Protein disulphide isomerase of Ostertagia ostertagi: an excretory-secretory product of L4 and adult worms?

Analysis of the immunomodulatory activity of excreted and secreted products from Haemonchus placei transition infective larvae (xL3)

The excretory/secretory (E/S) products released by infective transitory larvae (xL₃) of Haemonchus placei have an important biological function in stimulating immune mechanisms during the invasive process. Our objective was to analyse the modulatory activity of 15 and 70 kDa E/S products from H. placei xL₃. Both E/S products were collected from xL₃in vitro cultures at 24 and 72 h. Proteins were confirmed by SDS-PAGE, and the corresponding spots were elicited by gel isoelectrofocusing (IEF) and characterised by mass spectrometry. Additionally, flow cytometry of CD4⁺/γδ⁺ T cells and immune gene expression were performed by proliferation assays using each E/S product to stimulate lymphocyte and peripheral blood mononuclear cells (PBMCs) from non-infected calves. The IEF results displayed two spots of 7.0 and 5.7 pI for the 15 and 70 kDa products, respectively. Additionally, 29 and 17 peptides from the 15 and 70 kDa E/S products, respectively, were identified with the hypothetical neurotransmitter and enzymatic functions necessary for larval development. The relative expression displayed upregulation of IL4, 5, 6, 8, 10, 13, IFNγ, and FCεR1A genes (from 2.0- to 17.6-fold, p < 0.05) stimulated by the 15 and 70 kDa proteins, indicating specific genes against haemonchosis. Although the percentage of median florescence intensity (MFI%) of CD4⁺/γδ⁺ T cells did not change for both E/S products compared to the negative control and concanavalin-A stimulated cells as the positive control (p > 0.05), the 15-kDa protein reduced the levels of both T cells, and the 70-kDa proteins increased the γδ⁺ cells slightly. Additionally, there was increased PBMCs proliferation by the 70 kDa proteins (p < 0.05), denoting the biological role of other immune cells. The 15 and 70 kDa protein E/S products from H. placei xL₃ showed modulation of the immune response, and although more studies are required, they indicate important functions in the host/parasite interaction.

Gene expression plasticity across hosts of an invasive scale insect species

For plant-eating insects, we still have only a nascent understanding of the genetic basis of host-use promiscuity. Here, to improve that situation, we investigated host-induced gene expression plasticity in the invasive lobate lac scale insect, Paratachardina pseudolobata (Hemiptera: Keriidae). We were particularly interested in the differential expression of detoxification and effector genes, which are thought to be critical for overcoming a plant's chemical defenses. We collected RNA samples from P. pseudolobata on three different host plant species, assembled transcriptomes de novo, and identified transcripts with significant host-induced gene expression changes. Gene expression plasticity was pervasive, but the expression of most detoxification and effector genes was insensitive to the host environment. Nevertheless, some types of detoxification genes were more differentially expressed than expected by chance. Moreover, we found evidence of a trade-off between expression of genes involved in primary and secondary metabolism; hosts that induced lower expression of genes for detoxification induced higher expression of genes for growth. Our findings are largely consonant with those of several recently published studies of other plant-eating insect species. Thus, across plant-eating insect species, there may be a common set of gene expression changes that enable host-use promiscuity.

Proteomic analysis of Mecistocirrus digitatus and Haemonchus contortus intestinal protein extracts and subsequent efficacy testing in a vaccine trial

BACKGROUND

Gastrointestinal nematode infections, such as Haemonchus contortus and Mecistocirrus digitatus, are ranked in the top twenty diseases affecting small-holder farmers' livestock, yet research into M. digitatus, which infects cattle and buffalo in Asia is limited. Intestine-derived native protein vaccines are effective against Haemonchus, yet the protective efficacy of intestine-derived M. digitatus proteins has yet to be determined.

