Phenotypic analysis of host–parasite interactions in lambs infected with Teladorsagia circumcincta

Analysis of Protection and Immune Response against Teladorsagia circumcincta in Goats Immunised with Thiol-Binding Proteins from Adult Worms

In view of the increasing occurrence of anthelmintic-resistant strains of gastrointestinal nematodes in ruminants, various alternative control strategies have been investigated, such as those based on the induction of protective immune responses by immunisation with parasite antigens. In this study, the protective activity of somatic antigens from adult worms of Teladorsagia circumcincta purified by affinity chromatography on thiol-sepharose was analysed in goats. After challenge, the enriched products induced a slight reduction in the cumulative faecal egg counts (21%) and in the number of worms (23.3%), with a greater effect on female worms, which also showed a reduction in parameters related to their fertility. These parasitological findings were associated with a Th2 immune response, with a prominent local humoral response and an eosinophilic infiltrate in the gastric mucosa (negatively associated with the fertility of female worms and the number of worms, respectively), as well as an infiltration of MCHII+, CD4+, IgG+ and IgA+ cells. However, several analyses showed an increase in CD8+ cells in the mucosa, as well as IL-2 expression in the gastric lymph nodes, which may have been associated with inhibition of protective responses or with the development of mixed Th1/Th2 responses, a finding that should be analysed in future studies.

An evaluation of techniques to diagnose Dioctophyme renale in dogs

Dioctophyme renale is a nematode with zoonotic potential that affects the kidneys of carnivorous, wild, and domestic mammals. In this study, we sought to evaluate the indirect ELISA method against routine methods used to diagnose dioctophimosis. Hence, 38 dogs parasitized by D. renale, as confirmed by surgery, were selected. The dogs were evaluated by abdominal ultrasound and urinalysis, and their sera were tested by indirect ELISA using D. renale adult secretion and excretion antigen (DES). Five dogs were followed up with serum collections on day 0 (day of surgery) and 30, 60, and 90 days after surgery to evaluate antibody kinetics. Abdominal ultrasound and indirect ELISA successfully diagnosed 37 dogs parasitized by D. renale, while urinalysis diagnosed 29 animals. The positive animals were parasitized with 1-7 parasites; 17 dogs were infected by male and female parasites, 15 only by female parasites, and six were parasitized only by male parasites. When assessing specificity and sensitivity, all techniques showed 100% specificity and 81.6%, 97.4%, and 97.4% sensitivity for urinalysis, ultrasound, and ELISA, respectively (p < 0.001). The five positive dogs that were followed up after surgery showed a progressive decrease in mean absorbances in indirect ELISA (0.644, 0.516, 0.511, and 0.440, respectively). This study demonstrated that the indirect ELISA using the DE antigen could diagnose dioctophimosis regardless of the number, sex, and location of the parasites, with the potential to be used in epidemiological research and implementing immunological and molecular studies, opening new lines of research on D. renale.

Secretory IgA as Biomarker for Gastrointestinal Nematodes Natural Infection in Different Breed Sheep

Specific IgA antibody has been shown to play an important role in resistance to gastrointestinal nematode (GIN) infections in sheep, particularly in Teladorsagia circumcincta parasitosis. In some breeds, negative associations have been shown between IgA levels and worm burden in experimentally infected sheep. In the present study, we have studied the relationship between IgA levels in naturally infected sheep (582 ewes in total; 193 younger than one year old and 389 older than one year old) and fecal egg count (FEC) in the Assaf, Castellana, and Churra breeds. ELISA assays were performed to measure IgA levels against the somatic antigen of T. circumcincta third larval stage (L₃) and a 203-amino-acid fragment of the protein disulfide isomerase from the same GIN species. A multilevel random intercept model was developed to predict the infection risk according to age or breed. Spearman's correlation rank was used for statistical analysis. The prediction model showed that breed was not an influential factor in this study, although the Assaf breed could be considered slightly more susceptible than the others. In addition, age affected the infection risk, with the young ewes more susceptible to infection than the adult groups, except for the Castellana breed, whose risk of infection was similar at all ages. The most significant positive association was found between FEC and IgA measured in the nasal secretions of young ewes using both antigens (Rho = 0.5; p = 0.00); the correlation of FEC with IgA in serum was moderately significant (Rho = 0.306; p = 0.00). Comparing both antigens, the protein disulfide isomerase antigen was less reactive than the somatic antigen from L₃. In conclusion, under natural conditions, specific IgA against GIN was positively associated with FEC in sheep, with nasal secretions from young animals being the sample where this association is stronger, which, therefore, could be used as a marker of infection in further studies.

