Conceptus-modulated innate immune function during early pregnancy in ruminants: a review

Influence of sub-clinical endometritis on early pregnancy predictors and proinflammatory cytokines in circulating immune cells in dairy cows

In Experiment 1, PBMC were isolated from cows considered healthy or with SCE (n=6/group) on Days 0 (estrus) and 7 (diestrus) of a synchronized estrous cycle. In Experiment 2, on D21 (D0 was defined as the day of Fixed Timed Artificial Insemination (FTAI), cows were evaluated by ultrasonography to assess luteal blood perfusion and PBMC were isolated. On D32, cows were classified into: healthy pregnant (n=7), pregnant with SCE (n=4), healthy non-pregnant (n=8), and non-pregnant with SCE (n=10). Gene expression of ISGs (ISG15, OAS1, MX1 and IFI6) and proinflammatory cytokines (IL1-β, TNF-α and IFN-γ) were determined. Expression of ISG15, MX1, IFI6, TNF-α and IFN-γ did not differ between SCE and healthy cows and between Days 0 and 7. Expression of OAS1 and IL1-β were higher (P=0.02) on Day 7 than Day 0, regardlees of the SCE presence. In Exp.2, ISG15 abundance was 2.5-fold greater (P=0.0008), TNF-α was 2.2-fold greater (P=0.05), and IL1-β tended (P=0.06) to be 2.4-fold higher in pregnant than non-pregnant cows. Luteal blood perfusion was greater (P=0.01) in pregnant animals. In conclusion, OAS1 and IL1-β are transcripts upregulated in PBMC at diestrus, regardless of SCE occurrence. Proinflammatory cytokines are not affected by SCE occurrence, but IL1-β and TNF-α are upregulated in pregnant animals on D21 of pregnancy. ISG15 abundance is a good pregnancy predictor, regardless SCE presence.

Regulation of IkappaB Protein Expression by Early Gestation in the Thymus of Ewes

The thymus is an essential component of maternal immune systems that play key roles in recognizing the placenta as immunologically foreign. The inhibitor of the NF-κB (IκB) family has essential effects on the NF-κB pathway; however, it is unclear whether early pregnancy modulates the expression of the IκB family in the thymus. In this study, maternal thymuses were sampled on day 16 of nonpregnancy and different gestation stages in the ovine, and the expression of IκB proteins was analyzed. The data showed that B cell leukemia-3 and IκBβ increased; however, IκBα, IκBε, and IKKγ deceased during gestation. Furthermore, there was an increase in IκBNS and IκBζ expression values on day 13 of pregnancy; however, this decreased on day 25 of gestation. In summary, the expression of the IκB family was modulated in the thymus during early gestation, suggesting that the maternal thymus can be associated with maternal immunologic tolerance and pregnancy establishment in ewes.

Changes in expression levels of Nod-like receptors in the spleen of ewes

Nucleotide-binding oligomerization domain receptors (NOD-like receptors, NLRs) have critical effects on interfaces of the immune and reproductive systems, and the spleen plays a key role in both innate and adaptive immune functions. It is hypothesized that NLR family participates in maternal splenic immune regulation during early pregnancy in sheep. In this study, maternal spleens were collected on day 16 of the estrous cycle, and days 13, 16 and 25 of gestation (n = 6 for each group) in ewes. Expression of NLR family, including NOD1, NOD2, class II transactivator (CIITA), NLR family apoptosis inhibitory protein (NAIP), nucleotide-binding oligomerization domain, Leucine rich repeat and Pyrin domain containing 1 (NLRP1), NLRP3 and NLRP7, was analyzed using quantitative real-time PCR, Western blot and immunohistochemistry analysis. The results revealed that expression levels of NOD1, NOD2, CIITA and NLRP3 were downregulated at days 13 and 16 of pregnancy, but expression of NLRP3 was increased at day 25 of pregnancy. In addition, expression values of NAIP and NLRP7 mRNA and proteins were improved at days 16 and 25 of pregnancy, and NLRP1 was peaked at days 13 and 16 of pregnancy in the maternal spleen. Furthermore, NOD2 and NLRP7 proteins were limited to the capsule, trabeculae and splenic cords. In summary, early pregnancy changes expression of NLR family in the maternal spleen, which may be related with the maternal splenic immunomodulation during early pregnancy in sheep.

