Alice C. Cavanagh

Ovum Factor: A First Signal of Pregnancy?

ABSTRACT: Previous studies have shown that, in the mouse, a factor is produced by the fertilized ovum within 24 h of mating. It cooperates with prolactin to stimulate ovarian production of component B of early pregnancy factor (EPF). This paper presents an initial characterization of the substance, termed ovum facor (OF).

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.

Early pregnancy factor has immunosuppressive and growth factor properties

Early pregnancy factor (EPF) was first described as a pregnancy-associated substance, although recent studies suggest a more general link with cell development. It is a product of actively dividing cells and its apparent functional importance to them suggests its potential as a regulator of cell proliferation. The recent discovery of EPF in platelets has provided a comparatively rich and readily available source of EPF. The purification procedures employed to isolate EPF from this source have also been applied to pregnancy serum and urine, medium conditioned by oestrous mouse ovaries (stimulated with prolactin and embryo-conditioned medium), medium conditioned by tumour cells, and serum from rats 24 h after partial hepatectomy (PH). In all instances, biological activity followed the same pattern throughout. Furthermore, the final active reversed-phase high-performance liquid chromatography fraction from all sources was bound specifically by immobilized anti-EPF monoclonal antibodies (MAbs), indicating that the active fractions produced from these diverse sources are very closely related, if not identical. Some differences have been observed in the behaviour of EPF in various conditions. EPF is produced by proliferating tumour cells and by liver cells post-PH, and passive immunization studies with anti-EPF MAbs have shown that these cells need EPF for survival. In contrast, EPF has not been detected as a product of the pre-embryo, and addition of anti-EPF MAbs to embryo cultures does not adversely affect development from the 2-cell to the blastocyst stage. Although the pre-embryo is not dependent on EPF for its development in vitro, neutralization of EPF in vivo by anti-EPF MAbs retards its development. Thus, EPF appears to play an indirect role in maintaining the pre-embryo. By virtue of its ability to suppress the delayed-type hypersensitivity reaction, it has been suggested that EPF might act as an immunological response modifier of the maternal immune system. Alternatively, the effect of EPF on lymphocytes may be to reduce the expression of all or some cytokines and this could inhibit development. Whether or not EPF acts more directly as an autocrine growth factor from around the time of implantation, when the embryo first begins synthesis of EPF, is not known and remains to be investigated.

Ovum Factor and Early-Pregnancy Factor

Publisher Summary This chapter describes experimental evidences, which shows that production of early pregnancy factor (EPF) is initiated by fertilization and that its presence in serum monitors the viability of the conceptus for at least the first half of gestation. Furthermore, EPF is necessary for the continued survival of the conceptus. The tissues involved in the production of EPF are discussed and the role of EPF in the maintenance of the embryo is also considered. The role of EPF in maintaining embryonic viability may involve immunological protection. The characteristics of EPF meet the criteria needed for an effective immunosuppressant capable of inhibiting maternal rejection of the embryo. Immunomodulation begins within hours of fertilization and is reversible within 24 hours of loss of the embryo. The effect of EPF is selective; it binds to a specific lymphocyte population, recruiting suppressor cells that in turn release soluble suppressor factors, genetically restricted in their behavior. The target cells affected by these suppressor factors are of the same T-lymphocyte population as those involved in graft rejection. The discovery of EPF and the ensuing research has depended on the activity of EPF in the rosette inhibition test.

