Early pregnancy factor (EPF): a link between fertilization and immunomodulation

Comparison of immune modulatory properties of human multipotent mesenchymal stromal cells derived from bone marrow and placenta

Multipotent mesenchymal stromal cells (MSC) can be isolated from many tissues, including bone marrow (BM) and placenta (PL). Human placenta can be obtained readily without invasive procedures. There may be differences, however, in differentiation capacity and immunomodulation by MSC isolated from BM or PL. The early pregnancy factor (heat shock protein 10; EPF/Hsp10) is a small protein that exhibits immunomodulatory properties. We compared BM- and PL-MSC, and assessed their efficacy for suppressing T-cell proliferation in vitro and the role of EPF/Hsp10 in this process. PL-MSC were collected from whole placenta after removal of the amniotic and chorionic membranes followed by serial enzymatic digestions. The PL-MSC were compared to BM-MSC, obtained from healthy donors. Differentiation capacity, cytokine secretion, expression and secretion of immunomodulatory molecules, immunophenotype and real time proliferation were assessed using cytokine arrays, ELISA assays, flow cytometry, immunohistochemical staining and western blotting. Whereas BM-MSC consisted of a homogeneous cell population with strong expression of mesenchymal markers, PL-MSC consisted of a mixed population of cells with variable CD73, CD90 and CD105 expression. PL-MSC exhibited a significantly greater proliferation rate than BM-MSC. The presence of both stem cells and more mature cells in the PL-MSC cultures resulted in decreased differentiation capacity and reduced efficacy of immune suppression in co-cultures with T-cells. Although robust intracellular expression of EPF/Hsp10 in both BM- and PL-MSC was observed, secretion of the protein in response to immune activating stimuli remained below detectable levels. Secretion of pro-inflammatory cytokines was significantly greater in BM-MSC than PL-MSC, whereas no difference was observed in the secretion of hematopoiesis supporting growth factors. Development of culture methods for isolation of pure populations of PL-MSC may improve the quality of the product and reproducibility of results.

Symposium review: Predicting pregnancy loss in dairy cattle

Several tools exist to diagnose pregnancy in dairy cattle. However, substantial pregnancy loss occurs within the first 60 d of gestation in cattle, and these losses have a profound adverse economic impact on the dairy and beef cattle industries. Detecting these impending pregnancy losses could offer producers an opportunity to reduce costs associated with this source of reproductive inefficiency. Several of the pregnancy diagnostic tools currently available and new technologies are being examined for their ability to predict pregnancies at risk for failing in early pregnancy. This review provides a synopsis of work undertaken recently to predict pregnancy losses in cattle. Currently, opportunities to predict pregnancy loss include (1) using transrectal ultrasonography to detect loss of the fetal heartbeat, floating debris within the placental fluids, and reductions in fetal size; (2) observing reductions in circulating progesterone concentrations; (3) detecting reductions in concentrations of circulating placental products; namely, pregnancy-associated glycoproteins and microRNAs; and (4) detecting reductions in the early pregnancy-dependent increase in interferon-stimulatory gene expression in peripheral blood leukocytes. An achievable goal may be to identify markers of embryo mortality so that researchers and clinicians can focus their efforts on developing intervention strategies for cows identified to be at risk for pregnancy failure.

Embryo survival rate in cattle: a major limitation to the achievement of high fertility

Over the past 30-40 years genetic improvement and better nutrition of dairy cows have led to a significant increase in milk production per cow but this is associated with an increase in cow reproductive wastage. Reproductive wastage in the dairy herd particularly in a seasonal calving system, results in a serious financial loss. Early embryo death accounts for a significant portion of cow reproductive wastage and information is becoming available on the extent and timing of early embryo loss and on aspects of embryo growth, development, metabolism and viability. Such information is necessary to facilitate objective investigation of factors that contribute to early embryo death. For heifers and moderate yielding dairy cows published estimates of fertilisation rate of about 90%, and of average calving rates of about 55% indicate an embryonic and foetal mortality rate of about 40%. Of this total loss, 70 to 80% is sustained between days 8 and 16 after insemination, a further 10% between days 16 and 42 and a further 5-8% between day 42 and term. In high yielding cows there is some evidence of a higher increment of late embryo loss. During the period of greatest embryo loss, between days 8 and 16 after fertilisation, there is a dramatic increase in the growth rate and protein content of embryos, particularly from day 13 to day 16 when the increase is exponential. There is evidence that from day 13 to 15 cattle embryos undergo time and developmental stage-dependent changes in the rate of de-novo protein synthesis and protein phosphorylation. It seems that by the time cattle embryos have elongated they have passed their maximal synthetic activity in terms of protein synthesis and phosphorylation, which seems to occur at day 13 or earlier. While there is little published information on the causes of embryo loss it is clear that even a short-term reduction in energy intake near the time of insemination can significantly reduce embryo survival rate. Abo and low post-ovulatory systemic progesterone has been associated with increased embryo loss. Recent evidence shows that elevated systemic concentrations of ammonia and urea per se do not reduce embryo survival rate but there may be other modifying factors, such as negative energy balance, operating in the high yielding dairy cow that lead to reduced fertility when the systemic concentrations of urea and or, ammonia are high.

