Some of your cells are not genetically yours - what can they tell us about life and death?

"Mothers carry cells that came from their biological children, passed across the placenta when the baby was in the womb. Likewise, children carry cells that were transferred to them in utero from their mothers - some of which might even be from the child's maternal grandmothers, older siblings or twin. These 'microchimeric' cells have been found in every organ that has been studied so far."

"Microchimeric cells were, we learn, discovered through a series of accidental observations. In the late 1800s, pathologist Georg Schmorl described 'giant cells' in the lungs of people who had died from eclampsia - a life-threatening inflammatory condition that can occur during pregnancy. These giant cells resembled the cells of the placenta, leading Schmorl to suggest that fetal cells passing into the bloodstream of mothers was the norm, rather than the exception."

"But they are also rare - much rarer, for example, than the trillions of microorganisms that reside in our guts, on our skin and in many other organs. We carry only one microchimeric cell for every 10,000 to 1 million of our own cells. In Hidden Guests, the author invites readers to learn about the pioneering "microchimerists" - scientists who discovered these fascinating shared cells."

Microchimeric cells are cells from another individual that persist in a person's body after being transferred during pregnancy. Mothers can carry cells originating from their biological children, and children can retain cells received in utero from their mothers, maternal grandmothers, older siblings or twins. Microchimeric cells have been detected in every organ examined but exist at very low frequency, roughly one per 10,000 to one million host cells. The phenomenon was identified through accidental observations, including late-1800s reports of placental-like 'giant cells' in eclamptic lungs and later cytogenetic detections of male chromosomes in pregnant individuals' blood. Microchimerism influences immunity, tissue repair, autoimmune risks, and raises questions about individual biological identity.

Read at Nature