Early pregnancy factor treatment suppresses the inflammatory response and adhesion molecule expression in the spinal cord of SJL/J mice with experimental autoimmune encephalomyelitis and the delayed-type hypersensitivity reaction to trinitrochlorobenzene in normal BALB/c mice

Early pregnancy factor (EPF) is a secreted protein, present in serum during early pregnancy and essential for maintaining viability of the embryo. It is a homologue of chaperonin 10 (Cpn10) but, unlike Cpn10, it has an extracellular role. EPF has immunosuppressive and growth regulatory properties. Previously we have reported the preparation of recombinant EPF (rEPF) and shown that treatment with rEPF will suppress clinical signs of MBP-EAE in Lewis rats and PLP-EAE in SJL/J mice. In the present study, these findings have been extended to investigate possible mechanisms involved in the action of EPF. Following treatment of mice with rEPF from the day of inoculation, there were fewer infiltrating CD3+ and CD4+ cells in the parenchyma of the spinal cord during the onset of disease and after the initial episode, compared with mice treated with vehicle. Expression of the integrins LFA-1, VLA-4 and Mac-1 and of members of the immunoglobulin superfamily of adhesion molecules ICAM-1 and VCAM-1 was suppressed in the central nervous system (CNS) following rEPF treatment. The expression of PECAM-1 was not affected. To determine if rEPF suppressed T cell activation in the periphery, the delayed-type hypersensitivity (DTH) reaction of normal BALB/c mice to trinitrochlorobenzene (TNCB) following treatment with rEPF was studied. The results showed that treatment with rEPF suppressed the DTH reaction, demonstrating the ability of EPF to downregulate the cell-mediated immune response. These results indicate that suppression of immunological mechanisms by rEPF plays a major role in the reduction of clinical signs of disease in experimental autoimmune encephalomyelitis (EAE).

Early pregnancy factor suppresses experimental autoimmune encephalomyelitis induced in Lewis rats with myelin basic protein and in SJL/J mice with myelin proteolipid protein peptide 139-151

Early pregnancy factor (EPF) is a secreted protein with immunosuppressive and growth factor properties. During pregnancy, it appears in maternal serum within 6-24 h of fertilization, is present for at least the first two-thirds of pregnancy in all species studied and is essential for embryonic survival. It is a homologue of chaperonin 10, a heat shock protein, but, unlike other members of this family, EPF has an extracellular role. As it has the ability to modulate CD4+ T cell-dependent immune responses, its role in treatment of experimental autoimmune encephalomyelitis (EAE) was investigated. EAE is a CD4+ T cell-mediated disease, the best available animal model of multiple sclerosis (MS). Two models of EAE were investigated, acute EAE induced in Lewis rats by inoculation with myelin basic protein (MBP-EAE) and chronic relapsing EAE induced in SJL/J mice by inoculation with myelin proteolipid protein peptide (residues 139-151) (PLP-EAE). EPF, delivered intraperitoneally or orally to rats or intraperitoneally to mice, suppressed clinical signs of disease. Mice with PLP-EAE were also treated with interferon-beta, with and without EPF. Both EPF and IFN-beta suppressed clinical signs of EAE and, when administered together, gave greater suppression than when given separately. These findings suggest that EPF may be a potential candidate for use in treatment of MS and may be of use in combined therapy with IFN-beta.

A protective effect of early pregnancy factor on experimental autoimmune encephalomyelitis induced in Lewis rats by inoculation with myelin basic protein

Experimental autoimmune encephalomyelitis (EAE) is an organ-specific autoimmune disease characterised by inflammation and demyelination of the central nervous system and is the best available animal model of multiple sclerosis (MS). Since previous studies have shown that EAE is less severe or is delayed in onset during pregnancy and that administration of the pregnancy hormone early pregnancy factor (EPF) down-regulates EAE, experiments in the present study were designed to explore further the role of EPF in EAE. By using the rosette inhibition test, the standard bioassay for EPF and, by semi-quantitative RT-PCR techniques, we have now shown that inflammatory cells from the spinal cord of rats with EAE can produce and secrete EPF, with production being greatest during recovery from disease. Administration of EPF to rats with EAE resulted in a significant increase in the expression of IL-4 and IL-10 mRNA and a significant decrease in IFN-gamma mRNA expression in spinal cord inflammatory cells. Encephalitogenic MBP-specific T cell lines were prepared from popliteal lymph nodes of rats with EAE. Proliferation assays using these cells demonstrated the ability of exogenous EPF to down-regulate the responses of T lymphocytes to MBP.

