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What do we know about fetal-maternal microchimerism?

Microchimerism is a condition characterized by the presence of a small number of foreign cells genetically different from the host cells. Thus, during pregnancy maternal and fetal cells cross the placental barrier, enter the foreign bloodstream and settle in the organs, which leads to the formation of fetal-maternal microchimerism. This review covers some aspects of fetal-maternal microchimerism, including its impact on the course of pregnancy. The existence of fetal micro-chimerism during pregnancy confirms the fact that the maternal immune system interacts with fetal antigens long before delivery. Also, fetal microchimerism may influence the course of auto-immune diseases during pregnancy, which is associated with the fetal-maternal HLA compatibil-ity. Scientists suggest that autoimmune processes that develop after pregnancy are in fact “graft versus host” reactions that occur in response to fetal allogeneic cells. Maternal cells can also cross the placental barrier. This results in the development of tolerance to maternal antigens that are foreign to the fetus. This postnatal immune tolerance is presumably involved in the immuno-suppressive mechanisms that contribute to fetal survival in utero. It has been proven that the fetal immune system is functionally active and is formed in utero due to fetal-maternal microchimerism, non-sterile placental environment under the impact of maternal microbiota and transplacental transfer of immunoglobulins, by inflammatory mediators and cytokines. An important finding is the absence of signs of maternal microchimerism (MMc) in women with preeclampsia. Many questions remain unanswered, therefore, further studies on fetal-maternal microchimerism are needed to assess its impact on the human body. Key words: fetal-maternal microchimerism, immune tolerance, placental barrier, pregnancy, preeclampsia