Immunization with thiol-binding proteins from Haemonchus contortus adult worms partially protects goats against infection during prepatency

To contribute of the knowledge of the immune mechanisms underlying the response to the immunization of goats with thiol-binding proteins fractions (PBS-TSBP) from Haemonchus contortus (H. contortus) adult worms, this study analyzed the degree of protection and the immune responses developed against the parasite after vaccination with this antigenic complex during the time-elapsing between challenge with L3 of the parasite and the development of adult worms, evidenced by the appearance of first faecal eggs (prepatent period or prepatency). Goat kids immunized with PBS-TBSP generated an immune response during the prepatency which translates into a reduction in the number of worms, as well as a lower reduction on packed cell volume and plasma protein levels in relation to the non-vaccinated animals. As previously described in other studies carried out after the prepatent period, this protection was associated with a systemic humoral response. At the local level, a specific humoral response was also observed, together with an immune-inflammatory infiltrate in the gastric mucosa of MCH-II + cells and CD4⁺ lymphocytes, whose number was associated with a reduction in the number of worms and an increase in plasma proteins. A high peripheral eosinophilia was detected, but no corresponding increased infiltration of the gastric mucosa by eosinophils or globular leukocytes was observed. In agreement with previous data on the immunolocalization of the antigens used here, the results obtained contribute to the idea that these may be excretion/secretion (E/S) products necessary for parasite survival, whose inactivation during the larval and/or pre-adult stages may have contributed to immunoprotection.

Local immune response of Canarian Majorera goats infected with Teladorsagia circumcincta

BACKGROUND

Due to increased anthelmintic resistance, alternative methods to drugs are necessary to control gastrointestinal nematodes (GINs). Some of the most promising alternatives are based on the immune response of the host, such as the selection of genetically resistant breeds or the use of vaccines against these parasites. Given the limited information available on the immune response against GINs in goats, this study investigated the local immune response of goat kids of an indigenous Canary Islands breed (Majorera breed) experimentally infected with Teladorsagia circumcincta, one of the most pathogenic and prevalent GIN species.

METHODS

For this purpose, the relationship between different parasitological (number of mature and immature worms, worm length, and number of intrauterine eggs) and immunological parameters at the local level (related to both the humoral and cellular immune response) was analyzed at early (1 week post-infection [wpi]) and late (8 wpi) stages of infection.

RESULTS

Primary infection of goat kids with T. circumcincta infective larvae (L3) generated a complex immune response that could be defined as Th2 type, characterized by increased infiltration in abomasal tissues of several effector cells as well as a progressive presence of specific antibodies against parasitic antigens in the gastric mucus. Cellular responses were evidenced from 1 wpi onward, showing an increase in antigen-presenting cells and various lymphocyte subsets in the gastric mucosa.

CONCLUSIONS

The complexity of the host response was evidenced by statistically significant changes in the number of all these subpopulations (MHCII⁺, CD4⁺, CD8⁺, γδ⁺, CD45R⁺, IgA⁺, and IgG⁺), as well as in the evolution of the relative cytokine gene expression. From a functional point of view, negative associations were observed between the number of most of the immune cells (CD4, IgA, IgG, and CD45R cells) and parameters that could be related to the fecundity of worms, a phenomenon that was especially evident when the number of IgG and CD45R cells or the specific IgA levels of the gastric mucus were compared with parasitological parameters such as the female worm length or fecal egg counts at 8 wpi.

Immunoglobulins as Biomarkers for Gastrointestinal Nematodes Resistance in Small Ruminants: A systematic review

The rise of anthelmintic resistance worldwide has led to the development of alternative control strategies for gastrointestinal nematodes (GIN) infections, which are one of the main constraints on the health of grazing small ruminants. Presently, breeding schemes rely mainly on fecal egg count (FEC) measurements on infected animals which are time-consuming and requires expertise in parasitology. Identifying and understanding the role of immunoglobulins in the mechanisms of resistance could provide a more efficient and sustainable method of identifying nematode-resistant animals for selection. In this study we review the findings on immunoglobulin response to GIN in the literature published to date (june 2019) and discuss the potential to use immunoglobulins as biomarkers. The literature review revealed 41 studies which measured at least one immunoglobulin: 35 focused on lamb immune response (18 used non-naïve lambs) and 7 on yearlings. In this review we propose a conceptual model summarizing the role of immunoglobulins in resistance to GIN. We highlight the need for more carefully designed and documented studies to allow comparisons across different populations on the immunoglobulin response to GIN infection.

