Systemic release of a mast cell proteinase following nematode infections in sheep

The host immune response to gastrointestinal nematode infection in sheep

Gastrointestinal nematode infection represents a major threat to the health, welfare and productivity of sheep populations worldwide. Infected lambs have a reduced ability to absorb nutrients from the gastrointestinal tract, resulting in morbidity and occasional mortality. The current chemo‐dominant approach to nematode control is considered unsustainable due to the increasing incidence of anthelmintic resistance. In addition, there is growing consumer demand for food products from animals not subjected to chemical treatment. Future mechanisms of nematode control must rely on alternative, sustainable strategies such as vaccination or selective breeding of resistant animals. Such strategies take advantage of the host's natural immune response to nematodes. The ability to resist gastrointestinal nematode infection is considered to be dependent on the development of a protective acquired immune response, although the precise immune mechanisms involved in initiating this process remain to be fully elucidated. In this study, current knowledge on the innate and acquired host immune response to gastrointestinal nematode infection in sheep and the development of immunity is reviewed.

The relationship between protein nutrition, reproductive effort and breakdown in immunity toTeladorsagia circumcinctain periparturient ewes

A nutritional hypothesis for the occurrence of the periparturient relaxation of immunity (PPRI) to gastrointestinal nematodes was tested within the bounds of a nutrient partitioning framework. It was hypothesized that at times of a scarce supply of metabolizable protein (MP), an increase in MP supply or a reduction in MP demand (having singles instead of twins) should lower the extent of PPRI in sheep. Twenty-one single- and 21 twin-bearing and -rearing Finn-Dorset ewes, 2 to 7 years old, and repeatedly infected withTeladorsagia circumcincta, were given one of three pelleted foods (no. = 7). The foods were formulated to supply 0·8 (L), 1·0 (M) and 1·2 (H) times the MP requirements during lactation, and were offeredad libitumfrom d–21to d35(d0 is day of parturition). Faecal egg counts (FEC) were assessed twice weekly as an indicator for host resistance. Dry-matter intake (DMI) during late pregnancy was higher than expected, and MP supply did not limit performance at this stage. In accordance with the hypothesis, there were no indications of a breakdown of immunity toT. circumcinctaduring late pregnancy. DMI during lactation did not differ between the single- and twin-rearing ewes. Calculated milk production was lower for the L than for the M and H ewes, especially for the twin-rearing ewes. A temporarily elevated FEC was observed during the first few days in lactation, which was probably mainly due to changes in faecal output rather than to PPRI. The FEC returned to low, late pregnancy levels at d12and remained low for the single- but not for the twin-rearing ewes (P< 0·001). Overall, the L ewes had higher FEC than the M and H ewes from d19onwards; this effect was more pronounced for the twin- than for the single-rearing ewes. It was postulated that DMI achieved overcame MP scarcity and thus prevented breakdown in immunity in the single-rearing ewes. The data support the view that, at times of MP scarcity, an increase in MP supply and reduction in MP demand can lower the extent of the breakdown in immunity towardsT. circumcincta.

The Identification of Haemonchus Species and Diagnosis of Haemonchosis

Diagnosis is often equated with identification or detection when discussing parasitic diseases. Unfortunately, these are not necessarily mutually exclusive activities; diseases and infections are generally diagnosed and organisms are identified. Diagnosis is commonly predicated upon some clinical signs; in an effort to determine the causative agent, identification of genera and species is subsequently performed. Both identification and diagnosis play critical roles in managing an infection, and involve the interplay of direct and indirect methods of detection, particularly in light of the complex and expanding problem of drug-resistance in parasites. Accurate and authoritative identification that is cost- and time-effective, based on structural and molecular attributes of specimens, provides a foundation for defining parasite diversity and changing patterns of geographical distribution, host association and emergence of disease. Most techniques developed thus far have been grounded in assumptions based on strict host associations between Haemonchus contortus and small ruminants, that is, sheep and goats, and between Haemonchus placei and bovids. Current research and increasing empirical evidence of natural infections in the field demonstrates that this assumption misrepresents the host associations for these species of Haemonchus. Furthermore, the capacity of H. contortus to utilize a considerably broad spectrum of ungulate hosts is reflected in our understanding of the role of anthropogenic forcing, the 'breakdown' of ecological isolation, global introduction and host switching as determinants of distribution. Nuanced insights about distribution, host association and epidemiology have emerged over the past 30years, coincidently with the development of increasingly robust means for parasite identification. In this review and for the sake of argument, we would like to delineate the diagnosis of haemonchosis from the identification of the specific pathogen. As a foundation for exploring host and parasite biology, we will examine the evolution of methods for distinguishing H. contortus from other common gastrointestinal nematodes of agriculturally significant and free-ranging wild ruminants using morphological, molecular and/or immunological methods for studies at the species and genus levels.

An Immediate Innate Immune Response Occurred In the Early Stage of E. granulosus Eggs Infection in Sheep: Evidence from Microarray Analysis

BACKGROUND

Cystic Echinococcosis(CE), caused by infection with the larval stage of the cestode Echinococcus granulosus (E. granulosus), is a chronic parasitic zoonosis, with highly susceptible infection in sheep. However, the comprehensive molecular mechanisms that underlie the process of E. granulosus infection in the early stage remain largely unknown. The objective of this present study was to gain a cluster of genes expression profiles in the intestine tissue of sheep infected with CE.

METHODS

Nine healthy sheep were divided into infection group and healthy controls, with six infected perorally 5000 E. granulosus eggs suspended in 1000 μl physiological saline and three controls perorally injected 1000 μl physiological saline. All animals were sacrificed at 4 hours post-infection, respectively. The intestine tissue was removed and the RNA was extracted. In the infection group, the biology replicates were designed to make sure the accuracy of the data. The ovine microarrays were used to analyze changes of gene expression in the intestine tissue between CE infected sheep and healthy controls. Real-time PCR was used to assess reliability of the microarray data.

RESULTS

By biology repeats, a total of 195 differentially expressed genes were identified between infected group and controls at 4 hours post-infection, with 105 genes related to immune responses, while 90 genes associated with functions including energy metabolism, fat soluble transport, etc. Among the 105 immunity genes, 72 genes showed up-regulated expression levels while 33 showed down-regulation levels. Function analysis showed that most of up-regulated genes were related to innate immune responses, such as mast cell, NK cell, cytokines, chemokines and complement. In addition, Real-time PCR analysis of a random selection of nine genes confirmed the reliability of the microarray data.

CONCLUSION

To our knowledge, this is the first report describing gene expression profiles in the intestine tissue of CE infection sheep. These results suggested that the innate immune system was activated to elicit immediate defense in the intestine tissue where E. granulosus invaded in at 4 hour-post infection. Furthermore, future interest will also focus on unraveling similar events, especially for the function of adaptive immunity, but at late stage infection.

Changes in protein expression in the sheep abomasum following trickle infection with Teladorsagia circumcincta

Continual low-level exposure of sheep to the helminth Teladorsagia circumcincta elicits a temporary protective immunity, where factors in the immune abomasal mucosa prevent penetration of infective larvae, but which is essentially lost within 6 weeks of cessation of parasite challenge. Here, a proteomic approach was used to identify proteins that are differentially regulated in immune compared to naïve sheep, as potential key mediators of immunity. Six naïve sheep and 12 sheep trickle-infected with T. circumcincta were treated with anthelmintic, and the naïve (control) and 6 immune sheep were killed 7 days later. The remaining 6 sheep (immune waning) were killed 42 days after anthelmintic treatment. Abomasal tissue samples were subjected to 2D-gel electrophoresis and densitometric analysis. Selected spots (n=73) were identified by peptide mass fingerprinting and confirmatory Western blotting was carried out for 10 proteins. Spots selectively up-regulated in immune versus control, but not immune waning versus control sheep, included galectin-15 and thioredoxin, which were confirmed by Western blotting. In immune sheep, serum albumin was significantly down-regulated and albumin proteolytic cleavage fragments were increased compared to controls. Unexpectedly, albumin mRNA was relatively highly expressed in control mucosa, down-regulated in immune, and was immunolocalized to mucus-producing epithelial cells. Thus we have identified differential expression of a number of proteins following T. circumcincta trickle infection that may play a role in host protection and inhibition of parasite establishment.

