Immunological Aspects of Pregnancy

Pregnancy is a unique phenomenon for the human body’s immune system and makes a single natural model. The maternal immune system is active and functional during pregnancy. The immunological relationship between the mother and the fetus is a bi-directional communication determined on the one hand by fetal antigen presentation and on the other hand by recognition of and reaction to these antigens by the maternal immune system. Two main theories have been proposed to explain the phenomenon of pregnancy. One theory emphasizes the role of immune suppressive reactions to protect the fetus. A second one, the “immune tropism theory”, works on the importance of the maternal immune response to paternal antigens present in the conceptus. Today it is known the maternal immune system recognizes the embryo without triggering a response against its presence and development in the intrauterine environment. Several mechanisms allow for implantation of the embryo/ fetus and pregnancy progresses through a specific immunoregulatory response, known as immune tolerance. Its major events include decreased activity of natural killer cells, expression of regulatory proteins of the complement system, and progesterone action all acting to maintain a suitable intrauterine environment and promote fetal recognition. Inappropriate immune responses can endanger a pregnancy and may be clinically reflected by repeat abortions and restricted intrauterine growth. Although there have been proposed several theories to explain the different immunological pathways involved in this process, knowledge on major immunological changes occurring during pregnancy is key for guiding clinical practice and maintaining a healthy pregnancy for both the mother-to-be and her fetus.