Researchers, led by William Chan, currently at the University of Alberta, have found fetal cells in the brains of mothers. Yes, kids, you really are always on our minds.
I’ve written before about a phenomenon called ‘fetal microchimerism’. The tissues of any woman who has ever been pregnant, regardless of whether that pregnancy resulted in a live birth, contain a few cells from the fetus or fetuses she was carrying. For better or worse, these fetal cells remain in the mother for the rest of her life. They’ve been associated both with tissue repair and protection from cancer and with the initiation of autoimmune diseases. It hasn’t been clear, until now, whether the fetal cells can also make their way into women’s brains.
The easiest way to distinguish maternal from fetal cells is to screen for cells that have a Y chromosome, which will only be present in the cells of any male fetus they carry. This is exactly what the researchers did. They performed brain autopsies on 59 women (age 32 to 101 at time of death) and tested up to twelve regions within each brain for the presence of Y chromosomes.
Around 60% of the women had Y carrying fetal cells in their brains, and nearly all brain regions were affected. Clearly, fetal cells are crossing the blood-brain barrier and making homes for themselves in their mother’s brains. Remember, these experiments were conducted many decades after the pregnancies that gave rise to these cells. I’d also like to point out that the numbers of fetal cells would naturally have been much higher if the researchers could have screened for female fetal cells as well as male ones. It could be that the entire brain of any woman who has ever been pregnant is permeated with cells from all those fetuses. Even more interesting, since maternal cells pass into the infant during breastfeeding, it could be that a few of those cells are from prior siblings. We could all be multiple microchimeras.
The authors also investigated whether having this fetal microchimerism could affect whether women went on to suffer from Alzheimer’s disease (AD). Although they found that women who had suffered from AD were less likely to test positive for male fetal cells, this result was not significant. A far larger study will be needed before any general conclusions can be drawn about this.
Chan WF, Gurnot C, Montine TJ, Sonnen JA, Guthrie KA, & Nelson JL (2012). Male microchimerism in the human female brain. PloS one, 7 (9) PMID: 23049819.