METHODOLOGY/PRINCIPAL FINDINGS

A simplified protein extraction protocol (A) is described and compared to an established method (B) for protein extraction from H. contortus. Proteomic analysis of the H. contortus and M. digitatus protein extracts identified putative vaccine antigens including aminopeptidases (H11), zinc metallopeptidases, glutamate dehydrogenase, and apical gut membrane polyproteins. A vaccine trial compared the ability of the M. digitatus extract and two different H. contortus extracts to protect sheep against H. contortus challenge. Both Haemonchus fractions (A and B) were highly effective, reducing cumulative Faecal Egg Counts (FEC) by 99.19% and 99.89% and total worm burdens by 87.28% and 93.64% respectively, compared to the unvaccinated controls. There was no effect on H. contortus worm burdens following vaccination with the M. digitatus extract and the 28.2% reduction in cumulative FEC was not statistically significant. However, FEC were consistently lower in the M. digitatus extract vaccinates compared to the un-vaccinated controls from 25 days post-infection.

CONCLUSIONS/SIGNIFICANCE

Similar, antigenically cross-reactive proteins are found in H. contortus and M. digitatus; this is the first step towards developing a multivalent native vaccine against Haemonchus species and M. digitatus. The simplified protein extraction method could form the basis for a locally produced vaccine against H. contortus and, possibly M. digitatus, in regions where effective cold chains for vaccine distribution are limited. The application of such a vaccine in these regions would reduce the need for anthelmintic treatment and the resultant selection for anthelmintic resistant parasites.

Direct identification of the Meloidogyne incognita secretome reveals proteins with host cell reprogramming potential

The root knot nematode, Meloidogyne incognita, is an obligate parasite that causes significant damage to a broad range of host plants. Infection is associated with secretion of proteins surrounded by proliferating cells. Many parasites are known to secrete effectors that interfere with plant innate immunity, enabling infection to occur; they can also release pathogen-associated molecular patterns (PAMPs, e.g., flagellin) that trigger basal immunity through the nematode stylet into the plant cell. This leads to suppression of innate immunity and reprogramming of plant cells to form a feeding structure containing multinucleate giant cells. Effectors have generally been discovered using genetics or bioinformatics, but M. incognita is non-sexual and its genome sequence has not yet been reported. To partially overcome these limitations, we have used mass spectrometry to directly identify 486 proteins secreted by M. incognita. These proteins contain at least segmental sequence identity to those found in our 3 reference databases (published nematode proteins; unpublished M. incognita ESTs; published plant proteins). Several secreted proteins are homologous to plant proteins, which they may mimic, and they contain domains that suggest known effector functions (e.g., regulating the plant cell cycle or growth). Others have regulatory domains that could reprogram cells. Using in situ hybridization we observed that most secreted proteins were produced by the subventral glands, but we found that phasmids also secreted proteins. We annotated the functions of the secreted proteins and classified them according to roles they may play in the development of root knot disease. Our results show that parasite secretomes can be partially characterized without cognate genomic DNA sequence. We observed that the M. incognita secretome overlaps the reported secretome of mammalian parasitic nematodes (e.g., Brugia malayi), suggesting a common parasitic behavior and a possible conservation of function between metazoan parasites of plants and animals.

Parasitic nematodes are microscopic worms that cause major diseases of plants, animals, and humans. Infection is associated with secretion of proteins by the parasite; these proteins suppress the immune system and cause other changes to host cells that are required for infection. Identification of secreted proteins has been difficult because they are released only in trace amounts. We have developed very sensitive methods that enabled the discovery of 486 proteins secreted by the root knot nematode, Meloidogyne incognita; prior to this, only a handful of secreted proteins were known. Several secreted proteins appear to mimic normal plant proteins, and they may participate in the process by which the nematode hijacks the plant cell for its own purposes. Meloidogyne species infect many crops, including corn, soybean, cotton, rice, tomato, carrots, alfalfa, and tobacco. The discovery of these secreted proteins could lead to new methods for protecting these important crops from nematode damage. We observed that the secretome of the human pathogen, Brugia malayi, overlaps that of M. incognita, suggesting a common parasitic behavior between pathogens of plants and animals.