Small ruminant resistance against gastrointestinal nematodes: a case of Haemonchus contortus

Gastrointestinal nematode (GIN) infections are a common constraint to small ruminant industry throughout the world, and among those, haemonchosis has its own significance. Control of GIN primarily relies on the use of anthelmintics, but this approach has become less reliable due to the development of resistance in GINs against commonly used anthelmintics and an increased consumer demand for environmentally friendly animal products. These issues have stimulated investigations to find alternative sustainable control strategies, which are less reliant on anthelmintic input. One of such strategies is breeding of small ruminants for their resistance to the GINs. The susceptibility and resistance of animals to GIN infections varies within and between breeds. Various parasitological, biochemical and immunological parameters are employed to evaluate natural resistance status of animals both in natural pasture and artificial infections. The immune mechanisms responsible for resistance are not completely understood, but it has a significant effect in inherited resistance. Relatively resistant or tolerant animals show better local and generalised immune response as compared to susceptible. Immune response against GINs is influenced by many physiological factors. Determination of specific genes linked with host resistance will provide a valuable approach to find out the molecular mechanism of host resistance to GINs. Resistance has been reported to reduce pasture contamination, which in turn reduces re-infection and thus the requirement of the frequent anthelmintic treatments. The efficiency of control can be increased through objective and accurate identification of genetically tolerant individuals by natural and artificial infections with GINs. Complete resistance is the ultimate solution, but this has generally been ignored as a commercial reality. This paper reviews the published reports on natural resistance in small ruminants and discusses the prospects of developing small ruminants, which could be resistant to GINs.

Novel gene expression responses in the ovine abomasal mucosa to infection with the gastric nematode Teladorsagia circumcincta

Infection of sheep with the gastric nematode Teladorsagia circumcincta results in distinct Th2-type changes in the mucosa, including mucous neck cell and mast cell hyperplasia, eosinophilia, recruitment of IgA/IgE producing cells and neutrophils, altered T-cell subsets and mucosal hypertrophy. To address the protective mechanisms generated in animals on previous exposure to this parasite, gene expression profiling was carried out using samples of abomasal mucosa collected pre- and post- challenge from animals of differing immune status, using an experimental model of T. circumcincta infection. Recently developed ovine cDNA arrays were used to compare the abomasal responses of sheep immunised by trickle infection with worm-naïve sheep, following a single oral challenge of 50 000 T. circumcincta L3. Key changes were validated using qRT-PCR techniques. Immune animals demonstrated highly significant increases in levels of transcripts normally associated with cytotoxicity such as granulysin and granzymes A, B and H, as well as mucous-cell derived transcripts, predominantly calcium-activated chloride channel 1 (CLCA1). Challenge infection also induced up-regulation of transcripts potentially involved in initiating or modulating the immune response, such as heat shock proteins, complement factors and the chemokine CCL2. In contrast, there was marked infection-associated down-regulation of gene expression of members of the gastric lysozyme family. The changes in gene expression levels described here may reflect roles in direct anti-parasitic effects, immuno-modulation or tissue repair. (Funding; DEFRA/SHEFC (VT0102) and the BBSRC (BB/E01867X/1)).

Nutritional sensitivity of periparturient resistance to nematode parasites in two breeds of sheep with different nutrient demands

The periparturient relaxation of immunity (PPRI) to parasites in mammals is sensitive to both metabolisable protein (MP) supply and animal genotype (different reproductive outputs). We tested the hypothesis that the sensitivity of PPRI to MP scarcity would not differ between different levels of reproductive output when nutrient intake is adjusted for associated differences in MP demand; this hypothesis assumes that PPRI has a nutritional basis only. Scottish Blackface (BF) and the more productive Mule (MU) ewes were infected with the abomasal parasite Teladorsagia circumcincta, and from day -21 to day 32 (day 0 is parturition), they were fed restrictedly at either 0.8 (low protein (LP)) or 1.3 (high protein (HP)) times their breed-specific estimated MP requirement (n 18 for each breed-feeding treatment combination). During late pregnancy, LP feeding reduced ewe body weight gain in both breeds, tended to increase faecal egg count (FEC), but it did not affect plasma pepsinogen. During lactation, LP feeding reduced litter growth rate and ewe plasma urea and plasma albumin concentrations compared with HP feeding in both breeds. However, breed and feeding treatment interacted for ewe FEC, worm egg excretion and plasma pepsinogen, which were higher for the LP-MU ewes compared with the HP-MU and BF ewes. The lower degree of PPRI of the BF ewes during lactation compared with the MU ewes at a similar degree of MP scarcity suggests that the effect of reproductive output on nutritional sensitivity of PPRI cannot be explained by associated differences in nutrient demand only.

Proteomic approach to identify candidate effector molecules during the in vitro immune exclusion of infective Teladorsagia circumcincta in the abomasum of sheep

In the present study we have employed an in vitro organ challenge model to study the post-challenge responses in parasite naïve and immune gastric tissue of sheep, in an attempt to identify the host derived factors involved in immune exclusion of Teladorsagia circumcincta larvae. Proteins present in the epithelial cells and mucus from ovine abomasa following parasite challenge in previously naïve and immune animals were analysed through Matrix Assisted Laser Desorption/Ionization-Time of Flight (MALDI-Tof)-MS and shotgun proteomics. MALDI-ToF analysis of epithelial cell lysates revealed that a number of proteins identified were differentially expressed in naïve and immune cells. These included intelectin and lysozymes, which were present at higher levels in epithelial cell lysates derived from immune samples. A large number of proteins were identified in the mucosal wash from immune tissue which were not present in the mucosal wash of the naïve tissue. Some of these proteins were present in washes of immune tissue prior to the parasite challenge including immunoglobulin A, galectin 14 and 15 and sheep mast cell protease 1. However, other proteins, such as calcium activated chloride channel and intelectin were only detected in the washings from the challenged tissue. The latter may be related to an enhanced mucus release, which may result in entrapment of infective larvae and thus reduced establishment in tissue that has been previously challenged with the parasite. In conclusion, several proteins have been identified which may be involved, either directly or indirectly, in the exclusion and immune elimination of incoming infective larvae. In the present study, the usefulness of the in vitro model has been confirmed, and the global proteomic approach has identified proteins that had not previously been associated with parasite exclusion from abomasal mucosa, such as the calcium activated chloride channel.

Feeding practices and effects of gastrointestinal parasite infections on live weight gain of small ruminants in smallholder mixed farms in Kenya

The objective of this study was to quantify the effects of gastrointestinal nematodosis on live weight gain (LWG) of sheep and goats kept in smallholder farms in Kenya. A total of 307 sheep and goats from smallholder farms were sampled using a 2-stage cluster and systematic random approach. Sampled farms were visited once a month for nine months during which a health and production survey questionnaire was administered, animals weighed and fecal samples taken for fecal egg count. Descriptive statistics and a generalized linear mixed model were performed in SAS. The mean LWG of suckling kids and lambs was low (mean=46 g/day). High fecal egg count and lack of feed supplementation were identified as the main factors limiting growth. Improved helminth control and nutrition are required to optimize production.

Increased levels of cysteinyl leukotrienes and prostaglandin E2 in gastrointestinal tract mucus are associated with decreased faecal dry matter in Merino rams during nematode infection

Immune-mediated scouring in sheep is a mucosal hypersensitivity response incited by infective larvae of gastrointestinal nematodes in the southern half of Australia and in New Zealand, regions characterised by a Mediterranean, winter-rainfall climate. To gain insights into the underlying mechanism(s), this study investigated the relationship between nematode infection of sheep in pens, faecal dry matter and release of inflammatory mediators in the intestinal tract. Six worm-free, immune rams received a dose of 3000 Trichostrongylus third stage larvae (L3) and 3000 Ostertagia L3 per week for 6 weeks, after which they were euthanased. Three rams acted as uninfected controls. Faecal dry matter was significantly lower in the infected group from the first week of infection until the end of the trial. Concentrations of cysteinyl leukotrienes and prostaglandin E2 were higher in mucus from both the abomasum and the small intestine of infected rams compared with controls. Within the infected group, concentrations of both mediators were higher in mucus from the small intestine than from the abomasum. There were greater numbers of eosinophilic granulocytes and mucosal mast cells in abomasal and small-intestinal tissue sections from infected rams compared with the controls. The results are consistent with the hypothesis that nematode infection causes an inflammatory response in the gastrointestinal mucosa, characterised by increased fluid secretion.

