Induction and suppression of lymphocyte proliferation by antigen extracts of Ostertagia ostertagi

Differentiation and Regulation of Bovine Th2 Cells In Vitro

Bovine Th2 cells have usually been characterized by IL4 mRNA expression, but it is unclear whether their IL4 protein expression corresponds to transcription. We found that grass-fed healthy beef cattle, which had been regularly exposed to parasites on the grass, had a low frequency of IL4+ Th2 cells during flow cytometry, similar to animals grown in feedlots. To assess the distribution of IL4+ CD4+ T cells across tissues, samples from the blood, spleen, abomasal (draining), and inguinal lymph nodes were examined, which revealed limited IL4 protein detection in the CD4+ T cells across the examined tissues. To determine if bovine CD4+ T cells may develop into Th2 cells, naïve cells were stimulated with anti-bovine CD3 under a Th2 differentiation kit in vitro. The cells produced primarily IFNγ proteins, with only a small fraction (<10%) co-expressing IL4 proteins. Quantitative PCR confirmed elevated IFNγ transcription but no significant change in IL4 transcription. Surprisingly, GATA3, the master regulator of IL4, was highest in naïve CD4+ T cells but was considerably reduced following differentiation. To determine if the differentiated cells were true Th2 cells, an unbiased proteomic assay was carried out. The assay identified 4212 proteins, 422 of which were differently expressed compared to those in naïve cells. Based on these differential proteins, Th2-related upstream components were predicted, including CD3, CD28, IL4, and IL33, demonstrating typical Th2 differentiation. To boost IL4 expression, T cell receptor (TCR) stimulation strength was reduced by lowering anti-CD3 concentrations. Consequently, weak TCR stimulation essentially abolished Th2 expansion and survival. In addition, extra recombinant bovine IL4 (rbIL4) was added during Th2 differentiation, but, despite enhanced expansion, the IL4 level remained unaltered. These findings suggest that, while bovine CD4+ T cells can respond to Th2 differentiation stimuli, the bovine IL4 pathway is not regulated in the same way as in mice and humans. Furthermore, Ostertagia ostertagi (OO) extract, a gastrointestinal nematode in cattle, inhibited signaling via CD3, CD28, IL4, and TLRs/MYD88, indicating that external pathogens can influence bovine Th2 differentiation. In conclusion, though bovine CD4+ T cells can respond to IL4-driven differentiation, IL4 expression is not a defining feature of differentiated bovine Th2 cells.

Host protective ASP-based vaccine against the parasitic nematode Ostertagia ostertagi triggers NK cell activation and mixed IgG1-IgG2 response

The mucus-dwelling parasite Ostertagia ostertagi is one of the most important gastrointestinal nematodes in cattle. Our group has previously demonstrated the protective capacity of a vaccine against this parasite based on a native activation-associated secreted protein ASP1 (nASP) in combination with the saponin adjuvant QuilA. The aim of the current study was to analyse the effect of both antigen and adjuvant on the cellular and humoral vaccine-induced immune responses by comparing the native ASP to a recombinant version expressed in Pichia pastoris (pASP) and replacing QuilA by Al(OH)3. Immunization of cattle with the protective nASP+QuilA vaccine was associated with antigen-induced proliferation of natural killer (NK) cells combined with IFN-γ secretion and the induction of a mixed IgG1/IgG2 antibody response. ASP-specific activation and proliferation of NK cells was also observed in mice following the same vaccination regime. Replacing QuilA by Al(OH)3 or nASP by pASP significantly decreased the capacity of the vaccines to trigger both NK cell activation and antibody responses and failed to induce protection against a challenge infection. Reduction of the structurally anchoring disulphide bonds of the nASP completely abolished its ability to induce NK cell activation and antibody responses, highlighting the importance of protein conformation for the immunostimulatory activity.

