Interferon sequence homology and receptor binding activity of ovine trophoblast antiluteolytic protein

Emerging Role of Extracellular Vesicles in Embryo-Maternal Communication throughout Implantation Processes

In ruminants, the establishment of proper conceptus–endometrial communication is essential for conceptus implantation and subsequent successful placentation. Accumulated evidence supports the idea that extracellular vesicles (EVs) present in uterine lumen are involved in conceptus–endometrial interactions during the preimplantation period. EVs make up a new field of intercellular communicators, which transport a variety of bioactive molecules, including soluble and membrane-bound proteins, lipids, DNA, and RNAs. EVs thus regulate gene expression and elicit biological effects including increased cell proliferation, migration, and adhesion in recipient cells. Uterine EVs are interactive and coordinate with ovarian progesterone (P4), trophectoderm-derived interferon tau (IFNT) and/or prostaglandins (PGs) in the physiological or pathological microenvironment. In this review, we will focus on intrauterine EVs in embryo–maternal interactions during the early stage of pregnancy, especially the implantation period in ruminant ungulates.

Hemochorial placentation: development, function, and adaptations

Placentation is a reproductive adaptation that permits fetal growth and development within the protected confines of the female reproductive tract. Through this important role, the placenta also determines postnatal health and susceptibility to disease. The hemochorial placenta is a prominent feature in primate and rodent development. This manuscript provides an overview of the basics of hemochorial placental development and function, provides perspectives on major discoveries that have shaped placental research, and thoughts on strategies for future investigation.

Reproduction in domestic ruminants during the past 50 yr: discovery to application

The study of reproductive physiology in domestic ruminants has progressed from the whole animal to the molecular level in an amazingly short period of time. The volume of information on this subject is enormous; therefore, we have focused on domestic ruminants, with an emphasis on cattle. To date, artificial insemination (AI) is perhaps the most powerful technique that reproductive physiologists and geneticists have provided the livestock industry for genetic improvement. Early efforts to establish AI as a tool were initiated in Russia around 1899 and since that time major advances in methods of semen collection, evaluation of male fertility, cryopreservation of sperm, sex-sorted semen, and estrous cycle control have occurred. The preceding advances not only led to the widespread use of AI, but also contributed to our fundamental understanding of ovulation control, timing of insemination, gamete biology, and cryopreservation. In regards to anestrus, our understanding of the concept of neuroendocrine control of the pituitary gland and the role of steroid feedback led to the Gonadostat Theory, which proposes that onset of puberty is due to a decrease in the negative feedback of gonadal steroids over time. Subsequent studies in prepuberal and postpartum sheep and cattle established that a short luteal phase frequently precedes the first normal length cycle that is accompanied by estrous expression. This observation led to the common practice of treating prepuberal heifers and anestrous postpartum cows with a short-term progestin treatment (e.g., Controlled Internal Drug Release) to induce normal estrous cycles. In domestic ruminants, fertilization rate is high (85% to 95%); however, significant embryonic mortality before or around the time of maternal recognition of pregnancy (MRP) reduces the pregnancy rate to a single breeding. Significant effort has been directed at determining the time of MRP, the signal for MRP, as well as elucidating the physiological, cellular, and molecular dialogue between the conceptus and uterine environment. Advancements have now led us to the ability to edit the genome to alleviate disease and possibly improve production traits. In summary, major advancements in our understanding of reproductive biology have stemmed from efforts to establish the AI and embryo transfer technique and reduce the negative impact of anestrus and embryonic mortality in domestic ruminants.

Chronicling the discovery of interferon tau

It has been 38 years since a protein, now known as interferon tau (IFNT), was discovered in ovine conceptus-conditioned culture medium. After 1979, purification and testing of native IFNT revealed its unique antiluteolyic activity to prevent the regression of corpora lutea on ovaries of nonpregnant ewes. Antiviral, antiproliferative and immunomodulatory properties of native and recombinant IFNT were demonstrated later. In addition, progesterone and IFNT were found to act cooperatively to silence expression of classical interferon stimulated genes in a cell-specific manner in ovine uterine luminal and superficial glandular epithelia. But, IFNT signaling through a STAT1/STAT2-independent pathway stimulates expression of genes, such as those for transport of glucose and amino acids, which are required for growth and development of the conceptus. Further, undefined mechanisms of action of IFNT are key to a servomechanism that allows ovine placental lactogen and placental growth hormone to affect the development of uterine glands and their expression of genes throughout gestation. IFNT also acts systemically to induce the expression of interferon stimulated genes that influence secretion of progesterone by the corpus luteum. Finally, IFNT has great potential as a therapeutic agent due to its low cytotoxicity, anti-inflammatory properties and effects to mitigate diabetes, obesity-associated syndromes and various autoimmune diseases.

Continuous model of conceptus implantation to the maternal endometrium

As placental morphology as well as trophoblast characteristics exhibit wide diversity across mammalian species, underling molecules were also thought to vary greatly. In the majority of cases, however, regardless of the mode of implantation, physiological and biochemical processes in conceptus implantation to the maternal endometrium including the kinds of gene expression and their products are now considered to share many similarities. In fact, recent progress has identified that in addition to the hormones, cytokines, proteases and cell adhesion molecules classically characterized, molecules related to lymphocyte homing and epithelial-mesenchymal transition (EMT) are all required for the progression of conceptus implantation to placentation. In this review, therefore, the newest findings are all incorporated into the molecular and cellular events related to conceptus implantation to the maternal endometrium; primarily from non-invasive bovine placentation and also from invasive human implantation.

Preattachment Embryos of Domestic Animals: Insights into Development and Paracrine Secretions

In mammalian species, endometrial receptivity is driven by maternal factors independently of embryo signals. When pregnancy initiates, paracrine secretions of the preattachment embryo are essential both for maternal recognition and endometrium preparation for implantation and for coordinating development of embryonic and extraembryonic tissues of the conceptus. This review mainly focuses on domestic large animal species. We first illustrate the major steps of preattachment embryo development, including elongation in bovine, ovine, porcine, and equine species. We next highlight conceptus secretions that are involved in the communication between extraembryonic and embryonic tissues, as well as between the conceptus and the endometrium. Finally, we introduce experimental data demonstrating the intimate connection between conceptus secretions and endometrial activity and how adverse events perturbing this interplay may affect the progression of implantation that will subsequently impact pregnancy outcome, postnatal health, and expression of production traits in livestock offspring.

Conceptus implantation and placentation: molecules related to epithelial-mesenchymal transition, lymphocyte homing, endogenous retroviruses, and exosomes

Processes of conceptus implantation and placentation, unique to mammalian reproduction, have been extensively studied. It was once thought that processes of these events varied greatly, notably between invasive and noninvasive modes of implantation and/or placentation. Regardless of the mode of implantation, however, physiological and biochemical processes in conceptus implantation to the maternal endometrium including the kinds of gene expression and their products are now considered not to differ so much. Recent progress has identified that in addition to the hormones, cytokines, proteases and cell adhesion molecules classically characterized, epithelial-mesenchymal transition, molecules related to lymphocyte homing, the expression of endogenous retroviruses and possibly exosomes are all required for the progression of conceptus implantation to placentation. In this review, therefore, new findings related to these events are integrated into the context of conceptus implantation to the maternal endometrium.

