Establishment of the Porcine Epitheliochorial Placenta Is Associated with Endometrial T-Cell Recruitment

Deciphering immune tolerance in allogeneic pig pregnancy

Embryo transfer (ET) has transformed swine biotechnology, enabling genetic advancements and disease control. However, its success remains inconsistent, partly due to immune-mediated challenges at the maternal-fetal interface. This study explores the immunological environment of hemi-allogeneic pregnancies (via artificial insemination, AI) versus allogeneic pregnancies (via ET) in pigs during the critical implantation phase. Sows were categorized into groups based on pregnancy type and fetal counts, reflecting varying outcomes. Endometrial immune cell populations, including T lymphocytes, regulatory T cells (Tregs), natural killer (NK) cells, and macrophages, were analyzed using immunohistochemistry. Notably, allogeneic pregnancies with poor outcomes displayed elevated NK cell and macrophage infiltration alongside reduced Treg presence, contributing to a pro-inflammatory environment. In contrast, allogeneic pregnancies with favorable outcomes exhibited immune profiles resembling hemi-allogeneic pregnancies, suggesting enhanced maternal-fetal tolerance. These findings underscore the immunological variability driving embryo survival rates in ET pregnancies and highlight key cellular targets for improving reproductive efficiency. Further research on immunomodulatory strategies is vital to optimize ET success in swine and other species.

Insights into the single-cell transcriptome characteristics of porcine endometrium with embryo loss

Reproductive disorders are a concern in the pig industry. Successful gestation processes are closely related to a suitable endometrial microenvironment, and the physiological mechanisms leading to failed pregnancy during the peri-implantation period remain unclear. We constructed single-cell transcriptome profiles of peri-implantation embryo loss and successful gestation endometrial tissues and identified 22 cell subpopulations, with epithelial and stromal cells being the predominant endometrial cell types. The two tissues showed marked differences in cell type composition, especially among epithelial cell subpopulations. We also observed functional differences between epithelial and stromal cells in tissues from embryonic loss and successful gestation, as well as the expression levels and differentiation trajectories of genes associated with embryo attachment and endometrial receptivity in epithelial and stromal cells. The results of cell communication interactions analysis showed that ciliated cells were more active in endometrial tissue with embryo loss, and there were differences in the types of endometrial cells with major roles in embryo loss and embryo implantation successful tissues for bone morphogenic protein, insulin-like growth factor, and transforming growth factor-β signaling networks associated with embryo implantation. In addition, we compared the functional differences in immune cells between the two tissue types and the expression levels of genes related to the inflammatory microenvironment. Overall, the present study revealed the molecular features of endometrial cell transcription in embryo-lost endometrial tissues, providing deeper insights into the endometrial microenvironment of reproductive disorders, which may inform the etiological, diagnostic, and therapeutic studies of reproductive disorders.

Changes in Immune Response during Pig Gestation with a Focus on Cytokines

Pigs have the highest percentage of embryonic death not associated with specific diseases of all livestock species, at 20-45%. During gestation processes, a series of complex alterations can arise, including embryonic migration and elongation, maternal immunological recognition of pregnancy, and embryonic competition for implantation sites and subsequent nutrition requirements and development. Immune cells and cytokines act as mediators between other molecules in highly complex interactions between various cell types. However, other non-immune cells, such as trophoblast cells, are important in immune pregnancy regulation. Numerous studies have shed light on the crucial roles of several cytokines that regulate the inflammatory processes that characterize the interface between the fetus and the mother throughout normal porcine gestation, but most of these reports are limited to the implantational and peri-implantational periods. Increase in some proinflammatory cytokines have been found in other gestational periods, such as placental remodeling. Porcine immune changes during delivery have not been studied as deeply as in other species. This review details some of the immune system cells actively involved in the fetomaternal interface during porcine gestation, as well as the principal cells, cytokines, and molecules, such as antibodies, that play crucial roles in sow pregnancy, both in early and mid-to-late gestation.

