Breed differences in mucosal and systemic antibody response to nematode infection in sheep: an important role for IgE?

Variability in the Response against Teladorsagia circumcincta in Lambs of Two Canarian Sheep Breeds

The increasing resistance to anthelmintics has necessitated the exploration of alternative control strategies of gastrointestinal nematode (GIN) infections. A sustainable option is genetic selection based on differences in susceptibility to GIN infection between and within breeds of sheep. Here, three-month-old Canaria Hair breed (GIN-resistant) and Canaria Sheep breed (GIN-susceptible) showed no significant between-breed differences after trickle infection with Teladorsagia circumcincta, whereas considerable individual variability was found in both breeds. Next, data from lambs of both breeds were used to explore the relationships between parasitological variables and T. circumcincta-specific IgA levels, local immune cell populations, and abomasal lymph node gene expression to understand the possible mechanisms underlying resistance. Mucosal IgA levels as well as numbers of globular leukocytes and MHC-II⁺ cells were associated with protection. Analysis of lymph node gene expression revealed the associations between lower parasite numbers and cumulative fecal egg counts and several immune pathways, such as leukocyte cell adhesion, activation and differentiation of T cells, in particular CD4⁺ and IL-4 production. The data obtained here may inform on the relationship between phenotypic resistance variability and protective responses at the humoral, cellular, and transcriptomic levels, thus contributing to identifying immune responses in young lambs that could be used as markers for selection.

Physiological, Immunological and Genetic Factors in the Resistance and Susceptibility to Gastrointestinal Nematodes of Sheep in the Peripartum Period: A Review

Parasitic diseases of sheep involving gastrointestinal nematodes (GIN) are one of the main problems that affect fl ock productivity, especially during the peripartum period. Around lambing, the ewes are immunosuppressed and the nematode faecal egg count (FEC) increases at four weeks before lambing, reaching a peak between the fourth and sixth week postpartum and subsequently decreasing towards weaning. Prolactin has been credited with a suppressive effect on immune system, along with other hormones that intervene in metabolism, such as leptin, which has an important role in the activation of other hormones. Cortisol has also been included; this is stimulated by any stressful event and inhibits the proliferation of T-cells and alters the function of immunoglobulins. Another related hormone is pepsinogen, which is considered a marker of the integrity of the abomasum mucosa, as well as the albumin concentration that increases in the presence of a GIN infection. The humoral and cellular immune response, as well as inflammatory reactions, are the main mechanisms of action against GIN. Lymphocytes direct the effector mechanisms in a Th2 cell response, including interleukins (IL-4, IL-5, IL-9, IL-10) and transforming growth factor beta (TGF-β) together with immunoglobulins (IgA, IgG, IgM and IgE), which prevent the invasion of pathogens. Eosinophils with a cytotoxic effect are indicators of a parasitic infection, with importance in the immune protection of infected individuals. The genetic selection of resistant individuals measured by FEC is dependent on the heritability (h²), which is moderately inheritable and highly repeatable. Effects that influence the resistance or susceptibility of sheep to GIN infections in the peripartum period are determined by the interaction of various factors, such as genotype or breed, nutrition, age, type of birth, season and production system, etc., which are studied in this review.

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.

Immunogenomics of gastrointestinal nematode infection in ruminants - breeding for resistance to produce food sustainably and safely

Gastrointestinal nematode (GIN) infection of ruminants represents a major health and welfare challenge for livestock producers worldwide. The emergence of anthelmintic resistance in important GIN species and the associated animal welfare concerns have stimulated interest in the development of alternative and more sustainable strategies aimed at the effective management of the impact of GINs. These integrative strategies include selective breeding using genetic/genomic tools, grazing management, biological control, nutritional supplementation, vaccination and targeted selective treatment. In this review, the logic of selecting for "resistance" to GIN infection as opposed to "resilience" or "tolerance" is discussed. This is followed by a review of the potential application of immunogenomics to genetic selection for animals that have the capacity to withstand the impact of GIN infection. Advances in relevant genomic technologies are highlighted together with how these tools can be advanced to support the integration of immunogenomic information into ruminant breeding programmes.