Identification of immuno-reactive proteins from a sheep gastrointestinal nematode, Trichostrongylus colubriformis, using two-dimensional electrophoresis and mass spectrometry

Gastrointestinal nematode infections of livestock animals are prevalent and costly problems worldwide. Currently, infections are controlled by anthelmintic chemicals but increasing drug resistance has prompted research interest to shift towards alternative methods of control such as vaccine development and selection of worm-resistant animals. The present study analyses proteins from Trichostrongylus colubriformis infective L3s that are recognised by IgG of immune sheep. Following protein separation via two-dimensional electrophoresis and Western blot probing with plasma from sheep resistant to T. colubriformis, mass spectrometry-based proteomic analyses were used to identify immuno-reactive protein spots. We were able to identify 28 immune targets, including aspartyl protease inhibitor, enolase, chaperone proteins, galectin, glycolytic enzymes, kinase, phosphatase and structural muscle proteins such as myosin, paramyosin, calponin and DIM-1. The data suggest that immune responses to T. colubriformis are dispersed over a relatively large number of parasite antigens, including several cytoplasmically expressed proteins. The results have new implications for understanding the molecular mechanisms that underpin host-parasite interaction during gastrointestinal nematode infections.

Identification of three protein disulfide isomerase members from Haemaphysalis longicornis tick

Three genes encoding putative protein disulfide isomerase (PDI) were isolated from the Haemaphysalis longicornis EST database and designed as HlPDI-1, HlPDI-2, and HlPDI-3. All three PDI genes contain two typical PDI active sites CXXC and encode putative 435, 499, and 488 amino acids, respectively. The recombinant proteins expressed in Escherichia coli all show PDI activities, and the activities were inhibited by a PDI-specific inhibitor, zinc bacitracin. Western blot analysis and real-time PCR revealed that three HlPDIs were present in all the developmental stages of the tick as well as in the midgut, salivary glands, ovary, hemolymph, and fatbody of adult female ticks, but the three genes were expressed at the highest level in the egg stage. HlPDI-1 is expressed primarily in the ovary and secondarily in the salivary glands. HlPDI-2 and HlPDI-3 are expressed primarily in the salivary gland, suggesting that the PDI genes are important for tick biology, especially for egg development, and that they play distinct roles in different tissues. Blood feeding induced significantly increased expression of HlPDI-1 and HlPDI-3 in both partially fed nymphs and adults. Babesia gibsoni-infected larval ticks expressed HlPDI-1 and HlPDI-3 2.0 and 4.0 times higher than uninfected normal larval ticks, respectively. The results indicate that HlPDI-1 and HlPDI-3 might be involved in tick blood feeding and Babesia parasite infection in ticks.

Use of a 203 alphaalpha fragment of Tc-PDI to detect IgA activity during infection by Teladorsagia circumcincta in sheep

The objectives of this study are to find an appropriate ELISA technique to monitor IgA activity during infection by Teladorsagia circumcincta in sheep as well as to identify the degree of resistance to the infection. Previous studies have shown the relationship between IgA in infected sheep and the resistance to the infection. In this study, the titre of IgA in resistant and susceptible infected ewes was tested in blood, nasal secretions and saliva. ELISAs were carried out against somatic antigen from L4 and against a 203 amino acid fragment of a recombinant protein disulphide isomerase of T. circumcincta (Tc-PDI). The results showed that, in general, the titres of IgA against a fragment of a Tc-PDI were lower than against the somatic antigen. These lower levels are clearly shown in blood samples and nasal secretions in contrast to saliva samples where the titre reached higher values testing the IgA against Tc-PDI. This could be due to the fact that, in the detection of IgA against Tc-PDI, the antibody-antigen reaction is more specific than against the whole somatic antigen. To differentiate between resistant and susceptible animals, the significant differences were more present with the somatic antigen. Nevertheless, the ELISA technique using the somatic antigen cannot be standardized, and the antigen-antibody reactions are more unspecific; therefore, the recombinant Tc-PDI could be a better option.