Human decidual gamma/delta T cells possess unique effector and TCR repertoire profiles during pregnancy

Human γδ T cells are enriched at the maternal-fetal interface (MFI, decidua basalis) showing a highly differentiated phenotype. However, their functional potential is not well-known and it is not clear whether this decidua-enrichment is associated with specific γδ T cell receptors (TCR) as is observed in mice. Here we addressed these open questions by investigating decidual γδ T cells during early and late gestation, in comparison with paired blood samples, with flow cytometry (cytotoxic mediators, cytokines) and TCR high-throughput sequencing. While decidual γδ T cells expressed less perforin than their counterparts in the blood, they expressed significant more granulysin during early pregnancy. Strikingly, this high granulysin expression was limited to early pregnancy, as it was reduced at term pregnancy. In contrast to this granulysin expression pattern, decidual γδ T cells produced reduced levels of IFNγ and TNFα (compared to paired blood) in early pregnancy that then increased by term pregnancy. TCR repertoire analysis indicated that human decidual γδ T cells are not generated early in life as in the mouse. Despite this, a specific enrichment of the Vγ2 chain in the decidua in early pregnancy was observed that disappeared later onwards, reflecting dynamic changes in the decidual γδ TCR repertoire during human gestation. In conclusion, our data indicate that decidual γδ T cells express a specific and dynamic pattern of cytotoxic mediators, Th1 cytokines and TCR repertoire suggesting an important role for these unconventional T cells in assuring a healthy pregnancy in human.

Immunological uterine response to pig embryos before and during implantation

The establishment of a successful pregnancy can only occur through a concerted functioning of the entire female reproductive system, allowing for fertilization, subsequent embryo development and implantation of the conceptus. In this context, the uterine immunological responses responsible for rejection or tolerance of the conceptus are of critical importance. The aim of the present review is to summarize our current knowledge about those cellular and molecular immunological events occurring at the uterine level during pre-implantation and implantation stages of pregnancy in the pig. Advancing our understanding of the immune mechanisms involved in the success or failure of pregnancy will provide cues to develop novel strategies augmenting endometrial receptivity, finally increasing the efficiency of assisted reproductive technologies in pigs.

Changes in mononuclear immune cells during bovine pregnancy

This study aimed to determine the differences in gene expression between mononuclear cells derived from peripheral blood and endometrium during pregnancy in cattle and to determine the proportion of mononuclear cells in the endometrium of pregnant and diestrous cows. Endometrial tissue and peripheral blood were collected from Day 34±2 pregnant cows, and mononuclear cell populations were quantified and sorted (n =5). The relative mRNA levels of inflammatory mediators was assessed by quantitative real time polymerase chain reaction. During pregnancy, the proportion of CD8+ , CD4+ , CD4+ CD25- and CD4+ CD25dim cells among mononuclear cells was greater in blood than endometrium, and cells positive for CD14 and CD68 expressed greater mRNA amounts of interleukin (IL ) 6 , CXCL8 and IL10 in endometrium compared with blood. Cells positive for γ/δ-T cell receptor expressed greater amounts of IL1A transcript in the endometrium than in blood of diestrous cows, CD4+ CD25bright cells expressed more CTLA4 mRNA in the endometrium compared with blood of diestrous cows, and endometrial natural killer cells expressed greater CXCL8 mRNA compared with blood of pregnant and diestrous cows. The percentages of CD21+ , NCR1+ , CD8+ , FoxP3+ , CD3+ and CD68+ cells were greater in the endometrium of Day 35 pregnant cows compared with diestrous cows.

