Pregnancy process | Factors expressed or produced by uNK cells | Function | References |
Implantation | Prokinetincin1 (a marker of receptive endometrium) secreted by uNK cells | Facilitating the embryo to implant into the endometrium by regulating implantation factor like leukemia inhibitory factor, IL-11, and prostaglandins | [50] [51] . |
High expression of KIR2DL4 | Activating a pro-inflammatory/proangiogenic response by binding with its ligand HLAG on trophoblastic cells; this step is beneficial to the establishment of receptive endometrium | [48] | |
Decasualization | IL-25 secreted by dNK cells | Promotes the proliferation of DSCs and of the regulation of decasualization | [53] |
Killer immunoglobulin-like receptors | Control NK cell activity and cytotoxicity | [18] | |
Placentation | IL-8 and INF-γ inducible protein, IP10 | Increasing MMP-9 secretion, which reduces the apoptosis of extra villus trophoblastic cells (EVT) | [62] |
TNF-α, TGF-β and IFN-γ | Down-regulate the harmful excessive EVT invasion | [62] [63] | |
Spiral arteries remodeling | IL-8, TGF-β, angiopoietin-1/2 (Ang1/2), and VEGF-C | Contribute to increase the calibers diameter of spiral arteries to maintain satisfactory blood flow to the growing Festus | [60] [66] [67] |
Fetal development | dNK cells secrete growth-promoting factors like pleiotrophin (PTN)and osteoglycin (OGN) | Promote the growth and development of the fetus | [70] |