The immune system has been thought to present a barrier to the normal development of the fetus through maternal immunity to "foreign" paternal proteins. However, Hibey et al. now find that efficient activation of innate natural killer (NK) cells may actually help fetal growth.
The multiple receptors carried by NK cells exist in two basic forms, which lead to either cellular activation or inhibition. It is the balance between these signals that ultimately dictates the NK cell's response. Pregnant women carrying particular combinations of receptor genes and their polymorphic ligands that favor NK cell inhibition were more likely to develop the potentially lethal condition preeclampsia, in which placental blood flow becomes impaired. Thus, uterine NK cells and their cytokines may promote the trophoblast remodeling of the placental spiral arteries that generates the essential increase in blood flow required during placenta formation. Thus, by inhibiting, rather than activating NK cells, it is possible that this remodeling becomes less efficient and sets the stage for preeclampsia. -- SJS
J. Exp. Med. 200, 957 (2004).
