Immunological Role of the Placenta, Blocking Factors and NK Cells in Post-implantation Pregnancy.

The unexpected failure of the mother to immunologically reject the foetus is partly thought to result from immunological properties of the placenta. The placental trophoblast produces immunosuppressive factors including progesterone and blocking antibodies which together down-regulate maternal immune responses to the foetoplacental unit. This article reviews the post implantation immunology of pregnancy emphasizing the roles of placenta, blocking factors and natural killer (NK) cells.