Suppression of Lymphocyte Activation by a High-Molecular-Weight Glycoprotein Released From Preimplantation Ovine and Porcine Conceptuses

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Abstract
A high‐molecular‐weight (MW > 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 μg/ml; porcine, 5 μg/ml). Complete suppression of thymidine incorporation occurred at the highest doses evaluated (ovine, 200 μg/ml; porcine, 40 μg/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.