Reproductive immunology. Early pregnancy factor

Single Domain Antibodies as New Biomarker Detectors

Biomarkers are defined as indicators of biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention. Biomarkers have been widely used for early detection, prediction of response after treatment, and for monitoring the progression of diseases. Antibodies represent promising tools for recognition of biomarkers, and are widely deployed as analytical tools in clinical settings. For immunodiagnostics, antibodies are now exploited as binders for antigens of interest across a range of platforms. More recently, the discovery of antibody surface display and combinatorial chemistry techniques has allowed the exploration of new binders from a range of animals, for instance variable domains of new antigen receptors (V_NAR) from shark and variable heavy chain domains (V_HH) or nanobodies from camelids. These single domain antibodies (sdAbs) have some advantages over conventional murine immunoglobulin owing to the lack of a light chain, making them the smallest natural biomarker binders thus far identified. In this review, we will discuss several biomarkers used as a means to validate diseases progress. The potential functionality of modern singe domain antigen binders derived from phylogenetically early animals as new biomarker detectors for current diagnostic and research platforms development will be described.

Identification of heat shock protein 10 within the equine embryo, endometrium, and maternal peripheral blood mononuclear cells

Early pregnancy factor has been identified as a 10-kDa extracellular homolog of heat shock protein 10 (Hsp10). Hsp10 has been detected during early pregnancy in serum of mice, sheep, pigs, horses, cows, and humans by the rosette inhibition test. Hsp10 has also been associated with several neoplastic and autoimmune diseases. The goal of the present study was to determine if Hsp10 could be detected in the early equine embryo through the use of immunohistochemistry and quantitative real-time PCR. Additionally, analysis of systemically harvested peripheral blood mononuclear cells (PBMCs) from both pregnant and nonpregnant mares was evaluated to determine expression levels of HSP10. Embryos were collected from Quarter Horse mares by uterine lavage at either 8 or 25 days after ovulation. Collection and separation of PBMCs occurred on Day 8 for both pregnant and nonpregnant mares. Immunohistochemistry revealed cytoplasmic localization of HSP10 throughout the single layer of ectodermal cells forming the trophoblast in Day-8 embryos. Day-25 embryos demonstrated intense localization focally along the apical border of ectodermal cells forming the trophoblast layer of the developing chorion. There was no nuclear staining in either embryonic population. Quantitative real-time PCR detected the presence of mRNA for HSP10 in both 8- and 25-day equine embryos. Day-25 embryos exhibited an elevated degree of expression (P = 0.006) compared with the 8-day embryos for HSP10. Endometrial samples did not display any significant difference in degree of expression for HSP10 (P = 0.10). Finally, PBMCs from pregnant mares demonstrated elevated (P = 0.03) expression of HSP10 compared to the nonpregnant mares on Day 8 of the estrous cycle. This study confirmed the presence of HSP10 protein and mRNA expression of HSP10 in equine embryos at two maturation stages. Additionally, the presence of increased gene expression within PBMCs of pregnant mares suggests communication, possibly leading to necessary immunomodulatory effects between the embryo and mare.

Use of lymphocyte platelet binding assay for detecting a preimplantation factor: a quantitative assay

PROBLEM

To evaluate the ability of the lymphocyte/platelet binding assay to identify a preimplantation factor (PIF).

METHOD

Percentages of binding of lymphocytes by platelets in the presence of sera from 30 known pregnant and 30 nonpregnant individuals were compared using a novel lymphocyte/platelet binding assay. The assay is performed using a combination of a heat inactivated sera with donor O+lymphocytes, activated complement and an antibody against CD2 (T11, Ortho Pharmaceuticals).

RESULTS

In nonpregnant females (23.6 +/- 6.5%) and males (17.7 +/- 4.7%) the percentage of lymphocytes bound by platelets was significantly different from pregnant women (56.1 +/- 15.9%) (P < 0.0001). Serial sampling of blood in five women undergoing IVF/ET who had normal pregnancies showed the detection of PIF by 4 days after transfer. The lymphocyte/platelet binding assay was not influenced by hCG, progesterone and estradiol. The interassay and intrassay variabilities were < 3%.

CONCLUSIONS

The lymphocyte/platelet binding assay is a simple, reproducible, specific and cost efficient assay for measurement of PIF. Application of this assay will provide investigative and diagnostic tools for identifying and monitoring early pregnancy events.