The involvement of mast cells and mast cell proteinases in the intestinal response to equine cyathostomin infection

Cyathostomins (Cyathostominae) are regarded as the most pathogenic equine nematode worldwide. These nematodes are difficult to control in equine populations due to emerging anthelmintic resistance and evasion of encysted larval cyathostomins to regular modern anthelmintics. Mast cells and their proteinases have been shown to play a role in the mammalian immune response to nematode infections. Involvement of mast cells and mast cell proteinases in the equine immune response to cyathostomin infection is proposed. A technique was established to perform immunohistochemical staining using polyclonal rabbit anti-equine mast cell proteinase-1 (eqMCP-1) and anti-equine tryptase on formalin-fixed large intestinal sections, from horses classified as cyathostomin positive and negative at the time of death based upon larval enumeration. Quantitative analysis of antibody labelled mast cells was used to detect mast cell proteinases in equine large intestinal sections positive and negative for cyathostomin larvae. This demonstrated an increase in equine tryptase labelled mucosal and submucosal mast cells in cyathostomin positive horses. This study has established an immunohistochemical technique to demonstrate mast cell proteinases in formalin-fixed large intestinal sections. This technique may be used to determine possible involvement of mast cells and their proteinases in the equine immune response to cyathostomin larvae. Further studies are required to define a specific role.

Mast cell and eosinophils in the wall of the gut and eosinophils in the blood stream during Toxocara vitulorum infection of the water buffalo calves (Bubalus bubalis)

Toxocara vitulorum is a pathogenic nematode from the small intestine of very young buffalo calves. To understand the development of the inflammatory responses in the wall of the gut, samples of tissues were removed from the duodenum, jejunum and ileum of buffalo calves naturally infected with T. vitulorum during the beginning of the infection, at the peak of egg output, as well as during the periods of rejection of the worms and post-rejection. Two additional control groups of uninfected calves (by anti-helminthic therapy of their mothers and after the birth) were also necropsied on days 30 and 50 after birth. Blood samples were fortnightly collected from birth to 174 days post-birth. Blood smears were prepared and stained with Giemsa for eosinophils. The parasitological status of buffalo calves was evaluated through weekly fecal egg counts (EPG) from 1 to 106 days after birth, which revealed that T. vitulorum egg shedding started on day 11, reached the peak of the infection on day 49 and finally expelled the parasites between days 50 and 85 after birth. In the infected buffalo calves, the mast cell population increased significantly, by two-fold in the mucosa (villus-crypt unit (VCU)) of the duodenum and four-fold in the proximal jejunum; but these increases were statistically significant only at the peak of the infection. Although mast cell numbers increased in the mucosa of the ileum as well as in both the submucosal and muscle tissues of the duodenum, proximal jejunum and ileum, the data was not significantly different from the controls. Eosinophil numbers increased in the mucosa of the duodenum (two-five times higher than the control) and proximal jejunum (three-five-fold) during the period of the infection (beginning, peak and rejection). The relative numbers of eosinophils increased in the blood stream from the second to the seventh week. In conclusion, T. vitulorum infection elicited mastocytosis and tissue eosinophilia in the duodenum and proximal jejunum, as well as eosinophilia in the blood stream, during the beginning, at the peak and during the rejection of the worm. After the rejection of the worms, the numbers of these cells returned to normal levels suggesting that these cells may have a role in the process of rejection of T. vitulorum by the host.

Is the allocation of metabolisable protein prioritised to milk production rather than to immune functions in Teladorsagia circumcincta-infected lactating ewes?

It has been suggested that the periparturient breakdown of immunity to parasites has a nutritional basis. Our overall hypothesis is that it results from a prioritised scarce nutrient allocation to reproductive functions (e.g. milk production) rather than to immune functions. We tested this hypothesis by offering five levels of dietary metabolisable protein, ranging from 0.65 to 1.25 times their assumed requirements, for 4 weeks post-parturition to twin-rearing Greyface ewes, experimentally infected with Teladorsagia circumcincta. We hypothesised that the initial increments of metabolisable protein supply would increase milk production without affecting the degree of breakdown of immunity whilst later increments would reduce the degree of breakdown of immunity. The first two increments of metabolisable protein supply indeed increased milk production and did not affect final worm burdens, but in contrast to the expectation, reduced faecal egg counts and total egg output. The last two increments of metabolisable protein supply did not further affect milk production and egg output, but resulted in reduced final worm burdens. Metabolisable protein supply did not affect plasma IgG and IgE antibody against somatic L(3) antigen but the first three increments reduced plasma pepsinogen and plasma IgA antibody. The last increment did not further reduce plasma pepsinogen but increased plasma IgA. Metabolisable protein supply did not systematically affect abomasal mucosal mast cell, globule leukocyte and eosinophil counts. Our results support the view that the priority of scarce metabolisable protein allocation to milk production over immune functions may be gradual rather than absolute. The contrast between effects of metabolisable protein supply on faecal egg count and final worm burden points towards the possibility that if different effector responses regulate fecundity and worm expulsion, then they would differ in their sensitivity towards changes in the degree of nutrient scarcity.

Immune expulsion of the trichostrongylid Cooperia oncophora is associated with increased eosinophilia and mucosal IgA

Previous experiments have shown that a primary infection with 100000 infective larvae of the trichostrongylid Cooperia oncophora allows discrimination between different type of responder animals based on the speed by which the parasite is expelled from the host. In most of the animals (intermediate responders) the expulsion occurs 35-42 days after infection. This experiment was carried out to investigate which mechanisms contribute to the clearance of the parasite from the intestine. Sequential necropsy of the animals 14, 28 and 42 days after infection together with a segmental division of the small intestine, allowed us to characterise essential components associated with development of immunity and expulsion of the parasite from its niche. The results show that during the patent phase of the infection the parasite preferentially resides in the proximal gut. Forty-two days after infection ongoing expulsion is characterised by a migration of the worms to the more distal part of the intestine. Expulsion of the adult worm population appears to be mast-cell independent and is associated with a significant increase in parasite-specific mucous IgA and IgG1 as well as with an influx of eosinophils in the intestinal lamina propria. Although we did not observe a specific lymphocyte recruitment into the intestinal mucosa, the accumulation of eosinophils seems to be mediated by CD4+ cells. We measured significant negative correlations between the number of eosinophils and the expulsion rate of the parasite expressed by sex ratio and ratio eggs per gram faeces. Parasite-specific mucosal IgA levels were negatively correlated to the fecundity of the worms, expressed as number of eggs per female worm. Our results describe the involvement of both eosinophils and mucosal IgA in the regulation of C. oncophora expulsion and suggest the development of a Th2 effector immune response.

Tissue-specific expression of mast cell granule serine proteinases and their role in inflammation in the lung and gut

Serine proteinases with trypsin-like (tryptase) and chymotrypsin-like (chymase) properties are major constituents of mast cell granules. Several tetrameric tryptases with differing specificities have been characterized in humans, but only a single chymase. In other species there are larger families of chymases with distinct and narrow proteolytic specificities. Expression of chymases and tryptases varies between tissues. Human pulmonary and gastrointestinal mast cells express chymase at lower levels than tryptase, whereas rodent and ruminant gastrointestinal mast cells express uniquely mucosa-specific chymases. Local and systemic release of chymases and tryptases can be quantified by immunoassay, providing highly specific markers of mast cell activation. The expression and constitutive extracellular secretion of the mucosa-specific chymase, mouse mast cell proteinase-1 (mMCP-1), is regulated by transforming growth factor-beta1 (TGF-beta1) in vitro, but it is not clear how the differential expression of chymases and tryptases is regulated in other species. Few native inhibitors have been identified for tryptases but the tetramers dissociate into inactive subunits in the absence of heparin. Chymases are variably inhibited by plasma proteinase inhibitors and by secretory leucocyte protease inhibitor (SLPI) that is expressed in the airways. Tryptases and chymases promote vascular permeability via indirect and possibly direct mechanisms. They contribute to tissue remodelling through selective proteolysis of matrix proteins and through activation of proteinase-activated receptors and of matrix metalloproteinases. Chymase may modulate vascular tissues through its ability to process angiotensin-I to angiotensin-II. Mucosa-specific chymases promote epithelial permeability and are involved in the immune expulsion of intestinal nematodes. Importantly, granule proteinases released extracellularly contribute to the recruitment of inflammatory cells and may thus be involved in innate responses to infection.

