During pregnancy, some fetal cells migrate into their mother’s bloodstream and from there to all points beyond. These cells remain in the mother’s body for decades, possibly for the rest of the mother’s life. This means that women who have ever been pregnant, even if the pregnancy did not result in a living child, are essentially chimeras. That is, they have human cells with two distinct genomes living in their bodies. Granted the mother’s own cells far outnumber the fetal cells, but fetal cells are definitely present.
This information is intriguing to say the least. Is it a specific type of fetal cells that cross over into the mother? Are these fetal cells doing anything? And if so what? The first step in answering these questions is to find and quantify the fetal cells. Stephanie Pritchard and her colleagues from Tufts Medical Center, Tufts University and Sackler School of Graduate Biomedical Genetics used a combination of screening tools to detect fetal mouse cells in their mothers’ lungs.
The researchers bred normal females to male mice that contained a gene that makes their cells glow green. Any babies that resulted from this cross would inherit the green gene from the father. Thus, any cells within the mother’s body that fluoresced would have to be fetal cells. Once the fetal cells were identified, the scientists used gene expression tests to determine what kinds of cells they were.
In this way, they found a variety of types of fetal cells in their mothers’ lungs, including mesenchymal stem cells (MSCs). These are cells that can differentiate into bone, cartilage, fat cells, and other tissues. In fact, fetal MSCs have been observed to differentiate as a response to injury to the mother. In addition, fetal cells seem to be particularly prevalent at tumor sites within the mother. This presents the tantalizing possibility that the fetal cells may be acting as some sort of repair mechanism on behalf of the mother.
The benefit of spreading fetal cells throughout the mother’s body doesn’t just go one way though. The team also identified fetal immune cells in the mother mice, which may play a role in protecting the fetus from the mother’s immune system.
Obviously, there is much more to be learned about fetal cells. You can hear the excellent Robert Krulwich discussing this fascinating story with Kirby Johnson of Tufts University (who developed the fluorescent fetal cell test) on this episode of RadioLab. The story begins at the 2:45 mark.