Does levonorgestrel emergency contraceptive have a post-fertilization effect? A review of its mechanism of action

BACKGROUND

Recent studies have identified that levonorgestrel administered orally in emergency contraception (LNG-EC) is only efficacious when taken before ovulation. However, the drug does not consistently prevent follicular rupture or impair sperm function.

OBJECTIVE

The present systematic review is performed to analyze and more precisely define the extent to which pre-fertilization mechanisms of action may explain the drug's efficacy in pregnancy avoidance. We also examine the available evidence to determine if pre-ovulatory drug administration may be associated with post-fertilization effects.

CONCLUSION

The mechanism of action of LNG-EC is reviewed. The drug has no ability to alter sperm function at doses used in vivo and has limited ability to suppress ovulation. Our analysis estimates that the drug's ovulatory inhibition potential could prevent less than 15 percent of potential conceptions, thus making a pre-fertilization mechanism of action significantly less likely than previously thought. Luteal effects (such as decreased progesterone, altered glycodelin levels, and shortened luteal phase) present in the literature may suggest a pre-ovulatory induced post-fertilization drug effect.

LAY SUMMARY

Plan B is the most widely used emergency contraceptive available. It is important for patients and physicians to clearly understand the drug's mechanism of action (MOA). The drug was originally thought to work by preventing fertilization. Recent research has cast doubt on this. Our review of the research suggests that it could act in a pre-fertilization capacity, and we estimate that it could prevent ovulation in only 15 percent or less of cases. The drug has no ability to alter sperm function and limited ability to suppress ovulation. Further, data suggest that when administered pre-ovulation, it may have a post-fertilization MOA.

Predicting Embryo Presence and Viability

Pregnancy establishment, followed by birth of live offspring, is essential to all mammals. The biological processes leading up to pregnancy establishment, maintenance, and birth are complex and dependent on the coordinated timing of a series of events at the molecular, cellular, and physiological level. The ability to ovulate a competent oocyte, which is capable of undergoing fertilization, is only the initial step in achieving a successful pregnancy. Once fertilization has occurred and early embryonic development is initiated, early pregnancy detection is critical to provide proper prenatal care (humans) or appropriate management (domestic livestock). However, the simple presence of an embryo, early in gestation, does not guarantee the birth of a live offspring. Pregnancy loss (embryonic mortality, spontaneous abortions, etc.) has been well documented in all mammals, especially in humans and domestic livestock species, and is a major cause of reproductive loss. It has been estimated that only about 25-30% of all fertilized oocytes in humans result in birth of a live offspring; however, identifying the embryos that will not survive to parturition has not been an easy task. Therefore, investigators have focused the identification of products in maternal circulation that permit the detection of an embryo and assessment of its well-being. This review will focus on the advances in predicting embryonic presence and viability, in vivo.

Evaluation of the early conception factor (ECF) test for the detection of nonpregnancy in dairy cattle