Expression of the recombinant protein disulphide isomerase of Teladorsagia circumcincta

The aim of this experiment was to find an antigen from Teladorsagia circumcincta to measure the level of IgA in ovine serum samples. Previous experiments used the titre of IgA to select sheep resistant to infection with T. circumcincta. By Western blotting 22 experimentally infected ewes recognized many proteins, but not all of them were recognized by all animals. Sheep were divided into two groups of animals: those that recognized a protein in Western blotting and those that did not. Among all proteins, three showed significant associations between protein recognition and the titre of IgA in the serum.

Screening for immunomodulatory proteins of the intestinal parasitic nematode Heligmosomoides polygyrus

Parasitic nematodes are constantly exposed to the immune effector mechanisms of their hosts. One strategy of the worms to cope with these defence reactions is the secretion of modulatory proteins that down-regulate cell-mediated immune responses. We analysed the proliferation of mesenteric lymph node cells of mice infected with Heligmosomoides polygyrus and showed that cellular proliferation was strongly suppressed in the chronic phase of infection. To identify proteins of H. polygyrus that are involved in parasite-induced immunomodulation, worm extract and culture supernatant of adult H. polygyrus were fractionated by gel chromatography and activity of each fraction was determined. One of the fractions (fraction 9) of worm extract as well as worm secretory products inhibited the antigen-specific cellular proliferation by about 40%. This reduced cellular reactivity coincided with a down-regulation of inducible nitric oxide production of mouse macrophages by 57%. Furthermore, fraction 9 contained antigens that were recognized by IgE antibodies of H. polygyrus-infected mice and induced degranulation of an IgE-sensitized basophil cell line. Single proteins of fraction 9 were analysed by mass spectrometry. These data suggest that antigens that are recognised by IgE antibodies might play an important role in immunomodulation exerted by nematode infections.

Identification of a protein disulfide isomerase of Neospora caninum in excretory-secretory products and its IgA binding and enzymatic activities

A protein disulfide isomerase of Neospora caninum (NcPDI) with a molecular weight of 50kDa was identified in tachyzoite lysate and excretory-secretory (ES) products. The IgA antibody in 58.0% of the individual cattle tear samples recognized the NcPDI, which suggests that the PDI-specific antibody may be involved in defense against parasites. In addition, PDI-specific inhibitors and NcPDI antiserum showed inhibitory effects on the growth of N. caninum tachyzoites. Furthermore, the purified recombinant NcPDI demonstrated biological activities in vitro by catalysis and refolding of reduced RNase A and assisted in the recovery of native lysozyme. These findings indicate that NcPDI possesses PDI-specific enzymatic activity and could be a putative target for chemotherapy for neosporosis.

Approaches for the identification of potential excreted/secreted proteins of Leishmania major parasites

Leishmania parasites are able to survive in host macrophages despite the harsh phagolysosomal vacuoles conditions. This could reflect, in part, their capacity to secrete proteins that may play an essential role in the establishment of infection and serve as targets for cellular immune responses. To characterize Leishmania major proteins excreted/secreted early after promastigote entry into the host macrophage, we have generated antibodies against culture supernatants of stationary-phase promastigotes collected 6 h after incubation in conditions that partially reproduce those prevailing in the parasitophorous vacuole. The screening of an L. major cDNA library with these antibodies led us to isolate 33 different cDNA clones that we report here. Sequence analysis revealed that the corresponding proteins could be classified in 3 groups: 9 proteins have been previously described as excreted/secreted in Leishmania and/or other species; 11 correspond to known proteins already characterized in Leishmania and/or other species although it is unknown whether they are excreted/secreted and 13 code for unknown proteins. Interestingly, the latter are transcribed as shown by RT-PCR and some of them are stage regulated. The L. major excreted/secreted proteins may constitute putative virulence factors, vaccine candidates and/or new drug targets.

