Autoimmune diseases, in which the body attacks its own tissues, may in some cases be triggered by cells from your mother that have been lurking within you since you were in the womb. Researchers also have evidence that women may contract autoimmune diseases because of cells from their fetuses that persisted for decades after crossing the placenta.
Many autoimmune conditions appear similar to graft versus host disease, in which cells from a transplanted organ mount an immune response against the host. That has led some researchers to speculate that microchimerism-a condition in which small numbers of another person's cells persist in the body-could be involved in some cases of autoimmunity. The idea is bolstered by the fact that autoimmune diseases are more common in women, who may be repeatedly exposed to their fetuses' cells while pregnant.
Two years ago, researchers in Boston made the surprising discovery that fetal cells can survive in a woman for as long as 27 years after her last pregnancy. Since then, other studies have shown that women with autoimmune diseases such as scleroderma, which causes the skin to become thick and leathery and can damage internal organs, seem to have an unusually high incidence of microchimerism.
In one study, male cells were detected in 32 out of 69 women with scleroderma, but just one out of 25 women who did not have the disease. Women with scleroderma and microchimerism also seem to have ten or more times as many foreign cells in their bodies as women with microchimerism who are not suffering from any autoimmune disease.
The problem with the theory has been that men get autoimmune diseases too. But this week, at the Experimental Biology '99 meeting in Washington DC, researchers announced that maternal cells can also cross over to fetuses and survive for decades.
J. Lee Nelson and her colleagues at the University of Washington in Seattle hunted for maternal cells in a 47-year-old man with scleroderma, using the polymerase chain reaction (PCR) to search for the gene for a molecule found on the surface of his mother's cells but not his own. Sure enough, they found maternal cells.
The researchers also looked at blood from a 15-year-old boy with lupus, another autoimmune disease that attacks the skin and internal organs, using a technique that stains X chromosomes one colour and Y chromosomes another. They were able to find a female cell, which has two X chromosomes, and using PCR they confirmed that it came from the boy's mother.
Nelson admits that she is still some way from proving that maternal cells can trigger autoimmunity. "But I think they're likely to be a significant piece of the puzzle," she says. Antony Rosen, an expert on autoimmunity at Johns Hopkins University in Baltimore, says: "It's at that stage where the hypothesis is reasonable and the preliminary data are supportive. But you can't get unequivocal data in a minute."
Carol Artlett of Thomas Jefferson University in Philadelphia, who has found maternal cells in five out of eight men suffering from scleroderma, says that microchimerism cannot be the whole story, as it can occur in people without autoimmune disease. Artlett suggests that autoimmunity can arise when a trigger such as a viral infection spurs the foreign cells to begin attacking their host. This reaction disrupts the host's immune system so that it joins the attack against the body's own tissues, she believes.
Author: Nell Boyce, Washington DC
New Scientist issue 24th April 1999
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