Early pregnancy factor: biology and practical application

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.

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.

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.

Detection of early pregnancy factor-like activity in human amniotic fluid

Early pregnancy factor (EPF), an immunosuppressive substance, appears in mammalian maternal serum at a very early stage after fertilization. To investigate the normal distribution of EPF in the human body, the rosette inhibition test has been used to detect EPF in human amniotic fluid. The mean value of rosette inhibition titer (RIT) was significantly higher (5.93 +/- 0.43 SE) in 52 amniotic fluid samples (16-30 weeks' gestation) than in 23 nonpregnant sera (3.54 +/- 0.11), indicating that something in amniotic fluid inhibits rosette formation. This inhibitory factor is recognized as EPF or EPF-like substance for its activity significantly correlated with that of EPF in serum from the same donor (r = 0.756: P less than 10(-6]. The immunological significance of the EPF-like substance in amniotic fluid may be important to the survival of semiallogeneic conceptus.

Evaluation of a rosette inhibition test for pregnancy diagnosis in pigs

A rosette inhibition test was developed using pig lymphocytes and sheep red blood cells. Antilymphocyte serum (ALS) in the presence of complement inhibited rosette formation by greater than 95% at 1/250 declining to no inhibition at 1/8000. Sera obtained from a total of 14 pregnant sows before and 1, 2, 3 and 4 wk after mating were tested for their ability to augment the rosette depression caused by ALS. In one experiment in which the responses of 4 pregnant sows were compared to 4 non-pregnant sows by discriminant analysis, sera were classified correctly in 83% of the samples taken from either pregnant or non-pregnant sows. When the more usual method of calculating the rosette inhibition titre was used, the responses of sera from pregnant pigs were classified with 31% accuracy and those from non-pregnant pigs with 80% accuracy. In a second experiment, sera from 10 pregnant sows were classified with 25% accuracy using the rosette inhibition titre. Thus 4 of these pigs were classified as non-pregnant by this method. Data from the second experiment were not suitable for discriminant analysis. It was concluded that there was some factor present in the sera of pregnant pigs, particularly by 3 or 4 wk post-mating, which could be detected by the rosette inhibition test. However, the test is not sensitive enough to allow specific diagnosis of early pregnancy in pigs.

Improvement of the rosette inhibition assay for the detection of early pregnancy factor in humans using the monoclonal antibody, anti-human-Lyt-3

The detection of early pregnancy factor (EPF) is a controversial subject. The findings of independent groups attempting to confirm the phenomenon of EPF have been quite variable. The present article gives details of an improved rosette inhibition assay using a monoclonal antibody (anti-human-Lyt-3), instead of an anti-lymphocyte serum (ALS), in order to increase reproducibility. Results are calculated for the first time in terms of absolute monoclonal anti-Lyt-3 concentrations. It is suggested that results be expressed as the Rosette Inhibition Antibody Concentration (RIAC) or the more accurate extrapolated 25% Rosette Inhibition Antibody Concentration (25% RIAC), in place of the previously used Rosette Inhibition Titer (RIT), when monoclonal antibodies are used. Following a 1.5 h incubation period the mean 25% RIAC for pregnant serum was 15.9 +/- 4.0 ng/ml and for control serum 48.0 +/- 12.7 ng anti-Lyt-3/ml. The improved method described should enable different groups to establish the test and compare results.