Suppression of antigen- and mitogen-induced proliferation of bovine lymphocytes by excretory-secretory products of Oesophagostomum radiatum

Oesophagostomum dentatum: potential as a model for genomic studies of strongylid nematodes, with biotechnological prospects

There are substantial gaps in the knowledge of the molecular processes of development and reproduction in parasitic nematodes, despite the fact that understanding such processes could lead to novel ways of treating and controlling parasitic diseases, through blocking or disrupting key biological pathways. Biotechnological advances through large-scale sequencing projects, approaches for the analysis of differential gene and protein expression and functional genomics (e.g., double-stranded RNA interference) now provide opportunities to investigate the molecular basis of developmental processes in some parasitic nematodes. The porcine nodule worm, Oesophagostomum dentatum (order Strongylida), may provide a platform for testing the function of genes from this and related nematodes, given that this species can be grown and maintained in culture in vitro for periods longer than other nematodes of the same order. In this article, we review relevant biological, biochemical and molecular biological and genomic information about O. dentatum and propose that the O. dentatum - pig system provides an attractive model for exploring molecular developmental and reproductive processes in strongylid nematodes, leading toward new intervention methods and biotechnological outcomes.

Products of fourth-stage larvae of Oesophagostomum dentatum induce proliferation in naïve porcine mononuclear cells

Infection of pigs with Oesophagostomum dentatum is a major cause of economic losses in pig productions. Whether infection with this nematode results in a protective immunity is still in debate and information about immune-modulating properties of O. dentatum are lacking. The present study investigated the question whether products of O. dentatum larvae modulate the proliferative response of porcine blood mononuclear cells (poMNC) in vitro. The poMNC of naïve and O. dentatum-infected pigs were cultured for 72 h in the presence of products (total homogenates and culture supernates) derived from third- (L3) and fourth-stage larvae (L4) of O. dentatum. Numbers of vital cells and blast-transformed cells were determined flow cytometrically. No larvae product induced an accelerated death of poMNC in vitro. In contrast, products of L4 (but not L3) significantly increased the numbers of vital poMNC in vitro (up to 187%). In addition, L4 products (homogenates and supernates, 0.1-10 microg/ml) but not those of L3 induced significant blastogenesis of poMNC. This was seen with poMNC from naïve and from O. dentatum-infected animals. In spite of these effects, the larvae products were not able to modulate the mitogen-induced (Concanavalin A) poMNC proliferation of naïve and infected animals. In summary, larvae of O. dentatum contain and secrete products with potential immunomodulatory capacity for porcine peripheral blood mononuclear cells. The differential effects of L3 and indicate that the parasite alters its set immunomodulatory substances during its development. This has to be considered in further studies and may help to identify the mediators involved.

Ancylostoma secreted protein 2: cloning and characterization of a second member of a family of nematode secreted proteins from Ancylostoma caninum

Invading infective third-stage larvae (L3) of parasitic nematodes execute a series of programmed developmental events in response to a host-specific signal encountered during infection. One of these early events is the release of excretory/secretory products. Using an in vitro feeding assay that mimics these early events of infection, a protein released by in vitro activated larvae of the hookworm Ancylostoma caninum was identified. This protein, Ac-ASP-2, was partially sequenced, and the cDNA encoding it isolated by PCR and screening of an A. caninum L3 cDNA library. The Ac-asp-2 cDNA encodes a protein of 219 amino acids that is related to a previously identified protein, Ac-ASP-1, from hookworms. Both molecules are members of an evolutionarily diverse family of molecules that include the venom allergens of the Hymenoptera, and the testes specific proteins/sperm-coating glycoproteins of mammals. Homologues are present in nearly all nematodes tested, as demonstrated by PCR-hybridization and database searching. The Ac-asp-2 mRNA is synthesized in all life history stages, but the gene product is released only by L3 activated to feed in vitro. The wide distribution of the Ac-asp-2 in nematodes and its release in response to host specific signals suggests that Ac-ASP-2 serves an important function in nematode physiology and development, and possibly in the infective process of parasitic species.

