Human placentae: view from an immunological bias.

Human placentae form a major part of the interface between maternal and embryonic tissues. Placentae are morphologically complex organs that are lined with a trophoblastic tissue that provides anatomical constraints over which flows maternal blood. Maternal antibodies and immune cells thus contact the lining syncytiotrophoblast, and this paper considers some of the antigens that maternal immune components might encounter. The antigens have been grouped into those of unknown function, major histocompatibility antigens, and antigens of suspected function. The paper also details certain antigens of cytotrophoblasts. We discuss consequences of maternal immune responses to extraembryonic antigens and present evidence for amplification of these responses through the activation of hemostasis and fibrinolysis within the placenta and placental bed.