Lymphocyte soluble factors from pregnant cows modulate mRNA transcript abundances encoding for proteins associated with trophoblast growth and development

This study was conducted to determine whether T cell populations are responsible for modulating placental development during gestation in cattle. It was hypothesized that CD4+CD25+ and γ/δ+ T cells modulate gene expression, based on mRNA transcript abundances, and promote proliferation and survival of trophoblast cells. Peripheral blood was collected from cows at 160 to 180 days of gestation and non-pregnant cows, T cell populations CD8+, CD4+, CD4+CD25+, CD24+CD25-, and γ/δ+ T cells were isolated, cultured for 48 h, and supernatant was collected. Placental samples were digested, and trophoblast cells were cultured for 24 h. Trophoblast cells were cultured with 50 μL of T cell-conditioned media and 50 μL of fresh culture media for an additional 48 h. Samples in control wells were treated with unconditioned media. Trophoblast cell proliferation, apoptosis, and mRNA transcript assays were conducted. There was no effect of T cell population on trophoblast apoptosis rate, proliferation, and relative mRNA transcript abundances. The T cell supernatant from pregnant and non-pregnant cows induced greater apoptosis rates in trophoblast cells than unconditioned media. Trophoblast cells proliferated less when treated with T cell supernatant from pregnant compared to unconditioned medium and non-pregnant cows. Treatment with the T cell supernatant from pregnant cows resulted in larger abundances of BMP5, IGF1R, PAG10, FGF2, RSPO3 and TMED2 and also a lesser abundance of FGF2 mRNA transcript than non-pregnant group and unconditioned media treatments. Supernatant from T cell derived from pregnant cows modulates trophoblast mRNA transcript abundances differently from T cell supernatant of non-pregnant cows.

Allogeneic Embryos Disregulate Leukemia Inhibitory Factor (LIF) and Its Receptor in the Porcine Endometrium During Implantation

Despite its advantages for pig breeding, embryo transfer (ET) has a major handicap: high embryo mortality during the pre- and implantation period, probably caused by divergent phenomena of tolerance between the immunologically unrelated (i.e., allogeneic) embryos and the recipient sow. Thus, to reach a similar maternal tolerance as in conventional breeding by artificial insemination (AI) would be the key to ET-success. For this reason, we studied the expression of the leukemia inhibitory factor (LIF) cytokine and its receptor in the pig endometrium during the implantation period (days 18 and 24) in sows subjected to ET (AL group) vs. post-cervical-AI controls (Hemi-AL group). Quantification of expression was performed at both mRNA (rt-qPCR) and protein (WB) levels. The expression of endometrial LIF on day 24 was considerably lower in ET than in AI pregnancies. Correlations between endometrial mRNA levels of LIF and LIF-R showed that, contrary to early AI-pregnancies, ET-pregnancies lack an inverse relation between cytokine and receptor levels. In conclusion, ET-pregnancies lack sufficient endometrial levels of LIF to develop adequate immunotolerance mechanisms to prevent the rejection of allogeneic ET-embryos.

NK and T Cell Differentiation at the Maternal-Fetal Interface in Sows During Late Gestation