Early pregnancy factor is required at two important stages of embryonic development in the mouse

PROBLEM: The importance of early pregnancy factor (EPF) at the pre‐implantation stage of development (days 1–3 post‐coitum [p.c.]) has been previously established in this laboratory. However, the role of EPF at the implantation stage (days 4.5–5 p.c.) has not been determined. This present study therefore investigates the role of EPF at this important developmental stage, both in vivo and in vitro.
 METHOD OF STUDY: Mated mice were passively immunized with anti‐EPF antibodies at the peri‐implantation stage (days 3.5–4 p.c.) and embryo implantation recorded. Parallel studies were conducted in vitro, where the effect of anti‐EPF antibodies on trophoblast outgrowth of blastocysts was determined.
 RESULTS: Administration of anti‐EPF antibodies in vivo at the peri‐implantation stage of development resulted in failure of embryos to implant. Similarly, trophoblastic outgrowth of blastocysts was adversely affected in the presence of anti‐EPF antibodies.
 CONCLUSIONS: These results, together with previous findings that anti‐EPF antibodies retard embryonic development when administered at the early pre‐implantation stage, clearly demonstrate that EPF is required by the embryo at two important developmental stages – the one–two‐cell stage and the peri‐implantation stage.

Modified rosette inhibition test with mouse lymphocytes for detection of early pregnancy factor in human pregnancy serum

The rosette inhibition test has been modified so that early pregnancy factor (EPF) in human pregnancy serum can be detected with mouse lymphocytes. Interference with the assay, which would result from incubation of lymphocytes with heterologous serum proteins, is prevented by the introduction of an ion exchange chromatography step. This provides a simple and rapid method for separating EPF from interfering serum proteins. Human pregnancy and non-pregnancy sera were assayed for EPF with human lymphocytes and results compared with those obtained with DEAE-Sephacel fractions of the same sera tested with mouse lymphocytes. The 2 systems showed good agreement but the mouse assay gave greater differentiation between positive and negative results. When monoclonal anti-T cell antibodies, Hu Ly-m1 and anti-Ly-1.1, were substituted for anti-lymphocyte sera in the human and mouse assay systems respectively, similar results were obtained. The mouse assay system has several advantages over the human assay, including stability of the anti-mouse lymphocyte serum and the ready availability of mouse lymphocytes. Moreover the modified method may be applied not only to the assay of human EPF, but also to the assay of EPF from other species. This would be of value if several species were being studied in 1 laboratory, or if sufficient quantities of lymphocytes from a particular species were not available.

Production of a recombinant form of early pregnancy factor that can prolong allogeneic skin graft survival time in rats

Early pregnancy factor (EPF), an extracellular chaperonin 10 homologue, has immunosuppressive and growth factor properties. In order to carry out more extensive studies on the in vivo characteristics of EPF, a recombinant form of the molecule has been prepared. Recombinant human EPF (rEPF) was expressed in Escherichia coli using the plasmid pGEX‐2T expression system. Potency of rEPF in vitro in the rosette inhibition test, the bioassay for EPF, was equivalent to that of native EPF (nEPF), purified from human platelets, and synthetic EPF (sEPF). However, the half‐life of activity (50% decrease in the log value) in serum, following i.p. injection, was significantly decreased (3.2 h, compared with nEPF 6.2 days, sEPF 5.8 days). This was thought to be due to modification of the N‐terminus of the recombinant molecule inhibiting binding to serum carrier proteins. Because EPF can modify Th1 responses, the ability of the recombinant molecule to suppress allogeneic graft rejection was investigated. Following skin grafts from Lewis rats to DA rats and vice versa, rEPF was delivered locally at the graft site and the effect on survival time of the allografts noted. Results demonstrated that rEPF treatment significantly prolonged skin graft survival time by as much as 55% in stringent models of transplantation across major histocompatibility barriers.