Fig. 1. Role of natural killer (NK) cells in creating a supporting environment for embryo implantation. T cell immunoglobulin (type I membrane protein) and mucin-containing protein 3+ uterine NK cells combine with ligand galectin-9 (Gal-9) to secrete interleukin (IL)-4, transforming growth factor (TGF)-β, IL-10, with decreased production of tumor necrosis factor (TNF)-α, thereby inducing immune suppression and tolerance, and creating an environment conducive to embryo implantation.