Can the amount of digestible undegraded protein offered to ewes during late pregnancy affect the performance and immune response of their offspring to gastrointestinal nematodes?

Maternal nutrition during pregnancy is a major environmental influence on foetal development with consequent effects on postnatal performance. We hypothesised that the level of intake of digestible undegraded protein (DUP) by the dam in late pregnancy would impact on the effectiveness of the immune response by offspring to gastrointestinal nematode infection. Eighty-five twin/triplet-bearing ewes, which were indoors from mid-pregnancy, were randomly assigned to 4 treatment groups for the final 6 weeks of pregnancy. Treatments were silage plus one of two iso-energetic and iso-nitrogenous concentrates (differing in DUP concentration; 29 and 94g/kg DM) offered at one of two feed levels (18/30 and 24/35kg in total for twin/triplet-bearing ewes, respectively). Ewes with triplets had one lamb removed at birth so that all ewes nursed 2 lambs when put to pasture as one flock in a 5-paddock rotational grazing system; all lambs were slaughtered after 29 weeks. Faecal egg count (FEC) and levels of serum IgA and IgE specific for Teladorsagia circumcincta were assessed for all lambs at various time points between 10 weeks of age and slaughter. Animal performance (live weight, live-weight gain, carcass weight) was recorded for all lambs. Worm burden at slaughter was determined for a sample of 12 lambs from each treatment. Nematodirus spp. FEC, 'other strongyles' FEC, and serum IgA and IgE specific for T. circumcincta were unaffected either by the concentration of DUP in the concentrate or by the level of concentrate offered to ewes in late pregnancy (P>0.1). Likewise, the dietary regime of the dams had no effect on lamb performance (P>0.1). It is concluded that increasing the DUP intake of ewes in late pregnancy had no effect on the immune response of their offspring to gastrointestinal nematode infection acquired through grazing naturally infected pasture.

Fecal antibody levels as a noninvasive method for measuring immunity to gastrointestinal nematodes in ecological studies

Among‐individual variation in antibody‐associated immunity to gastrointestinal nematode parasites (GIN) is known be associated with life‐history traits and vital rates in wild vertebrate systems. To date, measurement of levels of antibodies against GIN antigens in natural populations has exclusively been based on invasive blood sampling techniques. Previous work in laboratory rodents and ruminant livestock suggests that antibody measures from feces may provide a viable noninvasive approach. We measured total and anti‐GIN antibodies of different isotypes (immunoglobulin (Ig) G, IgA and IgE) from paired samples of plasma and feces from free‐living Soay sheep of different ages and sexes. We tested the correlations among these measures as well as their associations with body mass and Strongyle nematode fecal egg counts (FEC). Significant positive correlations were present among plasma and fecal anti‐GIN antibody levels for IgG and IgA. Generally, correlations between total antibody levels in plasma and feces were weaker and not significant. No significant relationships were found between any antibody measures and body mass; however, fecal anti‐GIN antibody levels were significantly negatively correlated with FEC. Our data clearly demonstrate the feasibility of measuring anti‐GIN antibodies from fecal samples collected in natural populations. Although associations of fecal antibody levels with their plasma counterparts and FEC were relatively weak, the presence of significant correlations in the predicted direction in a relatively small and heterogeneous sample suggests fecal antibody measures could be a useful, noninvasive addition to current eco‐immunological studies.

