Antigen-specific peripheral immune responses are unaltered during normal pregnancy in sheep

Effects of early pregnancy on NOD-like receptor expression in the ovine endometrium

Introduction

Nucleotide-binding domain (NOD)-like receptors (NLRs) are expressed in the endometrium, and involved in modulating the female innate immune responses. There are conceptus-endometrial interactions during pregnancy, which ensure immune homeostasis of the maternal-fetal interface. The purpose of this study was to explore the effects of early pregnancy on NLR expression in the ovine endometrium.

Methods

Endometrial tissues were collected at day 16 of the estrous cycle, and at days 13, 16 and 25 of pregnancy (n = 6 for each group), and RT-qPCR, western blot and immunohistochemistry analysis were used to analyze the expression of NLRs, including NOD1, NOD2, major histocompatibility complex class II transactivator (CIITA), neuronal apoptosis inhibitor protein (NAIP), NLR family, pyrin domain-containing 1 (NLRP1), NLRP3 and NLRP7.

Results

Expression levels of NOD1, NOD2, NAIP, CIITA, NLRP1 and NLRP3 declined, but expression level of NLRP7 increased in the endometria during early pregnancy compared with nonpregnant ewes. In addition, NOD2 and CIITA proteins were located in the endometrium in a protein type-, cell type- and pregnancy status-specific manner.

Discussion

Early pregnancy modulated expression of NLR family in the ovine endometrium, which may be essential for conceptus-endometrial interactions and maternal-fetal interface immune homeostasis.

The Immune Response in the Uteri and Placentae of Chlamydia abortus-Infected Ewes and Its Association with Pregnancy Outcomes

The enzootic abortion of ewes, caused by the bacterium Chlamydia abortus (C. abortus), is one of the main causes of abortion in sheep. There are multiple contributory factors, including chlamydial growth, host immune response, and hormonal balance, that result in different pregnancy outcomes, such as abortion, the birth of weak lambs that may die, or healthy lambs. This study aimed to determine the relationship between phenotypical patterns of immune cell infiltration and different pregnancy outcomes in twin-bearing sheep (both lambs born dead; one alive and one dead; both alive) when experimentally infected with C. abortus. Both the sheep uteri and placentae were collected after parturition. All samples were analysed for specific immune cell features, including cell surface antigens and the T-regulatory (Treg) cell-associated transcription factor and cytokines, by immunohistochemistry and in situ hybridisation. Some of these immunological antigens were evaluated in ovine reproductive tissues for the first time. Differential patterns of T helper/Treg cells revealed significant group effects in the placentae. It suggests the potential role that the balance of lymphocyte subsets may play in affecting different pregnancy outcomes in C. abortus-infected sheep. The present study provides novel detailed information about the immune responses observed at the maternofoetal interface in sheep at the time of pre-term abortion or lambing.

Genes and Pathways Affecting Sheep Productivity Traits: Genetic Parameters, Genome-Wide Association Mapping, and Pathway Enrichment Analysis

Ewe productivity is a composite and maternal trait that is considered the most important economic trait in sheep meat production. The objective of this study was the application of alternative genome-wide association study (GWAS) approaches followed by gene set enrichment analysis (GSEA) on the ewes’ genome to identify genes affecting pregnancy outcomes and lamb growth after parturition in Iranian Baluchi sheep. Three maternal composite traits at birth and weaning were considered. The traits were progeny birth weight, litter mean weight at birth, total litter weight at birth, progeny weaning weight, litter mean weight at weaning, and total litter weight at weaning. GWASs were performed on original phenotypes as well as on estimated breeding values. The significant SNPs associated with composite traits at birth were located within or near genes RDX, FDX1, ARHGAP20, ZC3H12C, THBS1, and EPG5. Identified genes and pathways have functions related to pregnancy, such as autophagy in the placenta, progesterone production by the placenta, placental formation, calcium ion transport, and maternal immune response. For composite traits at weaning, genes (NR2C1, VEZT, HSD17B4, RSU1, CUBN, VIM, PRLR, and FTH1) and pathways affecting feed intake and food conservation, development of mammary glands cytoskeleton structure, and production of milk components like fatty acids, proteins, and vitamin B-12, were identified. The results show that calcium ion transport during pregnancy and feeding lambs by milk after parturition can have the greatest impact on weight gain as compared to other effects of maternal origin.