The parasitic phase of Ostertagia ostertagi: quantification of the main life history traits through systematic review and meta-analysis

Predictive models of parasite life cycles increase our understanding of how parasite epidemiology is influenced by global changes and can be used to support decisions for more targeted worm control. Estimates of parasite population dynamics are needed to parameterize such models. The aim of this study was to quantify the main life history traits of Ostertagia ostertagi, economically the most important nematode of cattle in temperate regions. The main parameters determining parasite density during the parasitic phase of O. ostertagi are (i) the larval establishment rate, (ii) hypobiosis rate, (iii) adult mortality and (iv) female fecundity (number of eggs laid per day per female). A systematic review was performed covering studies from 1962 to 2007, in which helminth-naïve calves were artificially infected with O. ostertagi. The database was further extended with results of unpublished trials conducted at the Laboratory for Parasitology of Ghent University, Belgium. Overall inverse variance weighted estimates were computed for each of the traits through random effects models. An average establishment rate (±S.E.) of 0.269±0.022 was calculated based on data of 27 studies (46 experiments). The establishment rate declined when infection dose increased and was lower in younger animals. An average proportion of larvae entering hypobiosis (±S.E.) of 0.041 (±0.009) was calculated based on 27 studies (54 experiments). The proportion of ingested larvae that went into hypobiosis was higher in animals that received concomitant infections with nematode species other than O. ostertagi (mixed infections). An average daily adult mortality (±S.E.) of 0.028 (±0.002) was computed based on data from 28 studies (70 experiments). Adult mortality was positively correlated with infection dose. A daily fecundity (±S.E.) of 284 (±45) eggs per female was found based on nine studies (10 experiments). The average female sex ratio of O. ostertagi based on individual animal data (n=75) from six different studies was estimated to be 0.55. We believe that this systematic review is the first to summarise the available data on the main life history traits of the parasitic phase of O. ostertagi. In conclusion, this meta-analysis provides novel estimates for the parameterization of life cycle-based transmission models, explicitly reports measures of variance around these estimates, gives evidence for density dependence of larval establishment and adult mortality, shows that host age affects larval establishment and, to our knowledge, provides the first evidence for O. ostertagi of a female-biased sex ratio.

A calcium-activated nucleotidase secreted from Ostertagia ostertagi 4th-stage larvae is a member of the novel salivary apyrases present in blood-feeding arthropods

Apyrases (ATP-diphosphohydrolase) comprise a ubiquitous class of glycosylated nucleotidases that hydrolyse extracellular ATP and ADP to orthophosphate and AMP. One class of newly-described, Ca2+-dependent, salivary apyrases known to counteract blood-clotting, has been identified in haematophagous arthropods. Herein, we have identified a gene (Oos-apy-1) encoding a protein that structurally conforms to the Ca2+-activated apyrase from the bed bug, Cimex lectularius, by immunologically screening an Ostertagia L4 cDNA expression library. The expressed protein (rOos-APY-1) was biochemically functional in the presence of Ca2+ only, with greatest activity on ATP, ADP, UTP and UDP. Host antibodies to the fusion protein appeared as early as 14 days post-infection (p.i.) and increased through 30 days p.i. Immunohistochemical and Western blot analyses demonstrated that the native Oos-APY-1 protein is present in the glandular bulb of the oesophagus and is confined to the L4. A putative signal sequence at the N-terminus and near 100% identity with a Teladorsagia circumcincta L4 secreted protein is consistent with the native protein being secreted at the cellular level. Predicated upon substrate specificity, the native protein may be used by the parasite to control the levels of host extracellular nucleotides released by locally-damaged tissues in an effort to modulate immune intervention and inflammation.

