Immunosuppressive activity associated with early pregnancy in the bovine

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.

In vitro effect of ketone bodies, glucocorticosteroids and bovine pregnancy-associated glycoprotein on cultures of bone marrow progenitor cells of cows and calves

Changes in the number, maturity and function of neutrophils, concomitant changes in plasma concentrations of hormones and metabolites, and the increased susceptibility of cows to infectious diseases around parturition, led us to investigate the effect of beta-hydroxybutyric acid (BHBA), acetoacetic acid (AcAc), hydrocortisone-21-acetate (HCAc) and bovine pregnancy-associated glycoprotein (bPAG) on the proliferation of bovine bone marrow progenitor cells in methylcellulose in vitro cultures. Myeloid progenitors were stimulated with concanavalin A-stimulated leukocyte conditioned medium (LCM) and erythroid progenitors with erythropoietin in the presence of hemin. Erythroid and myeloid colonies were scored after five and seven days, respectively. BHBA and AcAc induced inhibitory effects on the proliferation of bovine bone marrow cells at concentrations of 1.0, 2.5, and 5.0 mM. HCAc significantly inhibited growth of progenitors at concentrations of 10, 20, 50, and 100 ng/ml, and bPAG at concentrations of 2400 and 3000 ng/ml. The results of this study suggest that in the cow high concentrations of BHBA, AcAc, HCAc and bPAG, which can be reached in the circulation around calving, could alter the number of circulating neutrophils after parturition. This phenomenon might contribute to the increased susceptibility of dairy cows to environmental mastitis.

Isolation of immunologically active uterine luminal proteins associated with follicular and luteal phases of the ovary in buffalo (Bubalus bubalus)

Uterine luminal proteins (ULP) collected from the genital tract of buffalo during the follicular (Group F) and luteal (Group L) phases of the estrous cycle were chromatographed using sephacryl S-200 gel. Five peaks were detected in each group. Different protein concentrations (10 to 200 microg) from Peaks I and V in each group were examined for immunological activity on polymorph nuclear leukocytic cells (PMNL) in vitro. All concentrations except 10 microg of ULP Peak I (< or = 250 kDa) in Group F enhanced phagocytic activity of PMNL. Peak V (56 kDa) in the same group enhanced phagocytic activity of PMNL only at low protein concentrations (10, 20 and 40 microg protein), while at greater concentrations (80, 150 and 200 microg protein) PMNL activity was suppressed. On the other hand, all protein concentrations from Peak 1 (> or = 250 kDa) in Group L suppressed PMNL activity in a dose-dependent manner. Proteins from Peak V (31 kDa) in Group L suppressed PMNL phagocytic activity at all concentrations but not to the same extent as in Peak I. Electrophoretic analysis of Peaks I and V in both groups revealed only 3 detectable protein bands (subunits) in Peak I and 1 detectable subunit in Peak V. Several additional proteins were probably not detected. The molecular weights of the detected subunits in Peaks I and V in Group F were greater than those in Group L as indicated by SDS-PAGE analysis. The results of this study show that ULP collected from buffalo possessed proteins that modulated phagocytic activity of PMNL in vitro. Proteins collected during the follicular phase, especially Peak I, enhanced phagocytic activity of the PMNL, whereas those collected during the luteal phase (Peaks I and V) suppressed activity. Changes in the molecular weights of ULP detected in this experiment may be related to the changes in phagocytic activity of PMNL tested in vitro.

Effects of the whole extract and the chromatographic fractions of the pig placenta on lymphocyte proliferation and humoral immune response

