Human NK cell activity is not inhibited by pregnancy and cord serum factors and female steroid hormones in vitro

The effects of female sex steroid hormones and of pregnancy and cord sera on human NK cell activity against the NK sensitive K562 cells were studied. The cytotoxicity of adult peripheral blood lymphocytes was measured after incubation of peripheral blood effector cells in vitro with estrone, 17 beta-estradiol, estriol, or progesterone at concentrations ranging from 1 to 1000 nM. The cytotoxic activity of effector cells was not altered by pre-treatment of cells with steroid hormones, and the presence of the steroids in the NK assays caused minor changes only at the highest concentrations. Similarly, the effects of sera obtained from pregnant women during the third trimester and from cord blood were studied. Compared to normal pooled AB serum, pregnancy and cord sera had no effect on NK cell activity. On the contrary, the presence of fetal calf serum in the culture medium consistently resulted in a higher NK activity than that obtained with AB serum, cord serum, pregnancy serum, or the medium alone. The augmenting effect of human leukocyte interferon on NK cell activity was not inhibited by these sera. It is concluded that female sex steroid hormones and pregnancy and cord sera are not inhibitory in vitro to normal human NK cells.