The ability to detect conception and/or conception failure in cattle would be beneficial to producers in formulating reproductive management plans. A new diagnostic test, the early conception factor (ECF) test, has been developed forthis application yetthe accuracy of this test has not been adequately determined. The objectives of this study were to evaluate the effectiveness of the ECF test for detecting the nonpregnant cow, and to compare the reliability of serum versus milk ECF tests relative to actual pregnancy rates. In Trial 1, Holstein heifers were synchronized, the animals were bred (timed-AI), and serum ECF tests were performed 72 h later. Heifers exhibiting a negative ECF test after AI were re-synchronized, bred again, and re-tested for ECF for up to three services. Relative to actual pregnancy rates, a negative ECF test was correct (i.e., true negative) 38.5% of the time over the three services. In Trial II, Holstein heifers were bred (AI) after observed estrus and serum ECF tests conducted between Days 1 and 3 and Days 7 and 9 after AI. In this trial, only 44.4% and 55.6% of the confirmed nonpregnant heifers were identified correctly by serum ECF analysis at Days 1 to 3 and Days 7 to 9 post-AI respectively. In Trial III, 40 lactating cows were synchronized, the animals were bred (AI), and serum and milk ECF tests were performed on Days 3, 9, 15, 21 and 30 after AI. Pregnancy diagnosis (ultrasound on Day 30 and palpation on Day 51) confirmed that 50% of the cows were pregnant to AI, while serum and milk ECF analysis indicated a 100% and 37.5% predicted pregnancy rate, respectively, at 30 d post-AI. Moreover, results of the serum and milk ECF tests disagreed with one another 36.9% of the time overall, while agreement between ECF and actual pregnancy rates were 50.6% and 45.6% for milk and serum respectively. Additionally in Trial III, a negative ECF result only identified 5% and 28.8% of nonpregnant cows overall for serum and milk tests respectively (i.e., true negatives), with a high incidence of false positive ECF results noted (47.5% and 31.3% for serum and milk, respectively). Collectively, these data indicate that the current ECF test cannot accurately identify the nonpregnant cow with the precision needed by the dairy producer.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Early pregnancy factor: an extracellular chaperonin 10 homologue

Early pregnancy factor (EPF) has been identified as a homologue of chaperonin 10 (cpn10) with immunosuppressive and growth factor properties. As a homologue of cpn10, it belongs to the heat shock family of proteins (hsp) but, unlike other members of this family, EPF is detected extracellularly. Early pregnancy factor was first discovered in pregnancy serum by the rosette inhibition test, and the novelty of its discovery was that its presence could diagnose pregnancy within 6-24 h of a fertile mating. As well as being a monitor of the presence of a viable embryo, it is necessary for embryonic survival. In this capacity it acts as both an immunosuppressant and growth factor. Early pregnancy factor is also a product of proliferating primary and neoplastic cells and functions as an autocrine growth factor both in vivo and in vitro. It has a modifying effect on the outcome of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. Early pregnancy factor is considered to be one of the major factors involved in the modification of multiple sclerosis observed during pregnancy.

Synthesis of early pregnancy factor using red deer (Cervus elaphus) as a delayed implantation model

PURPOSE

This study measured serum early pregnancy factor (EPF) in pregnant red deer (Cervus elaphus) and ascertained whether EPF synthesis is associated with implantation.

METHODS

Serial serum samples were taken from mated hinds up to 42 days postconception and analyzed for EPF activity using the rosette inhibition test. EPF activity was then correlated with calving records and stages of preimplantation development.

RESULTS

EPF was detected in all pregnant animals, with a twin pregnancy giving increased EPF activity. Three animals gave an EPF response following fertilization but failed to continue beyond the preimplantation embryo stage. The increase in EPF synthesis previously associated with implantation in other mammals occurred at the blastocyst stage in red deer.

CONCLUSIONS

EPF synthesis in red deer (Cervus elaphus) is consistent with the preimplantation period, as occurs in other mammals. However, the second phase of the biphasic increase in early pregnancy factor production is associated with blastocyst formation, not implantation.

Bovine early pregnancy factor (EPF) activity dependent on a 67-kDa polypeptide

Maternal bovine EPF activity can be reduced to one single polypeptide enriched and identified from serum of cows in early pregnancy. The relative molecular weight of this active polypeptide was estimated at 67 kDa. This bovine EPF was labelled by 125I and peroxidase. In parallel investigations of non-pregnant animals a 67-kDa polypeptide was additionally identified in the last purification step, but without EPF activity in the rosette inhibition test. This indicated occurrence of an inactive pre-compound (or carrier protein) of the EPF in the non-pregnant state. On pre-incubation of lymphocytes with EPF analogues (inactive polypeptide from nonpregnancy serum) EPF retained its optimal activity, its lymphocyte receptors being unaffected. Monoclonal antibodies produced against HPLC-enriched EPF were reactive to the 67-kDa polypeptide in pregnancy material as well as in nonpregnancy material and were not able to differentiate between 'pregnant' and 'nonpregnant'. A mouse anti-EPF serum produced against highly purified EPF isolated from SDS PAGE showed reactivity only against the 67-kDa polypeptide of pregnancy serum but not against that of non-pregnancy serum. This is the first evidence for a difference in antigenic determinants of the two 67-kDa proteins found in pregnancy and non-pregnancy serum. Furthermore, a second higher molecular weight protein could be identified by this antiserum in pregnancy and non-pregnancy serum.