The immunoregulatory properties of pig fetal placenta extracts (PE) from 1 st, 2nd and 3rd month of pregnancy and five fractions (F1 to F5), isolated on Sephadex G-200 and additionally characterized by fast performance liquid chromatography, FPLC (Superose 12 HR) were studied in order to clarify the local immune regulation in diffuse epitheliochorial placentation. The obtained substances were added at 6.25 to 100 microg in cultures of Concanavalin A-stimulated mouse splenocytes and Phytohemagglutinin-stimulated pig and human PBL to monitor their influence on [(3)H]Thimidine uptake in proliferating lymphocytes. Their effects on the number of plaque-forming cells in spleen cell suspensions from mice treated ip simultaneously with sheep red blood cells and with 100 microg protein of PE, respectively, of each fraction were also investigated: PE and F1 had no effect while F4 and F5 suppressed the mitogen-induced lymphocyte proliferation in all studied species. F2 and F3 stimulated mouse and pig lymphocyte proliferation. The effects were dose-dependent and the suppression was not due to cytotoxic effects. The FPLC data allowed the suggestion that 110 kD protein(s) were involved in stimulation and 7 kD substance(s) - in suppression of cell proliferation. The PE from the 3 studied periods as well as the 5 fractions increased significantly the primary humoral immune response against T-dependent antigen. The results revealed that trophoblast of epitheliochorial placenta produces simultaneously immuno-stimulatory and -suppressive factors acting across the species barrier. Their presence at the feto-maternal interface may contribute to the regulation of local immune reactions and survival of the allogenic fetuses despite the morphological specificities of this type of placentation.

Inhibition of in vitro lymphocyte proliferation by ovine placenta-conditioned culture medium

Conditioned culture media of ovine placental tissues or fetal skeletal muscle collected at Days 60, 100 and 140 of pregnancy were tested for their ability to inhibit in vitro lymphocyte proliferation. All conditioned cultures contained low-molecular-weight factors which suppressed [3H]Tdr uptake by PHA-stimulated sheep lymphocytes. Non-dialyzable, inhibitory molecules were released only by placental tissues, with the greatest activity occurring for fetal cotyledonary placenta at Days 100 and 140 of gestation. Dialyzed conditioned culture medium of Day 100 cotyledonary placenta suppressed lymphocyte proliferation stimulated by PHA, PWM and MLR, but had no effect on ConA-stimulated cultures. Inhibitory actions were effective only during the first 24 h of lymphocyte activation and were abrogated with exogenous IL-2. Size-fractionation by gel filtration chromatography of the conditioned medium resolved the inhibitory activity into a peak of molecular weight greater than 4 X 10(6) Da and another peak with estimated molecular weight range of 46-162 kDa. Inhibitory action of the high molecular weight fraction was destroyed by sodium periodate oxidation whereas the lower molecular weight peak was sensitive to pronase. Presence of these immunosuppressive factors at the maternal-conceptus interface may contribute to down-regulation of local immune functions in the uterus and survival of the allogeneic conceptus.

The human blastocyst produces a soluble factor(s) that interferes with lymphocyte proliferation

Animal studies have reported that the blastocyst produces immunosuppressive factors that are critical to successful implantation. The production of such factor(s) by the human blastocyst has not yet been described. To test that hypothesis, the spent media of 67 human embryos developed in vitro was evaluated using either the allogeneic one-way mixed lymphocyte response (MLR) or the concanavalin A (Con-A) stimulated lymphocyte response (SLR). Conditioned embryo media was obtained at in vitro fertilization (IVF) in aliquots of (A) the first 24 hours in vitro, (B) the second 24 hours in vitro, and (C) from 24 hours until development of the blastocyst stage. Control media consisted of Ham's F-10 medium (Gibco, Grand Island, NY) with identical maternal serum concentration to test media. Conditioned media (either A, B, or C) or control media was added to 200-microL wells containing lymphocytes in either the MLR or SLR. A significant suppressive effect of 25% to 60% was observed in seven of nine samples of blastocyst-conditioned media (P less than 0.05). No significant suppressive effect was found in the earlier embryo media (A or B) in either the MLR or the SLR. These data suggest that the human blastocyst produces a factor(s) that interferes with lymphocyte proliferation.

Reduction in uterine intra-epithelial lymphocytes during early gestation in pigs

The numbers of intra-epithelial lymphocytes per 5 mm of uterine epithelium were counted in cyclic (n = 18) and pregnant (n = 18) gilts on days 10, 13, 16 and 19 postestrus. In cyclic animals these cells increased (P less than 0.01) from 26.4 +/- 1.1 per 5 mm at the mid-luteal phase (day 10) to 47.7 +/- 1.5 per 5 mm at proestrus (day 19). Intra-epithelial lymphocytes were significantly (P less than 0.01) fewer at all stages in pregnant females and were reduced from 17.7 +/- 1.5 on day 10 to 6 +/- 1.4 per 5 mm on day 19. The significant reduction in intra-epithelial lymphocytes during the second and third weeks of gestation indicates that the developing pig conceptus can reduce the numbers of potentially damaging cells at the placental interface.

