The use of electroblotted antigens of Trichostrongylus colubriformis to induce proliferative responses in sensitized lymphocytes from sheep

Relationships between immune indicators of parasitic gastroenteritis, nematode burdens and faecal dry matter in sheep

Immune-mediated scouring in sheep is a mucosal hypersensitivity response caused by ingesting infective parasite larvae. In this experiment we tested the hypothesis that levels of parasite-specific antibodies and also interleukin-5 (IL-5) would be negatively correlated with worm numbers, but also faecal dry matter (FDM), in parasite-resistant Merino sheep. Forty Merino rams were challenged with Trichostrongylus colubriformis and Teladorsagia circumcincta larvae every day for 6 weeks, after which they were euthanised and total worm burdens determined. Faecal samples were taken for measurement of worm egg counts and FDM. Serum was collected from the rams before and after the larval challenge commenced, and levels of ovine immunoglobulin light chain, IgG, IgM, IgA and IgE specific for T. colubriformis and T. circumcincta as well as IL-5 were determined by sandwich enzyme-linked immunosorbent assay. IL-5 and all serum antibodies apart from T. colubriformis-specific light chain were significantly increased by the larval challenge. However, none of the antibodies, or IL-5, was correlated with FDM. Negative correlations were observed between the number of adult T. circumcincta and antibody levels; however, there was little relationship between antibodies and numbers of T. colubriformis. It was concluded that serum antibody levels are a poor indicator of the susceptibility of sheep to immune-mediated scouring. Because of these results, sheep breeders should continue to select for low worm egg count and focus on phenotypic indicators of scouring, such as dags, as a means to reduce diarrhoea.

Characterization of a bioassay for detection of recombinant and native ovine interleukin-5

In order to analyse Th2-type immune responses in sheep by the assay of interleukin (IL)-5 in biological fluids, the ovine IL-5 gene was cloned and expressed in Spodoptera frugiperda Sf9 insect cells using the baculovirus expression vector system. The recombinant product was purified as BAC-OV-IL-5 from the supernatant fluid. The ovine IL-5 was biologically active in a bioassay using IL-5-dependent Baf cells, which have been used previously to specifically detect human IL-5. The specificity of Baf cells for ovine IL-5 was examined by two methods. First, Baf cells only proliferated in response to BAC-OV-IL-5 and did not respond to addition of recombinant ovine cytokines granulocyte-macrophage colony stimulating factor (GM-CSF), IL-1beta, IL-2, IL-3, IL-6, IL-8, stem cell factor (SCF) or IFN-gamma at doses from 0.01 to 1 microg/well. Second, the rat monoclonal antibody to murine IL-5, TRFK-5, neutralized murine, but not ovine, IL-5. However, rabbit antisera to BAC-OV-IL-5 neutralized murine and ovine recombinant IL-5 and abolished responses of Baf cells to IL-5 activity in supernatant fluids from mesenteric lymph node cells (MLNC) of parasitized sheep. The bioassay had a sensitivity to detect 8 ng in a 200 microL assay (40 ng/mL). Thus, the specificity of Baf cells to detect human IL-5 also extends to ovine IL-5 and therefore provides a method for monitoring the production of Th2 immune reactivity in sheep.

Attempts to generate immunity against Trichostrongylus colubriformis and Haemonchus contortus in young lambs by vaccination with viable parasites

The ability of young Merino lambs to achieve protective immunity following vaccination via viable nematode infections was assessed. Lambs were infected from 1 month of age by repeated continuous low dose (trickle) administration of Trichostrongylus colubriformis or Haemonchus contortus infective larvae (L3), or by truncated infections with high doses of viable T. colubriformis L3. After 7 weeks all groups were drenched with anthelmintic and at 3 months of age they were re-infected with the homologous species. Protection was assessed by faecal egg counts at 3, 4, 5, 6 and 7 weeks after challenge, and worm count at 7 weeks after challenge. Young lambs were partially protected by 3 months of age against Trichostrongylus by trickle infection. This protection correlated with local mast cell and T-cell priming, increased numbers of local antigen-presenting cells and T-cells and increased worm-specific antibody titres in the intestine. However, there was no evidence that young lambs were capable of immunologically recognising H. contortus antigens following trickle infection, nor did trickle infection significantly protect young lambs against Haemonchus challenge.

