ABSTRACT
Introduction From the early 1950s onward, immunological interest has been dedicated to maternal tolerance to the allogeneic foetus.1-3 Initially the uterus was considered primarily as an “immunoprivileged site” (as are the brain, the testis and the anterior chamber of the eye), where no interaction with the maternal immune cells could take place.4 Nowadays interest is concentrated more specificly on the local intermingling of foetal and trophoblast derived cells and maternal decidual cells at the uterine wall.5 Pregnancy is increasingly considered to occur in the setting of antigen-specific responses, that upregulate cellular circuits, inducing a state of maternal tolerance to the semi-allogeneic foetus. This process of downregulation of the immune response is reversible and occurs only during pregnancy as has been shown in mice, where implanted tumour cells, carrying a paternal alloantigen, were rejected directly after delivery.6 This special state of “immunoprivilege” or “induced tolerance” is a relative state, as immune responses cannot and should not be prevented completely.