Conjugated linoleic acid supplementation changes prostaglandin concentration ratio and alters the expression of genes involved in maternal-fetal recognition from bovine trophoblast cells in vitro

Early embryonic mortality caused by maternal-fetal recognition failure in the three weeks after fertilization represents a major cause of reproductive inefficiency in the cattle industry. Modifying the amounts and ratios of prostaglandin (PG) F_2α and PGE₂ can benefit the establishment of pregnancy in cattle. Adding conjugated linoleic acid (CLA) to endometrial and fetal cells culture affects PG synthesis, but its effect on bovine trophoblast cells (CT-1) is unknown. The aim of this study was to determine the effects of CLA (a mixture of cis- and trans-9, 11- and -10,12-octadecadienoic acids) on PGE₂ and PGF_2α synthesis and the expression of transcripts involved with maternal-fetal recognition of bovine trophectoderm. Cultures of CT-1 were exposed to CLA for 24, 48 and 72 h. Transcript abundance was determined by qRT-PCR and hormone profiles were quantified by ELISA. The PGE₂ and PGF_2α concentrations were reduced in the culture medium of CLA-exposed CT-1 compared to that of unexposed cells. Furthermore, CLA supplementation increased the PGE₂:PGF_2α ratio in CT-1 and had a quadratic effect (P < 0.05) on the relative expression of MMP9, PTGES2, and PTGER4. The relative expression levels of PTGER4 were reduced (P < 0.05) in CT-1 cultured with 100 μM CLA than in the unsupplemented and 10 μM-CLA groups. Treatment of CT-1 with CLA decreased PGE₂ and PGF_2α synthesis but a biphasic effect of CLA was observed on the PGE₂:PGF_2α ratio and relative abundance of transcripts with 10 μM CLA providing maximal improvements in each endpoint. Our data suggest that CLA may influence eicosanoid metabolic process and extracellular matrix remodeling.

Expression of IkappaB Family in the Ovine Liver during Early Pregnancy

During normal pregnancy, there is a dynamic regulation of the maternal immune system, including the liver, to accommodate the presence of the allogeneic foetus in the uterus. However, it was unclear that the expression of the IkappaB (IκB) family was regulated in the ovine maternal liver during early pregnancy. In this study, sheep livers were collected at day 16 of the oestrous cycle (NP16), and days 13, 16 and 25 of gestation (DP13, DP16 and DP25), and RT-qPCR, Western blot and immunohistochemistry analysis were used to analyse the expression of the IκB family, including B cell leukemia-3 (BCL-3), IκBα, IκBβ, IκBε, IKKγ, IκBNS and IκBζ. The results revealed that expression of BCL-3, IκBβ, IκBε and IKKγ peaked at DP16, and the expression of IκBα was increased during early pregnancy. In addition, the expression of IκBζ peaked at DP13 and DP16, and IκBNS peaked at DP13. IκBβ and IKKγ proteins were located in the endothelial cells of the proper hepatic arteries and portal veins, and hepatocytes. In conclusion, early pregnancy changed the expression of the IκB family, suggesting that the modulation of the IκB family may be related to the regulation of maternal hepatic functions, which may be favourable for pregnancy establishment in sheep.

Early Pregnancy Regulates Expression of IkappaB Family in Ovine Spleen and Lymph Nodes

Early pregnancy modulates the maternal immune system, including the spleen and lymph nodes, which participate in maternal innate and adaptive immune responses. Methods: Ovine spleens and lymph nodes were sampled at day 16 of the estrous cycle, and at days 13, 16 and 25 of gestation, and qRT-PCR, Western blot and immunohistochemistry analysis were used to analyze the expression of the IκB family, including BCL-3, IκBα, IκBβ, IκBε, IKKγ, IκBNS and IκBζ. Early pregnancy induced expression of BCL-3, IκBα, IκBε, IKKγ and IκBζ, and expression of BCL-3, IκBβ and IκBNS peaked at day 16 of pregnancy in the spleen. However, early pregnancy suppressed the expression of BCL-3 and IκBNS, but stimulated the expression of IκBβ and IκBζ, and expression levels of IκBα, IκBβ, IκBε and IKKγ peaked in lymph nodes at days 13 and/or 16 of pregnancy. Early pregnancy changed the expression of the IκB family in the maternal spleen and lymph node in a tissue-specific manner, suggesting that the modulation of the IκB family may be involved in regulation of maternal functions of the spleen and lymph nodes, which are necessary for the establishment of maternal immune tolerance during early pregnancy in sheep.

