The suppressive effect of progesterone on lymphocyte cytotoxicity: unique progesterone sensitivity of pregnancy lymphocytes.

The effect of progesterone on the cytotoxic activity of lymphocytes obtained from healthy pregnant women, women with threatened pre-term delivery, healthy non-pregnant women and healthy male donors has been compared. The cytotoxic activity of lymphocytes from healthy pregnant women was significantly reduced by progesterone at concentrations present in the serum during pregnancy. In contrast, a 100-fold higher concentration of progesterone was required to diminish the cytotoxic activity of lymphocytes from women with threatened pre-term delivery and from healthy male donors. Individuals with lymphocytes of high and low progesterone sensitivity could be found amongst non-pregnant women. The results of investigations at the single cell level suggested that although progesterone did not inhibit the ability of the lymphocytes to bind to the target cells, it markedly reduced the target cell lysing capacity of the bound effector cells.