At the innate frontiers between mother and fetus: linking abortion with complement activation.

The intricate mechanisms regulating fetomaternal interactions are still largely uncharacterized. Recent papers have revealed a major role for the innate immune system during abortion. Different experimental conditions-deletion of a complement regulator, injection of anti-phospholipid antibodies into mothers, or allo-recognition of fetuses in the presence of an IDO inhibitor-all lead to complement activation, inflammation, and fetal loss. These observations also raise new questions on the relationship between the adaptive and innate systems during pregnancy.