All of the billions of cells in our body come from a single fertilized egg. However, recent studies have revealed that cells from other people reside in our bodies. These are the cells of our immediate family members, our mother, twins, or our children in the case of parous women, exchanged during pregnancy. Surprisingly these cells are reported to last for more than a decade after birth. Where are they located in our bodies? Various body organs and parts are known to possess non-self cells, including the skeletal muscles; heart; skin; lung; thyroid gland; digestive tube; liver; and even immunity-related organs such as the thymus, spleen, lymph nodes, peripheral blood, and bone marrow. Even mouse brains have been found to carry the cells of their children. A body consisting of cells from 2 or more genetically distinct populations is called a chimera. Since the number of cells in pregnancy related chimera is relatively small (about 1 in 1000~10,000), the phenomenon is called âmicrochimerismâ. Meanwhile, despite their low frequency among our own cells, all people are considered to be in a microchimeric state, and parous women are considered to have cells of more than 3 different origins: their own cells, their motherâs cells, and those of their children. Materno-fetal microchimerism is a common, life-long chimeric state first established by the exchange of small numbers of cells between the mother and the fetus during pregnancy. This apparently trivial phenomenon is now attracting attention due to its unexpected and profound implications in the immune system. For example, is the placenta really an immunological barrier? How do we balance the internal environment despite the existence of an immunological non-self? In this review, I will discuss the pros and cons of materno-fetal microchimerism for our immune system (e.g., tolerance, materno-fetal immune disease, tissue regeneration, etc.) and the unanswered, puzzling aspects of microchimerism from the immunological point of view. Emerging Questions in Materno-Fetal Microchimerism, Naoki Irie.
Last date updated on June, 2014