Fetal cells pop up in mom's thyroid.

For about a decade, Diana W. Bianchi of the New England Medical Center in Boston has pursued the idea that fetal cells persist in mothers long after pregnancies and perhaps eventually trigger autoimmune disorders (SN: 8/2/97, p. 71). Now, there's evidence from her group that lingering fetal cells play a role in thyroid disease--but whether the cells harm or heal the thyroid gland remains an open question.

Women suffer autoimmune disorders much more frequently than men do, which is one reason Bianchi has studied long-lasting fetal cells. Thyroid diseases also afflict women more often than men and can worsen after pregnancies. So, Bianchi's team looked for fetal cells in thyroid tissue from women who had had various thyroid diseases--including goiter, cancer, and thyroiditis--and had the gland removed. As in their past work, the investigators searched for cells with a Y chromosome, which presumably derived from male fetuses the women had carried.

There were male cells in the tissue samples of 16 out of 29 women with thyroid disease, but no evidence of such fetal cells in autopsy tissue from seven women with no thyroid problems, Bianchi's colleague Bharath Srivatsa reports. In one woman, several portions of her thyroid gland were composed entirely of male cells that looked identical to normal thyroid cells.

That suggests that the persisting fetal cells can even mature into specialized tissues, says Srivatsa. Since fetal cells showed up in the thyroid glands of women whose thyroid disease wasn't autoimmune in nature, the investigators speculate that the cells may have tried to help repair the gland.