A preliminary proteomic survey of the in vitro excretory/secretory products of fourth-stage larval and adult Teladorsagia circumcincta

The nature of the proteins which comprise the in vitro excretory/secretory products (ES) of the fourth-stage larva (L4) and adult Teladorsagia circumcincta are largely undefined, despite the fact that this nematode induces profound changes, in part related to parasite ES, in the cellular architecture of the glands lining the abomasal surface of infected sheep and goats. In this study, the protein components of L4 and adult ES were fractionated using 1D gel electrophoresis and the major protein bands, detected by Coomassie blue staining, excised from the gel and subjected to tryptic digest and subsequent mass spectrometric analysis. The resultant peptide mass fingerprints were used to identify 15 L4 and 13 adult ES proteins. Several proteins, such as globin and some metabolic enzymes, were present in both ES. L4 ES alone contained thioredoxin peroxidase, an enzyme that can detoxify free radicals resulting from host inflammatory responses to the parasite, a cysteine proteinase which may aid penetration of the gastric mucosa and 2 different galectins which may influence cell differentiation and morphogenesis. Adult ES contained a nucleoside diphosphate kinase homologue, an enzyme which has been linked to cellular changes and can affect liquid secretion and goblet cell degranulation.

Neospora caninum protein disulfide isomerase is involved in tachyzoite-host cell interaction

We have previously shown that treatment of Neospora caninum tachyzoites with the aspartyl protease inhibitor pepstatin A reduces host cell invasion [Naguleswaran, A., Muller, N., Hemphill, A., 2003. Neospora caninum and Toxoplasma gondii: a novel adhesion/invasion assay reveals distinct differences in tachyzoite-host cell interactions. Exp. Parasitol. 104, 149-158]. Pepstatin A-affinity-chromatography led to the isolation of a major band of approximately 52 kDa which was identified as a homologue of a previously described Toxoplasma gondii putative protein disulfide isomerase (TgPDI) through tandem mass spectrometry. A BLAST search against N. caninum expressed sequence tags (ESTs) on the ApiDots server using TgPDI cDNA as query sequence revealed a 2251 bp PDI-like consensus (NcPDI), which shows 94% identity to the T. gondii homologue. In N. caninum tachyzoites, NcPDI was found mainly in the soluble hydrophilic fraction. Immunofluorescence showed that expression of NcPDI was dramatically down-regulated in the bradyzoite stage, and immunogold-EM on tachyzoites localised the protein to the cytoplasm, mostly in close vicinity to the nuclear membrane, to the micronemes, and to the parasite cell surface. However, NcPDI was absent in rhoptries and dense granules. Preincubation of tachyzoites with the sulfhydryl blocker 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), p-chloromercuribenzoic acid (pCMBA), and with the PDI inhibitor bacitracin reduced adhesion of parasites to host cells. In addition, incubation of N. caninum tachyzoites with affinity-purified anti-NcPDI antibodies reduced host cell adhesion. PDIs catalyse the formation, reduction or isomerisation of disulfide bonds. Many major components of the adhesion and invasion machinery of apicomplexan parasites are cysteine-rich and dependent on correct folding via disulfide bond formation. Thus, our data points towards an important role for surface-associated NcPDI in Neospora-host cell interaction.

Identification of excretory-secretory products of larval and adult Ostertagia ostertagi by immunoscreening of cDNA libraries

Excretory-secretory (ES) products of Ostertagia ostertagi, an abomasal nematode of cattle, are considered to be important for the development and survival of the parasite within the host. To gain insight in the composition of these ES products of both larval (L3, L4) and adult life stages of Ostertagia cDNA libraries of the parasite were immunoscreened with polyclonal rabbit serum raised against these ES products. This approach led to the identification of 41 proteins, amongst which are structural proteins such as actin, kinesin and vitellogenin, housekeeping proteins such as those involved in protein folding, different metabolic pathways or mitochondrial functioning and proteins associated with stress (heat shock protein) or antioxidantia (thioredoxin peroxidase). A large number of the isolated proteins were similar to hypothetical proteins of the model nematode Caenorhabditis elegans. Because somatic proteins can be non-specifically released during in vitro culturing as nematodes deteriorate, it was checked if the isolated proteins are genuinely secreted. The amino acid sequences of the translated cDNAs were investigated for signal peptides and monospecific antibodies against the isolated proteins were purified and used to develop Western blots of ES and somatic extracts. In this manner it could be proven that 15 cDNAs code for genuine secreted proteins. The identification of these ES antigens allows to select proteins with potential protective capacities, which are targets for vaccine development.