Proteolytic action of duodenase is required to induce DNA synthesis in pulmonary artery fibroblasts

Duodenase is a 29-kDa serine endopeptidase that displays selective trypsin- and chymotrypsin-like substrate specificity. This enzyme has been localized to epitheliocytes of Brunner's glands, and as described here, to mast cells within the intestinal mucosa and lungworm-infected lung, implying an important additional role in inflammation and tissue remodelling. In primary cultures of pulmonary artery fibroblasts, duodenase induced a concentration-dependent increase in [3H]thymidine incorporation with a maximal effect observed at 30 nm. Pretreating duodenase with soybean trypsin inhibitor abolished DNA synthesis, confirming that proteolytic activity was an essential requirement for this response. PAR1, PAR2 and PAR4 activating peptides were unable to induce [3H]thymidine incorporation in pulmonary artery fibroblasts. Likewise, pretreatment of fibroblasts with TNFalpha, known to up-regulate PAR2 expression in other systems, and IL-1beta, did not enhance the potential of duodenase to induce DNA synthesis. Furthermore, duodenase increased GTPgammaS binding to fibroblast membranes indicating that a G-protein-coupled receptor may mediate the effects of duodenase. Duodenase-induced DNA synthesis and GTPgammaS binding were both found to be inhibited by pertussis toxin, implying a role for Gi/o. Selective inhibitors of MEK1 (PD98059) and protein kinase C (GF109203X) only partially inhibited duodenase-induced DNA synthesis, but both wortmannin (100 nm) and LY294002 (10 microm) inhibited this response completely, indicating a key role for PtdIns 3-kinase. Furthermore, duodenase induced a 2.3 plus minus 0.1-fold increase in PtdIns 3-kinase activity in p85 immunoprecipitates, which was sensitive to inhibition by wortmannin. These results suggest that duodenase can induce pulmonary artery fibroblast DNA synthesis in a PtdIns 3-kinase-dependent manner via a G-protein-coupled receptor which is activated by a proteolytic mechanism.

Nutrient partitioning between reproductive and immune functions in animals

The physiological processes that underlie the reproductive cycle impose considerable metabolisable protein (MP) demands on a female, especially during the periparturient period. When MP supply falls short of MP demand (i.e. MP becomes scarce), certain, if not all, bodily functions are expected to be penalised. It has been proposed that partitioning of scarce MP is prioritised to reproductive rather than to immune functions. In other words, at times of MP scarcity, the penalty on expression of immunity would be expected to be greater than that on reproduction. This hypothesis forms a nutritional basis for the occurrence of periparturient breakdown of immunity to parasites (BIP), which can be observed in many host-parasite systems. In the present review we explore this nutritional basis, using periparturient sheep infected with the abomasal nematode Teladorsagia circumcincta as an example, and attempt to quantify its occurrence. Evidence supporting the nutritional basis of periparturient BIP is reviewed, covering experiments in which nutrient supply (from both exogenous and endogenous sources) and/or nutrient demand were manipulated. Quantitatively, MP requirements for expression of immunity to T. circumcincta were estimated to be about 1 g/kg metabolic body weight (body weight 0.75) per d, approximately 5% of the maximum MP requirements of periparturient sheep. The major component of this requirement was assumed to be for replenishing irreversible plasma protein losses into the gastrointestinal tract. Although confirmation of this estimate is required, such estimates may be used to improve the known MP requirements of periparturient animals, enabling the extent and the consequences of periparturient BIP to be minimised.

The expression of immunity to Teladorsagia circumcincta in ewes and its relationship to protein nutrition depend on body protein reserves

We hypothesized that expression of immunity to gastrointestinal nematodes and its relationship with dietary metabolizable protein (MP) supply in ewes depended on body protein--but not on body fat reserves. Twin-bearing ewes were trickle infected with Teladorsagia circumcincta. Three mid-pregnancy feeding treatments were used, calculated to maintain body reserves (HH), maintain body protein- and lose body fat reserves (HL), or lose body reserves (LL), and followed by 2 isoenergetic, periparturient feeding treatments, calculated to provide either scarce (LP) or adequate (HP) amounts of MP. At the end of the mid-pregnancy feeding treatment, HL- and LL-ewes had a smaller backfat depth (approximately body fat reserves) than HH-ewes, and LL-ewes had a smaller muscle depth (approximately body protein reserves) and higher faecal egg counts (FEC) than HH- and HL-ewes. Overall, LL-ewes had higher periparturient FEC than HH- and HL-ewes, and LP-ewes had higher periparturient FEC than HP-ewes. However, LL-ewes offered the LP feed had higher periparturient FEC than ewes on any of the other combinations of feeding treatments. Feeding treatments affected plasma pepsinogen but not plasma IgA. The results support the view that body protein- but not body fat reserves may overcome consequences of dietary MP scarcity on periparturient breakdown of immunity to gastrointestinal nematodes.

Parasitological characteristics and tissue response in the abomasum of sheep infected with Haemonchus spp

A histopathological study was conducted on the abomasal mucosa of 40 Corriedale sheep exposed to natural infection with Haemonchus spp. The sheep were allowed to graze on contaminated pastures for 14 days and, after being housed for 28 days, they were slaughtered. Fecal samples were collected for fecal egg counts (FEC) and abomasum samples were obtained for histopathological examination and eosinophil, mast cell and globule leucocyte counts. The number of Haemonchus spp. present in the abomasum was estimated from a 10% aliquot of its content. The number of eggs per female was estimated for 10 Haemonchus spp. females collected from each animal. The following significant correlation coefficients were obtained between the characteristics analyzed: number of Haemonchus and FEC (r = 0.86), female length and number of eggs per female (r = 0.60), female length and FEC (r = 0.53), number of eosinophils and number of Haemonchus (r = 0.48), number of eosinophils and number of globule leucocytes (r = 0.54), number of mast cells and female length (r = -0.39), and number of mast cells and number of globule leucocyte (r = 0.34). The characteristics that showed the highest correlation with animal load was FEC.

Mucosal defense against gastrointestinal nematodes: responses of mucosal mast cells and mouse mast cell protease 1 during primary strongyloides venezuelensis infection in FcRgamma-knockout mice

A possible role for the gamma subunit of immunoglobulin Fc receptors (FcR) in mucosal defenses against intestinal nematode parasites was studied using age-matched FcRgamma-knockout (FcRgamma(-/-)) and wild-type (FcRgamma(+/+)) C57BL/6 mice. Mice were infected subcutaneously with 3,000 infective larvae of Strongyloides venezuelensis, and the degree of infection was monitored by daily fecal egg counts and adult worm recovery on days 8 and 13 postinfection. Mucosal mast cell (MMC) responses were assayed by in situ intestinal mast cell counts in stained histological sections of the jejunum and by measuring mouse mast cell protease 1 (MMCP-1) release in serum using sandwich enzyme-linked immunosorbent assay. FcRgamma(-/-) mice had significantly higher egg counts (P<0.01) and numbers of adult worms (P<0.05) than FcRgamma(+/+) mice, but mastocytosis and serum MMCP-1 release were comparable. It was concluded that MMCP-1 release may be spontaneous, does not depend on mast cell degranulation via the FcRgamma signaling system, and appears to play no role in the expulsion of S. venezuelensis. The delay in worm expulsion in the FcRgamma(-/-) mice might be related to inability of the MMC to degranulate and release effector molecules other than MMCP-1, since FcRgamma deletion abrogates mast cell degranulative responses.

Can an increased intake of metabolizable protein affect the periparturient relaxation in immunity against teladorsagia circumcincta in sheep?

Within the overall hypothesis that the periparturient relaxation of immunity (PPRI) to gastrointestinal parasites has a nutritional basis, we studied whether an increased intake of metabolizable protein (MP) could affect the expression of immunity to Teladorsagia (Ostertagia) circumcincta of twin-bearing and -rearing Greyface ewes. Two sets of iso-energetic diets were formulated to provide either 85% (L-) or 130% (H-) of the MP requirements during the last 6 weeks of pregnancy (-P) and the first 6 weeks of lactation (-L). Thirty ewes were allocated to LP or HP. Six ewes of each group were slaughtered after lambing (S(0)); the remaining 24 ewes of each group were allocated to either LL or HL, thus creating four treatment combinations during lactation (LP/LL, LP/HL, HP/LL and HP/HL; n=12). Six ewes of each treatment combination were slaughtered at Week 3 (S(3)) or at Week 6 (S(6)) in lactation. The HP ewes were heavier at lambing, produced heavier lambs, had lower faecal egg counts (FECs), a lower concentration of plasma pepsinogen, a higher concentration of plasma albumin during late pregnancy and more abomasal globule leukocytes (GLs) but similar worm burdens at S(0) compared to the LP ewes. The LP/HL and HP/HL ewes had a higher calculated milk production than the LP/LL and HP/LL ewes. FECs increased for each treatment combination during the first 3 weeks of lactation. This increase concurred with fewer abomasal GLs at S(3) compared to S(0). The LP/HL and HP/HL ewes had a higher proportion of immature worms and more abomasal GLs than the LP/LL and HP/LL ewes at S(6). The FECs continued to increase during the second 3 weeks of lactation for the LP/LL ewes only, which concurred with an elevated plasma pepsinogen concentration and an absence of abomasal GLs at S(6). The plasma pepsinogen concentration decreased rapidly for the LP/HL ewes during lactation. We conclude that an increased intake of MP could enhance the expression of immunity to T. circumcincta of twin-bearing and -rearing Greyface ewes.