Reproductive immunology in viviparous mammals: evolutionary paradox of interactions among immune mechanisms and autologous or allogeneic gametes and semiallogeneic foetuses

Literally, reproductive immunology was born in bovine on-farm reproduction where seminal experiments intended for developing methods for embryo transfer in cattle were performed. Actually, these experiments led to two of major concepts and fundamental principles of reproductive immunology using the bovine species as a model for biomedical research, namely the concept of acquired immunological tolerance and the paradox of the semiallogeneic bovine foetus whereby such organism can develop within an immunologically competent host. Peter Medawar, a scientist who together with Frank Macfarlande Burnet shared the 1960 Nobel Prize in physiology or medicine for discovery of acquired immunological tolerance, while studying dizygotic cattle twins, thereby giving birth to reproductive immunology. Also, these findings significantly influenced development of organ transplants and showed that using farm animals as models for studying transplantation immunology had general relevance for mammalian biology and health including those of humans. However, the interest for further research of the fascinating maternal immune influences on pregnancy and perinatal outcomes and of the prevention and treatment of immunologically mediated reproductive disorders in viviparous mammals of veterinary relevance by veterinary immunologists and reproductive clinicians have been very scarce regarding the application of nonspecific immunomodulatory agents for prevention and treatment of subfertility and infertility in pigs and cattle, but still broadening knowledge in this area and hold great potential for improving such therapy in the future. The aim of the current overview is to provide up-to-date information and explaining/translating relevant immunology phenomena into veterinary practice for specialists and scientists/clinicians in reproduction of animals.

Immunological detection of pregnancy: Evidence for systemic immune modulation during early pregnancy in ruminants

Mammalian pregnancy creates unique challenges for immune systems highly evolved to detect and eliminate invading pathogens. Recognition of the challenges created by gestating a semi-allogeneic fetus evolved from the discipline of transplantation biology and were informed by studies on the unique natural parabiosis that occurs when female calves are gestated with twin male fetuses. These pregnancies typically result in an intersex female termed a freemartin, which revealed insights into development of the male and female reproductive tracts. However, they also uncovered important clues on immune tolerance with wide-ranging implications to reproductive biology, transplantation biology and autoimmune disease. Many studies focused on identifying mechanisms through which the fetus evades maternal immune detection and elimination. These included studies characterizing immune interactions between the fetus and mother at the nourishing interface of the placenta and uterine endometrium. This immunological forbearance only occurs under high concentrations of circulating progesterone. Beyond the requirement for progesterone, there has been considerable progress towards understanding the effects of conceptus signals on maternal immune function. One common theme is that pregnancy induces a T helper 2 immune bias as shown in several mammalian species, including domestic ruminants. However, a growing body of evidence shows that the fetus not only evades, but also provokes immune responses locally in the uterus and in peripheral tissues. This is perhaps most dramatically illustrated by domestic ruminants where the conceptus secretes a unique interferon in the opening salvo of hormonal communication with the maternal immune system. The role of interferon tau in regulating expression of genes of the innate immune system in the uterus has been extensively studied. More recently, it was determined that these same genes are also induced in peripheral immune cells and other tissues throughout the body. In addition to interferon tau and progesterone, pregnancy associate glycoproteins and chaperonin 10 (aka Early Pregnancy Factor) are implicated in altering immune function both locally and systemically during pregnancy. While it is tempting to speculate that this activation of innate immunity is designed to counteract selective immunosuppression, knowledge of the importance of local and systemic immune activation to the success of pregnancy remains incomplete. This area remains fertile ground for developing better approaches to diagnose and treat infertility in domestic farm species and humans alike.

