The identification of biological activities of pregnancy-associated proteins of the horse.

Antisera were raised in rabbits against serum samples taken from pregnant and non-pregnant mares. Using these antisera in two-dimensional crossed immunoelectrophoresis, a protein (beta2-hors.PP) was found to be pregnancy specific and first detectable in the maternal circulation 6 days after mating. beta2-hors.PP detection as a pregnancy test during the first 21 days after mating was found to be significant at the 10% level. Levels of the protein were also found to increase during this period. The protein, of possible uterine origin, may have a biological activity associated with implantation (day 37) as levels of beta2-hors.PP were elevated from around days 21 to 83. For the remainder of gestation, the concentration of beta2-hors.PP in the serum decreased. It is possible that beta2-hors.PP detection may be a means of monitoring foetal well being. Equine epitheliochorial placental extracts, taken from 2 mares 60 days and 80 days after mating, were found to induce a dose-dependent inhibition of lymphocyte proliferation in the mixed lymphocyte reaction (MLR) and mitogen stimulated assay (MSA), MLR supernatant reversed the inhibition and the addition of foetal tissue extracts to previously activated lymphocytes suppressed lymphocyte proliferation. This suggests suppression at the IL-1/IL-2 level of the immune response. Commercially available eCG inhibited lymphocyte proliferation. The presence of endometrial cup secretion containing high levels of eCG had no additive effect on the inhibitory activity of an extract of allantochorion (day 80), previously shown to induce less than 100% inhibition. This suggests that the commercially available eCG may contain an immunosuppressive contaminant.Equine and bovine epitheliochorial placental extracts (allantochorion) inhibited collagen and ADP-induced platelet aggregation respectively. The mode of action of the anti-aggregatory factors may be related to the vascularity of the placentae. Overall, it appears that local immunomodulatory and haemostatic mechanisms are important in the maintenance of pregnancy in species with epitheliochorial placentation.