Presence of Transcription Factor OCT4 Limits Interferon-tau Expression during the Pre-attachment Period in Sheep

Interferon-tau (IFNT) is thought to be the conceptus protein that signals maternal recognition of pregnancy in ruminants. We and others have observed that OCT4 expression persists in the trophectoderm of ruminants; thus, both CDX2 and OCT4 coexist during the early stages of conceptus development. The aim of this study was to examine the effect of CDX2 and OCT4 on IFNT gene transcription when evaluated with other transcription factors. Human choriocarcinoma JEG-3 cells were cotransfected with an ovine IFNT (-654-bp)-luciferase reporter (-654-IFNT-Luc) construct and several transcription factor expression plasmids. Cotransfection of the reporter construct with Cdx2, Ets2 and Jun increased transcription of -654-IFNT-Luc by about 12-fold compared with transfection of the construct alone. When cells were initially transfected with Oct4 (0 h) followed by transfection with Cdx2, Ets2 and/or Jun 24 h later, the expression of -654-IFNT-Luc was reduced to control levels. OCT4 also inhibited the stimulatory activity of CDX2 alone, but not when CDX2 was combined with JUN and/or ETS2. Thus, when combined with the other transcription factors, OCT4 exhibited little inhibitory activity towards CDX2. An inhibitor of the transcriptional coactivator CREB binding protein (CREBBP), 12S E1A, reduced CDX2/ETS2/JUN stimulated -654-IFNT-Luc expression by about 40%, indicating that the formation of an appropriate transcription factor complex is required for maximum expression. In conclusion, the presence of OCT4 may initially minimize IFNT expression; however, as elongation proceeds, the increasing expression of CDX2 and formation of the transcription complex leads to greatly increased IFNT expression, resulting in pregnancy establishment in ruminants.

Interferon-tau, a Type 1 interferon involved in maternal recognition of pregnancy

Interferon-tau is a major product of ovine and bovine conceptuses during the period before the trophoblast makes firm attachment to the uterine wall and begins to form a placenta. Its primary function is in preventing a return to ovarian cyclicity and hence ensuring the pregnancy continues, although it undoubtedly has other roles in ensuring receptivity of the maternal endometrium. Despite having properties similar to those of other Type 1, IFN-tau is not virally inducible and functions in a constitutive process unrelated to pathogenesis. The genes for IFN-tau (IFNT), which are confined to ruminant ungulate species, would appear to be the most recently evolved mammalian Type 1 gene family and are primarily under the transcriptional control of Ets2 and signal transduction pathways that target that transcription factor. The IFNT provide an illustration of how a gene control region can be commandeered and then refined to provide a radically changed pattern of expression.

Regulation of conceptus adhesion by endometrial CXC chemokines during the implantation period in sheep

To gain a better understanding of biochemical mechanisms of conceptus adhesion to the maternal endometrium in ruminant ungulates, the present study was performed to clarify roles of chemokines and extracellular matrix (ECM) components in the regulation of ovine blastocyst attachment to the endometrium. In addition to the chemokine, interferon-gamma inducible protein 10 kDa (IP-10, CXCL10), the chemokine receptor, CXCR3, also recognizes two other chemokines; monokine induced by IFN-gamma (MIG, CXCL9) and IFN-inducible T cell alpha chemoattractant (I-TAC, CXCL11). Similar to CXCL10, CXCL9, and CXCL11 were expressed in the uterus during the peri-implantation period, and CXCL9 mRNA expression was stimulated in endometrial explants from day 14 cyclic ewes by the addition of IFN-tau or IFN-gamma. Without ECM components, conceptus cell adhesion was low on day 14 of gestation and exhibited a 2.5-fold increase on day 17; adhesiveness on day 20 was 1/10 of that on day 14. Among various ECM components examined, trophoblast adhesion was greatest when fibronectin was used. Although day 14 conceptuses did not show much adhesive activity to fibronectin, day 17 trophoblast, and day 20 chorionic membrane exhibited 2.3-fold and 50-fold increase, respectively, which was enhanced by treatment with CXCL9 or CXCL10. These results indicate that through endometrial fibronectin and chemokines, ovine conceptus cells gain the ability to attach to the endometrium during pre-implantation period; however, elucidation of molecular mechanisms by which the conceptus acquires the adhesive ability during this time period awaits further investigation.

Regulation of the ovine interferon-tau gene by a blastocyst-specific transcription factor, Cdx2

Expression of ovine interferon-tau (oIFNtau), a factor essential for the process of maternal recognition of pregnancy in ruminant ungulates, is restricted to the trophoblast. However, the molecular mechanisms by which oIFNtau expression is restricted to the trophectoderm have not been fully elucidated. The objective of this study was to determine whether oIFNtau gene transcription could be regulated through Cdx2 expression, a transcription factor implicated in the control of cell differentiation in the trophectoderm. Human choriocarcinoma JEG3 cells were co-transfected with an oIFNtau (-654 base pair, bp)-luciferase reporter (-654-oIFNtau-Luc) construct and several transcription factor expression plasmids. Compared to -654-oIFNtau-Luc alone, transcription of the -654-oIFNtau-Luc increased more than 30 times when this construct was co-transfected with Cdx2, Ets-2, and c-jun. The degree of transcription decreased to 1/4 levels when the upstream region was reduced to -551 bp, and became minimal with further deletions; this was confirmed with the use of the reporter constructs with mutated c-jun, Ets-2, and/or Cdx2 sites. In trophoblast unrelated NIH3T3 cells, which do not support IFNtau gene transcription, the oIFNtau-Luc transcription was enhanced approximately eightfold when the cells were co-transfected with the Cdx2/Ets-2 or Cdx2/Ets-2/c-jun expression plasmids. These findings were confirmed by gel-shift assays examining Cdx binding site on the oIFNtau gene's upstream region, by immunohistochemical study identifying the presence of Cdx2 in day 15 and 17 ovine conceptuses, and by Western blot detecting Cdx2 in day 17 conceptuses. Our results indicate that oIFNtau gene transcription is regulated by Cdx2, and suggest that Cdx2 could be a key molecule in determining oIFNtau gene transcription by the trophectoderm.