Peripheral and placental immune responses in sheep after experimental infection with Toxoplasma gondii at the three terms of gestation

Although it is known that gestation could influence the clinical course of ovine toxoplasmosis, the precise effect of the term of gestation when sheep are infected are yet mostly unknown. The aim of this study was to evaluate the peripheral and placental immune responses developed in pregnant sheep after experimental infection with Toxoplasma gondii at different times of gestation. Thirty-six pregnant sheep were allocated in different groups, orally inoculated with sporulated oocysts of T. gondii at early, mid and late gestation and culled within 30 days post-infection. The peripheral humoral and cytokine responses were evaluated, as well as the transcription of cytokines at the placenta. Serological analysis revealed that, regardless the term of gestation when infected, specific IgG against T. gondii were detected from day 8 post-infection and there was an early peripheral release of IFN-γ at the first week post-infection followed by a short peak of IL10 and TNF-α at the second week post-infection. There were no significant differences in this response between infected groups. At the placenta, a similar increase in transcription of IFN-γ, and TNF-α was found at the three terms of gestation, while IL-4 increased mainly at the first and second terms and IL-10 transcription was higher at the last term. While these findings show that both Th1 and Th2 cytokines play a key role in the pathogenesis of ovine toxoplasmosis and that placental and peripheral immune responses do not closely correlate, there seems to be no clear modulation of these responses along the gestation.

Immunological Homeostasis at the Ovine Placenta May Reflect the Degree of Maternal Fetal Interaction

Successful mammalian pregnancies are a result of complex physiological, endocrinological, and immunological processes that combine to create an environment where the mother is tolerant to the semi-allogeneic fetus. Our knowledge of the mechanisms that contribute to maternal tolerance is derived mainly from human and murine studies of haemochorial placentation. However, as this is the most invasive type of placentation it cannot be assumed that identical mechanisms apply to the less invasive epitheliochorial placentation found in other species such as ruminants. Here, we examine three features associated with reproductive immune regulation in a transformed ovine trophoblast cell line and ex-vivo ovine reproductive tissues collected at term, namely: major histocompatibility complex (MHC) expression, Indoleamine 2,3 dioxygenase-1 (IDO-1) expression, and Natural Killer (NK) cell infiltration. High levels of MHC class I protein expression were detected at the surface of the trophoblast cell line using a pan-MHC class I specific monoclonal antibody. The majority of MHC class I transcripts isolated from the cell line clustered with classical MHC alleles. Transcriptional analysis of placental tissues identified only classical MHC class I transcripts. We found no evidence of constitutive transcription of IDO-1 in either the trophoblast cell line or placental tissues. Ex-vivo tissues collected from the materno-fetal interface were negative for cells expressing NKp46/NCR1. Collectively, these observations suggest that the relatively non-invasive synepitheliochorial placentation found in sheep has a more limited requirement for local immunoregulation compared to the more invasive haemochorial placentation of primates and rodents.

Phytosterols from Dunaliella tertiolecta Reduce Cell Proliferation in Sheep Fed Flaxseed during Post Partum

The post partum period is characterized by immunosuppression and increased disease susceptibility. Both phytosterols from microalga Dunaniella tertiolecta and dietary supplementation with n-3 polyunsaturated fatty acids (PUFA) influence cell proliferation and cytokine release during inflammation. The objective of this paper was the evaluation of the effects of physterols, extracted and purified from D. tertiolecta, on the in vitro immune responses of ewes supplemented with flaxseed during post partum. Twenty Comisana parturient ewes were divided in two balanced groups, and supplemented with flaxseed (FS, 250 g/day) or fed with a conventional diet (CON). Blood samples (15 mL) were collected for five weeks, starting from lambing, in order to isolate peripheral blood mononuclear cells (PBMC). Stimulated PBMC were treated with a total sterols fraction from D. tertiolecta (TS), a mix of ergosterol and 7-dehydroporiferasterol (purified extract, PE), and a mix of acetylated ergosterol and 7-dehydroporiferasterol (acetylated purified extract, AcPE), extracted and purified from D. tertiolecta at two concentrations (0.4 and 0.8 mg/mL). Results of the experiment demonstrated that n-3 PUFA from flaxseed induced an anti-inflammatory cytokine profile, with an increase of both IL-10, IL-6 and a decrease of IL-1β. TS, PE, and AcPE purified from D. tertiolecta showed an anti-proliferative effect on sheep PBMC regardless their chemical composition and concentration.