Heligmosomoides polygyrus immunomodulatory factor (IMF), targets T-lymphocytes

Experiments were performed to investigate the immunological site of action of an immunomodulatory factor (IMF), isolated from the gastrointestinal nematode Heligmosomoides polygyrus. IMF inhibited antibody production in murine and human 'T-helper (Th-2) driven' immunoassays. The effects were mediated via T lymphocytes as T cell-depleted cultures failed to respond to IMF, a result confirmed by prepulsing discrete cell subsets with the immunomodulant. Although the molecular nature and mode of action of IMF has yet to be determined, it would appear to be a relatively small non-proteinaceous molecule. From this data, we suggest that H. polygyrus secretes a systemically-active IMF from the intestinal lumen, to down-regulate Th-2 cell development in order to promote its survival in a potentially immunologically hostile environment.

Immunology and prevention of infection in feedlot cattle

This article reviews the basic types of immunity, the factors relevant to feedlot cattle that have been shown to suppress immune function, and what is known about the basis of protective acquired immunity against the common bovine respiratory pathogens. The characteristics and efficacy of vaccines for respiratory disease pathogens are also reviewed. Recommendations for optimizing vaccination are presented.

Advances in pulmonary immunology

Advances in pulmonary immunology often begin with better understanding of the mechanisms of pulmonary defenses. This leads to new technologies or better use of existing technologies to prevent pneumonia. These can be validated in challenge models, but ultimately, advances in pulmonary immunology come from demonstration that a management strategy reduces the burden of disease in a production setting. This can be difficult, and may require team efforts from producers, allied industry, and academia. Each team member brings a unique perspective and set of resources to the endeavor. The alternative is to use immunoenhancing management strategies based on extrapolation and faith.

A filarial cysteine protease inhibitor down-regulates T cell proliferation and enhances interleukin-10 production

Filarial nematodes are a cause of chronic debilitating diseases in the tropics. A hallmark of filariasis is the marked down-regulation and polarization of host immune responses, yet molecular constituents of parasites causing this state have remained undefined. We describe a 17-kDa antigen (Av17) of the rodent filarial parasite Acanthocheilonema viteae, which shows amino acid homologies to cystatin C, a major cysteine protease inhibitor belonging to family 2 of the cystatin superfamily. Av17 is released by filariae in vitro. Exported molecules of A. viteae worms are shown to markedly suppress mitogen-induced T cell proliferation of mice and jirds. Av17 accounts for 45.5% of this suppressive activity in the murine system. Recombinant Av17 (rAv17), expressed in Escherichia coli, exhibits biological activity as a cysteine protease inhibitor and was used to examine the immunomodulatory effects, rAv17 induces down-regulation of murine T cell responses to mitogens, to T cell receptor cross-linking by anti-CD3 antibodies and to specific antigens, and at the same time up-regulation of interleukin-10. Hence, this filarial cystatin is a likely effector molecule of immunomodulation and a potential target for antifilarial intervention.

Serological assays for the identification of Oesophagostomum dentatum infections in pigs

Oesophagostomum dentatum antigen preparations of third (L3) or fourth (L4) stage larvae were characterised by Western blotting. Panels of sera obtained from pigs infected with O dentatum and Ascaris suum, respectively, reacted with the same bands of L3 antigen. In contrast high specificity against a characteristic band, was observed when L4 extract was employed as antigen. To establish an enzyme-linked immunosorbent assay (ELISA), a panel of homologous and heterologous sera was tested against O dentatum L4 extract. The best combined specificity and sensitivity was obtained when horseradish peroxidase (HRP) goat anti swine IgG conjugate was used rather than HRP rabbit anti swine Ig conjugate. Testing series of sera from pigs infected with single doses of either 2000, 20,000 or 200,000 infective larvae by the ELISA, a significant dose dependency in the antibody response was observed between the low and high dosage groups. This assay may be useful in future studies of the immune-mechanisms against nodular worm infections in pigs.