Cytokine responses in immunized and non-immunized calves after Ostertagia ostertagi infection

The objective of this study was to evaluate abomasal cytokine responses in helminth-naive calves and calves vaccinated with protective antigen fractions from Ostertagia ostertagi after an experimental challenge infection with infective third stage (L3) larvae. Abomasal lymph nodes and/or abomasal mucosa were collected and messenger RNA for the Th1 cytokines (IFN-gamma, IL-2, IL-12 p40 subunit), the Th2 cytokines (IL-4, IL-5, IL-6, IL-10, IL-13, IL-15) and the Th3/Tr cytokine TGF-beta was quantified by real-time RT-PCR. Vaccination had no effect on cytokine profiles in either the abomasal lymph nodes or the abomasal mucosa. However, following infection all calves showed a significant decrease in the Th1 cytokines, IFN-gamma and IL-12 p40, and a significant increase in the Th2 cytokines, IL-4, IL-5, IL-10 and IL-13 in the lymph nodes, compared to non-infected calves. No correlation between the Th2 response and protection induced by vaccination could be demonstrated. In contrast, a Th2 pattern was not observed in the mucosa of the infected calves, which exhibited an increase in IFN-gamma as well as in the Th2 cytokines IL-4, IL-5 and IL-10 mRNA. No significant association was observed in the abomasal mucosa between any examined cytokine mRNA level and immune effector responses such as parasite-specific antibodies or the number of mucosal mast cells or eosinophils.

Inhibition of bovine T lymphocyte responses by extracts of the stomach worm Ostertagia ostertagi

Lowered immune responses during bovine ostertagiosis have been reported in both in vivo and in vitro assay systems. In the present study we have employed three different life cycle stages of the nematode Ostertagia ostertagi to determine if products of this economically important parasite inhibit in vitro proliferation of Con A-stimulated cells from uninfected animals. We have demonstrated an inhibitory effect upon the growth of Con A-stimulated lymphocytes after addition of fourth stage larval (L4) soluble extract (L4SE) to the cultures. In contrast, extracts from the third stage larvae (L3) had little or no inhibitory activity. The suppressive products were also shown to be secreted by the late L4. The suppressive activity is reversible if the L4 products are removed from culture. There is no immediate effect on proliferating cells and the L4SE must be in culture for 24-48 h before suppression is observable. The L4SE caused slight but not statistically significant decreases in the percentage of T cells and increases in B cell percentages in cultures when compared with cultures stimulated with Con A alone. No changes were seen in percentage of cells positive for markers for CD4, CD8, gammadelta T cells, or monocytes/macrophages as a consequence of the addition of L4SE. In contrast, there was a strong and significant reduction in the expression of the IL-2 receptors in cells cultured in the presence of the worm extract. There was no evidence of either necrosis or apoptosis resulting from the presence of L4 products in culture. The expression of messenger RNA for interleukin-2, -4, -13, tumor necrosis factor-alpha (TNF-alpha), and gamma-interferon (gamma-IFN) was decreased when L4SE was included in cultures of Con A-stimulated cells compared to cultures stimulated with Con A only. In contrast, messenger RNA expression of transforming growth factor-beta (TGF-beta) and interleukin-10 (IL-10) was increased in cells growing in the presence of L4 products. The potential role of these cytokines during ostertagiosis is discussed.

T-cell mediated immune responses in calves primary-infected or re-infected with Cooperia oncophora: similar effector cells but different timing