Evaluation of serum concentrations of tumor necrosis factor (TNF)-α, interleukin (IL)-2, IL-10, and nitric oxide (NO) during the estrous cycle, early pregnancy and abortion in goats

The aim of this study was to establish the serum concentrations, ranges, and trends of Th1 type cytokine (tumor necrosis factor (TNF)-α and interleukin (IL)-2), Th2 type cytokine (IL-10), and nitric oxide (NO) during the estrous cycle, early pregnancy and abortion in goats. Boer goats (n=25) having symptoms of normal estrous cycles were selected, 20 were mated and 15 conceived a pregnancy, and the remaining five were not mated and served as estrous controls. On the Day 60 of pregnancy, all 15 pregnant goats were induced to abort the pregnancy by intramuscular injection of prostaglandin (PG). Serum samples were collected on Days 1, 7, 14, and 19 of the estrous cycle, at Days 0, 10, 20, 30, 40, 50, and 60 of pregnancy, and at Days 1, 3, 8, 10 over the period when abortion were occurring. Results of the present study indicated that during the estrous cycle the balance between Th1 and Th2 cytokines slightly shifted toward Th1 cytokine production (TNF-α and IL-2). The NO may have a direct positive role in inducing a Th1 response. During early pregnancy, TNF-α and IL-2 serum concentrations markedly increased from Days 0 to 10, and gradually decreased from Days 10 to 60, while IL-10 and NO serum concentrations remained elevated from Days 0 to 60. The increased concentrations of IL-10 and decreased concentrations of TNF-α and IL-2 are characteristic of a Th2-enhanced response, which may be related to increased concentrations of NO. These changes may be essential to maintain a normal pregnancy. In addition, the serum concentrations of TNF-α, IL-2 and NO at Days 1, 3, 8 and 10 of the period of induced abortion were markedly greater than that on Day 60 of pregnancy. Conversely, IL-10 concentrations at these four time points of abortion were markedly less than that on Day 60 of pregnancy. After abortion, the Th2 response shifted to a Th1-enhanced response. Thus, NO concentrations increase and the Th1-enhanced response may function synergistically to be involved in physiologic responses that lead to abortion of the pregnancy. It is concluded that the serum concentrations of the Th1/Th2 cytokine and NO changed temporally as the estrous cycle, pregnancy and abortion progressed advanced. A Th2-enhanced state promoted normal pregnancy, while increased concentrations of Th1 were observed during the period of fetal abortion. The concentrations of NO varied in regulation of the Th1/Th2 cytokine concentration balance during the three phases (estrous cycle, pregnancy, and fetal abortion) of goats.

Experimental ovine toxoplasmosis: influence of the gestational stage on the clinical course, lesion development and parasite distribution

The relation between gestational age and foetal death risk in ovine toxoplasmosis is already known, but the mechanisms involved are not yet clear. In order to study how the stage of gestation influences these mechanisms, pregnant sheep of the same age and genetic background were orally dosed with 50 oocysts of Toxoplasma gondii (M4 isolate) at days 40 (G1), 90 (G2) and 120 (G3) of gestation. In each group, four animals were culled on the second, third and fourth week post infection (pi) in order to evaluate parasite load and distribution, and lesions in target organs. Ewes from G1 showed a longer period of hyperthermia than the other groups. Abortions occurred in all groups. While in G2 they were more frequent during the acute phase of the disease, in G3 they mainly occurred after day 20 pi. After challenge, parasite and lesions in the placentas and foetuses were detected from day 19 pi in G3 while in G2 or G1 they were only detected at day 26 pi. However, after initial detection at day 19 pi, parasite burden, measured through RT-PCR, in placenta or foetus of G3 did not increase significantly and, at in the third week pi it was lower than that measured in foetal liver or placenta from G1 to G3 respectively. These results show that the period of gestation clearly influences the parasite multiplication and development of lesions in the placenta and foetus and, as a consequence, the clinical course in ovine toxoplasmosis.

Lipopolysaccharide-Induced Preconditioning Attenuates Apoptosis and Differentially Regulates TLR4 and TLR7 Gene Expression after Ischemia in the Preterm Ovine Fetal Brain