Increase in DNA methylation downregulates conceptus interferon-tau gene expression

Expression of ovine interferon-tau (oIFNtau) genes, essential for the maternal recognition of pregnancy in ruminant ungulates, is restricted to the trophoblast and is not detected in any other cell types or tissues. Substantial secretion of oIFNtau starts on day 12-13 of pregnancy (day 0 = day of estrus), reaches the highest on day 16-17, and then declines rapidly. Ovine IFNtau mRNA, on the other hand, reaches the highest level on day 14 of pregnancy, 2-3 days before peak production of the protein. In this study, day 14 and 17 conceptuses treated with 5-aza-2'-deoxycytidine, an inhibitor of DNA methylation, were cultured in vitro and only day 17, not day 14, conceptuses resulted in upregulation of oIFNtau gene expression. To gain insight into the molecular mechanism of oIFNtau gene downregulation, the methylation status within 1 kb of the 5'-flanking region of oIFNtau-o10 gene was investigated: CpG dinucleotides of this gene in day 14 ovine conceptuses were hypomethylated compared to day 20 conceptuses or other tissues. In vitro methylation of oIFNtau-o10-reporter constructs caused suppression of reporter activity in transient transfections. Cotransfection of methyl-CpG-binding protein (MeCP2) with the reporter construct elicited further suppression of the reporter activity. In electrophoretic mobility shift assay (EMSA), patterns of shifted bands did not show much difference between methylated and unmethylated probes in distal regions, but exhibited differences in the proximal region of upstream sequences of the oIFNtau gene. These results provide evidence that changes in the degree of DNA methylation could be one of the major mechanisms leading to downregulation of the oIFNtau-o10 gene during early gestation, and possibly its silencing in nonconceptus tissues.

Biological activity of recombinant bovine interferon tau using an Autographa californica nuclear polyhedrosis virus expression system

Bovine interferon (bIFN) tau, which plays a key role in maternal-fetal recognition of pregnancy, was expressed by an Autographa californica nuclear polyhedrosis virus expression system. cDNA coding bIFNtau was derived from cultured trophoblast cells. The recombinant (r) bIFNtau had high antiviral activity (1 x 10 (8) IU/mg) and the molecular weight of rbIFNtau was estimated to be 23 kDa by Western blotting analysis. We investigated the biological effect of rbIFNtau on prostaglandin (PG) F(2alpha) synthesis in cultured bovine endometrial epithelial cells in the presence or absence of oxytocin (OT, 100 nM). rbIFNtau suppressed basal and OT-induced PGF(2alpha) production in a dose-dependent manner (1-1,000 ng/ml). These results showed that biologically active rbIFNtau was produced in the baculovirus expression system, and that rbIFNtau had the ability to suppress the synthesis of PGF(2alpha) from bovine endometrial epithelial cells.

Pre-Implantation Conceptus and Maternal Uterine Communications: Molecular Events Leading to Successful Implantation

Implantation, a critical step for mammals in establishing pregnancy, requires successful completion of sequential events such as maternal uterine development, conceptus development and attachment, and placental formation. To reach the stage of placental formation, synchronized development of the conceptus and uterus throughout the implantation period is absolutely required. A number of factors expressed at the uterine endometrium and/or conceptus, which are associated with peri-implantation development, have been identified. In addition to a temporal and spatial expression of these factors, their roles in intra- and inter-cellular interactions make it difficult to fully understand physiological roles played during the critical period. This paper focuses on early conceptus development, maternal preparation for implantation and uterine-conceptus communication during the pre-implantation period, rather than the subsequent events such as conceptus attachment to the maternal endometrium. New aspects of pre-implantation processes are evaluated through simultaneous expressions of transcription factors as they possibly regulate the complex processes of implantation events in murine species and ruminant ungulates.

The role of essential trace elements in embryonic and fetal development in livestock

This review addresses the concept that essential trace minerals play a vital role in many enzymatic and metabolic pathways that are critical for conceptus development during pregnancy in livestock species. The conceptus relies entirely on the maternal system for a sufficient supply of trace minerals and other nutrients needed for normal development. If this supply is inadequate, growth and/or health of the conceptus can be affected adversely, and many of these effects carry over into the neonatal period. Information, accumulated in our laboratory and presented herein, indicates that zinc, copper and manganese are among the trace minerals that have the greatest impact on reproduction. For example, levels of zinc, copper and manganese were several fold greater in the conceptus than in other reproductive tissues, indicating that the conceptus preferentially accumulates these minerals, an action that may be important for conceptus development, growth and survival. Moreover, some recent results indicate that increasing the biological availability of zinc, copper and manganese, by attachment to short peptide chains (i.e., proteinated trace minerals) can enhance reproductive performance of swine. Mineral concentrations in conceptuses from female pigs consuming proteinated trace minerals were greater than those from females that consumed only inorganic mineral salts. Elucidating the mechanisms whereby conceptus development and survival are enhanced by essential trace minerals may lead to development of specific feeding programs to increase the number and health of offspring at parturition, thereby allowing for further improvements in production efficiency in animal agriculture.

Progesterone-modulated induction of apoptosis by interferon-tau in cultured epithelial cells of bovine endometrium

Interferon-tau (IFN-tau) is produced by the trophoblast prior to implantation in ruminants. It is involved in maternal recognition of pregnancy, and is a pleiotropic molecule that can alter the synthesis of endometrial proteins and inhibit proliferation of some cells. We have observed that IFN-tau reduces the DNA content in cultures of bovine endometrial epithelial cells; therefore, the objective of this study was to determine whether IFN-tau would induce apoptosis in bovine endometrial cells. Epithelial cells were prepared, cultured to confluence, and then incubated for 24 or 48 h in the presence or absence of 10 ng/ml progesterone, 100 ng/ml IFN-tau, or 10 microg/ml cycloheximide (CHX; an apoptosis inducer used as a positive control). Cells undergoing apoptosis exhibit such characteristics as the appearance of apoptotic bodies and DNA fragmentation. The incidence of apoptosis was assessed by using TUNEL, DNA fragmentation analysis, and Western blot analysis of Bax-alpha protein expression. The results showed that IFN-tau and CHX significantly increased the percentage of cells with apoptotic nuclei (33.6% and 44.8%, respectively) compared with controls (11.7%; P < 0.05). Progesterone treatment of the cells significantly inhibited the ability of IFN-tau to induce apoptosis (14.6%) compared with IFN-tau alone (33.6%; P < 0.05). DNA fragmentation analysis showed that INF-tau and CHX treatment resulted in an increase in the appearance of DNA laddering compared with that in untreated control cultures. Western blot analysis showed that IFN-tau and CHX treatment resulted in a greater expression of the proapoptotic protein Bax-alpha compared with that in control cultures. These data demonstrate that IFN-tau can induce apoptosis in bovine uterine epithelial cells and that this effect is modulated by progesterone. We speculate that IFN-tau might play a critical role in the remodeling of the endometrium around the time of implantation.