The early pregnancy factor (EPF) in pregnancies of women with habitual abortions

The EPF activity of 67 sera, obtained during the 6th to 9th week of pregnancy, was determined using the rosette inhibition test. The sera of uncomplicated pregnancies (n = 9) and of women with habitual abortions who came to delivery during the most recent pregnancy (n = 10) contained the highest EPF activity during the 6th week of gestation. When pregnancies ended in another abortion (n = 10) the EPF was never detected, or disappeared at least 1-2 weeks before abortion. In the absence of EPF activity the relative risk of abortion was 7.6 (first determination) or 20.0 (second determination 1 week later). In comparison, the risk was lower when the more commonly used pregnancy parameters (HCG 4.4 (5.7), estradiol 2.6 (4.9), or progesterone (2.7 (2.7)) were depressed. Our results suggest that the EPF determination has high prognostic value in patients with high risk pregnancies and in pregnancies which follow treatment for sterility.

Human embryonic origin early pregnancy factor before and after implantation

Early pregnancy factor (EPF) is a factor that has been shown to be involved in the maintenance of the fetal allograft in several mammalian species including man. In that capacity it serves as a link between fertilization and immunomodulation. In the present study we have investigated the secretion of EPF by the human conceptus before and after implantation using rosette inhibition antibody concentration (T11 monoclonal antibody). In isolated trophoblastic cells at gestational week 7-9 there was a significant secretion of EPF. For the first 8 days in culture, secretion was maximal; later, however, at days 13 and 21 these levels declined. Further the EPF content of human embryonal extracts was examined. In various organs, spinal cord, liver, and kidney, significant EPF activity was detected. In women undergoing in vitro fertilization/embryo transfer, a total of 52 preimplantational embryos were cultured for 36 hours. No significant EPF activity was detected in the surrounding media. Two of the 11 patients studied became pregnant during the same cycle after embryo transfer. In conclusion, the preimplantational origin of EPF is maternal, while that of the post-implantational embryo is of embryonal origin.

Identification of a histamine-releasing factor secreted by human pre-implantation embryos grown in vitro

Human pre-implantation stage embryos cultured in vitro spontaneously secreted a factor capable of inducing histamine-release from human blood basophils. The embryo-derived histamine-releasing factor (EHRF) has been isolated from the culture medium by means of heparin-Sepharose affinity chromatography. The factor bound to the column and was then eluted by increasing the buffer molarity to 1.5 M NaCl. EHRF was detected using an enzymatic-isotopic microassay and sensitized basophils known to undergo release with anti-IgE. The EHRF-induced histamine-release was calcium and temperature dependent and the relatively slow kinetics (10 min) were similar to those obtained with anti-IgE. EHRF caused the release of a substantial amount of histamine (48%, n = 18) in a dose-dependent manner. The equivalent fraction isolated from medium containing unfertilized oocytes gave less than 10% of histamine-release using the same source of basophils, suggesting that EHRF was secreted after fertilization. EHRF was very stable since it was resistant to boiling, lyophilization, and to several freeze and thaw treatments. The histamine-releasing activity induced by EHRF was measured in vitro also by means of purified leukocytes containing sensitized basophils. EHRF could represent a message sent by the embryo to the mother to induce histamine release at the time of implantation.

Early pregnancy factor: large scale isolation of rosette inhibition test-active polypeptides from ovine placental extracts

Protocols are described for the isolation of substantial (mg) amounts of a rosette inhibition test (RIT)-active polypeptide fraction from ovine placental extracts. The main component of the preparation is a 12K polypeptide which contains a highly reactive thiol group. Oxidation may occur during isolation with the result that the final preparation is a mixture of the 12K polypeptide and a 25K disulphide linked dimer. The highly reactive thiol group was found to be directly involved in activity expression since gentle reduction followed by iodoacetylation resulted in a complete loss of activity. Antisera were prepared and the antibodies removed all the RIT activity from fresh ovine placental extracts, indicating that molecules related to those in the isolated preparation were responsible for all the activity in crude extracts. The antibodies also removed all the RIT activity from ovine and murine pregnancy sera, obtained both before and after implantation. Since EPF is defined as an RIT activity detected in pregnancy serum, these results establish that EPF activity is due to molecules similar to those isolated from the placental extracts. The availability of the preparative protocol and antibodies should hasten the biochemical definition of the EPF phenomenon.