Modulation of the natural killer cell activity in pregnant mice alters the spontaneous abortion rate

Effector cells associated with an aborting fetus appear to be both thymus derived (T) and natural killer (NK) cells. In order to test the hypothesis that NK cells are a major effector mediating early spontaneous abortion (less than day 8-10), CBA female mice mated by DBA/2 males were treated with either polyinosinic/cytidylic acid (poly I:C) to boost NK activity, or rabbit anti-asialo GM1 (RaASGM1) to decrease NK activity. The results of the NK assays of the spleens of treated mice confirmed that the reagents had the expected effect on NK activity and an inspection of the uteri indicated a significant increase in aborted embryos after poly I:C and a marked decrease in spontaneous abortions after RaASGM1 treatment. Therefore, spontaneous abortions may be mediated in part by the cytotoxic activity of unregulated NK cells.