Acute exposure to subclinical infection modulates subsequent hypoxia-ischemia (HI) injury in a time-dependent manner, likely by cross-talk through Toll-like receptors (TLRs), but the specific pathways are unclear in the preterm-equivalent brain. In the present study, we tested the hypothesis that repeated low-dose exposure to lipopolysaccharide (LPS) before acute ischemia would be associated with induction of specific TLRs that are potentially neuroprotective. Fetal sheep at 0.65 gestation (term is ∼145 days) received intravenous boluses of low-dose LPS for 5 days (day 1, 50 ng/kg; days 2-5, 100 ng/kg) or the same volume of saline. Either 4 or 24 h after the last bolus of LPS, complete carotid occlusion was induced for 22 min. Five days after LPS, brains were collected. Pretreatment with LPS for 5 days decreased cellular apoptosis, microglial activation and reactive astrogliosis in response to HI injury induced 24 but not 4 h after the last dose of LPS. This was associated with upregulation of TLR4, TLR7 and IFN-β mRNA, and increased fetal plasma IFN-β concentrations. The association of reduced white matter apoptosis and astrogliosis after repeated low-dose LPS finishing 24 h but not 4 h before cerebral ischemia, with central and peripheral induction of IFN-β, suggests the possibility that IFN-β may be an important mediator of endogenous neuroprotection in the developing brain.

Exploiting ovine immunology to improve the relevance of biomedical models

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Sheep make a valuable contribution to immunology research.

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Lessons to be learned from studying infections in the natural host.

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Factors to consider when selecting biomedical models.

Animal models of human disease are important tools in many areas of biomedicine; for example, in infectious disease research and in the development of novel drugs and medical devices. Most studies involving animals use rodents, in particular congenic mice, due to the availability of a wide number of strains and the ease with which they can be genetically manipulated. The use of mouse models has led to major advances in many fields of research, in particular in immunology but despite these advances, no animal model can exactly reproduce all the features of human disease. It is increasingly becoming recognised that in many circumstances mice do not provide the best model and that alternative species may be more appropriate. Here, we describe the relative merits of sheep as biomedical models for human physiology and disease in comparison to mice, with a particular focus on reproductive and respiratory pathogens.

Intranasal infection with Chlamydia abortus induces dose-dependent latency and abortion in sheep

Background

Latency is a key feature of the animal pathogen Chlamydia abortus, where infection remains inapparent in the non-pregnant animal and only becomes evident during a subsequent pregnancy. Often the first sign that an animal is infected is abortion occurring late in gestation. Despite this, little is understood of the underlying mechanisms that control latency or the recrudescence of infection that occurs during subsequent pregnancy. The aim of this study was to develop an experimental model of latency by mimicking the natural route of infection through the intranasal inoculation of non-pregnant sheep with C. abortus.

Methodology/Principal Findings

Three groups of sheep (groups 1, 2 and 3) were experimentally infected with different doses of C. abortus (5×10³, 5×10⁵ and 5×10⁷ inclusion forming units (IFU), respectively) prior to mating and monitored over 2 breeding cycles for clinical, microbiological, pathological, immunological and serological outcomes. Two further groups received either negative control inoculum (group 4a,b) or were inoculated subcutaneously on day 70 of gestation with 2×10⁶ IFU C. abortus (group 5). Animals in groups 1, 2 and 5 experienced an abortion rate of 50–67%, while only one animal aborted in group 3 and none in group 4a,b. Pathological, microbiological, immunological and serological analyses support the view that the maternal protective immune response is influenced by initial exposure to the bacterium.

Conclusions/Significance

The results show that intranasal administration of non-pregnant sheep with a low/medium dose of C. abortus results in a latent infection that leads in a subsequent pregnancy to infection of the placenta and abortion. In contrast a high dose stimulates protective immunity, resulting in a much lower abortion rate. This model will be useful in understanding the mechanisms of infection underlying latency and onset of disease, as well as in the development of novel therapeutics and vaccines for controlling infection.

Demystifying animal models of adverse pregnancy outcomes: touching bench and bedside

This represents an overview of the use of animal models to study the adverse pregnancy outcomes seen in humans. The purpose is to entice clinicians to utilize some of this information to seek out the literature and have more meaningful and profitable discussions with their academic colleagues and enhance transdisciplinary research in reproductive health.