Cooperia oncophora is the most prevalent intestinal nematode of cattle occurring in Western Europe. Primary infection with 100000 third stage infective larvae (L3) induces acquired immunity in a high proportion of the animals but there is little information on immunity against re-infection. In the current experiment, the contribution of the T-cell mediated immunity in protection against re-infection with C. oncophora was investigated in detail. Priming elicited long-lasting protective immunity that was evidenced by a significantly decreased worm burden and egg excretion in primed animals compared to challenge control animals. Lymphocyte proliferation tests with excretory/secretory products (ESP) of C. oncophora and with three distinct ESP fractions indicated an enhanced reactivity in primed animals and suggested that by fractionating of ESP we selected for proteins involved in protective immunity against re-infection with C. oncophora. Phenotypic analysis of T cell subsets at diverse anatomical locations revealed that the enhanced reactivity of lymphocytes from peripheral blood and lymph nodes of the infected animals coincided with a significantly increased frequency of CD4(+) cells at these locations but a deceased frequency of CD4(+) cells in the lamina propria. These findings were independent of the immune status of the animals but more pronounced in the primed animals than in the challenge control animals. In addition we demonstrated that primary and secondary infections with C. oncophora were associated with two waves of eosinophils and that the kinetics of this cell population differed as a result of priming. Based on the observed correlations we propose that the early increase of eosinophils is T cell independent and merely a consequence of inflammation in the parasitised gut. In contrast, the second wave of eosinophils depends upon CD4(+) cells and correlations with parasitological parameters at this time point support a role of eosinophils as effector cells against adult stages of C. oncophora.

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

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

Role of the bovine immune system and genome in resistance to gastrointestinal nematodes

Gastrointestinal nematode infections of cattle remain a constraint on the efficient raising of cattle on pasture throughout the world. Most of the common genera of parasites found in cattle stimulate an effective level of protective immunity in most animals within the herd after the animals have been on pasture for several months. In contrast, cattle remain susceptible to infection by Ostertagia for many months, and immunity that actually reduces the development of newly acquired larvae is usually not evident until the animals are more than 2 years old. This prolonged susceptibility to reinfection is a major reason that this parasite remains the most economically important GI nematode in temperate regions of the world. Although, animals remain susceptible to reinfection for a prolonged period of time, there are a number of manifestations of the immune response that result in an enhanced level of herd immunity. These include a delay in the development time of the parasites, an increase in the number of larvae that undergo an inhibition in development, morphological changes in the worms, stunting of newly acquired worms, and most importantly a reduction in the number of eggs produced by the female worms. The overall result of these manifestations of immunity is a reduction in parasite transmission within the cattle herd. The immune mechanisms responsible for these different types of functional immunity remain to be defined. In general, GI nematode infections in mammals elicit very strong Th2-like responses characterized by high levels of Interleukin 4 (IL4), high levels of IgG1 and IgE antibodies, and large numbers of mast cells. In cattle, the most extensively studied GI nematode, in regards to host immune responses, is Ostertagia ostertagi. In Ostertagia infections, antigens are presented to the host in the draining lymph nodes very soon after infection, and within the first 3-4 days of infection these cells have left the nodes, entered the peripheral circulation, and have homed to tissues immediately surrounding the parasite where they become established. The immune response seen in the abomasum is in many ways are similar to that seen other mammalian hosts, with high levels of expression of IL4 in the draining lymph nodes and in lymphocytes isolated from the mucosa. But unlike a number of other systems, lymphocyte populations taken from Ostertagia infected cattle seem to be up-regulated for a number of other cytokines, most notably Interferon (IFN, implying that in Ostertagia infections, the immune response elicit is not simply a stereotypic Th2 response. In addition, effector cell populations in the tissues surrounding the parasites, are not typical, inferring the Ostertagia has evolved means to suppress or evade protective immune mechanisms. Studies have also demonstrated that the number of nematode eggs/gram (EPG) in feces of pastured cattle is strongly influenced by host genetics and that the heritability of this trait is approximately 0.30. In addition, EPG values are not "normally" distributed and a small percentage of a herd is responsible for the majority of parasite transmission. This suggests that genetic management of a small percentage of the herd can considerably reduce overall parasite transmission. A selective breeding program has been initiated to identify the host genes controlling resistance/susceptibility to the parasites. The best indicator of the number of Cooperia infecting a host is the EPG value, while Ostertagia is best measured by serum pepsinogen levels, weight gain, and measures of anemia. Other phenotypic measures are either not significantly associated with parasite numbers or are very weakly correlated. In addition, calves can be separated into three types: (1) Type I which never demonstrates high EPG values, (2) Type II which shows rises in EPG values through the first 2 months on pasture which then fall and remain at levels associated with Type I calves, and (3) Type III calves which maintain high EPG levels. The approximate percentage of these calves is 25:50:25 respectively. Because these cattle are segregating for traits involved in resistance and susceptibility to GI nematodes, this resource population is being used to effectively detect the genomic locations of these Economic Trait Loci (ETL). For relational analysis between phenotype and genome location, over 80,000 genotypes have been generated by PCR amplification, and marker genotypes have been scored to produce inheritance data. The marker allele inheritance data is currently being statistically analyzed to detect patterns of co-segregation between allele haplotype and EPG phenotypes. Statistical power of this genome-wide scan has been strengthened by including genotypic data from the historic pedigree. In our herd, paternal half-sib families range from 5-13 progeny/sire, and extensive marker genotypes are available from ancestors of the population most of which are paternally descended from a single founding sire. Once ETL have been identified the next will be to refine ETL map resolution in attempt to discover the genes underlying disease phenotypes. Accurate identification of genes controlling resistance will offer the producer several alternatives for disease control. For a non-organic producer, the small percentage of susceptible animals can be targeted for drug administration. This approach would reduce both the cost of anthelmintics used and the odds for selection of drug resistant mutants, because the selective agent (drug) would not be applied over the entire parasite population. A second treatment option would be based on correcting a heritable immunologic condition. In this case, susceptible animals could be the targets for immunotherapy involving vaccines of immunomodulation. A final option would be genetic selection to remove susceptible animals from the herd. Producers with a high degree of risk for parasite-induced production losses, such as organic producers of producers in geographic areas with environmental conditions favorable to high rates of transmission would benefit the most from this strategy. In contrast, producers at low risk could take a more conservative approach and select against susceptibility when other factors were equal.