Cloning and characterization of Ancylostoma-secreted protein. A novel protein associated with the transition to parasitism by infective hookworm larvae

The developmentally arrested third stage infective larva of hookworms resumes development upon entry into the definitive host. This transition to parasitism can be modeled in vitro by stimulating infective larvae with a low molecular weight ultrafiltrate of host serum together with methylated glutathione analogues. When stimulated to resume development in vitro, activated larvae of the hookworm Ancylostoma caninum released a 42-kDa protein, termed Ancylostoma-secreted protein (ASP). ASP was the major protein released by activated hookworm larvae. Degenerate oligonucleotide primers, based on a partial internal amino acid sequence of the protein, were used together with flanking vector sequence primers to amplify a fragment from a third stage larval cDNA library by polymerase chain reaction. The fragment was used as a probe to isolate a longer clone from the larval cDNA library. The full-length ASP cDNA was found to encode a 424-amino acid protein with homology to the antigen 5/antigen 3 family of proteins from hymenopteran venoms and a family of cysteine-rich secretory proteins. ASP was expressed in bacterial cells, and a polyclonal antiserum against purified recombinant ASP was produced. The antiserum, which was demonstrated to be specific for ASP, was used as a probe to measure the kinetics of ASP release by hookworm larvae. ASP is released within 30 min of stimulation, with the majority released by 4 h. Low levels of ASP were released continuously following activation, but only if the stimuli were present in the incubation medium. The compound 4,7-phenanthroline, previously shown to inhibit larval activation, also inhibited release of ASP. The specific, rapid release of ASP by activated infective larvae suggests that this molecule occupies a critical and central role in the transition from the external environment to parasitism.

Immunisation of calves with Ostertagia ostertagi fourth stage larval antigens failed to protect calves from infection

Excretory-secretory and somatic antigens of Ostertagia ostertagi fourth stage larvae, emulsified with complete Freund's adjuvant, were intraperitoneally administered to calves on three occasions. Two weeks after the last immunisation all calves were infected with a single dose of 130,000 O. ostertagi third stage larvae. All animals were necropsied 25 days after infection. The immunisation procedure resulted in IgG1 and IgG2 antibodies, however no protective immunity was induced as O. ostertagi worm burdens and worm length were similar in all groups.

Cell-mediated immunity in Merino lambs with genetic resistance to Haemonchus contortus

Lymphocyte proliferation and skin hypersensitivity responses to parasite antigens were measured as indicators of cell-mediated immunity in genetically resistant and random-bred lambs following infection with Haemonchus contortus. Responses of PBMC to the mitogens PHA, PWM and LPS were also assessed to determine if infection was associated with suppression of general immune function. All lambs demonstrated significant antigen-specific lymphocyte proliferation prior to experimental infection. The responses did not differ between resistant and random-bred lambs and the correlation between pre-infection stimulation indices and resistance to challenge infection was also not significant. Following infection, PBMC from resistant lambs consistently exhibited higher blastogenic responses to both larval and adult antigens than PBMC from random-bred lambs. Addition of cyclosporin A to the antigen-stimulated cultures resulted in significant inhibition of blastogenesis, suggesting that the cells responding to parasite antigens were predominantly of the T-helper cell phenotype. Proliferation responses of resistant and random-bred sheep were similar for all mitogens tested. However, a transient suppression of lymphocyte reactivity to PHA and PWM was noted in all infected lambs. Responses to LPS remained unaffected during infection. There was no difference in the immediate hypersensitivity responses to intradermal inoculation of parasite antigens between the genotypes. However, the delayed-type hypersensitivity responses to parasite antigens were significantly greater in resistant lambs than those in random-bred lambs. Together, these data suggest that resistant lambs have an enhanced ability to mount parasite-specific cell-mediated immune responses when compared with random-bred lambs and that this may contribute to differences in the susceptibility of two genotypes to haemonchosis.