Effect of progesterone on Th1/Th2/Th17 and regulatory T cell-related genes in peripheral blood mononuclear cells during pregnancy in cows

T helper (Th) cells play a central role in immune responses and new Th1/Th2/Th17 and regulatory T (Treg)-cell paradigm in pregnancy has developed. Progesterone (P(4)) is essential for the maintenance of pregnancy; however the effect of P(4) on Th1/Th2/Th17 and Treg paradigm is unclear in cows. We evaluated the effect of P(4) on the expression of Th1/Th2/Th17 and Treg-related cytokines, transcription factors, and P(4) receptors in the peripheral blood mononuclear cells (PBMCs) from 8 pregnant (163.1 ± 16.9 days of gestation) and 8 non-pregnant luteal phase cows. PBMCs were stimulated with P(4) at 0, 0.1, 1 or 10 μg/ml, and the mRNA expression of Th1, Th2, Th17 and Treg-related cytokines (IFN-γ, IL-4, IL-17 and TGF-β), transcription factors (T-bet, GATA-3, RORC and Foxp3) and P(4) receptors (PGR, PGRMC1 and PGRMC2) were analyzed by real time RT-PCR. In both pregnant and non-pregnant cows, P(4) significantly inhibited the expression of IFN-γ and IL-17 dose-dependently, whereas P(4) did not affect the expression of TGF-β and Foxp3. In addition, P(4) significantly decreased the expression of T-bet and RORC, and enhanced the expression of IL-4 in the pregnant cows, but this reaction was not found in the non-pregnant cows. P(4) tended to increase PGRMC1 in the pregnant cows but not in the non-pregnant cows, indicating that PGRMC1 may be involved in the regulation of the effect of P(4) during bovine pregnancy. These results indicate that P(4) is an important regulator of Th1/Th2/Th17 and Treg immunity, and higher Th2 immunity is characteristic in the pregnant cows.

Caprine endometrial stromal cells modulate the effects of steroid hormones on cytokine secretion by endometrial epithelial cells in vitro

The main purpose of this study was to examine the effects of 17β-estradiol (E(2)) and progesterone (P(4)) on cytokine secretion by caprine endometrial epithelial cells (EEC) in vitro. Epithelial cells grown alone or in co-culture with stromal cells (ESC) were treated with E(2) or P(4), or both. Homogeneity of the endometrial cell populations was ascertained immunocytochemically. The quantities of cytokines secreted in this system were assessed by ELISA and their protein expression by Western blot. The exposure of EEC to P(4) alone or in combination with E(2) significantly increased the amount of TGF-β1, TNF-α and IL-18 secretion, whereas E(2) had no effect on the synthesis of these cytokines. When epithelial cells were co-cultured with ESC, the secretion of TGF-β1, TNF-α and IL-18 by EEC significantly increased compared to that by EEC alone. However, the treatment with both steroids decreased the secretion of TNF-α, IL-18 and TGF-β1 by EEC in the presence of ESC. In contrast to TGF-β1, TNF-α and IL-18, the secretion of leukemia inhibitory factor (LIF) by EEC was not affected by E(2) and/or P(4) either directly or indirectly. The present results indicate that the interactions between caprine endometrial stromal and epithelial cells can modulate the secretion of TGF-β1, TNF-α and IL-18 by EEC exposed to E(2) and/or P(4)in vitro.

New challenges for vaccination to prevent chlamydial abortion in sheep

Ovine enzootic abortion (OEA) is caused by the obligate intracellular Gram-negative bacterium Chlamydia abortus. OEA remains a common cause of infectious abortion in many sheep-rearing countries despite the existence of commercially available vaccines that protect against the disease. There are a number of confounding factors that influence the uptake and use of these vaccines, which includes an inability to discriminate between infected and vaccinated animals (DIVA) using conventional serological diagnostic techniques. This suggests that the immunity elicited by current vaccines is similar to that observed in convalescent, immune sheep that have experienced OEA. The existence of these vaccines provides an opportunity to understand how protection against OEA is elicited and also to understand why vaccines can occasionally appear to fail, as has been reported recently for OEA. Interferon-gamma (IFN-γ), the cytokine that classically defines Th1-type adaptive immunity, is a strong correlate of protection against OEA in sheep and has been shown to inhibit the growth of C. abortus in vitro. Humoral immunity to C. abortus is observed in both vaccinated and naturally infected sheep, but antibody responses tend to be used more as diagnostic markers than targets for strategic vaccine design. A future successful DIVA vaccine against OEA should aim to elicit the immunological correlate of protection (IFN-γ) concomitantly with an antibody profile that is distinct from that of the natural infection. Such an approach requires careful selection of protective components of C. abortus combined with an effective delivery system that elicits IFN-γ-producing CD4+ve memory T cells.