Possible Role of Interferon-.TAU. on In Vitro Development of Bovine Embryos

The effect of interferon-tau on in vitro development of bovine embryos was investigated. After in vitro fertilization, embryos developed to the morula stage were cultured for 3 days in TCM-199 or CR1 medium containing BSA or FCS supplemented with or without recombinant IFN-tau produced by a baculovirus expression system. Addition of baculovirus-expressed IFN-tau (100 ng/ml) significantly promoted development to the blastocyst stage in both culture media. Addition of E. coli expressed IFN-tau (2 microg/ml) also significantly promoted the embryonic development. Supplementation of BSA or FCS did not affect the growth-promoting effect of IFN-tau. To determine whether the growth-promoting effect of IFN-tau is related to the interferon type I receptors that bind to type I interferon such as IFN-alpha, embryos were cultured with IFN-alpha. Although IFN-alpha significantly promoted the development, a much higher concentration (25 microg/ml) was required than IFN-tau. A reverse transcription polymerase chain reaction analysis revealed the expression of mRNA encoded type-I IFN receptor subunit from morula to blastocyst stage embryos. The overall results suggest a novel function for IFNs in promoting embryonic development and the effect may be related to type-I IFN receptor expressed in the early stages of preimplantation embryos.

Expression of interferon receptor subunits, IFNAR1 and IFNAR2, in the ovine uterus

Interferon-tau (IFN-tau) is the antiluteolytic factor released by concepti of ruminant ungulate species prior to implantation. All type I interferons, including IFN-tau, exert their action through a common receptor, which consists of two subunits, IFNAR1 and IFNAR2c, but the distribution of the two polypeptides in uterine endometrium has not been examined. In situ hybridization and immunohistochemistry on sections from pregnant and nonpregnant ovine uteri at Days 14 and 15 after estrus and mating showed that both IFNAR1 and IFNAR2 mRNA and protein were strongly expressed in endometrial luminal epithelium (LE), superficial glandular epithelium (GE), and stromal cells, within but not outside caruncles. Similar staining patterns were noted in pregnant and nonpregnant uteri for both subunits. Western blot analysis of membrane fractions from cell lines derived from endometrial LE, GE, and stromal cells, and affinity cross-linking experiments with radioactively labeled IFN-tau performed on crude endometrial membranes indicated the presence of both high ( approximately 110 kDa) and low (75-80 kDa) molecular mass forms of the two receptor subunits. To localize where IFN-tau binds when it is introduced into the uterine lumen, immunohistochemistry with an antiserum against IFN-tau was performed on sections of uteri from Day 14 nonpregnant ewes whose uteri had previously been infused with IFN-tau. Staining was concentrated on the LE and superficial GE cells, and was absent from the deeper regions of the glands and from the stromal tissues. These studies demonstrate the heavy concentration of IFNAR1 and IFNAR2 in cells of the LE and superficial GE, which appear to be the main targets for IFN-tau.

Temporal expression of type I interferon receptor in the peri-implantation ovine extra-embryonic membranes: demonstration that human IFNalpha can bind to this receptor

Interferon-tau (IFNtau), produced by the trophectoderm of ruminant ungulates, binds to the type I IFN receptor (IFNAR) located at the uterine endometrium in a paracrine manner. Since IFNtau attenuates the secretory pattern of an endometrial luteolysin, prostaglandin F2alpha, IFNtau has been considered as a conceptus factor implicated in the process of maternal recognition of pregnancy. Here we report the presence of IFNAR subunit (IFNAR1) in ovine conceptuses during the period of peri-implantation development and demonstrate that 125I-human (h) IFNalpha binds to membrane preparations from ovine corpus luteum and conceptus. Using an antibody against hIFNAR1, immunohistochemical analysis revealed that IFNAR1 protein was present in day 14 and 16 conceptuses (day 0 = day of estrus) and luminal and glandular epithelia of the endometrium. Conceptus membrane proteins analyzed by western blot with the same antibody displayed immunoreactive bands at 95, 60 and 55 kDa while endometrial membrane proteins showed bands at 200, 95 and 55 kDa. Northern blot analysis revealed that IFNAR1 mRNA was present in days 15-19 conceptuses and day 18-19 allantoic membranes. Receptor binding studies indicated that 125I-hIFNalpha binding to day 16, but not earlier, conceptus membrane proteins could be displaced with hIFNalpha or ovine IFNtau. Based on Scatchard analysis, day 16 conceptus membranes contained 28 fmol IFNAR/mg protein with a dissociation constant of 300 pM. Cross-linking experiments demonstrated that 125I-hIFNalpha-receptor complex migrated at 120 kDa, indicating that the receptor component(s) was approximately 100 kDa. These data provide evidence that although the binding does not occur until day 16, ovine conceptuses possess IFNAR1 near or at the time of implantation, suggesting that IFNtau, a factor produced by the trophectoderm of ruminant ungulates, could act on the conceptus in an autocrine manner. In addition to functioning as an antiluteolytic factor, therefore, IFNtau may have a direct effect on conceptus development.

High-density ovine endometrial cells exhibit natural killer activity during early pregnancy

Natural killer (NK)-like activity was assessed for peripheral blood lymphocytes (PBL) and unfractionated and fractionated endometrial cells recovered from ewes during the estrus cycle (Days 12 to 14) and early pregnancy (Days 16 to 18). The PBL and endometrial cells (each designated as effector cells) were cocultured with chromium-51 (51Cr) labeled NK-sensitive K-562 target cells in effector:target cell ratios ranging from 25:1 to 200:1, respectively. Lytic activity (i.e., release of 51Cr into the medium) was assessed at 22 h of culture. A high-density (> or = 1.088 g/mL) population of endometrial cells from the pregnant ewes exhibited NK-like activity, whereas endometrial cells from the cyclic ewes failed to exhibit activity. Lytic activity of these cells was greater (P < 0.05) for pregnant than for cyclic ewes (12.0 and 2.1%, respectively) at the effector:target cell ratio of 100:1, respectively. For both groups of ewes, PBL exhibited NK-like activity. These data indicate that the ovine endometrium contains NK-like cells with lytic activity between Days 16 and 18 of pregnancy.

Immunosuppressive macromolecules of endometrial and conceptus origins in livestock species

Since the mid- to late-1970s, intrauterine immunosuppressive macromolecules recovered from endometrial and conceptus secretions have been reported for livestock species. Using primarily in vitro assays, in conjunction with a limited number of techniques conducted in vivo, these macromolecules were shown to suppress various T-cell responses. Some macromolecules were also shown to suppress cytolytic activities of non T-cells. It remains unknown as to whether these macromolecules actually afford protection to the conceptus by suppressing cell-mediated immune responses directed toward conceptus tissues. Endometrial effector cells in the ewe respond to antigenic stimulation and preattachment trophoblastic cells of pigs and sheep can be lysed by effector cells. Consequently, these observations suggest a need for immunosuppression, either locally at placentation sites or within the entire uterus. This review describes the intrauterine macromolecules that have been shown to suppress lymphocyte responses. Additional information, although limited at this time, refers to their origin and possible mechanisms of action. As more reagents become available to complete the identification of the intrauterine immune cells in livestock animals, experiments (e.g. antibody-mediated depletion of cells) can be conducted to determine the precise functions of all these cells. Knowing their functions will help delineate whether or not immunosuppressive macromolecules have a role in the regulation and maintenance of conceptus tissues during pregnancy.

