules

Given that signal sequences between secreted proteins of different species can be interchanged, it is reasonable to expect that both mammalian and yeast signal sequence trapping (SST) systems would secrete Haemonchus contortus proteins with similar efficiency and quality. To determine if H. contortus cDNAs that contain a signal sequence could re-establish secretion of a reporter protein, mammalian and yeast SST vectors were designed, 10 H. contortus genes selected, and their respective cDNAs cloned into these two SST vectors. The selected molecules included genes known to code for excretory/secretory or membrane-bound proteins as potential test 'positives', and genes known to code for non-secreted proteins as test 'negatives'. While differentiation between secretion and non-secretion was evident in both systems, the results indicated greater efficiency was achieved when the mammalian system was used. Therefore, mammalian SST using COS cells would be a more useful tool to screen H. contortus cDNA libraries for potential secreted and type-1 integral membrane proteins than yeast SST.

Vaccination against Ostertagia ostertagi with subfractions of the protective ES-thiol fraction

Previous vaccination trials against Ostertagia ostertagi in cattle have demonstrated the protective capacity of a protein fraction termed ES-thiol, which is enriched for activation-associated secreted proteins (ASPs) and cysteine proteases. In this study, ES-thiol was subfractionated through Q-Sepharose anion exchange chromatography to determine whether the ASPs and/or the cysteine proteases are responsible for the induced protection. Calves (seven/group) were immunized three times intramuscularly with 100 microg of ES-thiol or equivalent amounts of an ASP-enriched fraction, a cysteine protease-enriched fraction or a rest fraction, with QuilA adjuvant. A negative control group only received QuilA. After the final immunization the animals were challenged with a trickle infection of 25,000 infectious L3 larvae (1000 L3/day; 5 days/week). During a 2-month period the geometric mean cumulative faecal egg count (FEC) of the ES-thiol group was reduced by 62% compared to the QuilA control group (P<0.05). Groups injected with the ASP-enriched, the cysteine protease-enriched and the rest fraction demonstrated a reduction in cumulative FEC of 74, 80 and 70%, respectively (P<0.01). Although no significant reductions in worm burdens were observed, adult male and female worms were significantly smaller in all vaccinated groups (P<0.05), except for male worms from the ES-thiol group. These results suggest the protective capacity of ASPs and the presence of other protective antigens in the ES-thiol fraction.

Molecular cloning and analysis of a new venom allergen-like protein gene from the root-knot nematode Meloidogyne incognita

A new venom allergen-like protein gene isolated from Meloidogyne incognita (designated Mi-vap-2) was cloned and analysed. The genomic clone of Mi-vap-2 is 1917-bp long, contains three introns, which range in size from 39 to 797 bp, and four exons ranging in size from 37 to 361 bp. The cDNA of Mi-vap-2 contains an open reading frame encoding 294 amino acids, being the first 16 residues a putative secretion signal. Southern blot analysis suggested that Mi-vp-2 is probably a member of a small multigene family. In situ hybridization analysis showed that the transcripts of Mi-vap-2 accumulated exclusively within the subventral oesophageal gland cells of M. incognita. RT-PCR analyses confirmed that Mi-vap-2 was transcribed mainly in the pre-parasitic second-stage and early post-inoculated juveniles. Results indicated that this venom allergen-like protein gene may play an important role in establishment of the parasitic relationship between plants and nematodes.

Mesocestoides corti (syn. vogae, cestoda): Characterization of genes encoding cysteine-rich secreted proteins (CRISP)

With the aim of identifying genes involved in development and parasite adaptation in cestodes, four coding sequences were isolated from the cyclophyllidean Mesocestoides corti larval stage (tetrathyridium). Genes showed significant similarity to the cysteine-rich secreted protein (CRISP) encoding genes, a large family that includes stage and tissue-specific genes from diverse organisms, many associated with crucial biological processes. The full-length McCrisp2 cDNA encodes a predicted protein of 202 residues in length, containing 10 cysteines and a putative signal peptide. The expression level of McCrisp2 was estimated by Real-time PCR, relative to GAPDH, showing an increase of 75% in segmented worms compared to tetrathyridia. By in situ hybridization, McCrisp2 expression was localized mainly at the larvae apical region of tetrathyridia and in the proglottids of segmented worms. Taken together our results suggest a possible role for M. corti CRISP proteins as ES products, potentially involved in differentiation processes as proposed for homologs in other organisms.

