A MOTHER鈥橲 work is never done, it seems. If a child develops diabetes, maternal cells that sneaked in while the child was in the womb may help to fight the disease. The borrowed cells don鈥檛 appear to trigger an immune reaction, so they could some day be used therapeutically, the researchers suggest.
Instances in which cells from pregnant women have been incorporated into their offspring have been reported sporadically over the past two decades. The condition, which is known as maternal microchimerism, has been seen in children with severe combined immunodeficiency 鈥� a disorder characterised by little or no immune response 鈥� and the autoimmune disease neonatal lupus. Maternal cells have also been detected in cord blood samples and in healthy adults. It used to be thought that the rogue maternal cells simply appeared randomly, or that they might even trigger autoimmune diseases (New 杏吧原创, 24 April 1999, p 4), but Lee Nelson at the Fred Hutchinson Cancer Research Center in Seattle, Washington, now disputes that.
Nelson and her colleagues looked at DNA from blood samples taken from 94 people with type 1 diabetes and 54 of their healthy siblings, along with 24 healthy people plus all their mothers. This allowed them to pinpoint genes the children did not share with their mothers, and also to detect what proportion of cells from a sample of about 150,000 from each individual had been borrowed from the mother.
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Of people with type 1 diabetes, 51 per cent had maternal cells in their blood, as did 33 per cent of their siblings and 17 per cent of the healthy controls. Individuals with type 1 diabetes also tended to have more of these cells 鈥� sometimes numbering in the hundreds per sample 鈥� whereas in siblings and controls there were typically fewer than 10. Nelson suspects that if larger blood samples were taken, evidence of maternal microchimerism might be found in us all. 鈥淚t鈥檚 probably universal,鈥� she says.
鈥淚f a large enough sample were taken, it might show that everyone carries some of their mother鈥檚 cells with them鈥�
The fact that significantly more maternal cells were found in people with diabetes raises the question of what role, if any, they play in the disease. To investigate, the researchers studied tissue from the pancreas because a malfunction of the pancreas鈥檚 insulin-producing islet cells leads to diabetes. To see whether any maternal cells present there were interacting with islet cells they looked at autopsy samples from four young males, including one boy who had had type 1 diabetes. By labelling the X and Y chromosomes they were able to spot any female islet cells among the boys鈥� own. This showed that while all four samples contained islet cells derived from maternal cells, the sample from the boy with diabetes had the most (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0606169104).
Nelson鈥檚 team found no evidence that the maternal cells were provoking an immune response. 鈥淚f maternal cells were being attacked, I鈥檇 expect to see inflammatory cells around them,鈥� she says. 鈥淚 didn鈥檛.鈥�
The fact that the maternal cells were apparently replicating, especially in the pancreatic tissue from the boy with diabetes, suggests that they might be playing some positive role. 鈥淚t is likely the cells are helping to regenerate the tissue,鈥� says Nelson.
Anne Croy at Queen鈥檚 University in Kingston, Canada, who also studies maternal microchimerism, says she is intrigued by the idea that maternal cells may have a beneficial role.
One possible implication of the finding is that maternal cells could be isolated and used to treat any of a mother鈥檚 children who develop diabetes. 鈥淭here does seem to be some kind of [immune] tolerance to the cells,鈥� says Nelson. However, this idea is not accepted by all. Carol Artlett at Drexel University College of Medicine in Philadelphia, Pennsylvania, calls it 鈥減ie in the sky鈥�. There鈥檚 no reason to think maternal cells will be better tolerated than any other foreign cells, she says. Perhaps there are just so few cells that they don鈥檛 raise the alarm.