Production and verification of an anti-ovine IgE monoclonal antibody

Recombinant mouse/sheep IgE was used in the production of an anti-IgE monoclonal using conventional hybridoma techniques. The specificity of hybridomas secreting anti sheep IgE monoclonal antibodies was verified using a number of assays including competitive ELISAs, ability to induce mediator release from mast cells, and IgE binding using western blotting. Immunohistochemical staining demonstrated the binding of putative anti-IgE monoclonals to the sheep mast cell surface. The isotype of the antibody was IgG1:K.

Vaccination against worm parasites of animals

The 1990s have seen the culmination of decades of painstaking research with the registration and launch of Tickgard (Hoechst), a recombinant vaccine against Boophilus microplus, and the provisional registration of a Taenia ovis vaccine. Research continues to hold promise for immunological control of Echinococcus, Fasciola, Haemonchus, Trichostrongylus and Ostertagia. Blood-sucking parasites (e.g. ticks and H. contortus) are susceptible to control by vaccines containing 'novel' or 'concealed' antigens where serum antibodies in blood meals attack targets in the gut. Antibodies also provide protection in taeniid models, whereas the protective response to be sought in Fasciola remains unclear. More problematic are formulations and delivery strategies to induce expulsion of gastrointestinal nematodes, using vaccines containing recombinant 'conventional' antigens. The use of computer models to simulate vaccine efficacy in worm control and challenges to the concept of 'hypo-responsiveness' of young lambs will encourage cautious optimism and lively debate as to the prospects for integrated worm control using parasite vaccines. This review covers the aspirations, current success and problems faced by researchers in the parasite arena.

The effects of four neuropeptides on the degranulation of mucosal mast cells from sheep

Isolated mucosal mast cells (MMC) were used to examine the ability of four neuropeptides, substance P, vasoactive intestinal peptide, beta-endorphin and somatostatin, to release mediators in the presence or absence of parasite antigen. None of the neuropeptides induced the release of sheep mast cell protease (SMCP) or histamine from MMC of helminth-immune sheep in the absence of parasite antigen. Incubation of immune MMC with 100 and 1.0 microgram/mL parasite antigen induced 32.1 and 15.5% specific SMCP release, respectively. While the neuropeptides did not augment SMCP release at 100 micrograms/mL parasite antigen, significant enhancement (40-98%) of SMCP release at 1 microgram/mL antigen was obtained by each neuropeptide at concentrations from 10(-8) to 10(-12) mol/L. The results provide additional support for modulation of MMC degranulation by neural activity in sheep and, to our knowledge, this is the first demonstration that the threshold antigen concentration for allergic responses may also be lowered by neuropeptides to render the reaction more sensitive to antigen.

Effect of Freund's adjuvants on guinea pigs infected with, or vaccinated against, Trichostrongylus colubriformis

Soluble antigens that protected guinea pigs against experimental challenge with Trichostrongylus colubriformis were found to be less effective if injected as emulsions in Freund's adjuvants. This occurred despite the production of higher antibody titres in guinea pigs given emulsified antigen. Investigations of this phenomenon showed that an intraperitoneal injection of Freund's complete adjuvant (FCA) delayed rejection of primary infections and partially abrogated resistance to challenge infection. Administration of FCA/antigen emulsion to infected guinea pigs resulted in a prolonged blood eosinophilia which paralleled the increased longevity of the parasitosis. These findings suggest the need for caution in the selection of adjuvants for vaccination against gastrointestinal nematodes.

The sensitization of mucosal mast cells during infections with Trichostrongylus colubriformis or Haemonchus contortus in sheep