Hookworm vaccines: past, present, and future

Hookworms are gastrointestinal nematodes that infect almost 1 billion people in developing countries. The main clinical symptom of human hookworm infections is iron-deficiency anaemia, a direct consequence of the intestinal blood loss resulting from the parasite's feeding behaviour. Although treatment is available and currently used for the periodic removal of adult hookworms from patients, this approach has not effectively controlled hookworm in areas of rural poverty. Furthermore, treated individuals remain susceptible to reinfection following exposure to third-stage infective hookworm larvae in the soil as early as 4-12 months after drug treatment. Therefore, a prophylactic vaccine against hookworm infection would provide an attractive additional tool for the public-health control of this disease. The feasibility of developing a vaccine is based on the previous success of an attenuated larval vaccine against canine hookworm. Several laboratory and field studies have explored the development of a human anti-hookworm vaccine, describing potential protective mechanisms and identifying candidate antigens, one of which is now in clinical trials. The current roadmap that investigators have conceived has been influenced by vaccine development for blood-feeding nematodes of livestock and companion animals; however, recombinant vaccines have yet to be developed for nematodes that parasitise animals or human beings. The roadmap also addresses the obstacles facing development of a vaccine for developing countries, where there is no commercial market.

Evaluation of a recombinant excretory secretory Haemonchus contortus protein for use in a diagnostic enzyme-linked immunosorbent assay

The nematode Haemonchus contortus (H. contortus) is one of the most pathogenic and economically important parasites of sheep. A 24 kDa protein is one of the important components in H. contortus excretory/secretory (ES), which was shown to have important biological function. In our research, the cDNA of its open reading frame (ES24) was obtained and analyzed. Then the ES24 was sub-cloned into pET-30a expression vector. The recombinant vector that codes hexahistidyl peptide fusion protein (His-ES24) was transformed into Escherichia coli BL21 (DE3) strain. After induction, a high expression level of His-ES24 was found at 6h taking about 26% of the total bacterial protein analyzed by gel thin-layer scanning. The expressed His-ES24 was purified and then used in an enzyme-linked immunosorbent assay (ELISA) to detect specific antibodies in serum samples. The ELISA was able to differentiate between H. contortus-infected sheep serum and Fasciola hepatica-infected sheep serum or non-infected sheep serum. No cross-reaction was observed in sheep sera that have been experimentally infected with F. hepatica. A total of 153 field sheep serum samples conserved in our laboratory were examined using the His-ES24 ELISA, and 82 (53.6%) of them were found seropositive to H. contortus. Our results demonstrate that the prokaryotic-expressed His-ES24 might be a useful diagnostic reagent for epidemiological studies of H. contortus in sheep.

Identification of secreted cysteine proteases from the parasitic nematode Haemonchus contortus detected by biotinylated inhibitors

Seven cathepsin B-like cysteine proteases (CBLs) were identified from the immunoprotective excretory-secretory products of Haemonchus contortus. Two-dimensional (2-D) zymography and biotinylated inhibitors were employed to localize active CBLs in 2-D protein gels. Mass spectrometry provided the identification of AC-4, HMCP1, HMCP2, and GCP7 as well as three novel CBLs encoded by clustered expressed sequence tags.

