[Adaptation of the immune system as a response to pregnancy]

Pregnancy is an intriguing immunologic phenomenon. In spite of genetic differences, maternal and fetal cells are in close contact over the whole course of pregnancy with no evidence of either humoral and/or cellular immunologic response of mother to fetus as an allotransplant. The general opinion is that the fundamental protective mechanism must be located locally at the contact-plate, between the maternal and fetal tissues. Immunologic investigations proved the presence of specific systems which block the function of antipaternal maternal antibodies, as well as formation of cytotoxic maternal T-cells to paternal antigens. The system preventing rejection of graft during pregnancy is functioning at the level of maternal and fetal tissues. The protective mechanisms are coded by genes of MCH region, locus HLA-G.

The placenta protects itself against antibody-mediated damage. A high level of complement-regulatory proteins (CD46, CD55 and CD59), being the response to the synthesis of complement-fixing maternal antibodies to paternal antigens and regulation of the placental HLA expression as a preventive reaction of the feto-placental unit to the influence of maternal CTL, are the most important protective mechanisms of placenta.

Protective mechanisms common both for placenta and uterus are as follows: expressions of Fas ligand prevention of infiltration of activated immune cells, regulation of immunosuppression which prevents proliferation of immune cells and high natural immunity (Na cells and macrophages) of the decidua.