Interferon-tau stimulates granulocyte-macrophage colony-stimulating factor gene expression in bovine lymphocytes and endometrial stromal cells

Interferon-tau (IFN-tau), the antiluteolytic signal produced by the trophoblast prior to implantation in ruminants, exhibits immunomodulatory properties. It stimulates the production of prostaglandin (PG) E(2) in bovine endometrial cells via the induction of cyclooxygenase-2 (COX-2). We previously demonstrated that preconditioning lymphocytes with PGE(2) increases the expression of granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that promotes conceptus growth and survival. Our goal in the present study was to evaluate the impact of IFN-tau on the expression of GM-CSF in bovine peripheral blood lymphocytes (PBL) and endometrial epithelial and stromal cells. Changes in PGE(2) production and mRNA levels of COX-2 were also studied in PBL in response to IFN-tau. Gene expression was estimated by semiquantitative reverse transcription-polymerase chain reaction and Northern analysis. The expression of GM-CSF in PBL was stimulated by treatment with IFN-tau. Furthermore, GM-CSF mRNA levels were increased after preconditioning PBL for 3 days with IFN-tau, followed by a 12-h restimulation without IFN-tau. Inhibition rather than stimulation of PGE(2) production and COX-2 expression in PBL during treatment with IFN-tau suggests a direct effect on GM-CSF expression. Moreover, GM-CSF expression was stimulated in uterine stromal cells in response to IFN-tau. This study provides the first evidence for stimulation of GM-CSF expression by IFN-tau in both leukocytes and endometrial stromal cells. In view of the role of GM-CSF on fetal growth and survival, these results support the hypothesis that the conceptus mediates accommodation mechanisms in the uterus during early pregnancy by modulating the expression of beneficial cytokines at the fetomaternal interface.

Interferon tau-induced hepatocyte apoptosis in sheep

Clinical applications of Type I interferon (IFN) are limited by adverse side effects mediated largely by unknown mechanisms. This study examined the mechanisms of acute hepatic injury in lambs treated with systemic administration of IFN-tau, a Type I IFN. Liver tissues were collected at 24, 48, or 96 hours after treatment with either IFN-tau or saline. Histopathology revealed acute hepatopathy including cellular swelling, cytoplasmic aggregates, and apoptosis in all IFN-tau-treated lambs, which were accompanied by elevation of aspartate transaminase (AST) (P <.01). The number of apoptotic hepatocytes in IFN-tau-treated lambs was higher than for control lambs (P <.001). Immunohistochemistry for proliferating cell nuclear antigen (PCNA) revealed that IFN-tau induced hepatocyte growth arrest at the G0/G1 phase of the cell cycle and that the majority of hepatocytes in S or G2 phase were eliminated by apoptosis. We investigated expression of bax-alpha and bcl-2, acting as pro- and antiapoptotic molecules, in IFN-tau-induced apoptosis. Northern blot analysis revealed increased expression of bax-alpha messenger RNA (mRNA) in IFN-tau-treated lambs (P <.01) compared with control lambs, consistent with the expression pattern for bax-alpha protein. However, there was no detectable difference in expression of bcl-2 proteins between control and IFN-tau-treated lambs. The levels of bax-alpha associated with the mitochondria also increased during IFN-tau treatment. Bax-alpha immunostaining showed scattered immunoreactive hepatocytes with morphological hallmarks of apoptosis. These results suggest that IFN-tau induces growth arrest as well as apoptosis by regulating bax-alpha expression. These pathological effects of IFN-tau on sheep liver indicate potential mechanisms of Type 1 IFN-induced hepatotoxicity in animals and humans.

Loss of interferon alpha and interferon tau-induced antiviral protection in interferon regulatory factor-2 DNA-binding domain dominant negative mutants

The role of the interferon regulatory factory (IRF) family of transcription factors in regulation of interferon alpha and interferon tau antiviral activity was investigated using a dominant negative mutant of IRF-2. The IRF-2 DNA binding domain (DBD), without the C-terminal regulatory region, was stably transfected into myeloid U937 cells. Expression of the IRF-2 DBD resulted in an increase in constitutive 2'5' oligoadenylate synthetase (OAS) levels, indicative of an active repressive mechanism, but was not sufficient to protect cells from challenge with vesicular stomatitis virus. Treatment of the DBD clones with interferons alpha A and tau failed to upregulate 2'5' OAS expression and did not elicit an antiviral response. While interferon alpha A was more sensitive than interferon tau to the inhibitory effects of the IRF-2 DBD, IRF-mediated gene induction is involved in successful interferon alpha and tau-induced anti-VSV activity.

An IFN regulatory factor-2 DNA-binding domain dominant negative mutant exhibits altered cell growth and gene expression

In order to study interferon regulatory factor (IRF) family mediation of cell growth regulation, we established U937 cell lines stably transfected with a truncated form of IRF-2 lacking the transcriptional repressor domain. The truncated IRF-2 contained the DNA binding domain (DBD) and bound the ISRE. Phenotypically, the IRF-2 DBD transfectants exhibited reduced cell growth, altered morphology and increased cell death. Consistent with alterations in growth characteristics, the IRF-2 DBD transfectants constitutively expressed higher levels of the cyclin dependent kinase inhibitor p21WAF1/Cip1 than did control clones. The level of p21WAF1/Cip1 expression was positively correlated with the level of DBD expressed, as well as with the level of growth inhibition in these clones. DBD expression also correlated with expression of other members of the growth regulatory complex, cyclin dependent kinase 2 and cyclin A, but not proliferating cell nuclear antigen. These results imply active repression by IRF-2 to keep p21WAF1/Cip1 transcriptionally silent.

The cross-species antiviral activities of different IFN-tau subtypes on bovine, murine, and human cells: contradictory evidence for therapeutic potential

It is claimed that interferon-tau (IFN-tau) has broad cross-species reactivity and less cytotoxicity than other type I IFN when used at high concentration either in vitro or in living animals. It can also amelioriate the development of experimental allergic encephalomyelitis (EAE) without the usual side effects of IFN therapy in mice autoimmunized with myelin basic protein. For these reasons, IFN-tau may have therapeutic potential in humans. Here, the antiviral (AV) activities of eight different recombinant IFN-tau were compared with those of several bovine, human, and murine type I IFN on bovine MDBK cells, murine L929 cells, and human WISH cells. The data show that only one of the IFN-tau, OvIFN-tau4, has broad cross-species reactivity. It was comparable in this respect to HuIFN-omega1 and HuIFN-alpha1. The other IFN-tau, including the variant form (OvIFN-tau1mod) tested by others in cytotoxicity experiments and for its ability to protect mice against EAE, had relatively weak AV activity on mouse and human cells. It is possibly because this particular bioengineered form of IFN-tau binds the common type I receptor of these two species with such low affinity that it lacks cytotoxic effects. The basis for its potent anti-EAE activity is unclear, but it seems possible that it does not involve the type I IFN receptor.

