Human Term Pregnancy Decidual NK Cells Generate Distinct Cytotoxic Responses

Decidual NK cells (dNK) are the main lymphocyte population in early pregnancy decidual mucosa. Although dNK decrease during pregnancy, they remain present in decidual tissues at term. First trimester dNK facilitate trophoblast invasion, provide protection against infections, and were shown to have many differences in their expression of NKRs, cytokines, and cytolytic capacity compared with peripheral blood NK cells (pNK). However, only limited data are available on the phenotype and function of term pregnancy dNK. In this study, dNK from human term pregnancy decidua basalis and decidua parietalis tissues were compared with pNK and first trimester dNK. Profound differences were found, including: 1) term pregnancy dNK have an increased degranulation response to K562 and PMA/ionomycin but lower capacity to respond to human CMV-infected cells; 2) term pregnancy dNK are not skewed toward recognition of HLA-C, as was previously shown for first trimester dNK; and 3) protein and gene expression profiles identified multiple differences between pNK, first trimester, and term pregnancy dNK, suggesting term pregnancy dNK are a distinct type of NK cells. Understanding the role of dNK throughout pregnancy is of high clinical relevance for studies aiming to prevent placental inflammatory disorders as well as maternal-to-fetal transmission of pathogens.