ABSTRACT
Pregnancy represents a major immunological event in a woman’s life. The maternal immune response to the placental and fetal semiallograft largely remains an enigma. The maternal-fetal tolerance is very complex and probably continuously adapting to the different phases of a normal pregnancy. Only some aspects of early pregnancy have been understood, e.g. how a 6-day-old embryo initially attaches to the wall of the uterus by the same mechanism as neutrophils use to attach to the endothelium of the vessel wall in inflammation. This is only the beginning of the pregnancy Implantation is an active process between the blastocyst and the endometrium, and both secrete cytokines that influence each other and ultimately determine the next phase. What happens next is of a high magnitude of complexity. The final result is more than local tolerance. It is well recognized that fetal cells pass into the maternal circulation routinely during the course of pregnancy and that this influx increases at the time of parturition. Fetal-derived stem cells have been found to persist in maternal peripheral blood for decades after childbirth. This persistent micro-chimerism can play an important role in the tolerance of foreign, paternal-derived antigens by the pregnant woman, and has been implicated in some autoimmune disorders in later life1. The occurrence of anti-human leukocyte antigen (HLA) alloimmunization in pregnancy is high. Tissue-type antigens and especially HLA determinants have long been suspected of influencing the evolution of pregnancy and the immune response2. On the other hand, it has been shown that the child carries an almost lifelong immune memory to the non-inherited maternal HLA molecules (NIMAs) it contacted during embryonic and fetal life. In kidney transplantation programs these NIMAs can be used to select acceptable mismatches in difficult cases.