Reduction in popliteal lymph node graft-versus-host reactivity by homologous and heterologous pregnancy serum

The popliteal lymph node assay was used to investigate the effect of pregnancy on graft-versus-host reactivity (GvHR) of mouse spleen cells. After local injection of splenocytes from primiparous syngeneically pregnant (by BALB/cJ males) or allogeneically pregnant (by CBA/Ca males) mice no differences in lymph node weight gain were observed in F1 recipients (CBA/Ca x BALB/cJ) when compared to injections of cells from age-matched non-pregnant BALB/cJ mice. However, lymphocytes of pregnant BALB/cJ females which had previously been pregnant between 4 and 6 times by CBA/Ca males induced a significantly lower GvHR compared to cells of matched non-pregnant multiparous mice. These results suggested an inhibitory effect of gestation on cells possibly primed towards paternal antigens by multiple pregnancies. To test this hypothesis, virgin BALB/cJ mice were actively immunized with lymphocytes of male CBA/Ca mice. Before injection into F1 recipients, spleen cells of immunized animals were incubated for 1 h at 37 degrees C in heat-inactivated serum of primiparous pregnant or virgin non-pregnant mice. Pre-incubation in pregnancy serum had no effect on unprimed cells, but GvHR of cells derived from immunized donors was significantly depressed in female recipients. In male animals this effect was only irregularly observed. Inhibition of GvHR was also observed with serum from pregnant but not non-pregnant pigs. Depression of cellular immune response was observed as early as days 4-9 post-coitum (p.c.) with mouse serum and days 16-19 p.c. with pig serum. These results indicate that pregnancy serum contains factor(s) which modulates the GvHR of primed lymphocytes in both a species- and an antigen-non-specific manner while reactivity of naive spleen cells is not changed.

Monoclonal antibodies to early pregnancy factor perturb tumour cell growth

The pregnancy-associated substance early pregnancy factor (EPF) has previously been reported as a product of tumours of germ cell origin. More recently EPF (or an EPF-related substance, tEPF) has also been detected in the serum of patients bearing tumours of non-germ cell origin. We report here the production of tEPF by a variety of cultured transformed and tumour cell lines, of both germ and non-germ cell origin. Antibodies specific for EPF remove all tEPF activity from tumour cell conditioned medium. tEPF production is found to be associated with cell division; tEPF is no longer detected after growth arrest or differentiation. Co-culture of tumour cells with increasing doses of anti-EPF monoclonal antibodies resulted in a significant, dose-dependent decrease in rate of cell growth and viability. Similar anti-EPF concentrations had no effect on the concanavalin A induced proliferation of mouse spleen cells. These studies suggest, therefore, that tEPF is a growth-regulated product of cultured tumour and transformed cells. These cells are also dependent upon tEPF for continued growth, i.e. tEPF is acting in the autocrine mode.

Serological detection of early pregnancy in cattle and partial characterization of a serum glycoprotein associated with early pregnancy

Sera from heifers prior to artificial insemination (AI), 1-8 days after AI, and 7 days after embryo removal were investigated by crossed immunoelectrophoresis (CIE) by use of rabbit antiserum produced against bovine early pregnancy serum and intensively absorbed with non-pregnancy serum. One precipitation peak appeared in the alpha-globulin region when sera of non-pregnant heifers were under study. An additional peak could be demonstrated in the same region when sera of early pregnant heifers were investigated. By this method 91.5% of 71 sera samples were classified correctly to be pregnant or non-pregnant. The glycoprotein character of the above two serum components could be shown by binding to concanavalin A (Con A) in lectin affinity CIE. Relative molecular weights were estimated to be about 70,000 and 80,000 for the peptides of these two proteins applying sodium dodecyl sulfate polyacrylamide gel electrophoresis of precipitates cut out from CIE-plates. As shown previously close relation of this early pregnancy associated protein (EPAP) to the early pregnancy factor is supposed because of its characteristics and its ability to affect cellular immunity.

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.

Immunosuppressive effect of early pregnancy factor on early expression of cell surface membrane IgG

We have adopted a new assay to investigate the influence of early pregnancy factor (EPF) on the modulation of lymphocyte activity. Lymphocytes were attached to the plastic surfaces of microplates in serum-free medium in the presence of Sepharose-Con A. After 2-3 days incubation with EPF, and ELISA assay was used to detect the expression of surface membrane IgG (smIgG); this was done in the same microplates used for the culture, thus avoiding cell manipulation. Using only a few picograms of EPF a significant inhibition (in the range 26-40%) was obtained. The variation in the inhibition observed was mainly due to the different sources of lymphocytes used. Unrelated proteins and hormones, tested at the same concentration as EPF, did not show any inhibitory activity. Using the F(ab)2 fragment of anti-human IgG instead of the whole molecule the same levels of inhibition were obtained, suggesting that the observed inhibition by EPF was not due to a non-specific interaction between the anti-human IgG and the Fc receptors on the cell. Such inhibitory activity detected in vitro by this method provides additional support for a suppressive role for EPF during pregnancy.

Use of a modified test system to determine early pregnancy factor (EPF) levels in patients with normal first trimester pregnancy and after therapeutic abortion

Human pregnancy can be recognized as early as 48 hours after conception using the rosette inhibition test (RIT) to detect early pregnancy factor (EPF). A modification of the test as originally described by Morton et al. is demonstrated using a monoclonal pan T-cell antibody. Studies were performed to investigate the relationship between EPF levels during normal first trimester intact pregnancies and therapeutic abortions. The change in EPF levels is compared with those of hormones after interrupted pregnancy.

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.