The phenotype and function of immune cells that reside at the maternal-fetal interface in humans and mice have been, and still are, extensively studied with the aim to fully comprehend the complex immunology of pregnancy. In pigs, information regarding immune cell phenotypes is limited and mainly focused on early gestation whereas late gestation has not yet been investigated. We designed a unique methodology tailored to the porcine epitheliochorial placenta, which allowed us to address immune phenotypes separately in the maternal endometrium (ME) and fetal placenta (FP) by flow cytometry. In-depth phenotyping of NK cells, non-conventional and conventional T cells within maternal blood (mBld), ME, FP, and fetal spleen (fSpln) revealed major differences between these anatomic sites. In both maternal compartments, all NK cells were perforin⁺ and had NKp46-defined phenotypes indicative of late-stage differentiation. Likewise, T cells with a highly differentiated phenotype including CD2⁺CD8α⁺CD27^dim/–perforin⁺ γδ T cells, CD27^–perforin⁺ cytolytic T cells (CTLs), and T-bet⁺ CD4⁺CD8α⁺CD27^– effector memory T (Tem) cells prevailed within these compartments. The presence of highly differentiated T cells was also reflected in the number of cells that had the capacity to produce IFN-γ. In the FP, we found NK cells and T cell populations with a naive phenotype including CD2⁺CD8α^–CD27⁺perforin^– γδ T cells, T-bet^–CD4⁺CD8α^–CD27⁺ T cells, and CD27⁺perforin^– CTLs. However, also non-naive T cell phenotypes including CD2⁺CD8α⁺CD27⁺perforin^– γδ T cells, T-bet⁺CD4⁺CD8α⁺CD27^– Tem cells, and a substantial proportion of CD27^–perforin⁺ CTLs resided within this anatomic site. Currently, the origin or the cues that steer the differentiation of these putative effector cells are unclear. In the fSpln, NKp46^high NK cells and T cells with a naive phenotype prevailed. This study demonstrated that antigen-experienced immune cell phenotypes reside at the maternal-fetal interface, including the FP. Our methodology and our findings open avenues to study NK and T cell function over the course of gestation. In addition, this study lays a foundation to explore the interplay between immune cells and pathogens affecting swine reproduction.

Immune Suppression in Pregnancy and Cancer: Parallels and Insights

Immune system has evolved to maintain homeostatic balance between effector and regulatory immunity, which is critical to both elicit an adequate protective response to fight pathogens and disease, such as cancer, and to prevent damage to healthy tissues. Transient immune suppression can occur under normal physiological conditions, such as during wound healing to enable repair of normal tissue, or for more extended periods of time during fetal development, where the balance is shifted towards regulatory immunity to prevent fetal rejection. Interestingly, tumors can exhibit patterns of immune suppression very similar to those observed during fetal development. Here some of the key aspects of normal patterns of immune suppression during pregnancy are reviewed, followed by a discussion of parallels that exist with tumor-related immune suppression and consequent potential therapeutic implications.

Identification of Differentially Expressed Gene Transcripts in Porcine Endometrium during Early Stages of Pregnancy

During the early stages of pregnancy, the uterine endometrium undergoes dramatic morphologic and functional changes accompanied with dynamic variation in gene expression. Pregnancy-stage specific differentially expressed gene (DEG)-transcript-probes were investigated and identified by comparing endometrium transcriptome at 9th day (9D), 12th day (12D) and 16th day (16D) of early pregnancy in Polish large-white (PLW) gilts. Endometrium comparisons between 9D-vs-12D, 9D-vs-16D and 12D-vs-16D of early pregnancy identified 6049, 374 and 6034 highly significant DEG-transcript-probes (p < 0.001; >2 FC). GO term enrichment analysis identified commonly shared upregulated endometrial DEG-transcript-probes (p < 0.001; >2 FC), that were regulating the gene functions of anatomic structure development and transport (TG), DNA-binding and methyltransferase activity (ZBTB2), ion-binding and kinase activity (CKM), cell proliferation and apoptosis activity (IL1B). Downregulated DEG-transcript-probes (p < 0.001; >2 FC) were involved in regulating the gene functions of phosphatase activity (PTPN11), TC616413 gene-transcript and Sus-scrofa LOC100525539. Moreover, blastn comparison of microarray-probes sequences against sus-scrofa11 assembly identified commonly shared upregulated endometrial DEG-transcript-probes (E < 0.06; >2 FC), that were regulating the gene functions of reproduction and growth (SELENOP), cytoskeleton organization and kinase activity (CDC42BPA), phosphatase activity (MINPP1), enzyme-binding and cell-population proliferation (VAV3), cancer-susceptibility candidate gene (CASC4), cytoskeletal protein-binding (COBLL1), ion-binding, enzyme regulator activity (ACAP2) Downregulated endometrial DEG-transcript-probes (E < 0.06; >2FC) were involved in regulating the gene functions of signal-transduction (TMEM33), catabolic and metabolic processes (KLHL15). Microarray validation experiment on selected candidate genes showed complementarity to significant endometrial DEG-transcript-probes responsible for the regulation of immune response (IL1B, S100A11), lipid metabolism (FABP3, PPARG), cell-adhesion (ITGAV), angiogenesis (IL1B), intercellular transmission (NMB), cell-adhesion (OPN) and response to stimuli (RBP4) was confirmed by RT-PCR. This study provides a clue that identified pregnancy-stage specific microarray transcript probes could be considered as candidate genes for recognition and establishment of early pregnancy in the pig.

