• Progesterone;
  • prostaglandin E2;
  • fetal placental macrophages

ABSTRACT: The role of progesterone in immunoregulation at the fetomaternal interface at physiological concentrations (2–6 μg/ml) is controversial. This study examines the effect of progesterone on maternal lymphocyte proliferation in a one-way mixed lymphocytic reaction (MLR) stimulated by allogenic lymphocytes as well as on prostaglandin production and secretion by fetal placental macrophages. No suppressive effect on maternal lymphocyte proliferation was found at progesterone levels of up to 20 μg/ml. However, physiological concentrations of progesterone were found to induce a significant increase in the fetal macrophage release of PGE2, which is well known as a strong immunosuppressant. PGI2 production and secretion by these cells, measured by the appearance of its 6-ket-PGF1α product, was not affected by incubation with progesterone. Enhancement of PGE2 secretion by progesterone may partly explain the roles of progesterone and fetal placental macrophages in immunosuppression at the fetomaternal interface.