Immunological paradigms and the pathogenesis of ovine chlamydial abortion

Successful mammalian pregnancy involves complex immunological interactions between the mother and foetus that are not yet fully understood. A number of immunological paradigms have been established to explain the failure of the maternal immune system to reject the semi-allogeneic foetus, mainly based on studies in mice and humans. However, as placental structure, gestation periods and number of concepti per pregnancy can vary greatly between mammals, it is not always clear how applicable these immunological paradigms are to reproduction in other species. Here, we discuss the predictions of three important immunological paradigms in relation to the pathogenesis of ovine enzootic abortion (OEA), a common cause of infectious abortion in sheep and other ruminants. OEA is caused by the intracellular Gram-negative bacterium Chlamydophila abortus that exhibits a tropism for placental trophoblast. The paradigms of particular relevance to the pathogenesis of OEA are as follows: (i) intracellular bacterial infections are controlled by T(H)1-type CD4(+ve) T cells; (ii) indoleamine 2,3-dioxygenase is expressed in the placenta to prevent immunological rejection of the semi-allogeneic foetus; and (iii) pregnancy is a maternal T(H)2-type phenomenon. We discuss the relevance and validity of these paradigms for chlamydial abortion and reproductive immunology in sheep.

Relative quantitative kinetics of interferon-gamma and interleukin-10 mRNA and protein production by activated ovine peripheral blood mononuclear cells

Interferon-gamma (IFN-gamma) and interleukin (IL)-10 are cross-regulatory cytokines capable of driving and controlling the adaptive host immune response. The inter-relationship between IFN-gamma and IL-10 expression has not been defined in sheep despite biological evidence suggesting that they perform similar functions to their orthologues described in other species. To address this, we have developed a quantitative (q)PCR method to assess relative levels of IFN-gamma and IL-10 mRNA expression in activated ovine peripheral blood mononuclear cells (PBMC) and compared the kinetics of mRNA expression with amounts of cytokine secreted by the cells over a 96h period. PBMC were collected from sheep immunised with the nominal antigen ovalbumin (Ova) and re-stimulated in vitro with antigen and the T cell mitogen concanavalin A (ConA). The recall response to antigen was characterised by a single peak in IFN-gamma mRNA expression at 48h of culture (13-fold increase over unstimulated cells) and relatively lower expression of IL-10 mRNA (average 2-3-fold increase over the 96h culture period). Antigen-driven IFN-gamma protein concentration was greatest at the end of the culture period (96h) whereas IL-10 protein level was not elevated above that observed in unstimulated cells. The typical response to ConA was greater for both cytokines, with IFN-gamma mRNA expression peaking at 6h of culture (133-fold increase) then declining rapidly whereas IL-10 mRNA expression peaked at 24h (16-fold increase) and declined more gradually. Despite these differences in the relative kinetics of mRNA expression in mitogen-activated PBMC, the typical pattern of protein expression of the two cytokines was similar. Both showed a gradual rise in protein concentration starting from 12h of culture which was still rising at the end of the culture period (96h). These data demonstrate that the kinetics of mRNA expression for IFN-gamma and IL-10 in activated ovine PBMC do not necessarily correlate with detectable protein in culture.

The ovine placenta and placentitis-A review

An appreciation of the complexities of placental structure and function is essential to understanding the pathogenesis of infectious placentitis and abortion. This review aims to illustrate aspects of ovine pregnancy and placentation that will assist both the research worker and the diagnostic pathologist. Morphologically, the ovine placenta is classified as being chorioallantoic, villous, cotyledonary and synepitheliochorial. Apposition of foetal and maternal tissues in early pregnancy eventually leads to the formation of the definitive placenta. Physiological features of placentation that are essential to normal pregnancy and foetal development include modulation of immune responses at the placental interface, increasing placental bloodflow to allow for increasing foetal demand and the secretion of hormones for the recognition and maintenance of pregnancy. Descriptions of the morphology of the near-term placenta in a normal pregnancy and of the foetal membranes that are voided during normal parturition provide the proper context for understanding the morphological changes associated with placentitis and how these changes are likely to affect placental function.