Resistance to Haemonchus contortus in Corriedale sheep is associated to high parasite-specific IgA titer and a systemic Th2 immune response

Gastrointestinal nematode infections, including Haemonchus contortus, are one of the main causes of economic losses to ovine farmers worldwide. In order to contribute to the control of nematode infections and avoid parasite spreading we generated divergent resistant and susceptible sheep breeds and evaluated the adaptive immunity of these animals developed upon experimental infection against H. contortus. The selection of resistant or susceptible animals from the Corriedale Breed has been based on Expected Progeny Differences for faecal egg counts per gram. Furthermore, animals from the resistant Corriedale line were inseminated with imported semen from Australian Rylington Merino rams. Thus, the objective of this work was to analyze the adaptive immune response in both susceptible and resistant obtained lambs. Our results indicate that there is a potent parasite-specific local and systemic immune response in resistant animals and that although susceptible lambs can produce high levels of IgA antibodies during the infection, their antibody response is delayed which, together with an impaired specific-Th2 response, does not contribute to initial parasite elimination. Our results shed light into the immune mechanisms that mediate resistance to H. contortus and could constitute important assets to sheep farmers, not only as a means to detect resistance, but also to enhance the efficiency of selection in stud flocks.

Bioinformatic analysis of eosinophil activity and its implications for model and target species

Eosinophils are important immune cells that have been implicated in resistance to gastrointestinal nematode (GIN) infections in both naturally and experimentally infected sheep. Proteins of particular importance appear to be IgA-Fc alpha receptor (FcαRI), C-C chemokine receptor type 3 (CCR3), proteoglycan 3 (PRG3, major basic protein 2) and EPX (eosinophil peroxidase). We used known human nucleotide sequences to search the ruminant genomes, followed by translation to protein and sequence alignments to visualize differences between sequences and species. Where a sequence was retrieved for cow, but not for sheep and goat, this was used additionally as a reference sequence. In this review, we show that eosinophil function varies among host species. Consequently, investigations into the mechanisms of ruminant immune responses to GIN should be conducted using the natural host. Specifically, we address differences in protein sequence and structure for eosinophil proteins.

Immune response in goats vaccinated with thiol-binding proteins from Haemonchus contortus

The experimental protocol of immunization tested here confirms its protective effect against Haemonchus contortus in goats. This protection translated into a 65.5% mean reduction in adult worm burden after a homologous challenge, and a significant decrease (73.2%) in cumulative faecal egg counts (FECs). These parasitological findings were consistent with the levels of some biopathological parameters. Thus, the reduction in adult worms and FEC observed in immunized animals were associated with increased levels of packed cell volume as well as plasma proteins. This response seems to be related to an important increase in specific antibodies (in serum and gastric mucus) and eosinophilia in response to challenge. At the local level, a cellular response was also observed in which CD4⁺ lymphocytes and globule leucocytes played a predominant role. Finally, it should be noted that the study of immunolocalization of proteins used in the vaccination trial suggests that these antigens have an internal location (at intestinal and reproductive tissues) in the adult worm. This observation, in conjunction with the kinetics of specific antibody levels after the challenge, suggests that these antigens may be part of excretory/secretory (E/S) products.

A candidate gene approach to study nematode resistance traits in naturally infected sheep

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SNPs within genes associated with the development of nematode resistance were sequenced.

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The SNPs were segregating in two unrelated, domestic and feral, sheep breeds.

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More samples are required to determine significant associations between SNPs and traits.

Sheep naturally acquire a degree of resistant immunity to parasitic worm infection through repeated exposure. However, the immune response and clinical outcome vary greatly between animals. Genetic polymorphisms in genes integral to differential T helper cell polarization may contribute to variation in host response and disease outcome. A total of twelve single nucleotide polymorphisms (SNPs) were sequenced in IL23R, RORC2 and TBX21 from genomic DNA of Scottish Blackface lambs. Of the twelve SNPs, six were non-synonymous (missense), four were within the 3′ UTRs and two were intronic. The association between nine of these SNPs and the traits of body weight, faecal egg count (FEC) and relative T. circumcincta L3-specific IgA antibody levels was assessed in a population of domestic Scottish Blackface ewe lambs and a population of free-living Soay ewe lambs both naturally infected with a mixture of nematodes. There were no significant associations identified between any of the SNPs and phenotypes recorded in either of the populations after adjustment for multiple testing (Bonferroni corrected P value ≤ 0.002). In the Blackface lambs, there was a nominally significant association (P = 0.007) between IL23R p.V324M and weight at 20 weeks. This association may be worthy of further investigation in a larger sample of sheep.