Progress in the development of a recombinant vaccine for human hookworm disease: the Human Hookworm Vaccine Initiative

Hookworm infection is one of the most important parasitic infections of humans, possibly outranked only by malaria as a cause of misery and suffering. An estimated 1.2 billion people are infected with hookworm in areas of rural poverty in the tropics and subtropics. Epidemiological data collected in China, Southeast Asia and Brazil indicate that, unlike other soil-transmitted helminth infections, the highest hookworm burdens typically occur in adult populations, including the elderly. Emerging data on the host cellular immune responses of chronically infected populations suggest that hookworms induce a state of host anergy and immune hyporesponsiveness. These features account for the high rates of hookworm reinfection following treatment with anthelminthic drugs and therefore, the failure of anthelminthics to control hookworm. Despite the inability of the human host to develop naturally acquired immune responses to hookworm, there is evidence for the feasibility of developing a vaccine based on the successes of immunising laboratory animals with either attenuated larval vaccines or antigens extracted from the alimentary canal of adult blood-feeding stages. The major antigens associated with each of these larval and adult hookworm vaccines have been cloned and expressed in prokaryotic and eukaryotic systems. However, only eukaryotic expression systems (e.g., yeast, baculovirus, and insect cells) produce recombinant proteins that immunologically resemble the corresponding native antigens. A challenge for vaccinologists is to formulate selected eukaryotic antigens with appropriate adjuvants in order to elicit high antibody titres. In some cases, antigen-specific IgE responses are required to mediate protection. Another challenge will be to produce anti-hookworm vaccine antigens at high yield low cost suitable for immunising large impoverished populations living in the developing nations of the tropics.

Vaccination against the nematode Haemonchus contortus with a thiol-binding fraction from the excretory/secretory products (ES)

Fractionated excretory/secretory products (ES) of adult Haemonchus contortus were evaluated as protective antigens. The proteins were successively eluted from a Thiol Sepharose column using 25 mM cysteine followed by 25 mM Dl-dithiothreitol (DTT). Sheep were vaccinated three times and challenged with 5000 third stage infective larvae (L3) of H. contortus. Highest level of protection was found in sheep vaccinated with the DTT-eluted fraction in which egg output and worm burden were reduced by 52 and 50%, respectively, compared to the adjuvant control group. There was a positive correlation between fecundity (number of eggs per female) and the cumulative EPG or worm burden. Serum and mucus antibody levels of ES-specific immunoglobulins increased after immunizations and after challenge for IgG, IgA and IgE. The harvesting of H. contortus from animals clustered per group revealed the presence of cysteine protease activity in the ES of all groups but in addition to that, metalloprotease activity was also detected in the groups vaccinated with the DTT-eluted fraction, total ES and adjuvant only, in contrast to previous batches of ES (completely inhibited by E64) obtained from non vaccinated animals.

Molecular characterisation of the Ancylostoma-secreted protein family from the adult stage of Ancylostoma caninum

The Ancylostoma-secreted proteins are a family of nematode-specific cysteine-rich secreted proteins belonging to the pathogenesis-related protein superfamily. Previously we reported that third stage infective larvae of Ancylostoma caninum produce two different Ancylostoma-secreted proteins, a single and double-domain Ancylostoma-secreted protein, designated as Ancylostoma-secreted protein-1 and Ancylostoma-secreted protein-2, respectively. Here we report that adult A. caninum hookworms produce and release four additional Ancylostoma-secreted proteins (Ancylostoma-secreted protein-3-6). Using antiserum against adult excretory/secretory products, Ancylostoma-secreted protein cDNAs were isolated from cDNA expression libraries. Immunolocalisation experiments using specific antisera indicated that the single-domain Ac-Ancylostoma-secreted protein-3 is located in the adult pharyngeal and oesophageal glands. Ac-Ancylostoma-secreted protein-4, Ancylostoma-secreted protein-5 and Ancylostoma-secreted protein-6 are composed of two pathogenesis-related protein domains linked in tandem as a heterodimorphic repeat. Ac-Ancylostoma-secreted protein-4 is localised to the cuticular surface of the adult hookworm, whereas Ac-Ancylostoma-secreted protein-5 was found in the intestinal brush border membrane, and Ancylostoma-secreted protein-6 in the cephalic and excretory glands. All of the adult Ancylostoma-secreted proteins were identified in excretory/secretory products of adult hookworms by Western blotting and are presumably released by the parasite. None of the adult Ancylostoma-secreted proteins were detected by immunoblotting in L3 extracts, although mRNAs of Ac-Ancylostoma-secreted protein-3 and Ac-Ancylostoma-secreted protein-4 were present in the larval stage. The functions of the adult Ancylostoma-secreted proteins are unknown, although the secretion of multiple family members by the adult suggests an important role in the establishment or maintenance of the parasitic relationship.