Immunosuppressive proteins secreted by the gastrointestinal nematode parasite Heligmosomoides polygyrus

Experiments are described in which the conditions for the production, assay and isolation of immunomodulatory factors from the excretory-secretory (ES) products of Heligmosomoides polygyrus have been standardized. For the inhibition of an in vitro antibody response to keyhole limpet haemocyanin, immunosuppressive activity was most reproducibly produced by 10-20-day-old adult worms maintained in culture for 24 h. This activity was relatively stable at room temperature, at 50 degrees C and pH 2, but was destroyed by boiling. Immunosuppressive activity was eluted from Sephadex G-100 in fractions preceding those containing the bulk of ES proteins, and resolved on sodium dodecyl sulphate-polyacrylamide gel electrophoresis with molecular masses of 67, 54 and 20 kDa. The relative purity of these factors was confirmed by iso-electric focusing, where immunosuppressive activity was associated with proteins of pI values of approximately 4.2 and 4.35.

Immunization of the beef cow and its influence on fetal and neonatal calf health

Specific vaccine recommendations should be made by you, the veterinarian familiar with the operation, the type of cattle handled, and the disease problems cattle typically experience. There are few cookbook solutions. Fine turning the program by including or excluding certain vaccines requires working to identify the specific disease entities present in an operation. This requires good records, complete postmortem examinations, and a good diagnostic support system. Effective management to optimize the immunocompetence of the cow and the timing of administration of the vaccine is as important as selecting the correct antigens and type of vaccines to be used.

The veterinary importance of nodular worms (Olesophagostomum spp)

The nodular worms (Oesophagostomum spp) are important parasites of food animals and primates. The archaic line that parasitizes pigs appears to be less pathogenic than the parallel evolutionary lines in ruminants and primates. Morphological types of O. dentatum in pigs and an apparent new host record for O. venulosum, which normally affects sheep and wild ruminants, in cattle suggests aggressive recruitment within the genus. The same Oesophagostomum spp occur in humans and in non-human primates but it is not clear which is the natural host.

Protection from parasite-induced weight loss by the vaccination of calves with excretory-secretory products of larval Oesophagostomum radiatum

Excretory-secretory products (ESP) were collected from in vitro maintained Oesophagostomum radiatum larvae during the period in which the larvae molt from the third to fourth larval stage. The ESP were used to immunize 13 uninfected calves which were subsequently challenged with 1.7 X 10(4) infective O. radiatum larvae. Worm recoveries from immunized calves were reduced 23% compared to 12 unimmunized controls, while the number of intestinal nodules was 72% greater compared to unimmunized controls; however, neither difference was statistically significant. Immunized calves had enhanced serum IgG and IgA anti-ESP antibody responses upon challenge. No differences in serum IgG2 or IgM antibody or cellular immune responsiveness, as determined by in vitro antigen-induced lymphocyte proliferation, were seen. Vaccination with ESP did significantly protect calves from the weight loss seen in non-immunized calves. Unimmunized calves ceased gaining weight approximately 5 weeks after challenge and by 10 weeks after challenge had lost an average of 4 lbs. per calf. Over the same time interval (i.e., 5-10 weeks after challenge), the immunized calves gained an average of 23 lbs. per calf. These results strongly suggest that vaccination with ESP conferred an advantage to calves that is not correlated solely with the number of worms developing from challenge infection.

Anisakis simplex: larval excretory secretory protein production and cytostatic action in mammalian cell cultures

Excretory secretory proteins produced in vitro by Anisakis simplex larvae incubated in Medium 199 or phosphate buffered saline with dextrose are similar with respect to protein content and biological activity. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggested that the molecular weight of the component(s) responsible for inhibition of mitogen induced lymphocyte blastogenesis is between 66,000 and 95,000. In vitro production of excretory secretory protein, approximately 1 microgram/24 hr by a single larva, was sufficient to inhibit lymphocyte blastogenesis. Serum from a human anisakiasis patient reacted with these proteins in immunoblots, indicating that, during invasion of the gastric mucosa, enough of them are produced in vivo to induce an immune response. The excretory secretory proteins significantly inhibited proliferation of transformed mammalian cell lines of lymphoid (P3/X63-Ag8) and epithelioid (HeLa) origin. As in mitogen stimulated lymphocytes, the inhibitory effect was cytostatic rather than cytotoxic. These findings suggest that, in addition to being potent immunogens, larval excretory secretory proteins are produced in sufficient quantity to modulate the host response in anisakiasis.