This week we discussed the concept of fetal cells in maternal circulation, in particular the implication of the Rh factor. I found an interesting article that reviews the concept of Michrochemerism (MC).
A normal pregnancy is accompanied by major physiological changes. Adaptation by the mother to the foreign fetus requires major immunolical changes that even to this date are not completely understood. It is clear however, that the fetus is not protected from the maternal immune system by physical barriers such as the placenta. Extant research supports that the two circulations are in close approximation and there is bidirectional flow of maternal and fetal cells throughout the pregnancy. The maternal system does recognize the fetal cells' paternal antigens and produces antigen specific cytotoxic T cells and antibodies. These are thought to be prevented from attacking fetal cells by the stimulation of paternal antigen specific Treg cells.
MC refers to the DNA or low levels of viable cells present in the circulation of and/or organs of an individual that clearly originate from another genetically distinct individual. MC was first identified in mice. In 1996 the first identification of MC in humans was found. The prescence of male progenator cells was found in the blood of women. MC appears to be able to live in the maternal blood for years.
MC is thought to engraft in the bone marrow of the mother and differentiate into leukocytic cells. Data supports the theory that MC cells are progenator stems cells capable of multiple differentiation depending on their location. It is currently thought that the maternal immune response toward fetal cells is suppressed when maternal and fetal circulations intersect in the syncitiotrophoblast. Here the unique pregnancy associated human leukocyte antigen HLA-G is expressed in the cells. It is thought HLA-G induces the production of treg cells and suppress NK cells. T regs suppress the maternal immune response to fetal cells.
The exact role of MC in women's health is as yet unclear. Study is hampered by difficulty in measurement. Some theories implicate MC in the role of autoimmune disease in women whereas other theories propose beneficial health effects. Implications for future research are huge.
Groer, M. W., Manion, M., Szkeres, C., & El-Badri, N. (2011). Fetal michrochimerism and women's health: a new paradigm. Biological Research for Nursing, 13(4), 346-350.
"In 1996 the first identification of MC in humans was found. The prescence of male progenator cells was found in the blood of women. MC appears to be able to live in the maternal blood for years."
ReplyDeleteWhat it sounds like they are thinking is that fetal cells will be viable in the mother during and after pregnancy because of an immunological loophole that allows women to carry children without launching an immune attack against them. The fetal cells then can integrate into the woman for years as "progenitors". Does this study say whether the women who had male progenitor cells had male children?
This is really interesting and does seem like a potential (partial) explanation for the increased incidence of autoimmune disease in women. Something neat to follow in the coming years for sure!
BrookeB, great idea that the opportunity to respond to a partly-identical, partly different cell type in a woman with MC might in some way increase the possibility of autoimmunity. Or maybe evolution would have already dealt with that risk?
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