125I uptake by FRTL5 cells: a screening test to detect pregnant women at risk of giving birth to hypothyroid infants.

Thyroid-growth-blocking antibodies are present in large proportion of mothers who give birth to hypothyroid infants. In order to devise a prenatal screening test to replace the time-consuming cytobiochemical assay for measurement of the maternal antibodies, a cloned rat-thyroid cell-line (FRTL5) was used. Several approaches that had been tried previously had proved fruitless--eg, in FRTL5 cells immunoglobulin of mothers of affected infants did not displace 125I-labelled TSH from its receptor, did not block TSH-induced increase of cyclic AMP, and did not block TSH-induced 3H-thymidine incorporation. By use of 125I uptake by the cells, mothers of the hypothyroid children were readily distinguished from normal female subjects and normal pregnant women.