Mucosal Expression of T Cell Gene Variants Is Associated with Differential Resistance to Teladorsagia circumcincta

Resistance of sheep to the gastrointestinal nematode Teladorsagia circumcincta is a heritable characteristic. Control of parasite colonization and egg production is strongly linked to IgA antibody levels regulated by Th2 T cell activation within lymphoid tissue; and persistently-infected susceptible animals develop an inflammatory Th1/Th17 response within the abomasum that fails to control infection. Differential T cell polarization therefore is associated with parasite resistance and/or susceptibility and is controlled by a specific set of transcription factors and cytokine receptors. Transcript variants of these genes have been characterized in sheep, while in humans and mice different variants of the genes are associated with inflammatory diseases. RT-qPCR was used to quantify mucosal expression of the transcript variants of the sheep genes in trickle-infected animals with defined phenotypic traits. Genes that encode full-length GATA3 and IL17RB were shown to be significantly increased in resistant sheep that had controlled parasite infection. Expression levels of both were significantly negatively correlated with abomasal worm count (a parameter of susceptibility) and positively correlated with body weight (a parameter of resistance). These data show that polarized Th2 T cells within the abomasal mucosa play an important role in the maintenance of resistance.

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.

Which is the best phenotypic trait for use in a targeted selective treatment strategy for growing lambs in temperate climates?

Targeted selective treatment (TST) requires the ability to identify the animals for which anthelmintic treatment will result in the greatest benefit to the entire flock. Various phenotypic traits have previously been suggested as determinant criteria for TST; however, the weight gain benefit and impact on anthelmintic efficacy for each determinant criterion is expected to be dependent upon the level of nematode challenge and the timing of anthelmintic treatment. A mathematical model was used to simulate a population of 10,000 parasitologically naïve Scottish Blackface lambs (with heritable variation in host-parasite interactions) grazing on medium-quality pasture (grazing density=30 lambs/ha, crude protein=140g/kg DM, metabolisable energy=10MJ/kg DM) with an initial larval contamination of 1000, 3000 or 5000 Teladorsagia circumcincta L3/kg DM. Anthelmintic drenches were administered to 0, 50 or 100% of the population on a single occasion. The day of anthelmintic treatment was independently modelled for every day within the 121day simulation. Where TST scenarios were simulated (50% treated), lambs were either chosen by random selection or according to highest faecal egg count (FEC, eggs/g DM faeces), lowest live weight (LW, kg) or lowest growth rate (kg/day). Average lamb empty body weight (kg) and the resistance (R) allele frequency amongst the parasite population on pasture were recorded at slaughter (day 121) for each scenario. Average weight gain benefit and increase in R allele frequency for each determinant criterion, level of initial larval contamination and day of anthelmintic treatment were calculated by comparison to a non-treated population. Determinant criteria were evaluated according to average weight gain benefit divided by increase in R allele frequency to determine the benefit per R. Whilst positive phenotypic correlations were predicted between worm burden and FEC; using LW as the determinant criterion provided the greatest benefit per R for all levels of initial larval contamination and day of anthelmintic treatment. Hence, LW was identified as the best determinant criterion for use in a TST regime. This study supports the use of TST strategies as benefit per R predictions for all determinant criteria were greater than those predicted for the 100% treatment group, representing an increased long-term productive benefit resulting from the maintenance of anthelmintic efficacy. Whilst not included in this study, the model could be extended to consider other parasite species and host breed parameters, variation in climatic influences on larval availability and grass growth, repeated anthelmintic treatments and variable proportional flock treatments.

Variations in T Cell Transcription Factor Sequence and Expression Associated with Resistance to the Sheep Nematode Teladorsagia circumcincta