Modulation of Nod-like Receptor Expression in the Thymus during Early Pregnancy in Ewes

Nucleotide-binding oligomerization domain receptors (NOD-like receptors, NLRs) are involved in modulating the innate immune responses of the trophoblast and the placenta in normal pregnancy. The thymus participates in regulation of innate and adaptive immune responses. However, it is unclear whether expression of NLR is modulated in the maternal thymus during early pregnancy. In this study, thymuses were sampled at day 16 of the estrous cycle, and at days 13, 16 and 25 of gestation (n = 6 for each group) from ewes after slaughter. Different stages were chosen because the maternal thymus was under the different effects of interferon-tau and/or progesterone or not. RT-qPCR, Western blot and immunohistochemistry analysis were used to analyze the expression of the NLR family, including NOD1; NOD2; major histocompatibility complex class II transactivator (CIITA); NLR family apoptosis inhibitory protein (NAIP); nucleotide-binding oligomerization domain and Leucine-rich repeat and Pyrin domain containing protein 1 (NLRP1), NLRP3 and NLRP7. The results showed that expression level of NOD1 was changed with the pregnancy stages, and expression levels of NOD2, CIITA, NAIP, NLRP1, NLRP3 and NLRP7 mRNA and proteins were peaked at day 13 of pregnancy. The levels of NOD2 and CIITA were increased during early pregnancy. The stainings for NOD2 and NLRP7 proteins were located in epithelial reticular cells, capillaries and thymic corpuscles. In summary, pregnancy stages changed expression of NLR family in the maternal thymus, which may be related to the modulation of maternal thymic immune responses, and beneficial for normal pregnancy in sheep.

Decisive points for pregnancy losses in beef cattle

Beef cattle producers rely on each of their cows to produce a marketable calf each year to maintain a sustainable operation. Within the first month of gestation, pregnancy failures have been recorded to be upwards of 40-50%. From fertilisation to birth, there are numerous factors contributing to pregnancy failure. From the beginning of gestation oocyte competence is often a large factor impacting fertility as the dam contributes all mRNA for initial embryo development. Other factors contributing to early embryonic infertility include hormonal concentration and heat stress. After the embryo enters the uterus, it becomes critical for the uterus to be receptive to the developing conceptus. The embryo then begins to elongate and secrete interferon-tau to initiate maternal recognition of pregnancy; a requirement to establish and maintain bovine pregnancies. After a pregnancy completes these steps, placentation actively begins around day 22 of pregnancy and lasts until organogenesis. The fetal phase follows the embryonic phase where disease and/or toxins are often the cause of pregnancy failure at this period. However, fetal mortality has been reported to occur in less than 10% of pregnancies. Understanding of the many factors influencing infertility needs to be further investigated to increase pregnancy success in beef cattle.

Early Pregnancy Modulates Expression of the Nod-like Receptor Family in Lymph Nodes of Ewes

NOD receptors (NLRs) mediate adaptive immune responses and immune tolerance. Nevertheless, it is not clear if gestation modulates the NLR signaling pathway in lymph nodes of ewes. In this study, lymph nodes of ewes were collected at day 16 of the estrous cycle, and at days 13, 16 and 25 of gestation (n = 6 for each group). RT-qPCR, Western blot and immunohistochemistry analysis were used to analyze the expression of the NLR family, including NOD1, NOD2, CIITA, NAIP, NLRP1, NLRP3 and NLRP7. The data showed that early gestation enhanced expression of NOD1, CIITA, NLRP1, NLRP3 and NLRP7 mRNA, as well as proteins at day 16 of gestation, and the expression levels of NOD2, CIITA, NLRP1 and NLRP7 were higher at days 13 and 25 of gestation than day 16 of the estrous cycle. However, NOD1 expression was lower on days 13 and 25 of gestation compared to day 16 of the estrous cycle, and early gestation suppressed NAIP expression. In summary, early pregnancy modulated expression of the NLR family in ovine lymph nodes, which participates in immune regulation, and this modulation may be necessary for pregnancy establishment in ewes.

