All human beings are not entirely just themselves. In part, they are also the woman who gave birth to them.
A small fraction of our cells — about one in every million — are not actually ours, but come from our mothers.
This means that each of us has millions of cells that our immune system would normally recognize as foreign. Yet somehow, in most of us, they remain peacefully without causing any immune problems.
Naked study recently in Immunitya group of immunologists discovered why.
As explained by , a small number of maternal immune cells that cross the placenta during pregnancy actively train the fetus’ immune system to tolerate the mother’s cells throughout life.
The exchange of cells between a mother and a fetus is a well-documented phenomenon, known to scientists for more than 50 years. It’s called microchimerism and it goes both ways: all women who have ever been pregnant retain cells from their fetus, and all humans retain cells from their mother.
These persistent cells represent a conundrum for immunology, which is based on the idea that the immune system must launch an attack against foreign cells.
The team at Cincinnati Children’s Hospital Medical Center wanted to better understand how these foreign maternal cells keep the immune system in check and what role they play in shaping the fetus’ immune system.
To find out, the researchers bred mice with immune cells genetically modified to express specific markers on the cell surface. This allowed researchers to selectively eliminate these cells and observe whether immune tolerance was maintained or not.
“This is where things became fascinating”, says Science Alert.
A small subset of maternal immune cellswith properties similar to those of bone marrow myeloid cells and dendritic cells, persisted long after birth.
These cells were also strongly associated with both immune activity and the expansion of regulatory T cells — the cells that tell the immune system that everything is in order.
To confirm, the researchers then proceeded to selectively eliminate these specific maternal cells in the offspring mice. Result: regulatory T cells disappeared, and immune tolerance to maternal cells disappeared.
The conclusion is that the Lifelong tolerance to maternal microchimeric cells probably depends only on a small subset of maternal cells. Remove these cells, and immune chaos is likely to ensue.