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.

Progress and new technologies for developing vaccines against gastrointestinal nematode parasites of sheep

Despite the identification of highly effective native antigens for vaccination against Haemonchus contortus, particularly 'hidden' antigens derived from the intestine of adult worms, to date similar efficacy has not been shown with recombinant antigens. In addition, progress towards identification of protective antigens from other sheep gastrointestinal (GI) nematode species is limited. Coupled with this is an incomplete understanding of the mechanism of natural immunity to GI nematodes, making selection of appropriate immunization strategies and adjuvants for evaluation of candidate 'natural' antigens problematic. The current explosion in new high-throughput technologies, arising from human studies, for analysis of the genome, transcriptome, proteome and glycome offers the opportunity to gain a better understanding of the molecular pathways underlying pathogen biology, the host immune system and the host-pathogen interaction. An overview is provided on how these technologies can be applied to parasite research and how they may aid in overcoming some of the current problems in development of commercial vaccines against GI nematode parasites.

Parasitic nematode interactions with mammals and plants

Parasitic nematodes that infect humans, animals, and plants cause serious diseases that are deleterious to human health and agricultural productivity. Chemical and biological control methods have reduced the impact of these parasites. However, surviving environmental stages lead to persistent reinfection of host species. In addition, development of resistance to nematicides and anthelmintics by these parasites and reduced availability of some nematicides, for environmental protection, pose significant obstacles for current and future prospects of effective parasite control. Due to marked differences in host species, research on animal and plant parasitic nematodes often proceeds independently. Despite the differences between animals and plants, basic cellular properties are shared among these host organisms. Some common properties may be important for mechanisms [homologous or convergent (homoplastic)] by which nematodes successfully infect these diverse hosts or by which animal and plant hosts resist infections by these pathogens. Here we compare host/parasite interactions between plant parasitic nematodes (PPN) and animal parasitic nematodes, with an emphasis on mammalian hosts (MPN). Similarities and differences are considered in the context of progress on molecular dissection of these interactions. A comprehensive coverage is not possible in the space allotted. Instead, an illustrative approach is used to establish examples that, it is hoped, exemplify the value of the comparative approach.

A family of activation associated secreted protein (ASP) homologues of Cooperia punctata

Activation-associated secreted proteins (ASP) of nematodes have been studied as potential vaccine components. In this study we report the cloning and analysis of cDNA and genomic sequences of Cooperia punctata and establish the presence of two 75% identical ASP-1 genes in C. punctata. Additional C. punctata ASP paralogues were shown to be present. Analysis of PCR products amplified from genomic DNA from a pool of worms revealed extensive sequence diversity within this family of proteins, reflecting the presence of different ASP paralogues in a single worm as well as extensive polymorphisms between different worms. ASP proteins contain a conserved region called the sperm-coating protein (SCP) domain of unknown function, which is present as a single copy in proteins from yeast and a wide range of multi-cellular organisms. Only in three nematodes has a protein composed of duplicated SCP-domains been identified. C. punctata is the first organism in which at least two such genes are found. Database searches identified similarity of the C-terminal cysteine-rich domain of ASP proteins to a nematode metallothionein motif. Cp-asp-1b was expressed in Escherichia coli and both the N-terminal and C-terminal domain were shown to be recognized by sera of C. punctata infected bovines. The description of the asp gene family of C. punctata provides the basis for more detailed studies into the extent of variation and immunological recognition of this family that may assist in rational vaccine design.