Functional characterization of monoclonal antibodies to interferon-tau

Interferon tau (IFNtau) produces an array of biological effects, including antiluteolytic, antiviral, antiproliferative and immunomodulatory activities, without the consequent cytotoxicity associated with other type I IFNs. Four anti-IFNtau monoclonal antibodies (MAbs) have been characterized by determining regional epitopes and observation of their effects on IFNtau binding, antiviral and antiproliferative activity. Using an enzyme-linked immunoadsorbent assay (ELISA) developed against six overlapping synthetic peptides representing the entire linear sequence of IFNtau, three antibodies, HL-98, HL-100 and HL-127, were found to react with the carboxy terminal peptide, while HL-129 bound the penultimate amino terminal peptide. Binding studies indicated that MAbs directed against either region could effectively inhibit the binding of alkaline phosphatase labeled IFNtau to cells expressing type I IFN receptors. While only two of the MAbs significantly reversed IFNtau-induced growth inhibition, the antiviral activity of IFNtau was significantly inhibited by MAbs that bound the amino and carboxy termini, confirming the functional importance of these domains in the binding and subsequent activity of IFNtau.

Differential effects of intrauterine and subcutaneous administration of recombinant ovine interferon tau on the endometrium of cyclic ewes

Interferon tau (IFNtau) is the antiluteolytic signal produced by the conceptus of ruminants. Intrauterine administration of recombinant ovine IFNtau suppresses expression of endometrial estrogen receptor (ER) and oxytocin receptor (OTR) in the luminal and superficial glandular epithelia to abrogate the production of luteolytic prostaglandin F(2alpha) (PGF(2alpha)) pulses. Subcutaneous (s.c.) injections of recombinant ovine (o) IFNtau appear to extend the interestrous interval by altering uterine PGF(2alpha) response to oxytocin. The present study tested the hypothesis that antiluteolytic effects of roIFNtau injected into the uterine lumen (paracrine) or s.c. (endocrine) are equivalent in suppressing expression of endometrial ER and OTR and inducing uterine expression of type I IFN-regulated Mx and ubiquitin cross-reactive proteins (UCRP). Sixteen cyclic ewes were fitted with uterine catheters on Day 5 (Day 0 = estrus), were assigned randomly to receive treatment with control proteins or roIFNtau (2 x 10(7) antiviral units/day) by either intrauterine or s.c. injections from Days 11 to 15, and were ovariohysterectomized on Day 16. Results indicated that expression of ER and OTR mRNAs in endometrial epithelium was suppressed by intrauterine but not by s.c. injections of roIFNtau. Intrauterine injections of roIFNtau increased expression of Mx and UCRP mRNA in the endometrium. Subcutaneous injections of roIFNtau increased endometrial Mx mRNA levels but not UCRP mRNA. Unexpectedly, intrauterine and s.c. injections of roIFNtau were equally effective in inducing expression of Mx and UCRP mRNA in the corpus luteum. Although s.c. injections of roIFNtau induced Mx mRNA in the endometrial epithelium, s.c. injections of roIFNtau did not abrogate activation of the uterine luteolytic mechanism by suppressing epithelial ER and OTR expression. Therefore, results of this study failed to support the assumption that endocrine roIFNtau mimics antiluteolytic effects of paracrine IFNtau to improve pregnancy rates in sheep.

The effects of group size on development and interferon-tau secretion by in-vitro fertilized and cultured bovine blastocysts

The effects of culturing bovine embryos in groups were investigated. In the first experiment, 1000 oocytes were matured, fertilized and then cultured in groups of 40 in 25 microl of medium. From half of these groups, blastocysts were removed and cultured separately, while in the other half blastocysts were allowed to remain in the group culture microdrop. Blastocysts developed equally well in both groups, although hatching was reduced in those blastocysts removed from the culture droplet. In the second experiment, 1000 zygotes were cultured from the 8-cell stage to the blastocyst stage either individually or in groups of 40. Culture in groups increased the formation of blastocysts, the percentage of hatching blastocysts, the number of cells within blastocysts and the production of interferon-tau. In the final experiment, 1000 zygotes were cultured in groups up to the blastocyst stage. Two-thirds of these blastocysts were then cultured in groups of three, while the remaining blastocysts were cultured individually. Co-culture did not affect hatching or cell number but significantly elevated interferon-tau secretion. These results demonstrate that group culture either before or after blastocyst formation can alter the expression of a specific gene important for the establishment of pregnancy.

The ovine uterus as a host for in vitro-produced bovine embryos

A series of experiments were conducted to determine whether bovine blastocysts would develop beyond the blastocyst stage in the ovine uterine environment. In Experiment 1, in vitro matured, fertilized and cultured (IVM/IVF/IVC) expanded bovine blastocysts were transferred into uteri of ewes on Day 7 or 9 of the estrous cycle and collected on Day 14 or 15 to determine if the bovine blastocysts would elongate and form an embryonic disk. Springtime trials with ewes that were synchronized with a medroxyprogesterone acetate (MAP) sponge resulted in a 78% blastocyst recovery rate, and 68% of the recovered spherical or elongated embryos had embryonic disks. In Experiment 2, transfer of 4-cell bovine embryos to the oviducts of ewes at Day 3 resulted in a lower recovery (47 vs 80%) than the transfer of blastocysts at Day 7 when embryos were recovered at Day 14. However, the percentage of embryos containing embryonic disks was higher for embryos transferred at the 4-cell stage (71%) than for embryos transferred as blastocysts (50%). In Experiment 3, IVF embryos from super-ovulated cows or Day 8 in vitro produced embryos transferred to cows were collected at Day 14 and were found to be similar in size to those produced by transfer to ewes in Experiment 2. In Experiment 4, the transfer of bovine blastocysts to ewes did not prolong the ovine estrous cycle. In Experiment 5, extension of the ovine estrous cycle by administration of a MAP releasing intravaginal device allowed bovine embryos to elongate extensively and to become filamentous. In Experiment 6, uterine flushings on Day 14 or Day 16 contained elevated levels of interferon-tau when bovine blastocyst were transferred on Day 7. Transfer of bovine embryos to the reproductive tract of a ewe allows some embryos to develop normally to advanced perimplantation stages and may be a useful tool for studying critical stages of embryo development and the developmental capacity of experimental embryos.

