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Some of our cells are outsiders — and they’re doing a lot inside our bodies

The nucleus is blue.
Courtesy of Dr. J. Lee Nelson and Coline Gentil
A visual of what microchimerism looks like. The cells with two green dots are of female, presumed maternal (XX) cells in male lung (XY). The male cells have a red and a green dot.

This story originally aired on January 25, 2020.

Not all of the cells in your body actually belong to you. Some cells might be from your mother, passed to you from when you were in utero. If you had children, their cells passed into your body the same way.

Researchers say that this can sometimes even be true for women who have a miscarriage in the second trimester or later, or who decided to terminate a pregnancy. 

This phenomenon is called microchimerism. So, what are these cells doing in our bodies? Scientists are just scratching the surface of this and what they are finding is incredibly fascinating.

Dr. J. Lee Nelson is a member of the Fred Hutchinson Cancer Research Center. She also is a professor of medicine in Rheumatology at the University of Washington. Nelson first became aware of microchimerism when she was studying medical cases involving pregnant women with rheumatoid arthritis.

For women with rheumatoid arthritis, an autoimmune disease, the painful condition often gets better or goes into remission when they are pregnant.

“And then shortly after they deliver it returns,” Nelson said.

Figuring out why this was happening and what potential role fetal cells were playing in the remission of rheumatoid arthritis in these women sparked Nelson’s curiosity.

It led her to wonder: what good, and what harm, could these outsider cells be doing? Apparently, even though they are small in number, these cells are doing a lot.

For example, researchers have found that women who have malaria when they are pregnant are more likely to have children who have an increased chance of being diagnosed with malaria. That doesn't sound good, right? However, researchers also have found these children are less likely to exhibit symptoms of the disease.

It’s as if the mother’s cells that are in the children are saying, “These mosquitoes are everywhere. I cannot protect you from this malaria, but let me show you how not to die,” Nelson said.

In this story, Sound Effect host Gabriel Spitzer and Dr. Nelson take a deep dive into the subject of microchimerism and explore the known benefits and a few downsides of this amazing and tiny transfer that our bodies perform.


Jennifer Wing is a former KNKX reporter and producer who worked on the show Sound Effect and Transmission podcast.
Gabriel Spitzer is a former KNKX reporter, producer and host who covered science and health and worked on the show Sound Effect.