Microchimerism is the presence of a small number of cells in an individual that originate from another genetically different individual. These cells contain the DNA of the genetically different individual and may have consequences for human health.
Causes of microchimerism
The most common cause of naturally acquired microchimerism is pregnancy. The transfer of cells during pregnancy is bidirectional. During pregnancy, fetal cells can cross the placenta and reside in the mother’s circulation. Similarly, the mother’s cells can cross the placenta and stay in the fetus. Therefore, microchimerism in a mother consists of cells from her own mother, as well as cells from all her children that she had borne in her womb.
Other causes of microchimerism are iatrogenic, i.e., resulting from medical therapy. These include transplantation of organs, such as a liver or kidney and blood transfusion. One who has an organ transplant from another individual would have the cells from that genetically different individual residing in his or her body. This can pose a problem when the body recognizes these cells as foreign, and the immune systems attack those foreign cells. Therefore, high doses of immunosuppressants are necessary after an organ transplant to prevent organ rejection.
Implications of maternal microchimerism
Microchimerism has different implications for the mother and the baby. Because the baby is exposed to the maternal cells in an early stage of its development, before the immune system is fully developed, the baby becomes tolerant to the foreign maternal cells. However, the mother comes into contact with the baby’s cells when her immune system is already fully developed. Therefore, the baby’s cells, which are foreign to her immune system, may trigger an immune response.
Autoimmune diseases, such as systemic lupus erythematosus (SLE), autoimmune thyroid disease, and rheumatoid arthritis, are more common in women than men. It is postulated that microchimerism could play a role in the development of autoimmune disease in women. The immune response triggered by the baby’s cells in the mother’s circulation may set off an autoimmune reaction, causing the mother’s immune system to attack her own cells. If the immune system attacks the thyroid cells, this results in autoimmune thyroid disease. If the immune system attacks the cells in the joints, this can result in rheumatoid arthritis.
Research on microchimerism
The study of microchimerism has been hampered in the past by technological limitations. Scientists are now able to detect chimeric cells and fetal DNA in the blood circulation, making it possible to research into whether microchimerism plays a role in diseases such as autoimmune disease and cancer.