The immunobiology of gastrointestinal nematode infections in ruminants

The major gastrointestinal nematode parasites of ruminants all belong to the Order Strongylida and the family Trichostrongyloidea. Despite this close evolutionary relationship, distinct differences exist in the microenvironmental niches occupied by the developmental stages of the various parasites, which may account for the variable susceptibility of the different parasite species to the immune effector mechanisms generated by the host. In addition, different manifestations of resistance have been observed against the adult and larval stages of the same parasite species, and even against the same parasite stage. In particular, both rapid and delayed rejection of infective larval stages of gastrointestinal nematode parasites has been documented. This review will give an overview of the various manifestations of resistance to gastrointestinal nematode parasites of ruminants, as well as the immune mechanisms and antigens associated with the generation of immunity by the ruminant hosts to these parasites. In addition, a working model is provided aimed at reconciling most of the present knowledge on the different immune responses generated during infection with the various parasite rejection profiles. Extrapolation of these results to field conditions will need to take into account the variability imposed by seasonal changes and management practices, as well as the individual variability in immune responsiveness present in outbred animal populations.

The rat mucosal mast cell chymase, RMCP-II, alters epithelial cell monolayer permeability in association with altered distribution of the tight junction proteins ZO-1 and occludin

Mucosal mast cells undergo hyperplasia in a variety of inflammatory bowel diseases including nematode infection in man and animals. The intra-epithelial localization of these cells make their soluble mediators prime candidates for modulators of epithelial function. In particular previous in vivo and ex vivo studies have established a link between the release of the highly soluble mast cell granule chymases and increased mucosal permeability. The hypothesis that the rat mast cell protease, RMCP-II, directly increases permeability to macromolecules via the paracellular route is tested in this study. Monolayers of epithelial cells (Madin-Darby canine kidney cell line) were exposed to varying concentrations of RMCP-II in vitro, in the absence of other cell types or mediators, and the effect on permeability and tight junction associated proteins was investigated. Basolateral, but not apical, exposure of polarized MDCK monolayers on porous supports to RMCP-II led to concentration- (> 100 microg/ml) and time-dependent increases in electrical conductance and permeability to mannitol (MW182) and inulin (MW5000), which was accompanied by decreases in the immunostaining of the tight junction-associated proteins occludin and ZO-1. Furthermore, prolonged exposure to RMCP-II (> 12 hours) resulted in the formation of identifiable gaps separating adjacent epithelial cells, in the absence of evidence of cytotoxicity. Inhibition of RMCP-II with Soya bean trypsin inhibitor completely abrogated the response, demonstrating that proteolysis was required. These data provide direct evidence that the rat mast cell chymase RMCP-II can, in the absence of other inflammatory mediators, increase epithelial permeability via an effect on the paracellular route.

Pathogenicity and immunogenicity of different isolates of Teladorsagia circumcincta

The effects on liveweight gain and development of immunity were studied in lambs trickle infected for 8 weeks with either a benzimidazole-resistant isolate (Moredun ovine resistant isolate, MORI), a multiple benzimidazole + ivermectin-resistant isolate (Moredun caprine resistant isolate, MCRI) or an unselected susceptible isolate (Moredun ovine susceptible isolate, MOSI) of Teladorsagia circumcincta. Plasma pepsinogen concentrations of infected groups were significantly elevated compared to an uninfected control group (P < 0.001) by day 14. The liveweight gains varied markedly but there were no statistical differences between the infected and uninfected control groups at any point in time during the study. Lambs infected with the MORI had significantly lower faecal consistency scores than the other challenged groups on days 7 and 14 (P < 0.05) but from day 21 onwards, faecal consistencies were similar in all of the groups. There was a notable difference in the pre-patent periods of the different isolates with the MOSI producing positive faecal egg counts (FECs) by day 14 of the study. The FECs remained reasonably low once infections had reached patency and there were no further differences between the groups. Following administration of anthelmintic to remove residual worms from the trickle infection, no differences between the infected groups in terms of worm burden or mucosal mast cell numbers were evident as a consequence of a single challenge infection. The changes in genetic code associated with enhanced resistance against anthelmintics do not appear to have resulted in any fundamental alteration of the pathogenicity and immunogenicity of these three isolates of Teladorsagia.

The isolation and purification of a dual specific mast cell-derived protease from parasitised caprine jejunal tissue

A mast cell granule protease has been isolated and purified from nematode-infected caprine jejunal homogenate by FPLC techniques and termed Goat Mast Cell Protease (GMCP). The purification steps were monitored for proteolytic activity against the synthetic substrate carboxybenzoyl-L-lysine thiobenzyl ester (BLT) and the presence of a homogenous protease preparation in the final sample was shown by SDS-PAGE electrophoresis. This protease was compared with enzymatic activity from isolated mucosal mast cells, which demonstrated the putative mast cell-derived source of the purified enzyme. Rabbit antiserum was raised against the protease and through the use of immunohistochemistry and Western blotting techniques the mast cell origin of the protease was confirmed. NH2-Terminal amino acid sequence analysis demonstrated a high degree of homology between GMCP and other previously isolated mast cell proteases including sheep mast cell protease (SMCP). Substrate analysis showed that GMCP also had an unusual dual chymotrypsin-like and trypsin-like activity similar to SMCP and bovine duodenase.

The effects of recombinant ovine interleukin-3 and recombinant ovine stem cell factor on the growth and mediator expression of caprine and ovine bone marrow-derived mast cells

The growth of ovine and caprine mast cells in bone marrow cultures has been achieved using recombinant ovine interleukin-3 (rOvIL-3) and recombinant ovine stem cell factor (rOvSCF). After approximately 2-3 weeks' growth in optimal concentrations of either rOvIL-3 alone or a combination of rOvIL-3 and rOvSCF, the majority of the cells produced in bone marrow culture from both species were mast cells. The significant increase in the total numbers of cells and survival times of the cultures when both cytokines were present compared to either alone, indicated synergy between rOvIL-3 and rOvSCF on mast cell growth. Ovine and caprine cells cultured in rOvIL-3 alone produced a four-fold increase in cell numbers compared with medium only controls. The resulting cultures contained up to 52% mast cells by day 18 and had a lifespan of 3-4 weeks. In contrast, cells from both species grown in both rOvIL-3 and rOvSCF produced up to six times more cells than the equivalent rOvIL-3 stimulated cultures, contained up to 69% mast cells by day 21 and could be maintained for at least 6 weeks. Ovine cells grown in rOvIL-3 alone or rOvIL-3 and rOvSCF contained significantly more aryl-sulfatase and serine protease but similar amounts of beta-hexosaminidase compared with caprine cells during the second week of culture. There were no significant differences in the granule-associated mediator content of cells from either individual species grown in rOvIL-3 alone compared with those grown in rOvIL-3 and rOvSCF during the first 21 days of culture.

Persistence of immunity of Nematodirus battus infection in lambs

Fifty-four Greyface Suffolk lambs aged 3 months were allocated to six groups of seven and one group of 12. Three groups were infected continuously with Nematodirus battus larvae (L3) over a 7-week period and three groups remained worm-free. One week after the last larval dose all six groups were treated with anthelmintic and challenged with a single dose of 30,000 N. battus L3 either 1, 6 or 12 weeks post-treatment (PT) and killed 10 days later. A seventh continuously infected and treated group (n = 12) was segregated into four sub-groups of three lambs which were used as tissue cell count controls and provided data on local cellular responses prior to challenge. Lambs in the first sub-group were killed immediately after anthelmintic treatment and those in the other sub-groups were killed on the same day that the lambs in the other main groups were challenged. Overall post-challenge worm burdens did not differ significantly between previously infected and challenge control groups although they were significantly reduced in both treatment groups by Week 12 PT. The principal manifestation of acquired immunity that was maintained throughout 12 weeks without further infection was retardation in larval development. There was also evidence of preferential rejection of male worms from immune lambs. Local mast cell, but not eosinophil, responses were significantly enhanced by previous infection and persisted up to Week 12 PT. The numbers of bone marrow eosinophils were significantly increased as a result of previous infection and this response persisted up to Week 12 PT. During primary infection anti-L4 and anti-adult worm IgG responses were significantly increased in the previously infected lambs by Day 42 post-infection. Eosinophil responses during this period did not differ between groups. The inflammatory cell responses, coupled with the parasitological observations, suggest that immunity to previous infection is maintained for up to 12 weeks PT without further antigenic stimulation. This 'immunological memory' may have waned partially after 6 weeks PT although the superimposition of age resistance may have masked the effect.

