Natural Killer Cells: An Insight into its Role in Pregnancy

Tight regulation of immunotolerance at fetomaternal interface facilitates the survival of allogeneic embryo. Natural Killer (NK) cells are immune cells capable of lysing the target cells via the release of cytolytic granules containing perforin, granzyme and granulysin. Besides the peripheral circulation, NK cells are also present in the uterine mucosa. In contrast to peripheral NK (pNK) cells, uterine NK (uNK) cells are not the killer cells, rather they provide a suitable microenvironment in the pregnant uterus making it compatible to the growing foetus and promoting normal placentation, vascular remodeling and trophoblast infiltration, all of which are essential for healthy pregnancy. Although, uNK cells are loaded with cytolytic factors which can lyse the trophoblasts if activated, the control mechanisms mediated by balance between activating and inhibitory receptors block the cytolytic function of these uNK cells. Intensive research has elucidated the roles of NK cells in normal and abnormal pregnancy outcomes, such as recurrent spontaneous abortion. Much of the facts are still to be unraveled to fully understand the underlying mechanisms and to introduce newer and potential treatment modalities to support healthy pregnancy.