Current knowledge on natural killer cells, pregnancy and pre-eclampsia. Introduction

The introduction to this review discusses briefly why immunology, perceived as difficult by assisted reproduction technology clinicians, need nevertheless be envisaged as a central actor in the reproduction process, and how the maternal immune system, initially perceived as a threat to the fetoplacental unit, is in fact utterly necessary for successful pregnancy. The key cells in such a process are uterine natural killer cells, which can act as friend or foe to the fetus, but are now known to play a key role in local vasculogenesis. As an ultimate consequence in cases of dysfunction/dysregulation, these factors result in implantation failure, abortion or pre-eclampsia.