Characterization of a recombinant immunodiagnostic antigen (NIE) from Strongyloides stercoralis L3-stage larvae

Due to the process of internal autoinfection, even chronic asymptomatic infections with Strongyloides stercoralis have the potential to become severe disseminated disease with fatal outcome. Intermittent and scanty larval excretion makes parasitologic diagnosis difficult. Serodiagnosis is helpful, but antigen preparation from infective larvae requires access to patients or immunosuppressed experimental animals. For these reasons, attention has turned to recombinant antigens for immunodiagnosis. A 31-kDa candidate antigen (NIE) derived from an L3 cDNA library is described in this report. Multiple alignment of the deduced amino acid sequence of NIE showed approximately 12-18% identity with various other organisms, including 17.9% of Asp1 of Ancylostoma caninum, 12.6% of Hemonchus contortus, and 17.6% of insect venom allergen 5 of yellow jacket. By ELISA, antibodies to the purified recombinant NIE antigen were demonstrated in 87.5% of 48 sera from strongyloides-infected patients and in only 6.5% of sera from presumed normal controls. Immunoreactivity of purified NIE antigen with parasite-specific IgE from sera of strongyloides-infected patients indicated its potential use as an immediate sensitivity skin test antigen. This application of the NIE antigen was supported by its capacity to trigger release of histamine upon in vitro exposure to blood from strongyloides-infected patients and its failure to produce histamine release from blood of normal controls.

Protection studies with recombinant excretory/secretory proteins of Haemonchus contortus

The efficacy of two recombinant proteins of Haemonchus contortus was studied in both adult sheep and young lambs. These 15 and 24 kDa excretory/secretory proteins were given combined, either supplemented or not with a glycan-rich insect cell extract. In 9-month-old sheep (trial 1), faecal egg output and worm burden were reduced by 49% and 55%, respectively, after vaccination with rec15/24, and by 46% and 65% after vaccination with rec15/24 and glycan extract. No reduction in egg output or number of worms was found in young lambs using the above recombinant proteins plus glycan-rich extract (trial 2). When trial 1 was repeated (trial 3), the protection could not be reproduced, possibly due to differences in batches of recombinant proteins. In all sheep, independent of their age, rec15/24-specific immunoglobulin (Ig)G1 and IgA titres were present, but 9-month-old protected sheep had significantly higher IgA titres than the lambs. Addition of glycans resulted in lower rec15/24-specific IgG1 and IgA in 9-month-old sheep after challenge. This did not affect the level of protection. A significant negative correlation was found between IgA and worm numbers in protected sheep immunized with rec15/24 supplemented with glycans. Total IgE and rec15/24 specific IgE titres were low. The number of eosinophils, mast cells, sheep mast cell protease (SMCP)+ cells and IgA+ cells did not differ between the protected and unprotected sheep, but the lambs had significantly fewer mast cells independent of their immunization.

Molecular characterisation and expression of two venom allergen-like protein genes in Heterodera glycines

Secretory proteins encoded by genes expressed in the oesophageal gland cells of plant-parasitic nematodes have key roles in nematode parasitism of plants. Two venom allergen-like protein cDNAs (designated hg-vap-1 and hg-vap-2)were isolated from Heterodera glycines gland cell cDNA libraries. Both cDNAs hybridised to genomic DNA of H. glycines in Southern blots. The hg-vap-1 cDNA contained an open reading frame encoding 215 amino acids with the first 25 amino acids being a putative secretion signal. The hg-vap-2 cDNA contained an open reading frame encoding 212 amino acids with the first 19 amino acids being a putative secretion signal. Genes of hg-vap-1 and hg-vap-2 contained four introns, which ranged in size from 44 to 574 bp, and five exons ranging in size from 43 to 279 bp. In situ hybridisation analyses showed that mRNAs of both vap genes accumulated specifically in the subventral gland cells of H. glycines during parasitism. The gland cell-specific expression and presence of predicted secretion signal peptides in both VAPs suggest that these proteins are secreted from the nematode and may play a role in the infection of host plants by this parasite.