Defence against the immune barrage: helminth survival strategies

Parasites have generated a range of countermeasures against the host immune system which allows their survival long enough for reproduction to occur. Parasite subsistence is enhanced by evasion of the immune response utilizing mechanisms such as antigenic variation of exposed immunogenic proteins, shedding of surface proteins which are the target of an immune response, and protease production to neutralise specific anti-parasite immune components. Recent advances in the fields of immunology and parasitology have highlighted a range of mechanisms by which the parasite actively modulates the immune response to allow survival. Parasite factors can directly suppress the function of certain subsets of immune cells as well as stimulating other cell populations which have suppressive activity. Strategies such as the skewing of the type 1-type 2 cytokine profile to that of a less appropriate response, and the mimicry of host immune regulatory proteins are becoming more widely acknowledged as means by which helminths enhance their survival. An illustration of the extent by which parasites can exploit host immune components is emphasized by the use of host cytokines as parasite growth factors. This review will examine some of the strategies developed by helminths which enables them not only to survive in the host, but also to prosper.

The response of breeding doses to nematodiasis: segregation into "responders" and "non-responders"

Responder and non-responder does were identified from a flock of 95 Scottish cashmere 2-6 year-old does exposed to natural nematode infection over a 12-month period. Every 5 weeks, the does were faecal sampled for worm-egg counts prior to anthelmintic treatment. Responsive and non-responsive individuals were identified on the basis of their cumulative faecal egg count (FEC) rankings: the 8 lowest and 8 highest rankings were deemed to be responders and non-responders, respectively. Retrospective analysis showed that the mean egg count of the 8 responders was significantly lower than that of the 8 non-responders. The selected responders and non-responders were subsequently housed together with 8 randomly selected does from a control line, and given a mixed trickle challenge with Teladorsagia circumcincta and Trichostrongylus vitrinus larvae (L3). Mean responders FEC was significantly lower following artificial infection than that of non-responder and unselected does. Peripheral eosinophilia was significantly greater in responders in the first 3 weeks of this infection. On day 60, the infection was terminated with anthelmintic and 7 days later the goats were given a single challenge of 50,000 T. circumcincta L3. The mean responder worm burden was lower, and exhibited greater evidence of retardation of worm development, than those of non-responder and unselected does. Responders had significantly more mast cells and globule leukocytes post-challenge than did the other 2 groups. These results suggest that under the conditions encountered in this experiment, it is possible to segregate goats into responders and non-responders using simple parasitological criteria, as individual responsiveness is a relatively repeatable phenomenon.

The pathophysiology and development of immunity during long-term subclinical infection with Trichostrongylus colubriformis of sheep receiving different nutritional treatments

The objective of this study was to investigate the relationship between protein nutrition, the pathophysiology, and acquisition and expression of immunity in long-term subclinical intestinal parasitism in sheep. Growing sheep were either uninfected controls or parasitised for 27 weeks with a daily dose of 2500 larvae of Trichostrongylus colubriformis, whilst they were given access to: (1) a low protein food, (2) a high protein food, or (3) a choice between the two foods, where they were allowed to select their diet. Blood samples were taken weekly for determination of serum albumin, total protein, Ca, P, urea and fructosamine concentrations. At the end of the study all sheep received a single (secondary) challenge infection (30,000 T. colubriformis L3) after treatment with anthelmintic to assess their immune status. The concentrations of sheep-mast cell proteinases (SMCP) in intestinal tissue, the number of circulating eosinophils and the total worm numbers recovered from the intestinal tract were used to investigate the effects of previous nutrition on the acquisition and expression of immunity. From the biochemical variables measured over 27 weeks, only serum fructosamine was affected by the interaction between feeding treatment and parasitism: fructosamine concentrations declined only in the parasitised animals on the low protein food during Weeks 6-15 of infection. This casts doubt on the usefulness of plasma fructosamine levels as an indicator of gastrointestinal parasitism, due to its being influenced by the nutritional environment. Total protein, albumin, calcium and phosphorus concentrations in the serum were affected by parasitism, but independently of feeding treatment. During the period of secondary challenge eosinophil numbers and SMCP concentrations were higher in the parasitised animals, reflecting the animals immune responsiveness. The numbers of worms recovered from the intestine of previously parasitised sheep were low; all three indicators of the development of acquired immunity were unaffected by previous nutritional treatment of the sheep. The results do not support the view that the pathophysiology of long term subclinical intestinal parasitism and the expression of acquired immunity induced by a trickle infection could be affected by the feeding treatment of the sheep (protein nutrition).

Phenotypic markers for selection of nematode-resistant sheep

Nematode-resistance of an animal can be defined as an enhanced natural ability, relative to its peers, to both prevent establishment of larval nematodes and evict any that do establish. These parameters are not measurable in a practical sense and consequently nematode-resistance has usually been defined in terms of low faecal nematode egg counts (FEC). Studies in New Zealand and Australia have demonstrated that nematode-resistance, as measured by FEC, has a heritability of about 0.3 in Romney and Merino sheep. However as a selection trait FEC has practical limitations and its use may incur production penalties through withholding drench treatment for prolonged periods or from a need for artificial challenge. FEC is influenced by the level and composition of a natural nematode challenge and especially the expression of the immune response. Thus immunological parameters which reflect the underlying genetic resistance could potentially be used as phenotypic markers. Ideally, a useful phenotypic marker would be easy to sample and its assay would be inexpensive and able to be automated, in addition to being strongly correlated with nematode-resistance. Results from several New Zealand trials have indicated that antibody levels (particularly IgG1) to excretory/secretory antigens of L3 nematodes such as Trichostrongylus colubriformis may meet these criteria. Levels of antibody against L3 antigens are also independent of on-farm drenching strategies. Blood eosinophil count has also been considered for use as a selection parameter but a high degree of sample variability reduces its potential. Other immunological parameters associated with nematode-resistance which have potential as phenotypic markers include serum nematode-specific IgE and products of mucosal mast cells such as proteinases. It is likely that as the critical immune responses of sheep to nematodes become more clearly defined, new immunological parameters with potential for use as phenotypic markers will be found. The definition of these immune responses will also assist in the identification and characterization of genetic markers.

Prospects for the immunological control of ruminant gastrointestinal nematodes: natural immunity, can it be harnessed?

Current understanding of the mucosal immune response to nematode parasites is briefly reviewed with emphasis on the role of the cytokines interleukins-4 and -12 and gamma interferon (IFN gamma) in the development of T-helper responses in rodents. Data from laboratory animals and ruminants indicate that the events associated with a T-helper 2 (Th2) cell response, notably IgE synthesis, eosinophilia and mucosal mastocytosis are protective. Evidence that effector mechanisms may vary for different parasite species is considered. Current gaps in understanding such as the location in the gut and mechanism of antigen processing and presentation as well as the relative contribution of non-immunological effector responses, such as gut motility and mucus secretion, to worm expulsion are discussed.

Nutrition and parasite interaction

This overview focuses on the interaction between nutritional status and gastrointestinal nematode infection in ruminants and considers: (i) the influence of the parasite on host metabolism; and (ii) the effect of host nutrition on the establishment and survival of parasite populations, the development of the host-immune response and the pathophysiology of infection. Gastrointestinal nematodes reduce voluntary feed intake and efficiency of feed utilisation, a key feature being an increased endogenous loss of protein into the gastrointestinal tract. Overall there is movement of protein from productive processes into repair of the gastrointestinal tract, synthesis of plasma proteins and mucoprotein production. Although reduction in feed intake is a major factor contributing to the reduced performance of parasitised ruminants, the underlying mechanisms of the anorexia are poorly understood. Supplementation of the diet with additional protein does not appear to affect initial establishment of nematode infections but the pathophysiological consequences are generally more severe on lower planes of protein nutrition. The main effect of protein supplementation is to increase the rate of acquisition of immunity and increase resistance to reinfection and this has been associated with an enhanced cellular immune response in the gastrointestinal mucosa. The unresponsiveness of the young lamb can be improved by dietary protein supplementation. Recent trials have shown that growing sheep offered a free choice between a low and a high protein ration are able to modify their diet selection in order to alleviate the increase in protein requirements which result from gastrointestinal nematode infection. Studies on the influence of nutrition on the expression of genotype have shown that the benefits of a superior genotype are not lost on a low protein diet whereas a high protein diet can partially emeliorate the disadvantages of an inferior genotype. In addition to dietary protein both macro-minerals and trace elements can influence the host-parasite relationship.