Immunosuppression by retroviruses: implications for xenotransplantation

Retroviruses induce in the infected host an immunosuppression the severity of which depends on the viral load. A pronounced immunosuppression is induced by human and simian immunodeficiency viruses (HIV and SIV) ultimately leading to AIDS. It is very likely that HIV originated by trans-species transmission from primates. In contrast, SIVs are not pathogenic for their natural hosts probably as the result of virus-host coevolution. We have shown that a retroviral protein, the transmembrane envelope protein, may play an important role in retrovirus-induced immunosuppression and that all retroviruses share an evolutionarily highly conserved domain in this protein. We demonstrate that synthetic peptides corresponding to this domain of different retroviruses, including HIV, the baboon endogenous virus (BaEV), and different porcine endogenous retroviruses (PERVs), are immunosuppressive. We provide evidence that BaEV and different PERVs, including those able to grow in human cells, are immunosuppressive for lymphocytes of different species including human. This implies that xenotransplantation may result in a trans-species transmission of endogenous retroviruses derived from the donor animal. In analogy to HIV and SIV high-titer virus replication may cause an AIDS-like disease in the immunosuppressed human transplant recipient. Two additional points have to be considered: First, human anti-complement proteins produced by transgenic animals will also protect the virus and, second, the virus may be transmitted to other humans and thus increase its pathogenic potential.

Cytokines in implantation

Implantation is a complex process which involves the 'invasion' of the maternal endometrium by the trophoblast surrounding the developing blastocyst. In response to this interaction there is a cellular reaction within the endometrium which has some features analogous to invasion by a tumour and some which are more characteristic of an inflammatory response. In addition, and also in common with cancer and inflammation, there is a release of biologically active molecules, including cytokines, at and around the implantation site. The information on cytokines is complex and often contradictory but it is recognised that they play an important role in the successful establishment of pregnancy. The evidence for this role is examined in this review.

IFN-tau: a novel subtype I IFN1. Structural characteristics, non-ubiquitous expression, structure-function relationships, a pregnancy hormonal embryonic signal and cross-species therapeutic potentialities

IFN-tau (IFN-tau) constitutes a new class of type I IFN which is not virus-inducible, unlike IFN-alpha and IFN-beta, but is constitutively produced by the trophectoderm of the ruminant conceptus during a very short period in early pregnancy. It plays a pivotal role in the mechanisms of maternal recognition of pregnancy in ruminants and it displays high antiviral and antiproliferative activities across species with a prominent lack of cytotoxicity at high concentrations in vitro in cell culture and possibly in vivo. It exhibits high antiretroviral activity against HIV and exhibits immunosuppressive activity in a multiple sclerosis model and reduces embryo and fetal mortality by stimulation of IL-10 production. In this review all the biochemical and para-hormonal properties of this novel IFN-tau are described in detail: structural characteristics of proteins and genes, trophoblast expression, regulation of its expression, structure of its gene promoter, its absence in human species and in non-ruminant animals, the evolution of the IFN-tau genes, its structure-function relationships with its three-dimensional structure, structural localization of biological activities, its lack of cytotoxicity and its receptor. Surprisingly, for an IFN, IFN-tau is also a pregnancy-embryonic signal with paracrine antiluteolytic activity. In order to maintain luteal progesterone secretion, IFN-tau inhibits PGF-2alpha pulsatile secretion and oxytocin uterine receptivity in early pregnancy. It is believed to suppress pulsatile release of endometrial PGF-2alpha by preventing oxytocin and estrogen receptor expression. Additionally, it directly regulates prostaglandin metabolism and possibly the PGE:PGF-2alpha ratio.

Effect of human and murine interferon-alpha on steroid production by rat ovarian cells

The effect of interferon on the rat ovarian cell function was investigated. Cells from the ovary of juvenile rats were used as a model to investigate the effect of IFN-alpha on the secretion of estradiol and testosterone. In addition the effect of human IFN-alpha (hIFN-alpha) on the secretion of testosterone by the rat adult testis was studied. Present results show that leukocyte hIFN-alpha decreased the human chorionic gonadotropin (hCG) stimulated secretion of estradiol and testosterone by ovarian cells, and the production of testosterone by testis cells. Basal secretion of steroids was affected later and in less proportion than the hCG-dependent production. The IFN-alpha obtained from murine leukocytes, also inhibited the response of ovarian cells to the hCG stimulus.The nature of this effect in the secretion of the steroids is dose and time-dependent. The incubation of hIFN-alpha with an specific antibody completely blocked the effect of the cytokine on ovarian cells.

Molecular cloning of ovine and bovine type I interferon receptor subunits from uteri, and endometrial expression of messenger ribonucleic acid for ovine receptors during the estrous cycle and pregnancy

Interferon-tau (IFN-tau), a type I IFN structurally related to IFN-alpha, is regarded as the major antiluteolytic factor secreted by the conceptus of ruminant ungulate species before definitive trophoblast attachment and implantation. It mediates its effects by acting on the uterine endometrium, where it blunts the normal pulsatile production of PGF2alpha, presumably as a result of its binding to type I IFN receptors. In this study, we describe the complementary DNAs for the two known subunits, IFNAR1 and IFNAR2, of this receptor isolated from bovine and ovine endometrial complementary DNA libraries by homology cloning. Although there is extensive inferred amino acid sequence similarity between bovine and ovine IFNAR1 (92% identity) and between bovine and ovine IFNAR2 (88% identity), they have diverged extensively from the human receptor subunits (approximately 67% and approximately 58% identity, respectively). Despite these differences in primary structure, the respective subunits from all three species are organized similarly in their extracellular and cytoplasmic regions, and the bovine and ovine subunits have each retained a number of polypeptide motifs implicated in signal transduction. These uterine receptors also appear not to be splice variants. The cloned ovine IFNAR1 subunit, for example, possesses the expected four extracellular SD100 domains of full-length bovine and huIFNAR1, and only the homologs of the so-called long form (huIFNAR2c) of human IFNAR2 have so far been identified. RT-PCR procedures indicate that the messenger RNA for both subunits are found, not only in endometrium, but in all other tissues examined except those ofpreimplantation conceptuses, which presumably cannot respond to the IFN-tau they produce. Quantitative RNase protection assays of ovine endometrial RNA show that the expression of neither subunit changes greatly during the estrous cycle or pregnancy. These data suggest that the type I IFN receptor, which is expressed by the endometrium and binds IFN-tau, is probably not a structurally unusual form.

Placental interferons

Trophectoderm of ruminant conceptuses (embryo and associated membranes) secrete tau interferons (IFN tau) as the pregnancy recognition signal. Secretion of IFN tau on gestational days 12-13 for sheep and gestation days 14-17 for cows and goats is critical for pregnancy recognition. IFN tau acts on uterine epithelium to suppress estrogen receptor and oxytocin receptor gene expression, which prevents uterine release of luteolytic pulses of prostaglandin F2 alpha (PGF). Expression of the progesterone receptor (PR) gene in uterine endometrium is not affected by oIFN tau. Maintenance of progesterone secretion by the corpus luteum (CL) ensures establishment of pregnancy. Pig conceptuses secrete both IFN alpha and IFN gamma between days 15-21 of gestation, but their role(s) in early pregnancy is unknown. Estrogen secreted by pig trophoblast between gestational days 11-13 and 15-25 increases endometrial receptors for prolactin and causes exocrine secretion of PGF into the uterine lumen to prevent luteolysis. Shared cell-signaling mechanisms by IFNs and lactogenic hormones through Janus kinases (JAK) 1 and 2 may provide a common pathway to abrogate luteolytic mechanisms to ensure establishment of pregnancy. The role(s) of IFNs produced by human and rodent placentae is not known.