This study used selected lambs that varied in their resistance to the gastrointestinal parasite Teladorsagia circumcincta. Infection over 12 weeks identified susceptible (high adult worm count, AWC; high fecal egg count, FEC; low body weight, BW; low IgA) and resistant sheep (no/low AWC and FEC, high BW and high IgA). Resistance is mediated largely by a Th2 response and IgA and IgE antibodies, and is a heritable characteristic. The polarization of T cells and the development of appropriate immune responses is controlled by the master regulators, T-bet (TBX21), GATA-3 (GATA3), RORγt (RORC2) and RORα (RORA); and several inflammatory diseases of humans and mice are associated with allelic or transcript variants of these transcription factors. This study tested the hypothesis that resistance of sheep to T. circumcincta is associated with variations in the structure, sequence or expression levels of individual master regulator transcripts. We have identified and sequenced one variant of sheep TBX21, two variants of GATA3 and RORC2 and five variants of RORA from lymph node mRNA. Relative RT-qPCR analysis showed that TBX21, GATA3 and RORC2 were not significantly differentially-expressed between the nine most resistant (AWC, 0; FEC, 0) and the nine most susceptible sheep (AWC, mean 6078; FEC, mean 350). Absolute RT-qPCR on all 45 animals identified RORVv5 as being significantly differentially-expressed (p = 0.038) between resistant, intermediate and susceptible groups; RORCv2 was not differentially-expressed (p = 0.77). Spearman’s rank analysis showed that RORAv5 transcript copy number was significantly negatively correlated with parameters of susceptibility, AWC and FEC; and was positively correlated with BW. RORCv2 was not correlated with AWC, FEC or BW but was significantly negatively correlated with IgA antibody levels. This study identifies the full length RORA variant (RORAv5) as important in controlling the protective immune response to T. circumcincta infection in sheep.

Variable exon usage of differentially-expressed genes associated with resistance of sheep to Teladorsagia circumcincta

The resistance and susceptibility of sheep to the common abomasal nematode parasite, Teladorsagia circumcincta is strongly associated with the differential polarization of the immune response. Resistant animals control larval colonization by the production of a protective antibody response regulated by Th2 T cells. Susceptible sheep respond to infection by developing an inflammatory Th1/Th17 response that fails to control infection. Previous microarray analysis identified genes associated with T cell polarization that were differentially expressed between the resistant and susceptible sheep. RT-qPCR confirmed the microarray data for ALOX15 and IL13. Both ALOX15 exon 9 and IL13 exon 4 were significantly increased in resistant animals and copy number RT-qPCR showed that expression levels of these exons were significantly negatively correlated with quantitative phenotypic traits, including abomasal worm counts and faecal egg counts. Sequencing of the intronic regions 5' to these genes failed to identify any potential genetic links to differential exon usage.

Exploring the abomasal lymph node transcriptome for genes associated with resistance to the sheep nematode Teladorsagia circumcincta

This study exploited Blackface lambs that varied in their resistance to the abomasal nematode parasite, Teladorsagia circumcincta. Infection of these lambs over 3 months identified susceptible (high adult worm count, high faecal egg count and low IgA antibody) and resistant animals that had excluded all parasites. Previous work had shown that susceptibility and resistance is dependent on the differential immune response to the parasite, which occurs within the abomasal (gastric) lymph node (ALN) that drains the site of infection. The Affymetrix ovine gene array was used to interrogate the transcriptome of the ALN to identify genes and physiological pathways associated with resistance. We used a bovine RT-qPCR array of 84 genes to validate the gene array, and also report digital gene expression analysis on the same tissues, reanalysed using the Oar v3.1 sheep genome assembly. These analyses identified Humoral Immune Response, Protein Synthesis, Inflammatory Response and Hematological System Development and Function as the two top-ranked networks associated with resistance. Central genes within these networks were IL4, IL5, IL13RA2 and in particular IL13, which confirmed that differential activation of Th2 polarized responses is critical to the resistance phenotype. Furthermore, in resistant sheep there was up-regulation of genes linked to control and suppression of inflammation. The identity of differentially-expressed chemokines and receptors in the resistant and susceptible sheep also begins to explain the cellular nature of the host response to infection. This work will greatly help in the identification of candidate genes as potential selectable markers of genetic resistance.

The immunology and genetics of resistance of sheep to Teladorsagia circumcincta

Teladorsagia circumcincta is one of the most economically important gastrointestinal nematode parasites of sheep in cool temperate regions, to which sheep show genetically-varying resistance to infection. This is a very common parasite and viable sheep production requires the extensive use of anthelmintic drugs. However, the emergence of drug-resistant parasites has stimulated the search for alternative control strategies to curb production losses. Lambs become infected soon after weaning and begin to control parasite burden within 8-10 weeks of continual infection. This control is an acquired characteristic mediated by the development of parasite-specific antibodies. This paper describes the immunology associated with resistance and susceptibility, focussing on differential T cell activation that regulates the production of specific effector mechanisms. It continues by summarizing the methods used to identify genes that could be exploited as molecular markers of selection for resistance. In particular it focusses on the link between understanding the molecular immunology of infection and the identification of candidate genes for selection.