Changes in expression of nuclear factor kappa B subunits in the ovine thymus during early pregnancy

There is a pregnant maternal immunological tolerance that protects the fetus and promotes its growth, and nuclear factor kappa B (NF-κB) family participates in the regulation of innate immune and adaptive immune responses. The thymus is related to establishing central tolerance, and early pregnancy has effects on expression of a good number of genes and proteins in the maternal thymus in sheep. However, it is unclear whether early pregnancy changes expression of NF-κB subunits in the ovine thymus. In this study, the thymic samples were collected from day 16 of non-pregnant ewes, and days 13, 16 and 25 of pregnant ewes, and the expression of NF-κB members (NF-κB1, NF-κB2, RelA, RelB and c-Rel) was analyzed through real-time quantitative PCR, Western blot and immunohistochemical analysis. The results showed that c-Rel mRNA and protein upregulated at day 25 of pregnancy, and NF-κB1 mRNA and proteins increased at days 16 and 25 of pregnancy, and RelB mRNA and proteins enhanced during early pregnancy. However, expression levels of NF-κB2 and RelA were decreased during early pregnancy, but upregulated from day 13 to 25 of pregnancy. In addition, the RelA protein was located in the epithelial reticular cells, capillaries and thymic corpuscles. This paper reported for the first time that early pregnancy induced expression of NF-κB1, RelB and c-Rel, but inhibited expression of NF-κB2 and RelA in the maternal thymus during early pregnancy, which is involved in the central immune tolerance, and helpful for successful pregnancy in sheep.

Early pregnancy regulates the expression of prolactin and its receptor in the thymus, the liver, the spleen and lymph nodes in sheep

As a pituitary hormone, prolactin (PRL) is also synthesized by immune system cells, and exerts its effects on the immune system by binding to its receptor (PRLR) via endocrine and paracrine/autocrine pathways. The immune organs adapt to the presence of fetal alloantigens during pregnancy, and the immune system is composed of primary organs and secondary organs. The objective of this study is to analyze the effects of early pregnancy on expression of PRL and PRLR in maternal immune organs in sheep. In this study, the thymus, lymph node, the spleen and the liver were sampled at day 16 of the estrous cycle, and at days 13, 16, and 25 of pregnancy in ewes. Expression of PRL and PRLR was analyzed through quantitative real-time PCR, Western blot and immunohistochemistry. Our data showed that there were an upregulation of PRL and PRLR in the thymus, lymph node and the spleen, and a downregulation in the liver during early pregnancy in ewes. In conclusion, it is reported for the first time that early pregnancy has tissue specific effects on expression of PRL isoform and PRLR isoform in the thymus, lymph node, the spleen and the liver, which may be owing to these organs exerting different functions during early pregnancy, and necessary for the successful pregnancy in sheep.

Mesenchymal Stem Cells in Embryo-Maternal Communication under Healthy Conditions or Viral Infections: Lessons from a Bovine Model

Bovine mesenchymal stem cells are a relevant cell population found in the maternal reproductive tract that exhibits the immunomodulation capacity required to prevent embryo rejection. The phenotypic plasticity showed by both endometrial mesenchymal stem cells (eMSC) and embryonic trophoblast through mesenchymal to epithelial transition and epithelial to mesenchymal transition, respectively, is essential for embryo implantation. Embryonic trophoblast maintains active crosstalk via EVs and soluble proteins with eMSC and peripheral blood MSC (pbMSC) to ensure the retention of eMSC in case of pregnancy and induce the chemotaxis of pbMSC, critical for successful implantation. Early pregnancy-related proteins and angiogenic markers are detected as cargo in EVs and the soluble fraction of the embryonic trophectoderm secretome. The pattern of protein secretion in trophectoderm-EVs changes depending on their epithelial or mesenchymal phenotype and due to the uptake of MSC EVs. However, the changes in this EV-mediated communication between maternal and embryonic MSC populations infected by viruses that cause abortions in cattle are poorly understood. They are critical in the investigation of reproductive viral pathologies.

