Natural killer cells in pregnancy: How do they avoid attacking fetal tissues?

Fetal tissues in contact with mother's blood tack classical HLA-class I mol ecules,thus escaping T cell-mediated recognition and rejection. However, ho w does the fetus escape killing by NK cells which sense the lock of HLA exp ression? Here, Maria Cristina Mingari and colleagues address this question and report recent data indicating that, during pregnancy, maternal NK cells display a general upregulation of inhibitory receptors specific for HLA-G. More importantly, oil decidua-associated NK cells express one or more of t hese receptors,thus preventing their attack of fetal tissues.