Variation in the Ovine Abomasal Lymph Node Transcriptome between Breeds Known to Differ in Resistance to the Gastrointestinal Nematode

Texel lambs are known to be more resistant to gastrointestinal nematode (GIN) infection than Suffolk lambs, with a greater ability to limit infection. The objectives of this study were to: 1) profile the whole transcriptome of abomasal lymph node tissue of GIN-free Texel and Suffolk lambs; 2) identify differentially expressed genes and characterize the immune-related biological pathways and networks associated with these genes. Abomasal lymph nodes were collected from Texel (n = 6) and Suffolk (n = 4) lambs aged 19 weeks that had been GIN-free since 6 weeks of age. Whole transcriptome profiling was performed using RNA-seq on the Illumina platform. At the time of conducting this study, a well annotated Ovine genome was not available and hence the sequence reads were aligned with the Bovine (UMD3.1) genome. Identification of differentially expressed genes was followed by pathway and network analysis. The Suffolk breed accounted for significantly more of the differentially expressed genes, (276 more highly expressed in Suffolk v 162 in Texel; P < 0.001). The four most significant differentially expressed pathways were all related to immunity and were classified as: Role of Pattern Recognition Receptors in Recognition of Bacteria and Viruses, Activation of IRF by Cytosolic Pattern Recognition Receptors, Role of RIG-I-like Receptors in Antiviral Innate Immunity, and Interferon Signaling. Of significance is the fact that all of these four pathways were more highly expressed in the Suffolk. These data suggest that in a GIN-free environment, Suffolk lambs have a more active immune profile relative to the Texel: this immune profile may contribute to the poorer efficiency of response to a GIN challenge in the Suffolk breed compared to the Texel breed.

Breed differences in humoral and cellular responses of lambs to experimental infection with the gastrointestinal nematode Teladorsagia circumcincta

While Texel lambs have increased resistance to infection with the gastrointestinal nematode Teladorsagia circumcincta compared to Suffolk lambs, the underlying resistance mechanisms are still unknown. The aim of this study was to compare parasitological, humoral and cellular responses of Texel and Suffolk lambs over time following a single experimental infection with T. circumcincta. Gastrointestinal nematode free (but not naïve) lambs received a single oral dose of 3 × 104 infective T. circumcincta larvae. The variables examined included worm burden, mucosal and serum IgA, abomasal mast cells and eosinophils, haematological parameters and plasma pepsinogen. Texel lambs had significantly lower worm burden on day 14 and lower plasma pepsinogen concentration from day 14 onwards than Suffolks and their response in mucosal IgA to infection occurred earlier. The results from the study suggest that an earlier local IgA response in the Texel contributes to the resistant characteristics of the breed, while the increased level of plasma pepsinogen in the Suffolk lambs implies greater abomasal tissue damage arising from the nematode infection.

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 immune response to parasitic helminths of veterinary importance and its potential manipulation for future vaccine control strategies

Despite the increasing knowledge of the immunobiology and epidemiology of parasitic helminths of the gastrointestinal system and the cardiorespiratory system, complications arising from infections of animals and humans with these parasites are a major clinical and economic problem. This has been attributed to the high incidence of these parasites, the widespread emergence of multi-drug resistant parasite strains and the lack of effective vaccines. Efforts to develop and produce vaccines against virtually all helminths (with the exception of Dictyocaulus viviparus and some cestode species) have been hindered by the complexity of the host-parasite relationship, and incomplete understanding of the molecular and immune regulatory pathways associated with the development of protective immunity against helminths. Novel genomic and proteomic technologies have provided opportunities for the discovery and characterisation of effector mechanisms and molecules that govern the host-parasite interactions in these two body systems. Such knowledge provided clues on how appropriate and protective responses are elicited against helminths and, thus, may lead to the development of effective therapeutic strategies. Here, we review advances in the immune response to selected helminths of animal health significance, and subsequent vaccine potential. The topics addressed are important for understanding how helminths interact with host immune defences and also are relevant for understanding the pathogenesis of diseases caused by helminths.

