[Immunity, the trophoblast and decidua]

It is as if the embryo has learnt to foil the maternal inflammatory/immune system. Acting through trophoblastic protein-1, the conceptus inhibits prostaglandin F-2a synthesis and thereby prolongs corpus luteum survival. In addition, that protein (an interferon variant), suppresses T cell proliferation. Other interferons (b and g), prostaglandin E-2 and progesterone, synthesized by trophoblast and decidua, act in concert to help the embryo to elude the aggression of the immune system. Failure of these mechanisms leads to reactivation of maternal killer T cells, mononuclear infiltration in the conceptus and its demise.