Existence of Microchimerism in Pregnant Women Carrying a Boy!

icrochimerism is considered as the occurrence of small populations of cells with a diverse genetic setting within a person (1). Tissue microchimerism is enhanced during pregnancy and is frequently associated with femaledominant autoimmune disorders, response to injury from malignancy, and transplantation effect (2). Recently, a group of pathologists at Leiden University Medical Center in the Netherlands carried out an experiment that seemed to be doomed to failure. They performed in-situ hybridization of the Y chromosome on paraffin-embedded autopsy samples of different organs collected from 26 women who died while pregnant or within one month after delivery of a son. In fact, the group was looking for male cells in female bodies. Surprisingly, their search was successful. They found Y chromosomes cells in each tissue samples that they analyzed. The obtained chimeras were from lung followed by spleen, liver, kidney, brain and heart (3). In the 1990s, scientists established the first evidences that the cells of the children can get away from the uterus and they can be expanded within the mother’s body. This incidence was identified as a fetal microchimerism, after the chimera, a monster in Greek mythology that consists of different parts of lion, goat and dragon. Fetal cells do not flow and accumulate without direction. It has been reported that fetal cells that move toward heart can develop into cardiac tissue in female mice and be a part of beating heart cells eventually (2, 4). A recent study proposes that women approximately at all times obtain fetal cells when they get pregnant. These have been noticed in the begin ning of seven weeks of pregnancy. Later, the cells can be disappeared, though the cells may stay for a lifetime. Chan et al. reported that Y chromosomes were present in the brains of 63 percent of 59 deceased older women. Several researches evaluated the cells left behind by sons regarding fetal microchimerism, due to ease for its discrimination from the cells of their mothers (5). It has been demonstrated that microchimerism may have an effect on woman’s health. Based on the maternal health, three hypotheses regarding the role of fetal cells have been suggested: 1. fetal cells are harmful that may associate with the inflammatory response resulting in maternal tissue damage, 2. fetal cells play protective roles with fetal progenitor cells that may assist for maintenance of maternal tissues, and 3. Fetal cells are only bystanders, with no effect on maternal health (6). Furthermore, fetal cells have been proposed to produce chemicals affecting the mother’s health which