Mothers could be unwittingly responsible for their offspring suffering some types of autoimmune diseases.

Autoimmune diseases are caused by the body attacking itself - immune cells think the body's own tissue is foreign and seek to eradicate it.

Cells that cause autoimmune diseases could be transferred to unborn children in the womb, researchers have found.

The scientists suspect they then linger in the baby's system and cause such diseases later in life.

The researchers also found that foetuses may pass on cells that trigger such diseases to the mother.

The research is being presented at the Experimental Biology '99 meeting in Washington DC, and is reported in New Scientist magazine.

Immune system reaction

The process by which autoimmune diseases work is similar to the reaction a host body when it rejects a transplanted organ.

Researchers used genetic tests to identify maternal cells

They are also more common in women.

This has led researchers to speculate that a process called microchimerism is involved in their development.

Microchimerism is when small numbers of another person's cells live in the body.

A 1997 study in Boston found that cells from a foetus can survive in a woman for up to 27 years after pregnancy.

Since then other studies have connected autoimmune diseases such as scleroderma seem to have an unusually high incidence of microchimerism.

Scleroderma causes the skin to become thick and leathery and can damage internal organs.

In one study, 32 out of 69 women with the condition had male cells in their system. This compared to one woman in 25 who did not have it.

Men suffer too

However, the flaw in this theory is that - although it is rarer - men get autoimmune diseases too.

A blood test revealed the presence of female cells in a man

The new research, led by J. Lee Nelson and colleagues at the University of Washington in Seattle, could resolve the conundrum.

It found that cells from the mother can cross into the baby and remain there for decades.

The researchers used the polymerase chain reaction (PCR) technique to gather genetic evidence.

A PCR multiplies genetic material until there is enough of it for scientists to examine.

The researchers studied a 47-year-old man with scleroderma.

They were searching for the gene for a molecule that was found on his mother's cells but not his own - and found it.

Mother's cells were present

They also looked at blood from a 15-year-old boy suffering lupus.

Lupus is another autoimmune disease, that attacks the skin and internal organs.

In the blood test they found female cells, and using a PCR they were able to confirm it was from the boy's mother.

Dr Nelson told New Scientist 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 said.