Culture of endometrial epithelial cells collected by a cytological brush in vivo

In cattle, mechanistic studies of endometrial function rely on cell lines or primary culture of cells harvested postmortem. Understanding the endometrial physiology in dairy cows is essential, because approximately 50% of pregnancies are lost in the first 3 wk of gestation for unknown reasons. The objective was to validate an in vivo, minimally invasive, and estrous cycle stage-specific method to obtain endometrial luminal epithelial cells for culture. The uterine body of 26 cows was sampled using a cytology brush (cytobrush) 4 d after estrus. The viability of cells was measured by flow cytometry (80% live cells) and epithelial identity was determined by anti-vimentin and anti-cytokeratin immunofluorescence and quantitative PCR for KRT18 and VIM. A pool of cells from 15 animals was passaged 4 times in culture until confluent and then treated with 0, 0.1, 1, or 10 ng/mL of recombinant bovine interferon-tau (rbIFN-τ). The relative expression of transcripts related to IFN-τ signaling (IFNAR1), early (IRF2) and late (ISG15, OAS1) response to IFN-τ stimulus, and other IFN-τ-stimulated genes (CCL8, CXCL10, and FABP3) was measured by quantitative PCR. The relative expression of KRT18 transcripts was similar across passages; the relative expression of VIM increased at passage 2, and IFNAR1 transcripts decreased in cultured compared with that in fresh cells. The relative expression of ISG15, OAS1, CCL8, and FABP3 increased in response to rbIFN-τ. In conclusion, culture of endometrial luminal cells collected by cytobrush was feasible, generating a monolayer enriched in epithelial cells, and therefore constitutes a novel model by which to study endometrial luminal epithelial cell function, including responses to IFN-τ.

Selection of early pregnancy specific proteins and development a rapid immunochromatographic test strip in cows

The most of embryo losses occur before the day 16 after artificial insemination, but there is no low cost and easy operation that can detect pregnancy with high accuracy within three weeks post-insemination in cattle. In this study, blood samples were collected at day 18 of the estrous cycle, and days 18, 25 and 35 of pregnancy, and relative levels of interferon stimulated genes (ISGs), Toll-like receptor (TLRs), complement components, early pregnancy factor (EPF) and pregnancy-associated plasma protein A (PAPPA) proteins were analyzed through Western blot. In addition, a colloidal gold immunochromatographic test strip was developed using the selected antibody, and the test was used for early pregnancy diagnosis. The results showed that there were changes in relative levels of plasma ISGs, TLRs, complement components, EPF and PAPPA proteins during early pregnancy in cattle, and complement component 1q (C1q) could be used as an ideal marker to develop a colloidal gold immunochromatographic test strip for early pregnancy diagnosis. In addition, the accuracy of pregnancy diagnosis by this test strip was 91.67% (11/12) for pregnant cows and 80% (8/10) nonpregnant cows at day 18 after insemination. In conclusion, the changes in plasma ISGs, TLRs, complement components, EPF and PAPPA proteins may be related to the maternal systemic immune modulation during early pregnancy, and a colloidal gold immunochromatographic test strip was developed for early pregnancy diagnosis using C1q as the ideal marker in cows. However, this colloidal gold immunochromatographic test strip needs further studies to improve the accuracy.

Possible impact of neutrophils on immune responses during early pregnancy in ruminants

The interaction between early embryo and maternal immune system for the establishment of pregnancy is the focus of several studies; however, it remains unclear. The maternal immune response needs to keep a balance between avoiding any damage to the conceptus and maintaining its function in combating microbes as well. When conceptus-maternal crosstalk cannot achieve this balance, pregnancy losses might occur. Intercommunication between mother and conceptus is fundamental during early pregnancy to dictate the outcome of pregnancy. In ruminants, the embryo reacts with the maternal system mainly via interferon tau (IFNT) release. IFNT can act locally on the embryo and endometrial cells and systemically in several tissues and cells to regulate their response via the expression of interferon-stimulated genes (ISGs). Also, IFNT can induce the expression of inflammatory-related genes in immune cells. Day 7 embryo induces a shift in the maternal immune response towards anti-inflammatory (Th2) immune responses. During maternal recognition of pregnancy, peripheral mononuclear cells (PBMCs) and polymorphonuclear cells (PMNs) express markers that configure an anti-inflammatory response. However, PMNs response is more sensitive to the effects of IFNT. PMNs are more likely to express interferon-stimulated genes (ISGs), transforming growth factor-beta (TGFB), interleukin 10 (IL10), and arginase-1 (ARG1), configuring one of the most rapid immune responses to early pregnancy. This review focus on the local and peripheral immune responses during early pregnancy in ruminants, mainly the PMNs function in the immune system.