Background: Some so-called autoimmune diseases in women might be alloimmune and represent a chronic graft-versus-host response attributable to transplacentally acquired fetal cells. Thyroid disease is more common in women than men, and post partum exacerbation of thyroiditis is common. Our aim was to investigate whether there is an association between fetal cell microchimerism and thyroid disease in women.
Methods: Surgical specimens were obtained from 29 women who underwent thyroidectomy for various thyroid disorders. Control specimens were taken from clinically and histologically normal thyroids obtained at necropsy from eight women who died from unrelated conditions. Medical records and pregnancy histories were reviewed. Fluorescence in-situ hybridisation analysis was done with probes specific for X and Y chromosomes. Slides were examined with a fluorescence microscope to detect the presence of male cells-with one X and one Y signal in the nucleus-among maternal cells containing two X signals.
Findings: Male cells were seen in thyroid sections from 16 patients but not in those from controls (p=0.01). Male cells (1-165 per slide) were seen individually or in clusters in all thyroid diseases and were not restricted to inflammatory thyroid diseases. In one patient with a progressively enlarging goitre, we noted fully differentiated male thyroid follicles closely attached to and indistinguishable from the rest of the thyroid.
Interpretation: Our findings suggest a relation between fetal cell microchimerism and thyroid disease. Furthermore, fetal stem cells might be capable of differentiation into mature thyroid follicles in their mothers with favourable environmental and developmental factors.