Sequential cellular and humoral responses in the abomasal mucosa and blood of Romney sheep dosed with Trichostrongylus axei

Abomasal cannulae were surgically placed in 7 2-year-old New Zealand Romney sheep which had been maintained parasite-free from birth. Four of these sheep were randomly selected and dosed orally with 10,000 infective Trichostrongylus axei larvae per week for 8 weeks, while the remaining 3 sheep served as uninfected controls. Abomasal biopsy, blood and faecal samples were obtained from all sheep at regular intervals from 5 days before and until 58 days after the first infection. The sheep were then killed, worm burdens assessed and abomasal and small intestinal samples collected Faecal egg counts of all 4 dosed sheep were low and only one (No. 701) had a substantial worm burden (8400) post mortem. Overall, levels of mucosal mast cells/globule leukocytes, eosinophils, T19+ cells and larval migration inhibitory activity increased significantly in the abomasal mucosa of the dosed sheep compared to the controls. The CD4+:CD8+ cell ratio in the abomasal mucosa of the dosed sheep also increased compared to that of the controls (P = 0.06). In blood, T. axei-specific antibody (total and IgG1) and eosinophil numbers increased significantly in the dosed sheep. Mucosal cells staining for IgE (IgE+), and blood and mucosal eosinophils showed the earliest substantive increases in number followed by increases in specific serum antibody levels, numbers of mucosal cells fluorescing under UV light (UVf) and T19+ cells. The difference in the IgE+ and UVf cell responses indicated that expansion of globule leukocyte numbers lagged behind that of mucosal mast cells. The results supported the concept of CD4+ T cell help in the abomasal mucosa and defined the sequential expression of components of the immunological responses potentially mediating resistance to T. axei. In sheep No. 701, persistence of adult worms was associated with lower mucosal IgE+ cell and eosinophil responses compared with the other dosed sheep.

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.

Dietary protein influences upon immunity to Nematodirus battus infection in lambs

Several indices of the immune response to Nematodirus battus infection in lambs offered differing levels of dietary protein were quantified. Lambs were offered either a complete basal ruminant diet (13.2% crude protein (CP)) or the same diet supplemented with fish meal as a source of rumen bypass protein (18.3% CP). Lambs from each dietary treatment group were given either a 7-week continuous trickle infection with N. battus L3 or remained uninfected. All lambs were drenched with anthelmintic at week 8 post-infection (PI), challenged with a single dose of 30,000 N. battus L3 1 week later, and killed 9 days post-challenge (PC). Previous infection induced a significant reduction in worm burdens (p < 0.001) and enhancement of immune responses when compared to challenge controls. Among previously infected lambs, protein supplementation did not reduce worm burdens significantly, although there was a trend for fewer worms in the supplemented lambs. However, a significant increase in mucosal globule leucocyte (p < 0.05) and eosinophil (p < 0.05) numbers was evident. Supplementation (p < 0.05) and previous infection (p < 0.001) both enhanced serum anti-worm IgG titres over time. Peripheral blood eosinophil counts were not affected by supplementation but were significantly elevated over time as a result of previous infection (p < 0.001). Since there were no significant differences in worm burdens of supplemented and unsupplemented previously infected lambs, it was of interest to determine whether lambs possessed an innate ability to regulate their parasite burden. Hence they were re-grouped based on an arbitrary cut-off burden of 1000 worms. High responders (HR) had burdens below 1000 worms, while low responders (LR) had burdens above this value and challenge controls were pooled. The data were re-analyzed based on these groupings and showed significant reduction in worm burdens between all three groups (p < 0.001). Globule leucocytes were the only cell type that appeared to be significantly more abundant in the intestinal mucosa of HR (p < 0.001). Serum antibody responses (p < 0.05) and peripheral blood eosinophil counts (p < 0.01) were significantly elevated over time in accord with the degree of responsiveness. The results of this study suggest that supplementation of protein upon an adequate basal diet of lambs previously exposed to N. battus does not significantly enhance worm regulation despite significant increases in cellular and antibody responses. The immunity acquired is characterized by reduction in worm burdens, elevated anti-worm antibodies and a cellular inflammatory response. The identification of HR and LR essentially shows that when the protein supply is adequate, the predominant host effect influencing the pathogenicity of the parasites is the level of genetically determined susceptibility of the host.

Serum mast cell proteinase responses of sheep to challenge with Trichostrongylus colubriformis and the effect of dexamethasone treatment

Eight-month-old random bred Romney wethered lambs were reared nematode-free in pens and assigned to 4 groups of 5 lambs. Lambs in 2 groups were dosed orally, twice a week, with 5000 Trichostrongylus colubriformis infective larvae (L3) for the duration of the experiment. These 2 groups were treated weekly with dexamethasone (0.5 mg kg(-1) body-weight), one between days -7 and 70, the other between days 77 and 147. A third group was dosed with L3 until anthelmintic treatment on day 133. A fourth group remained uninfected throughout and served as a control group. Nematode eggs in sheep faeces (FEC) were monitored at weekly intervals. Serum samples were taken twice a week and assayed for sheep mast cell proteinase (SMCP). Serum levels of SMCP in uninfected control sheep were 459 +/- 190 pg ml(-1). Twenty-eight days after nematode dosing commenced, SMCP levels were significantly above control sheep levels and after 49 days reached a plateau level of 1154 +/- 364 pg ml(-1). The SMCP response persisted even after cessation of dosing, and SMCP levels remained significantly above control levels to the end of the experiment (day 213). Dexamethasone treatment prevented elevation of SMCP and resulted in a rapid reduction of extent SMCP levels in resistant sheep. Overall, serum levels of SMCP were significantly correlated (P<0.001) with specific anti-T. colubriformis L3 antibody in serum (r = 0.601, d.f. = 78), blood eosinophils (r = 0.609, d.f. = 78) and log(FEC+15) (r = -0.521, d.f. = 78). These results show that serum levels of SMCP correlate with other indicators of parasitism and may have potential use as a non-invasive indicator of gastrointestinal mast cell responses to nematode infection.

Dietary protein for young grazing sheep: interactions with gastrointestinal parasitism

Effects of protein supplementation and of nematode control on production responses in young grazing sheep and on nematode population dynamics were assessed. Young Merino wether sheep (n = 270) were allocated to one of three supplementation (Su) treatments and one of three regimes of nematode control (drench, Dr) in a factorial design. Each of the nine treatments was replicated three times in a randomised complete block. Animals received no supplement (Su0) or were given supplements at a level equivalent to 200 g day-1, fed three times a week. The supplements contained 25% lucerne meal with either 75% sunflower meal (Su1) or 75% formaldehyde-treated sunflower meal (Su2). Nematode control regimes were: not drenched unless survival of individual animals was threatened (Dr0); drenched according to a strategic drenching programme (Dr1); treatment with a controlled-release albendazole capsule (Dr2). Infections with Haemonchus contortus were suppressed by use of closantel. Due to drought conditions and lack of pasture growth, lucerne hay was fed to all sheep from Week 14 onwards (350 g per head per day, fed twice a week). Supplementation reduced the need for 'survival drenching' in Dr0 sheep considerably. Live-weight gain was increased significantly by supplementation with Su1 or Su2 during the 36-week experiment. Undrenched animals given Su1 or Su2 tended to grow faster than unsupplemented animals in the Dr1 and Dr2 groups. Greasy wool production and fibre diameter were increased by supplementation and anthelmintic treatment. Faecal worm egg counts (FEC) in undrenched sheep were significantly lower for Su1 and Su2 sheep than for Su0 sheep. There were no effects of supplementation on FEC in Dr1 or Dr2 sheep. Worm burden was generally unaffected by supplementation, while the drenching treatments Dr1 and Dr2 reduced worm burden at Week 16 and to a lesser extent at Week 27. Trichostrongylus colubriformis was the predominant nematode species, with smaller numbers of Nematodirus spp., Trichostrongylus vitrinus, Trichostrongylus axei and Ostertagia circumcincta also present. It was concluded that supplementary feeding with protein meal substantially reduced production losses attributable to nematode infections in young grazing sheep. This appears to be due to an enhanced resilience of the host, rather than any major changes in development of protective immunity.

Ovine mast cell heterogeneity is defined by the distribution of sheep mast cell proteinase

The presence or absence of the granule chymase, sheep mast cell proteinase (SMCP), was determined in trachea, bronchus, bronchial lymph node, lung, thymus, spleen, liver, flank skin, abomasum, duodenum, jejunum, ileum, colon and mesenteric lymph node by immunohistochemistry and by enzyme-linked immunosorbent assay using a polyclonal, affinity purified anti-SMCP antibody. Additionally, the presence of putative ovine mast cell subsets was investigated by comparing the number of mast cells identified histochemically (toluidine blue pH 0.5) with the number detected by immunostaining. The thymus had the greatest density of mast cells (225.7 +/- 23.4 cells mm-2, histochemically) and the highest concentration of SMCP (19.7 +/- 9.3 micrograms SMCP g-1 wet tissue). There was a high degree of correlation between toluidine blue and anti-SMCP cell counts for all tissues (r2 = 0.96, P < 0.001) with the exception of skin and liver. On the basis of reactivity to the anti-SMCP antibody, two populations of mast cells were defined, notably those in gastrointestinal tissues (analogs to the mucosal mast cell subset) and those present in skin (the putative ovine connective tissue mast cell subset). Ovine mast cell heterogeneity, resulting from differential expression of SMCP, was thus confirmed.