Variable chemokine expression in porcine trophoblasts and endometrium during the peri-implantation period

Successful embryo implantation and its further development depends on appropriate endometrial remodelling. Porcine early pregnancy is associated with intensive endometrial angiogenesis and establishment of an immunotolerant environment for the embryo. An increasing number of factors are believed to participate in endometrial remodelling. The aim of this study was to elucidate the involvement of selected chemokines at the porcine maternal-foetal interface during the peri-implantation period. Real-time PCR analysis revealed several upregulated chemokines during the time of implantation, and Western blot/ELISA analyses and immunohistochemical staining confirmed their presence at the protein level. The gene expression of several chemokines and receptors was also confirmed in early porcine trophoblasts. The results indicated that IFNG, a porcine trophoblast signal, positively influenced the expression of some chemokines in endometrial cells. In conclusion, we suggest that some of the examined chemokines may be involved in endometrial communication with the trophoblast (CCL2, CCL5, CCL11, CXCL12), whereas others are implicated in the recruitment of immune cells and establishment of an immunotolerant environment for the embryo (CXCL9, CXCL10).

Pregnancy and spontaneous fetal loss: A pig perspective

Pigs have a unique, non-invasive epitheliochorial placenta where maternal and fetal layers lay in apposition. Indentation of fetal capillaries into the trophoblasts and maternal capillaries into the uterine epithelium reduce the distance between the fetal and maternal blood, ensuring nutrient transfer for proper conceptus development. Another unique feature of pig pregnancy is conceptus-mediated immune cell enrichment during the early stages of conceptus attachment (around gestation Day 15). This period coincides with the development of vasculature networks at the maternal-fetal interface, which is critical for successful conceptus growth. Specific chemokines, their receptors, and chemokine decoy receptor networks coordinate this immune cell enrichment and the positioning at the maternal-fetal interface. The recruited immune cells, in turn, adopt a specialized phenotype to support key processes of maternal-fetal adaptations, including tolerance to the semi-allogeneic fetus and supporting vascularization. Disturbance in coordinated cross talk between the conceptus and maternal endometrium is an important mechanism associated with spontaneous fetal loss. The exact mechanism of fetal loss is still not yet identified, although research in the last two decades point to various factors including genetics, nutrition, uterine capacity, placental efficiency, and imbalanced immune factors at the maternal-fetal interface. In this review, we summarize some of the recent advances in endometrial immune cell functions and their regulation. We also provide insights into endometrial/placental transcriptome, microRNA biology, and extravesicular transport across the maternal-fetal interface, as well as their potential implications in porcine pregnancy success or failure.

Altered expression of chemokines and their receptors at porcine maternal-fetal interface during early and mid-gestational fetal loss