Responses of isolated mucosal mast cells (MMC) during infections with either Trichostrongylus colubriformis or Haemonchus contortus were examined by measuring the release of sheep mast cell protease (SMCP) in a degranulation assay. MMC from sheep immune to T. colubriformis released maximal amounts of SMCP and histamine within 0.5h of incubation with larval antigen whereas maximum secretion of leukotrienes occurred 3h after addition of antigen. It was only after 8 weeks of a primary T. colubriformis infection, that MMC released significantly elevated levels of SMCP (23%); this occurred when the worm burden was being rejected. In contrast, the SMCP release from MMC of immune sheep was significantly higher at 40%, and occurred within 1-4 days after challenge (DAC). The SMCP release peaked at 6-8 DAC at 51%, and declined after 56 DAC to < 25%. MMC isolated from the duodenum and mid-small intestine of immune sheep released 2-3 times higher proportion of SMCP than did cells recovered from the terminal ileum. Mast cell numbers were similar in the 3 regions but the quantity of globule leucocytes (GL) was 2.5 times higher in the duodenum. During infections with H. contortus in the abomasum, MMC isolated from the small intestine released greater levels of SMCP when incubated with larval antigens than did abomasal MMC. There was no increased release during the first 12 weeks of a primary infection although the SMCP release (23%) from immune MMC at 7-10 DAC was significantly enhanced. Once again the release from MMC isolated from the three intestinal regions of sheep immune to H. contortus was lowest in the terminal ileum.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary protein intake on responses of young sheep to infection with Trichostrongylus colubriformis

The effects of protein supplementation and infection with Trichostrongylus colubriformis on production responses and immune function in young sheep and on nematode population dynamics were assessed. Eighty-four 3-month-old Merino wether sheep were housed in individual pens and fed ad libitum chopped oaten hay containing 0.5% urea, together with 50 g day-1 lucerne meal. Fish meal (FM) was given as a source of protected protein at 0, 50 or 100 g day-1 (FM0, FM50, FM100; from Days --28 to 140). From Days 1 to 140, 0 or 1000 T. colubriformis infective larvae were given on Mondays, Wednesdays and Fridays. Infected sheep were slaughtered after 35, 70, 105, or 140 days of infection. Live-weight gain was reduced significantly by infection with T. colubriformis in sheep given FM0, but not in sheep given FM50 or FM100. Greasy wool production and fibre diameter were increased by FM, whereas the effects of infection with T. colubriformis on wool measurements depended on the level of FM given. Worm egg concentrations in faeces were significantly lower for sheep given FM100 than for those given FM0 or FM50 during the last 28 days of infection. Similarly, the apparent rate of worm expulsion was considerably higher in sheep given FM than in those not given FM. The rate of expulsion of T. colubriformis correlated with levels of circulating eosinophils as well as with the concentration of intestinal sheep mast cell proteases. Levels of parasite-specific and non-specific circulating antibodies were either unaffected or reduced as a result of supplementation with FM, although lymphocyte stimulation in vitro in response to T. colubriformis third stage larval antigen was enhanced significantly in infected animals given FM100. It was concluded that supplementary feeding with FM substantially reduced the production losses attributable to infection with T. colubriformis and was associated with enhanced expulsion of the parasite burden.

Expulsion of Trichostrongylus colubriformis by high and low responder guinea-pigs

Guinea-pigs with genetically determined susceptibility to infection with Trichostrongylus colubriformis (or low responders) rejected both primary and secondary infections with this parasite more slowly than resistant animals (high responders). Low responders were not protected with a vaccination procedure which was highly effective in outbred animals. The relatively poor protective immune responses that develop in low responder guinea-pigs are evocative of the responses of the natural host to infection with this parasite and suggest that low responder guinea-pigs have potential for the study of T. colubriformis protective antigens and for the development of adjuvants to enhance antiparasitic effector responses in vaccinated hosts.

Production of vaccines against gastrointestinal nematodes of livestock

Three international collaborations involving Australian research scientists are currently developing vaccines against Haemonchus, Trichostrongylus and Ostertagia parasites using recombinant DNA technology. The variety of protective antigens identified can be classified as 'conventional' (stimulate naturally acquired immunity) or 'novel'/'convert'/'concealed' (protective once immunity is induced by vaccination). To date, the most gratifying progress has resulted in 60-90% protection against Haemonchus and other blood-sucking parasites (e.g. ticks) using novel antigens, where high titres of serum antibody ingested by feeding worms leads to their demise. A great deal of research effort is unravelling the complexity of naturally acquired immunity so that conventional antigens, which may be the principal means of removing 'mucosal-browsing' parasites, may be formulated and delivered to achieve optimal efficacy. This work reveals that to remove early stages of parasites before they take up residence, deliberate induction of hypersensitivity responses akin to asthma, may be a desirable goal for vaccines and that the two models have much in common.