Identification of Ostertagia ostertagi specific cells in bovine abomasal lymph nodes

To investigate the contribution of different bovine cell subpopulations in the development of in vitro induced responses by Ostertagia ostertagi third larval antigen extract (L3), bovine abomasal lymph node cell suspensions were depleted of specific cell populations. The depleted cell suspensions were subsequently assayed for their proliferative responses to O. ostertagi L3 antigen extract. Proliferative responses to O. ostertagi L3 antigen extract were restricted to a CD2+ CD4- CD8- cell population and MHC II+ cells different from B-cells were of major importance. Depletion of CD4, CD8, CD4CD8, IgM or CD21 positive cells did not decrease proliferation to L3 antigen extract. Depletion of gammadelta T-cells, which also comprise a subpopulation of CD2+ CD4- CD8- cells, reduced proliferation to L3 antigen extract only in one animal. The results suggest that either gammadelta T-cells could be involved in the proliferation or that another as yet unidentified population is important for proliferation. The precise role of these populations during infection with O. ostertagi and the mechanism by which these cells may influence the host immune response are important issues that remain to be elucidated.

Integrated control of nematode infections in cattle: a reality? A need? A future?

Helminth infections are a major cause of production loss in cattle. Great progress has been achieved in the design of control strategies for these infections. Control is based mainly on the use of anthelmintics, and these have become more potent and easier to administer. However, the most effective control is possible only through the integration of different approaches. Moreover, an increasing number of disadvantages of chemotherapy/prophylaxis--biological, economical and environmental--have been suggested. In sheep, the high incidence of anthelmintic resistance has simply forced veterinarians/producers to adopt alternative control strategies; in cattle, no real need for deviation from the actual control programmes seems to exist. Therefore, the following questions are discussed: (1) Based on the distribution of cattle worldwide, what are the target parasites? (2) Can we continue to rely on control based mainly on the use of (highly effective) anthelmintics? (3) What are the prospects for non-chemical control? (4) Who will develop and implement integrated control systems? (5) In the case of parasite control in Western Europe, has it been efficient and can/need it be changed? (6) How can we integrate helminth control in the general design of herd disease control?