*2.9. Immune Cells in Implantation*

A role for the immune system in embryo implantation has been widely investigated for obvious reasons. The decidua plays a fundamental role in ensuring immune tolerance toward the semi-allogenic conceptus, protecting it from the mother's immune system. Regulatory T cells (Tregs) are CD4+ CD25+ T cells, having the role to suppress the immune response [193]. During early pregnancy, in the decidua there is an increase in Tregs, which produce immunosuppressive cytokines, such as IL-10, for inducing immune tolerance [194–197]. Other cells involved in maternal immune tolerance are the uNK, a particular type of NK cells, which lose their cytotoxic functions during pregnancy andplay a supportive role by enhancing angiogenesis. uNK cells induce immune tolerance by reducing inflammation through interferon-γ (IFN-γ) [198] and by inhibiting the function of T cells through the expression of immunomodulatory molecules such as galectin-1 and glycodelin A [199].