Assessment of immunoregulation by cultured, pre-attachment bovine embryos

The possibility that the viability of bovine embryos might be predicted by measuring their release of immunoregulatory substances during culture has been investigated. Bovine embryos between days 2 and 19 of gestation were cultured for 24-48 h, the embryo-conditioned medium was harvested and studied for suppression of PHA-stimulated bovine leukocyte cultures. Medium incubated in the absence of any conditioning tissues served as control. Artefactual immunosuppression was detected in incubated control material that could be attributed, in part, to the mixing of different tissue culture media, the type of plastic-ware employed for incubation and supplementation of media with additional L-glutamine. It was observed that day-2 to day-9 bovine embryos, cultured in medium able to support the lymphocyte proliferation assay, did not release immunosuppressive substances. Medium conditioned by day-10 to day-12 embryos produced variable immunosuppression while that conditioned by trophoblastic vesicles derived from day-14 to day-19 embryos was consistently highly suppressive. Since bovine embryo transfer is normally conducted at 6-8 days of gestation, it is unlikely that measuring the immunosuppressive products released from bovine embryos will be of value for predicting their viability.

Immunosuppressive effects of rabbit blastocoelic fluid and embryo culture medium

In order to understand the mechanism of the feto-maternal immune relationship, we assayed the immunosuppression activities of fresh blastocoelic fluid and decomplemented peripheral serum collected from day-9 pregnant white New Zealand rabbits and of rabbit embryo culture medium (ECM). Because the viability of the human lymphocytes was not affected by either of these biological fluids and since they were easy to obtain in sufficient quantities, they were used uniformly in all the experiments. Immunosuppressive effect was calculated by the relative inhibition of proliferation of Con A-stimulated lymphocytes. The immunosuppressive effect of blastocoelic fluid of the 9-day pregnant rabbits was significantly higher than that of autologous decomplemented serum (P less than 0.001). The inhibition by the serum was non-specific because sera from non-pregnant animals as well as sera from different stages of pregnancy and pseudo-pregnancy showed the same level of inhibition. The ECM of 6.5-7-day-old embryo showed a pronounced immunosuppressive effect. When embryos of 1,3 and 5 days were cultured and their culture media were assayed only with 5-day-old embryo the effect had begun to appear, but it was far less than that of 7-day-old embryo (P less than 0.02). The suppressive activity of both the blastocoelic fluid and ECM was not due to cytotoxic effect, since this fluid supported the in vitro growth of single-cell rabbit embryos up to the stage of blastocyst. These results suggest that the immunologic tolerance of the embryo might be due to the immunosuppressors secreted by the embryo and that there might be a localized effect at the implantation site rather than a maternal systemic immunosuppressive effect.

Identification of two species of suppressive factor of differing molecular weight released by in vitro fertilized human oocytes

Preimplantation human embryos have been shown to release factors that have immunosuppressive activity and that are highly correlated with successful implantation. The present study was undertaken to determine the molecular weight of these factors using HPLC. Two peaks of suppressive activity were found associated with molecular weights of 3.7 +/- 0.3 and 1.2 +/- 0.1 kd, respectively. The potential significance of low molecular weight immunosuppressor factors in avoiding maternal inflammatory and immunologic responses is discussed.

Suppression of lymphocyte activation by a high-molecular-weight glycoprotein released from preimplantation ovine and porcine conceptuses