Role of interferon-alpha in arachidonic acid metabolism by the rat uteri from spayed animals: effect of 17 beta-estradiol

Interferon-like trophoblastic proteins modulate prostaglandin (PG) synthesis from endometrium in early ovine and bovine pregnancy. We attempted to explore the effect of interferon (IFN)-alpha in the isolated rat uterus from ovariectomized animals on the metabolism of labelled arachidonic acid (AA). The experiments were performed with uterine preparations isolated from spayed rats treated or untreated with 17 beta-estradiol prior to sacrifice. The pre-incubation of uterine tissue isolated from ovariectomized rats with three different doses (4, 150 and 300 IU/ml) of IFN-alpha decreased the radioconversion of [14C]AA into 6-keto PGF1 alpha, PGF2 alpha and PGE2, whereas the formation of thromboxane B2 (TXB2) decreased after treatment with 4 IU/ml of INF-alpha but was augmented with 150 and 300 IU/ml. The three doses used diminished the synthesis of 5-hydroxyeicosatetraenoic acid (5-HETE) and increased the production of 12-HETE. We also studied the synthesis of uterine products of cyclooxygenase and lipoxygenase in uterine tissue from ovariectomized rats injected with 17 beta-estradiol and preincubated with IFN-alpha. We found that the three doses of IFN-alpha diminished the production of 6-keto-PGF1 alpha, PGE2, PGF2 alpha and TXB2 as well as 5-HETE and 12-HETE. These findings show that IFN-alpha modifies the basal synthesis of PGs from uterine tissue. Ovine and bovine trophoblastic protein prevents luteolysis by inhibiting the synthesis of PGF2 alpha. On the other hand, IFN-alpha shows 70% homology with ovine trophoblastic protein and binds to the same receptor. The results of the present study suggest that IFN-alpha may also act in the rat as a luteotrophic agent.

The control of prostaglandin production by the endometrium in relation to luteolysis and menstruation

Oestradiol acting on a progesterone-primed uterus stimulates prostaglandin (PG) F2 alpha synthesis by the endometrium. In some species (notably the sheep, cow and goat) oxytocin released from the ovary also forms part of the physiological stimulus for increased endometrial PGF2 alpha production. The corpus luteum contains high concentrations (> 1 microgram/g tissue) of this peptide in these species. The intracellular mechanisms by which these three hormones control endometrial PGF2 alpha synthesis and release are far from clear. Oxytocin stimulates the synthesis of inositol phosphates and diacylglycerol in the endometrium of some species, but whether this pathway is involved in endometrial PGF2 alpha synthesis is still open to question. There is evidence that increased endometrial PGF2 alpha synthesis is dependent upon increased endometrial protein synthesis but, apart from the recorded effects of steroid hormones on the concentrations of phospholipase A2, prostaglandin H synthase and oxytocin receptors, it is not known what other endometrial proteins are involved. Some disorders of menstruation are associated with abnormal PG production by the endometrium, but the reasons for this abnormality are not clear. During early pregnancy an increase in PGF2 alpha synthesis by the endometrium is prevented, except in the pig where the PGF2 alpha produced is directed from the venous drainage to the uterine lumen. In those species in which endometrial PGF2 alpha synthesis is dependent upon oxytocin secreted by the ovary, the conceptus secretes an interferon-tau (previously named trophoblast protein-1) which prevents oestradiol and oxytocin acting on a progesterone-primed uterus from stimulating endometrial PGF2 alpha synthesis. The identities of the factors produced by the conceptus which prevent endometrial PGF2 alpha synthesis during early pregnancy in other species are not known, although it is clear that they are not interferons.

In vivo immunosuppressive effects of recombinant ovine interferon-tau (trophoblastin): r.oTP (r.oIFN-tau) inhibits local GVH reaction in mice (PLN assay), prevents fetal resorptions, and favors embryo survival and implantation in the CBA/J x DBA/2 mice combination

PROBLEM

Ovine trophoblastin protein, be it natural or recombinant (oTP,r.oTP), a member of the tau interferon family (r.oIFN-tau), has been shown to possess immunosuppressive properties in vitro. It acts as a cytostatic agent across species. Indeed, it was immunosuppressive when tested on human and murine lymphocytes in a variety of in vitro immune assays, as it is also on syngenic (ovine) lymphocytes.

METHODS

In the present paper, we first verified that this property to act across species also occurred in vivo assays; r.oTP was able to down regulate a local GVH reaction assay (PLN assay) in mice. We then took advantage of these properties of r.oTP to investigate its in vivo effects during murine pregnancy as there is no ovine equivalent of the murine CBA/J x DBA/2 resorption prone mating combination.

RESULTS

When given in the postimplantation period, r.oTP drastically boosted resorptions in the CBA/J x DBA/2 matings, as did murine recombinant gamma interferon. However, the same r.oTP treatment in the peri-implantation period resulted in a reduction in resorptions in this spontaneous abortion system.

CONCLUSION

The data suggested that r.oTP might have acted more by favouring implantation and embryo survival than by preventing the resorption process itself. The mechanisms possibly underlying these effects, as well as the putative uses of r.oTP evolving from these data, are discussed.

Structure/function studies with interferon tau: evidence for multiple active sites

A novel interferon (IFN), called IFN-tau (IFN-tau), has recently been discovered and has been shown to be a pregnancy recognition hormone. Unlike known IFNs, however, IFN-tau exhibits high antiviral and antiproliferative activity without cytotoxicity. The structural basis for IFN-tau function has been examined using six overlapping synthetic peptides corresponding to the entire ovine (Ov) IFN-tau sequence. Four peptides representing amino acids 1-37, 62-92, 119-150, and 139-172 inhibited OvIFN-tau antiviral activity in a dose-dependent manner. Polyclonal antipeptide antisera directed against the same four peptides blocked OvIFN-tau binding and antiviral activity, confirming the specificity of the peptide competitions. Because IFN-tau and IFN-alpha both interact with the type I IFN receptor, peptide inhibition of bovine and human IFN alpha activity was also determined. Of importance, only three peptides, OvIFN-tau (62-92), (119-150), and (139-172) inhibited IFN-alpha antiviral activity. The amino-terminal IFN-tau peptide, OvIFN-tau(1-37), was not inhibitory. These data suggest that the internal and carboxy-terminal reactive domains of IFN-tau may interact with a common type I IFN site on the receptor, while the amino terminus interacts with a site that elicits activity unique to OvIFN-tau. Finally, the antiproliferative activity of OvIFN-tau was localized primarily to the broad carboxy-terminal region, with OvIFN-tau(119-150) being the most effective inhibitor of OvIFN-tau-induced reduction of cell proliferation. Thus, multiple domains of IFN-tau have functional significance.(ABSTRACT TRUNCATED AT 250 WORDS)