Expression of sheep interleukin 23 (IL23A, alpha subunit p19) in two distinct gastrointestinal diseases

This paper reports the sequence of sheep interleukin 23A (p19), and shows that it shares 98% identity with bovine IL23A, 85% with human and 76% with mouse IL23A. It also reports the existence of two allelic variants that differ largely within the region encoding the amino terminal polypeptide signal sequence. An optimized RT-qPCR assay was used to quantify IL23A transcripts in sheep infected with two common gastrointestinal pathogens, the intracellular bacterium Mycobacterium avium subspecies paratuberculosis and the parasitic nematode Teladorsagia circumcincta. No differential expression of IL23A was detected in the mesenteric lymph node of sheep with the different pathogenic forms of paratuberculosis, however significantly high levels of IL23A were detected in the ileal mucosa of the paucibacillary form in comparison with the asymptomatic or multibacillary forms. Similarly, significantly high levels were present in the gastric lymph node draining T. circumcincta-infected abomasum in susceptible sheep. High levels of IL23A seem to be associated with lymphocytic infiltration and inflammation in both diseases but not with the macrophage infiltrate of multibacillary paratuberculosis.

Relationship between susceptibility of Blackface sheep to Teladorsagia circumcincta infection and an inflammatory mucosal T cell response

Teladorsagia circumcincta is the most economically important gastrointestinal (abomasal) nematode parasite of sheep in cool temperate regions, to which sheep show genetically-varying resistance to infection. Lambs, from parents with genetic variation for resistance, were trickle infected with L3 larvae over 12 weeks. 45 lambs were identified with a range of susceptibilities as assessed by: adult worm count at post mortem, faecal egg count (FEC) and IgA antibody levels. This project investigated the correlation of T cell cytokine expression and resistance to infection at the mature stage of response, when the resistant lambs had excluded all parasites.

Histopathology showed only minor changes in resistant animals with a low level lymphocyte infiltration; but in susceptible lambs, major pathological changes were associated with extensive infiltration of lymphocytes, eosinophils and neutrophils.

Absolute quantitative RT-qPCR assays on the abomasal lymph node (ALN) revealed a significant positive correlation between IL6, IL21 and IL23A transcript levels with adult worm count and FEC. IL23A was also negatively correlated with IgA antibody levels. Significantly positive correlation of TGFB1 levels with adult worm count and FEC were also seen in the abomasal mucosa. These data are consistent with the hypothesis that the inability to control L3 larval colonization, adult worm infection and egg production is due to the activation of the inflammatory Th17 T cell subset.

Digital gene expression analysis of gastrointestinal helminth resistance in Scottish blackface lambs

Digital gene expression (DGE) analysis offers a route to gene discovery which by-passes the need to develop bespoke arrays for nonmodel species, and is therefore a potentially valuable tool for molecular ecologists. Scottish blackface sheep, which vary in resistance to the common abomasal parasitic nematode Teladorsagia circumcincta, were trickle-infected with L3 larvae over 3 months to mimic the natural progression of infection. DGE was performed on abomasal lymph node tissue after the resolution of infection in resistant animals. Susceptible (low resistance) animals showed a large number of differentially expressed genes associated with inflammation and cell activation, but generally few differentially regulated genes in either the susceptible or the resistant group were directly involved in the adaptive immune function. Our results are consistent with the hypothesis that both resistance and susceptibility are active responses to infection and that susceptibility is associated with dysfunction in T cell differentiation and regulation.

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.

Teladorsagia circumcincta in the sheep abomasum: defining the role of dendritic cells in T cell regulation and protective immunity

Parasitic nematodes of the small-ruminant gastrointestinal tract pose a problem worldwide. The impact of these pathogens is worsened by the emergence of anthelmintic resistance to all three available classes of drugs. In addition to causing considerable economic loss, these parasites are detrimental to the health and welfare of sheep and goats. Vaccination offers an alternative approach to drug-based control and a great deal of investment has gone into the investigation of protective antigens for some of these nematode species. However, attempts at vaccination are hindered by a lack of understanding of how best to promote protective immunity to nematode species, such as Teladorsagia circumcincta, which inhabits the abomasum of sheep. This situation contrasts with that in murine models of gastrointestinal nematode infection, where the basis of protective immunity is increasingly well understood. In this review, we discuss the current knowledge of the immune effector mechanisms elicited by T. circumcincta and consider the probable role of dendritic cells in the initiation of both effector and regulatory responses in the abomasum.