A high-molecular-weight (MW greater than 660,000), acidic glycoprotein (HMWGP) was purified from incubation medium of preimplantation, elongating ovine (day 16 and 17) and porcine (day 16) conceptuses. HMWGP was tested for its ability to inhibit [3H-methyl]thymidine incorporation into lymphocytes stimulated by phytohemagglutinin or two-way mixed lymphocyte cultures. Ovine and porcine HMWGP inhibited the incorporation of [3H-methyl]thymidine into lymphocytes in a dose-dependent manner. An approximately 50% inhibition was detected at the lowest dose tested (ovine, 25 micrograms/ml; porcine, 5 micrograms/ml). Complete suppression of thymidine incorporation occurred at the highest doses evaluated (ovine, 200 micrograms/ml; porcine, 40 micrograms/ml). This immunosuppressive effect was not the result of an overall cytotoxic effect on lymphocytes as evaluated by trypan blue exclusion. In conclusion, an ovine and porcine conceptus glycoprotein, HMWGP, has potent in vitro immunosuppressive activity in both phytohemagglutinin and mixed lymphocyte cultures. In vivo, HMWGP may have an immunoregulatory role during early pregnancy in the sheep and pig by providing a local immunosuppressive environment within the uterus to prevent conceptus rejection.

Identification of a low molecular weight polypeptide of pregnant bovine uterine origin (LMW-UDF): influence on coagulation system in vitro. Part I

Acidified extracts of pregnant bovine uterus were found to contain a heparin-affinity polypeptide(s). The eluted peak was assayed in the Chandler loop method for whole blood and fibrin thrombus generation. Significant differences in the mean weight and size of whole blood thrombi (243.5 +/- 50 mg and 3.5 cm +/- 0.6 cm) occurred with 1 microgram of purified polypeptide when compared to control samples containing albumin (47.87 +/- .30 g and 0.8 cm +/- 0.3 cm). This activity was detected by the Chandler loop method with 100 ng to 10 micrograms of protein when analyzed in a dose-response fashion. When tested for fibrin thrombus formation this activity persisted. Experiments with 125I fibrinogen revealed no net increase or decrease of uptake into whole blood thrombi when purified polypeptide was added. The heparin-affinity polypeptide(s) possessed a molecular weight of approximately 6-4 kDa when examined by SDS-PAGE. We have therefore designated this polypeptide as low molecular weight-uterine derived factor (LMW-UDF).

Production of immunosuppressor factor(s) by preimplantation human embryos

Embryonic loss prior to implantation appears to be a significantly frequent phenomenon and this is further reinforced by the very low pregnancy rates reported by in vitro fertilization and embryo transfer programs. Implantation failure may possibly be the result of rejection of the antigenic embryo by the hostile maternal immune system. The mechanism by which embryos in successful pregnancies escape these rejection responses may depend upon their ability to produce factor(s) that suppress in vitro mitogen-induced lymphocyte proliferation. Only 43% of cleaved embryos demonstrated this ability. We postulate that successful pregnancies are dependent upon the production by embryos of immunosuppressor factor(s) that has a direct suppressive effect on the maternal immune response.

Immunosuppressive activity of uterine luminal protein from steroid-treated ovariectomized heifers

Uterine luminal protein (ULP) collected from ovariectomized steroid-treated crossbred heifers was tested for immunosuppressive activity in vitro. Heifers were allotted to treatment groups and for 16 d received daily injections of the following steroids or vehicle: Control (C, corn oil only, n=10); estradiol-17beta (E(2), 1.1 mug/kg body wt, n=10); progesterone (P(4), 2.2 mg/kg body wt, n=10); and E(2)+P(4) (1.1 mug + 2.2 mg/kg body wt, n=9). On Day 17, uterine flushings were collected, concentrated and quantitated for total ULP. ULP was tested for suppression of lymphocyte blastogenesis. For each experiment, 5 x 10(5) bovine lymphocytes were incubated with 0.4 mug of phytohemagglutinin (PHA) and ULP (25 to 400 mug ULP/ml) using standard culture conditions. At 48 h, 0.5 muCi of (3H) thymidine was added to cultures with cells harvested at 60 +/- 1 h by automation. Incorporated thymidine was measured by scintillation chromatography. Mean total ULP values for C-, E(2)-, P(4)- and E(2)+P(4)-treated groups were 4.7, 8.4, 13.6, and 25.5 mg, respectively (E(2)+P(4)>C and E(2), P<0.05). ULP from all treatment groups suppressed (P<0.0001) lymphocyte blastogenesis (thymidine incorporation) to PHA; however, suppression was greater (P<0.0001) for ULP from E(2)- and P(4)-than C-treated heifers at 100 and 200 mug ULP/ml. In conclusion, E(2) and P(4) injections enhanced immunosuppressive activity of ULP secretions.