Accommodation and the Fetus

The mammalian fetus usually expresses major histocompatibility antigens not present in the mother. Such incompatibility of major histocompatibility antigens between “ordinary” grafts and the recipient provokes a powerful immune response and rejection of the grafts. Survival of the fetus despite this barrier has been ascribed to a low level of expression of histocompatibility antigens or to maternal immune tolerance or to the existence of a barrier posed by the placenta. Here, we discuss a fourth potential mechanism. The mechanism involves acquired resistance to immune-mediated injury and was originally described in organ transplants found to resist injury by antibodies and complement. The mechanism is called accommodation.