Resorption of CBA/J x DBA/2 mouse conceptuses in CBA/J uteri correlates with failure of the feto-placental unit to suppress natural killer cell activity.

Lipid extraction was used to study the natural killer (NK) suppressive activity of individual feto-placental units. Normal pregnancies showed a lipophilic NK cell suppressive factor that was gestational day specific. Feto-placental units from CBA/J x DBA/2 pregnancies were deficient in the NK cell suppressive factor when compared to normal CBA/J x BALB/c pregnancies. The frequency of non-suppressive feto-placental units from CBA/J x DBA/2 pregnancies correlated with the frequency of feto-placental units infiltrated with NK cells and the frequency of spontaneous resorption. Our results implicate a deficiency of NK suppressive activity in the feto-placental unit as a contributing factor in spontaneous fetal resorption.