Chemokines play a significant role in pregnancy, especially during embryonic attachment and placental development. During early pregnancy, immune cells are recruited extensively to the endometrium in several species including pigs. However, this recruitment is solely mediated by the presence of the conceptus in pigs making it a unique feature compared with other species (humans, primates and mice). To understand the biological significance of chemokine expression and immune cell recruitment in the context of fetal loss, we investigate a well-characterized porcine fetal loss model during the window of early pregnancy at gestational day (gd) 20 and mid-pregnancy (gd50). These periods coincide with 25-40 % of conceptus loss. Using targeted quantitative polymerase chain reaction and Western blot approaches, we screened a specific set of chemokines. Comparisons were made with endometrial lymphocytes (ENDO LY), endometrium and chorioallantoic membranes (CAM) associated with spontaneously arresting and healthy conceptus attachment sites (CAS). mRNA expression studies revealed an increased expression of CXCR3 and CCR5 in ENDO LY and of CXCL10, CXCR3, CCL5 and CCR5 in the endometrium associated with arresting CAS at gd20. DARC was decreased in the endometrium at gd50. CCL1 was increased in CAM associated with arresting CAS at gd50. Some of these differences were also noted at the protein level (CXCL10, CXCR3, CCL5 and CCR5) in the endometrium and CAM. CD45+ immunohistochemistry demonstrated a significantly higher localization in ENDO LY in the endometrium associated with healthy versus arresting counterparts. Most of these differences were observed in early pregnancy and might contribute towards a shift in immune cell functions.

Placentation, maternal-fetal interface, and conceptus loss in swine

Pregnancy is a delicate yet complex physiological process that requires fine-tuning of many factors (hormones, growth factors, cytokines, and receptors) between the mother and the conceptus to ensure the survival of the conceptus(es) to term. Any disturbance in the maternal-conceptus dialog can have detrimental effects on the affected conceptus or even the outcome of pregnancy as a whole. Being a litter-bearing species, such disruptions can lead to a loss of up to 45% of the totally healthy offspring during early (periattachment) and midgestation to late gestation in pigs. Although the exact mechanism is not entirely understood, several factors have been associated with the fetal loss including but not limited to uterine capacity, placental efficiency, genetics, nutrition, and deficits in vascularization at the maternal-fetal interface. Over the years, we investigated how immune cells are recruited to the porcine maternal-fetal interface and whether they contribute to vascularization. We also delineated how cytokines, chemokines, and cytokine destabilizing factors fine-tune inflammation and whether the cytokine shift from early to midpregnancy exists at the porcine maternal-fetal interface. Finally, we evaluated the role of microRNAs in regulating immune cell recruitment and their angiogenic functions during pregnancy. Collectively our research points out that the immune-angiogenesis axis at the porcine maternal interface is significantly involved in promoting new blood vessel development, regulating inflammatory responses and ultimately contributing to pregnancy success. In this review, we summarized current knowledge on spontaneous fetal loss in swine, with special attention to the mechanisms in immune reactivity and interplay at the maternal-fetal interface.

Effects of seminal plasma and the presence of a conceptus on regulation of lymphocyte-cytokine network in porcine endometrium

Infusion of seminal plasma in the uterus is known to elicit an instant inflammatory response in the porcine uterus, but whether or not it prepares a uterine immunological response to the presence of conceptuses is not well understood. Seminal plasma induced long-term modulatory effects and conceptus-induced immune changes in leukocyte populations were measured by flow cytometry and mRNAs for various cytokines by quantitative reverse-transcriptase PCR in porcine endometrium collected on Days 6 and 13 from cycling and pregnant animals or from animals given seminal plasma infusions. Seminal plasma infusion induced long-term modulatory effects, resulting in significantly more endometrial FoxP3-positive T-regulatory and T-helper cells 6 days after infusion as compared to cycling and pregnant animals. The number of T-cytotoxic and T-null cells did not change between the studied groups. The early molecular effects of seminal plasma were not observed at 13-days post-infusion, although animals on Day 13 of pregnancy did show significantly more T-cells (of any type investigated). Seminal plasma also showed a delayed effect on cytokine expression, specifically exhibiting a significant increase in interleukin 10 (IL10) and a decrease in granulocyte macrophage colony-stimulating factor (GMCSF) gene expression on Day 13 as compared to Day 6 of cycling or pregnant gilts. The results indicate a delayed regulatory effect of seminal plasma on immune responses in the porcine uterus, which are similar to immune changes generated by implanting conceptuses.

