Suppression of mixed lymphocyte reaction by progesterone and estradiol-17beta.

The effects of estrone, estradiol-17beta, estriol, testosterone, progesterone, and 20alpha-dihydroprogesterone on incorporation of 3H-thymidine into cultured lymphocytes from normal men and nonpregnant women in response to allogeneic stimulation was investigated with two-way MLR. A dose-dependent reduction in the mean percent incorporation was observed in the range of progesterone concentration between 2 x 10(3) and 10(4) ng/ml with statistically significant differences from the control cultures. Estradiol-17 beta at 10(4) ng/ml produced a slight but significant inhibition of incorporation. No significant change in incorporation occurred with the other steroids tested. Since the suppressive property of progesterone in phytohemagglutinin-induced lymphocyte culture reported in our previous communication was reproduced by the present investigation in MLR, the possible role of progesterone in immunoregulation during pregnancy is emphasized as has been postulated previously.