Natural killer cell-mediated recognition of human trophoblast

Large numbers of natural killer cells are present within the maternal decid ua close to the extravillous trophoblast cells. Most of these natural kille r cells express high levels of inhibitory NK receptors (KIR) specific for H LA class I molecules. Since trophoblast cells only express HLA-C and HLA-G, the KIR expressed by decidual NK cells can only recognize these HLA class I molecules in order to avoid NK-mediated rejection of fetal tissues. We sh ow that HLA-C recognition by decidual NK cells can be mediated by p58, LIR- 1 and (indirectly) by CD94 / NKG2A receptors. On the other hand, HLA-G reco gnition is not only mediated by LIR-1 and (indirectly) by CD94 / NKG2A but also by a newly identified receptor termed p49. The p49 receptor, unlike th e other KIR, appears to be selectively expressed by decidual NK cells.