Transcriptome changes in the porcine endometrium during the preattachment phase

The porcine conceptus undergoes rapid differentiation and expansion of its trophoblastic membranes between Days 11 and 12 of gestation. Concomitant with trophoblast elongation, production of conceptus estrogen, the porcine embryonic pregnancy recognition signal, increases. Conceptus attachment to the uterine surface epithelium starts after Day 13, initiating epitheliochorial placentation. To analyze the transcriptome changes in the endometrium in the course of maternal recognition of pregnancy, deep sequencing of endometrial RNA samples of Day 12 pregnant animals (n = 4) and corresponding nonpregnant controls (n = 4) was performed using RNA sequencing (RNA-Seq). Between 30 000 000 and 35 000 000 sequence reads per sample were produced and mapped to the porcine genome (Sscrofa10.2). Analysis of read counts revealed 2593 differentially expressed genes (DEGs). Expression of selected genes was validated by the use of quantitative real-time RT-PCR. Bioinformatics analysis identified several functional terms specifically overrepresented for up-regulated or down-regulated genes. Comparison of the RNA-Seq data from Days 12 and 14 of pregnancy was performed at the level of all expressed genes, the level of the DEG, and the level of functional categories. This revealed specific gene expression patterns reflecting the different functions of the endometrium during these stages (i.e., recognition of pregnancy and preparation for conceptus attachment). Genes related to mitosis, immune response, epithelial cell differentiation and development, proteolysis, and prostaglandin signaling and metabolism are discussed in detail. This study identified comprehensive transcriptome changes in porcine endometrium associated with establishment of pregnancy and could be a resource for targeted studies of genes and pathways potentially involved in regulation of this process.

Pathogenesis and prevention of placental and transplacental porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome virus (PRRSV)-induced reproductive problems are characterized by embryonic death, late-term abortions, early farrowing and increase in number of dead and mummified fetuses, and weak-born piglets. The virus recovery from fetal tissues illustrates transplacental infection, but despite many studies on the subject, the means by which PRRSV spreads from mother to fetus and the exact pathophysiological basis of the virus-induced reproductive failure remain unexplained. Recent findings from our group indicate that the endometrium and placenta are involved in the PRRSV passage from mother to fetus and that virus replication in the endometrial/placental tissues can be the actual reason for fetal death. The main purpose of this review is to clarify the role that PRRSV replication and PRRSV-induced changes in the endometrium/placenta play in the pathogenesis of PRRSV-induced reproductive failure in pregnant sows. In addition, strategies to control placental and transplacental PRRSV infection are discussed.

An overview of molecular and cellular mechanisms associated with porcine pregnancy success or failure

Prenatal mortality remains one of the major constraints for the commercial pig industry in North America. Twenty to thirty per cent of the conceptuses are lost early in gestation and an additional 10-15% is lost by mid-to-late gestation. Research over the last two decades has provided critical insights into how uterine capacity, placental efficiency, genetics, environment, nutrition and immune mechanisms impact successful conceptus growth; however, the exact cause and effect relationship in the context of foetal loss has yet to be determined. Similar to other mammalian species such as the human, mouse, rat, and primates, immune cell enrichment occurs at the porcine maternal-foetal interface during the window of conceptus attachment. However, unlike other species, immune cells are solely recruited by conceptus-derived signals. As pigs have epitheliochorial placentae where maternal and foetal tissue layers are separate, it provides an ideal model to study immune cell interactions with foetal trophoblasts. Our research is focused on the immune-angiogenesis axis during porcine pregnancy. It is well established that immune cells are recruited to the maternal-foetal interface, but their pregnancy specific functions and how the local milieu affects angiogenesis and inflammation at the site of foetal arrest remain unknown. Through a better understanding of how immune cells modulate crosstalk between the conceptus and the mother, it might be possible to therapeutically target immune cells and/or their products to reduce foetal loss. In this review, we provide evidence from the literature and from our own work into the immunological factors associated with porcine foetal loss.