A differential interplay between the expression of Th1/Th2/Treg related cytokine genes in Teladorsagia circumcincta infected DRB1*1101 carrier lambs

Substantial debate exists on whether the immune response between sheep resistant and susceptible to gastrointestinal nematodes can be differentiated into a Th1 and Th2 phenotype. The present study addresses the hypothesis that variation in resistance to Teladorsagia circumcincta between DRB1*1101 (associated with reduced faecal egg count and worm burden) carriers and non-carriers is due to a differential interplay in the expression of Th1/Th2 and regulatory T (Treg) related cytokine genes. Lambs from each genotype were either slaughtered at day 0 (un-infected control) or infected with 3 × 10⁴ Teladorsagia circumcincta L3 and slaughtered at 3, 7, 21, and 35 days later. Lambs carrying the DRB1*1101 allele had a significantly lower worm burden (P < 0.05) compared to the non-carriers. Abomasal mucosal cytokine gene expression was evaluated by quantitative real-time PCR and comparison made for time and genotype effects. The response generated varied through the course of infection and was affected by genotype. DRB1*1101 carriers had an up-regulated expression of the Th1-related cytokine genes (IL-1β, TNFα, and IFN-γ) at day 3, but this was replaced by an up-regulated expression of Th2-related cytokine genes (IL-10 and IL-13) and Treg-related cytokine genes (IL-2RA-CD25, TGFα, TGFβ, Arg2, MIF and FOXP3) by day 7. Conversely, in the non-carriers these changes in gene expression were delayed until days 7 and 21 post infection (pi), respectively. It is concluded that resistance to Teladorsagia circumcincta in animals carrying the DRB1*1101 allele is influenced by an earlier interplay between Th1, Th2 and T regulatory immune response genes.

The dynamic influence of the DRB1*1101 allele on the resistance of sheep to experimental Teladorsagia circumcincta infection

Suffolk sheep carrying the DRB1*1101 (previously referred to as-DRB1*0203 or G2) allele have been reported to show increased resistance to natural Teladorsagia circumcincta infection compared to non-carriers. The objective of this study was to compare the biochemical and physiological responses of DRB1*1101 carrier and non-carrier twin lambs to an experimental infection with 3 × 10⁴ L3 Teladorsagia circumcincta. The variables studied included worm burden, faecal egg count, abomasal mast cells, IgA, IgE, IgG1 plus IgG2 and haematological parameters at 0, 3, 7, 21 and 35 days post infection (dpi), and duodenal smooth muscle contractility at 0 and 35 dpi. DRB1*1101 carrier lambs had significantly lower worm burden, higher mast cell and plasma platelet counts than the DRB1*1101 non-carriers (P < 0.05). Before infection, the non-carrier lambs exhibited significantly higher mucosal levels of all antibody isotypes measured compared to the carriers; these levels remained relatively stable over the course of infection in the non-carriers while there was a slow build up of these antibodies in the carriers up to day 21 post infection (pi). The DRB1*1101 non-carrier lambs had a significantly higher plasma lymphocyte count, and produced greater duodenal contractile force relative to the carrier lambs (P < 0.05). There was no significant difference between genotypes in the level of plasma eosinophils, monocytes, neutrophils or FEC. This evidence suggests that resistance conferred by DRB1*1101 is acquired rather than innate, depends on worm expulsion rather than fecundity and is dependent on mucosal mast cell proliferation, platelet activation, and IgA and IgE antibody responses.

Ovine IgE and its role in immunological protection and disease

The importance of internal and external parasites in limiting productivity and compromising the welfare of sheep has provided the impetus for extensive research on ovine IgE with the objectives of better understanding protective immunological responses and developing novel methods of control; particularly vaccination. The molecular structures of ovine IgE and its high affinity receptor have been determined and the former information has assisted the development of monoclonal antibodies (mAb) to ovine IgE by 2 of 3 groups who have produced these reagents. The availability of these mAbs has enabled the description of IgE responses following infections with a wide variety of parasites in sheep and in an ovine model of atopic asthma. While IgE responses are consistently associated with parasitic diseases of sheep, it has not been proven that this antibody isotype is involved in protection. The foundation of present knowledge and reagents, together with new emerging technologies, should allow the role of IgE in parasitic diseases of sheep to be determined.