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Why the Body Attacks Itself

Autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis, lupus, fibromyalgia and some types of asthma, are among the most mysterious of human maladies. Why do our bodies suddenly attack and destroy themselves?

Scientists now say that the trigger may be two generations of "foreign" cells in a mother's body, and that this may explain why these diseases attack three times as many women as men.

The first foreign cells are picked up when a fetus shares blood with its mother. When that fetus is born, grows up and becomes pregnant herself, a second set of cells infiltrates her body from her own unborn baby.

Autoimmune symptoms usually appear during and after the reproductive years, so J. Lee Nelson, of the Fred Hutchinson Research Center in Seattle, decided to examine mothers who had the autoimmune disease systemic sclerosis.

She found that women with the disease had 20 times more fetal cells in their blood than those who did not have the disease. These fetal cells persisted in the mothers' blood for decades after the birth of their children.

Nelson examined the surface proteins on the fetal cells, called HLAs, which the immune system uses to distinguish its own cells from others. She found that if the mother matched some of her child's HLA, she had 9 times more risk of contracting the disease. She thinks this is because the cells escapebeing destroyed by the mother's immune system right away, but trigger a stronger attack later on.

She realized that a mother might also be carrying cells from her own mother, setting up a possible 3-generation clash of HLA types, and found that a close match between the HLA of a grandmother and the child further increases the mother's disease risk.

"It's a war across generations that takes its toll on the body," Nelson says.

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