A woman's cells may protect her child's organs throughout lifeThe Economist, 25 January 2007
interfere with their children's lives even more than most offspring
realise. That they nag about eating habits and short hemlines is well
known. What goes unnoticed is that mothers leave cells inside their
children's bodies, which may help with repairs when a child's own cells
This form of maternal meddling is called
microchimerism. A mother's cells can endure until a child reaches
adulthood and perhaps throughout life. But scientists do not know
exactly how common microchimerism is. It is detected more often in
people with autoimmune conditions, which has led to the suggestion that
the maternal cells could trigger those diseases. But healthy people
have them too, seemingly with no ill effects.
Lee Nelson, of the
University of Washington, in Seattle, suspects that everybody has a few
maternal cells. Her most recent work, published in the Proceedings of
the National Academy of Sciences, argues that, at least in some cases,
they help rather than harm. Her research consisted of two parts. In the
first, Dr Nelson and her colleagues took blood samples from three
groups of young volunteers and their mothers. The first group comprised
94 young volunteers who had type 1 diabetes; the second were 54 of
their healthy siblings; and a further 24 were children without diabetes
who were not related to anyone else in the study. The researchers then
compared DNA from the mothers and their children.
mothers pass copies of about half their genes to their children, some
genes in any child-mother pairs will be unique to the mother—those that
the child has not inherited from her. Others—versions of genes that
came from dad—will be unique to the child. Dr Nelson used the uniquely
maternal genes to find mothers' cells in the volunteers' blood. The
technique found maternal cells in about half the diabetics' samples,
but in only about one-third of the healthy siblings' samples and in
less than one-fifth of those from the unrelated volunteers. Moreover,
the microchimerism was not only more common but also more pronounced in
diabetics. Dr Nelson found that diabetics with maternal cells tended to
have more of them than did non-diabetics with maternal cells. Why?
the second half of the study, Dr Nelson examined the pancreatic tissue
of four dead boys, one of whom had been diabetic. Specialised cells
within that tissue, called islet beta cells, make insulin. Usually, by
the time diabetes is diagnosed most islet beta cells have stopped
working. Dr Nelson wanted to know whether maternal cells had made their
way to the pancreas, especially in the diabetic child, and, if so, what
they had done there.
To her surprise, she found female cells
(presumably from mother) in all four samples. Furthermore, these cells
had transformed themselves into the insulin-producing islet beta cells.
They also produced insulin, demonstrating that mothers do indeed
interfere at a cellular level.
Dr Nelson also looked for signs
that the maternal cells had caused the diabetes but found no evidence.
So, contrary to established opinion, she believes maternal cells can do
children good—and that there is no reason to think they do so only in
the pancreas. These cells may help any bodily organ work better, she
says, apart from the reproductive kind. Mothers' protective meddling
goes on—seen and unseen.