Women May Keep Fetal Cells From Past Pregnancies
Talk about never being free of your kids: New research shows that fetal cells from a years-ago pregnancy can persist in a woman’s body and sometimes may cause disease.
According to studies being done at the Tufts University Medical School in Boston, thyroid disorders such as tumors are often made up of foreign cells, apparently fetal cells that remain alive in the women’s bodies for decades. In one recent case, whole sections of one woman’s thyroid gland were entirely male--a contribution probably left by her son, who was born in 1967.
“Over half of the women with thyroid disease had evidence of fetal cells in their thyroid biopsies,” Diane Bianchi and her colleagues reported at the 50th annual meeting of the American Society of Human Genetics. And finding the one 54-year-old woman with large chunks of male tissue in her gland implies that “a fetal stem cell from her son had differentiated into mature thyroid tissue.” Stem cells--which can mature into various types of tissue in the body--are now the focus of intense research interest in biomedicine.
Stem cells eventually may be used to grow and replace damaged body parts, such as brain tissue or bone marrow.
Except for the presence of the Y chromosome in the male cells, the woman’s two types of thyroid tissue--male and female--essentially looked the same. But she was having thyroid trouble and was undergoing surgery to remove the gland because it contained enlarging thyroid goiters.
A member of the research team, Sumathi Srivatsa, explained at the conference that the studies were being done to explain why women seem to be at more risk than men for some diseases, such as autoimmune disorders like scleroderma and lupus. Women also seem more susceptible to thyroid tumors, adenomas and carcinomas.
“One in four women develops some form of thyroid disease over her lifetime,” the researchers said. “We have been investigating the role of fetal-cell microchimerism and its association with disease.” The term microchimerism refers to the survival and growth of foreign cells in a host organism. The Greeks used the word “chimera” to describe mythical beasts made up of different animals, such as a lion with horses’ hooves. Usually, the growth of foreign cells in someone’s body is impossible because they are quickly killed off, rejected by the immune system. But somehow a few fetal cells seem able to persist in mothers.
Srivatsa explained that it has been known for more than a century that small numbers of fetal cells can get into the mother’s bloodstream during pregnancy, or during a difficult birth. Their research suggests that most fetal cells are routinely eliminated soon after they enter the mother’s bloodstream. They essentially commit suicide, a vital process called apoptosis. But now it seems that fetal cells are more likely to survive if the mother has experienced difficulty giving birth.
The researchers also found that women who were not experiencing thyroid problems did not show signs of fetal cells being present. This, too, suggests that invasion of the thyroid gland by cells from the fetus is likely to cause, or at least influence, the disorders.
In their study, the Boston team examined the tissues taken during thyrectomies done on 29 women. They used screening techniques that allowed them to spot the male Y chromosome in mixtures of the mother’s cells and the son’s cells. The cells that contain Y chromosomes are the male cells. In addition, the researchers did similar studies on thyroid tissues taken from seven autopsy cases.
In many of the tissues they studied, Srivatsa said, clumps of male cells could be seen living among the far larger numbers of female cells in the women’s thyroid glands. On average, the male clumps each contained eight to 10 cells, and more than half of the women had male cells in their thyroid glands.
One possible alternative source of male cells, rather than from the fetus, would be via blood transfusions, Srivatsa said. But only three of the women in the study had ever been transfused.
