Millions of our mothers’ cells continue to exist within our bodies. American researchers have explained how this is possible.
Approximately one in a million of our cells (a tiny fraction) is actually not our own but comes from our . This means that each of us carries millions of cells that our immune system typically recognizes as foreign; however, somehow, in most of us, they coexist peacefully without causing any issues for the immune system.
Recently, immunologists uncovered the reason behind this phenomenon. A small number of maternal immune cells that penetrate the placenta during pregnancy actively train the fetus’s immune system to recognize maternal cells throughout its life.
The exchange of cells between mother and fetus—known as microchimerism—is a well-documented phenomenon that scientists have been aware of for over half a century. It is bidirectional: every woman who has ever been pregnant retains cells from her fetus, and every person retains cells from their mother.
These residual cells pose a mystery for immunology. It has always been believed that the immune system should attack foreign .
What Did the Scientists Discover?
A team of researchers led by pediatric infectious disease specialist Sing Sing Wei from Cincinnati Children’s Hospital Medical Center set out to determine how foreign maternal cells influence the development of the and what role they play in shaping the fetus’s immune system.
The scientists studied maternal microchimerism in mice, as reported by Science Alert. First, the team bred mice with immune cells modified to express specific surface markers. This allowed them to selectively remove these cells and check whether immune tolerance was maintained.
And that’s where things got interesting. A small subgroup of maternal immune cells, possessing properties similar to myeloid bone marrow cells and dendritic cells, persisted in the body long after birth. They were also closely linked to both immune activity and the expansion of regulatory T cells (the ones that inform the immune system that everything is okay).
To confirm their findings, the researchers selectively removed these specific maternal cells in the offspring of the mice. The results were striking. Regulatory T cells disappeared, and so did the immune tolerance to maternal cells.
This suggests that lifelong tolerance to maternal microchimeric cells likely depends solely on this tiny subgroup. If they are eliminated, it is likely to result in immune chaos. It also indicates that immune tolerance must be actively and continuously maintained; it is not a one-time process that occurs only during pregnancy.
The researchers also focused on diseases and conditions associated with microchimerism. “The new tools we developed to study these cells will help scientists accurately determine what these cells do and how they function in various contexts, such as autoimmune diseases, cancer, and neurological disorders,” noted Dr. Wei.
“Microchimerism is increasingly linked to many diseases. This research provides scientists with a convenient platform to explore whether these rare cells are the cause of diseases,” he added.
The study’s results were published in the journal Immunity.
Photo: Unsplash
