INCREASED PROGESTERONE CONCENTRATIONS ARE NECESSARY TO SUPPRESS INTERLEUKIN-2 ACTIVATED HUMAN MONONUCLEAR CELL CYTOTOXICITY

Fetal trophoblast is generally resistant to lysis by cytotoxic cells. Trophoblast progesterone and estrogens may act at the choriodecidual interface, where they are present in high concentrations to provide a local, paracrine immunosuppressive effect on cellular cytotoxicity. However, interleukin activation of these cytotoxic lymphocytes enhances their ability to lyse trophoblast. Recent evidence suggests that immunoactivation occurs in certain aberrant pregnancy conditions, including preeclampsia. Preeclamptic placentas produce more progesterone in vitro than do normal placentas. To study the potential association between progesterone production and immunoactivation, we evaluated the immunomodulatory effect of progesterone on cellular cytotoxicity. Comparisons were made with the use of both normal and interleukin-2-stimulated peripheral blood mononuclear cells as effector cells in a cytotoxicity assay. Progesterone suppressed cytotoxicity in a dose-dependent manner. Interleukin-2 augmented cellular cytotoxicity, and higher concentrations of progesterone were required to attenuate this response. An additive suppression of cytotoxicity was also observed when estrone, estradiol, estriol, and progesterone were combined. We speculate that the higher placental production of progesterone seen in preeclampsia may be a trophoblast compensatory response to immunoactivated maternal effector cells.