Adaptation of uteroplacental arteries in patients with early-onset preeclampsia combined with IUGR is compromised due to insufficient invasion of extravillous trophoblast cells (EVT) into the spiral artery wall. The underlying molecular mechanisms are widely unknown. We investigated expression and possible mechanisms of regulation of different matrix-metalloproteases (MMPs) by EVT in placental bed biopsies from patients with early onset preeclampsia combined with IUGR and healthy pregnant women. Expression of MMP-3 and MMP-7 by EVT was markedly reduced in preeclamptic patients, especially close to spiral arteries. In contrast to healthy pregnancies these cells strongly expressed the receptor for leukemia inhibitory factor (LIF). LIF is known to suppress MMP-expression and is produced by uterine natural killer (uNK) cells which we found to be present in higher concentrations in the placental bed of preeclamptic patients, and accumulating aside the spiral arteries. We speculate that in preeclampsia a maternal immune cell network accumulating and interfering in the placental bed leads to an altered cytokine environment, resulting in disturbed trophoblast cell function such as impaired MMP expression and reduced invasiveness.