Studies of natural killer cells in pregnancy. I. Analysis at the single cell level

In using both a ⁵¹Cr-release assay and a single cell technique we measured different parameters of the effector lymphocytes killing process in pregnant and control women on a cell population and single cell level. Total NK activity was lower in pregnancy, but the difference was not significant. Parity showed no cumulative effect. Pregnant women had normal percentages of potentially cytotoxic target binding cells, however, the relative number of lymphocytes that could kill bound targets (i.e. active NK cells) was significantly depressed in pregnancy when compared with normal controls (p < 0.05). This diminished number of active NK lymphocytes was, however, normal in all phases of the lytic procedure. Interferon (IFN) treatment of effector cells in pregnant women in vitro did not alter target cell binding, but did increase the percentage of active NK cells. The level of stimulation by IFN was the same in pregnancy and control patients. The kinetics of response were the same for both cell populations and different doses of interferon caused a similar level of augmentation. In conclusion we suggest that the here demonstrated deficiency of active NK lymphocytes in pregnancy may represent a function of pregnancy associated immunoregulatory molecules which prevent a population of pre-NK cells to express their cytotoxic potential.