Characterization of the mRNA encoding a proline-rich 37-kilodalton glycoprotein from the excretory-secretory products of Trichostrongylus colubriformis

A glycoprotein, with apparent molecular weight in SDS-polyacrylamide gels of 37 kDa, has been isolated from the excretory-secretory (ES) products of the adult stage of Trichostrongylus colubriformis, a parasitic nematode. This protein is the major ES product recognized in immunoblots by lymph from a naturally infected sheep. A synthetic oligonucleotide, based on peptide sequence data from a digest of the purified protein was used to successfully screen a cDNA library. A cDNA clone was isolated which encoded a presumptive protein precursor of 220 amino acids that contained a 63 amino acid region of which more than 35% of the residues were proline, three peptide sequences determined from the natural component, and three potential N-glycosylation sites, consistent with the protein being isolated from the lectin-bound fraction of the adult ES products. The presumptive, processed, amino terminus encoded by the cDNA clone was preceded by a signal-like, hydrophobic-rich region of 16 amino acids.

Isolation and degranulation of mucosal mast cells from the small intestine of parasitized sheep

The isolation of mucosal mast cells and globule leucocytes from the small intestine of sheep immunized with Trichostrongylus colubriformis is described. Sheep mast cell protease was released from these cells in a dose-dependent fashion after incubation with soluble protein from T. colubriformis larvae. Release also occurred with other T. colubriformis antigens whereas non-parasite antigens at comparable protein concentrations evinced only a minimal response. Mucosal mast cells prepared from worm-free sheep also produced a similar minimal response. This is the first report describing the release of sheep mast cell protease from isolated sheep intestinal mucosal mast cells after addition of specific parasite antigens.

A serial study of rejection of Trichostrongylus colubriformis by immune sheep

Host responses and the rejection of worms were measured at intervals following challenge of immune and susceptible sheep with T. colubriformis infective larvae. Immune sheep rejected most of their larvae within the first day after infection. This early rejection was associated with local appearance of globule leucocytes and increased concentration of T. colubriformis-specific IgG1 and IgG2 in intestinal mucus. Rejection of the remaining worms occurred between 3 and 14 days after infection and was associated with increased T. colubriformis-specific IgA and IgG2 in intestinal mucus, local T cell infiltration, activation, differentiation and epithelial necrosis. Local T cell changes included expansion of the T19- gamma delta+ populations in the villous lamina propria and epithelium.

The isolation, characterization and cloning of a globin-like, host-protective antigen from the excretory-secretory products of Trichostrongylus colubriformis

An 18-kDa component from the excretory-secretory (ES) products of adults of Trichostrongylus colubriformis was isolated and characterized, and was shown to induce 60-84% protection of guinea pigs from challenge infection following a single intraperitoneal injection. Amino-terminal sequence analysis of gel-purified protein enabled oligonucleotides to be synthesized and used to screen a lambda gt10 cDNA library made from young adult worm mRNA, and to synthesize full-length clones from cDNA using the polymerase chain reaction (PCR). The full-length clones coded for a 20-kDa precursor protein of 173 amino acids which had a strongly hydrophobic leader sequence of 15 residues. The mature protein sequence of 158 amino acid residues was rich in charged amino acids (32%), including 8 oppositely charged pairs of amino acids. The protein sequence contained no half-cystine residues and no potential N-glycosylation sites. Unlike 2 other fully characterized ES components which are expressed only in the parasitic stages, mRNA coding for the 20-kDa component was present in both the parasitic and free-living stages of T. colubriformis. The parasite protein had approximately 20% identity with globins from human and from the larvae of the insect Chironomus thummi thummi. The homology included the invariant distal histidine and phenylalanine, and a number of other residues highly conserved in globins.

Vaccines against gastrointestinal nematode parasites of ruminants

A consequence of intensive livestock production is an increase in the incidence and impact of gastrointestinal (GI) parasites. Farmers have sought to redress this shift in the natural host-parasite relationship by chemotherapy. However, with the widespread development of resistance to anthelmintics and the current impetus for sustainable agricultural practices, alternatives such as vaccines are being sought to maintain animal productivity. In this article, David Emery and Barry Wagland discuss recent advances in immunity to nematode infections of ruminants and the development of vaccines made possible by the dogged persistence and ingenuity of cadres of parasitologists who have done more than 'go through the motions'.