Infiltrating decidual natural killer cells are associated with spontaneous abortion in mice

Immunohistochemistry was used to study a murine model which spontaneously aborts at a frequency of 25 to 30%. Our results show that natural killer (NK) cells are not only the predominant infiltrating cells in aborting feto-placental units, but that they also appear in a similar proportion of feto-placental units before abortion is detectable. The frequency of feto-placental units with significantly elevated NK infiltrates corresponds to the subsequent abortion frequency, indicating a causal relationship. Immunization of the mother with BALB/C splenocytes prevents these NK infiltrates and decreases the abortion frequency to normal levels. These results suggest for the first time that maternal NK cells may have an instrumental role in the etiology of spontaneous abortion.