Studies on the inhibition of rejection of Trichostrongylus colubriformis larvae from immune sheep

A total of 8 drugs were examined for their ability to suppress the rejection of Trichostrongylus colubriformis infective larvae (L3) from immune sheep. Specific antagonists of leukotrienes (piroxicam), prostaglandin (indomethacin) and the immunosuppressant cyclosporin A were given orally, while injectable preparations of dexamethasone, chlorpheniramine, BN 52051, WEB 2086 (anti-platelet-activating factor) and theophylline were administered as directed. The drugs were given for 5 days prior to and 4 days after challenge with 20,000 L3, when worm counts were done. Corticosteroids inhibited rejection by around 70% in two experiments, and none of the remaining compounds were effective. In the third study, six of the drugs were given to susceptible sheep and did not affect the establishment of a primary infection with T. colubriformis.

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)

Immunization of sheep against parasitic nematodes leads to elevated levels of globule leukocytes in the small intestine lumen

In sheep that had been given three immunizing infections with Trichostrongylus colubriformis and Ostertagia circumcincta infective (L3) larvae, drenched after the last infection and challenged with larvae of the same species, there was a significant increase in numbers of small intestine mucosal tissue globule leukocytes (TGLs) and lumenal globule leukocytes (LuGLs) compared with sheep that had only been drenched and challenged. There was a positive correlation between the numbers of LuGLs and TGLs in the small intestine but the ratio of these two cell types was lower in non-immunized than immunized sheep. In immunized sheep positive correlations were observed between LuGLs and levels of arylsulphatase and peroxidase in the intestinal mucus and between arylsulphatase and larval migration inhibition (LMI) activity in mucus. Lumen eosinophils correlated with blood eosinophils, serum antibody against T. colubriformis correlated with peroxidase in the mucus and blood eosinophils correlated with nematode specific IgM levels in the intestinal mucus. In the abomasum, TGLs were present but not LuGLs. Sheep repeatedly infected with T. axei also had significantly more LuGLs in the small intestine than control animals. Two sheep that had a surgically prepared isolated small intestinal loop, after oral infection with T. colubriformis had TGLs and LuGLs in the intact intestine, but not in the isolated loop. Significantly more LuGLs were produced in sheep by allowing repeated T. colubriformis L3 infections to develop to adult stages compared to sheep treated with the same number of larvae, but where the infections were terminated by drenching at various intervals.

A comparison of the mast cell and eosinophil responses of sheep and goats to gastrointestinal nematode infections

The mucosal mast cell and eosinophil responses of goats and sheep to a mixed gastrointestinal nematode infection were compared. Groups of eight does and nine ewes, previously maintained on pasture and treated with anthelmintic when they were housed and five worm-free lambs were challenged with 10,000 Trichostrongylus vitrinus third stage larvae (L3) and 10,000 Teladorsagia circumcincta L3. Eleven days after challenge, the ewes had significantly (P < 0.001) lower burdens of abomasal and intestinal worms than the does or naive lambs, but significantly higher (P < 0.001) tissue concentrations of mast cell proteinase. Toluidine blue-stained sections indicated a paucity of mast cells in the does compared with the ewes, whereas the immunolocalisation of sheep mast cell proteinase revealed similar numbers of stained cells in the two species. This discrepancy was due to the relatively high proportion of globule leucocytes (77 and 91 per cent in the jejunum and abomasum, respectively) in the does compared with the ewes (7 and 24 per cent in the jejunum and abomasum, respectively). No differences were detected between the numbers of circulating or tissue eosinophils in the ewes and does.

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.

Changes in inflammatory mediators and larval inhibitory activity in intestinal contents and mucus during primary and challenge infections of sheep with Trichostrongylus colubriformis

Helminthologically naive merino sheep were given either a single infection of 30,000 or a trickle infection of 6000 Trichostrongylus colubriformis infective larvae (TcL3) per week. Faecal egg counts started to fall after 8 weeks in the single infection and after 11 weeks in the trickle infection. Small intestinal contents were collected from indwelling intestinal fistulae over the next 14 weeks. Concentrations of sheep mast cell protease (SMCP) in these contents increased to highest levels 9-11 weeks and 6-10 weeks after the single infection and from the start of the trickle infection, respectively. Similarly, peptidyl leukotriene (PLT) concentrations were highest at 6 weeks and at 6-9 and 13 weeks, respectively. Histamine concentrations increased slightly after both infections to peak values at 7 weeks and 9 weeks, respectively. Inhibition of migration of larvae in vitro was increased in contents sampled at 8 weeks after the single infection and after 6-10 weeks of the trickle infection. Another 2 groups of sheep were immunised by repeated infections with TcL3. Gut contents from 1 group sampled immediately before and after challenge with 30,000 TcL3 at 0 and 18 days had increased levels of larval migration inhibitory (LMI) activity throughout the 35 day period, especially 7-14 days after challenge (DAC). The mediators SMCP increased significantly 5-7 DAC while PLT increased 7-14 DAC. In the second group of immunised sheep, levels of SMCP and PLT increased rapidly within 1 DAC and further increased 3-14 DAC.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological relationships during primary infection with Heligmosomoides polygyrus: Th2 cytokines and primary response phenotype

The primary immune response to infection with Heligmosomoides polygyrus was studied in mice differing in response phenotype (fast-SWR, intermediate-NIH, slow-CBA). Marked IgG1 and IgE but not IgG2a antibody responses were detected in infected mice and the former were more intense in fast compared with slow responder strains. Mastocytosis, MMCP-1, and the secretion of cytokines by mesenteric lymph node cells, following stimulation in vitro by Con A, were also more intense initially in SWR mice. Secretion of IL-4 declined in all strains by the 4th week of infection, irrespective of response phenotype. IL-10 was only produced briefly by SWR mice. However, the temporal patterns of secretion of IL-3 and IL-9 clearly distinguished fast from slow responder phenotypes. Following initial intense secretion of IL-3, production declined in all strains but in the 5-6th weeks enhanced secretion was evident in SWR and NIH mice and was sustained until week 10 p.i. In contrast, CBA mice never recovered from the initial down-regulation in weeks 3-4 and secretion declined to background levels by week 6 p.i. despite the continued presence of adult worms. Temporal changes in the secretion of IL-9 were very similar: secretion declined in CBA mice by week 6 p.i., whilst SWR and NIH mice continued to secrete high amounts. We suggest that fast and slow responder mice differ not only in their initial responsiveness to parasite antigens but also in their ability to sustain a Th2 response to the parasite and we propose that the latter is in part determined by their different susceptibilities to parasite-mediated immunomodulation. Only the fast responder strains can sustain a Th2 response of sufficient intensity to facilitate expulsion of adult worms.

Local eosinophil- and mast cell-related responses in abomasal nematode infections of lambs

Eosinophil numbers in peripheral blood and eosinophil potentiating activity (EPA) and sheep mast cell protease (SMCP) in efferent gastric lymph were monitored in lambs during infections with Ostertagia circumcincta. Worm burdens, eosinophil numbers in bone marrow, abomasal mucosa and gastric lymph node, as well as mast cell numbers and SMCP concentrations in mucosa and mucus, were determined in post mortem samples. In naive lambs, high and relatively uniform worm burdens were present 10 days after primary infection and these were associated with only mild blood and tissue eosinophilia. By day 21 worm burdens were markedly lower and more variable. There was more evidence of eosinophil and mast cell accumulation in mucosa, and numbers in bone marrow were also higher than on day 10. However, neither EPA nor SMCP were detectable in lymph. By contrast, EPA and SMCP were present in substantial amounts in draining lymph within 48 h of challenge (secondary) infection of previously exposed lambs. EPA was inversely related to worm burdens recovered on day 10, as were abomasal mucosal and mucus SMCP concentrations. Elevated eosinophil numbers were also consistently detected in blood, bone marrow, mucosa and gastric lymph node. The results suggest that host immune defence against secondary, but not primary, exposure to O. circumcincta involves a rapidly mobilised local inflammatory component.