Thyroid hormone binding to putative nuclear receptors in human mononuclear blood cells

Nuclear protein extracts from mononuclear cells in normal subjects, subjects with the clinical syndrome of thyroid hormone resistance and cultured B lymphocytes bound thyroxine (T4) Ka; 1 . 3-3 . 5 X 10(9) m-1) and triiodothyronine (T3) (Ka; 1 . 2-3 . 9 X 10(9) m-1) with similar affinities. When an extra wash step was introduced, the maximum specific binding of T4 and T3 was reduced by 75% and binding was abolished by three washes. These data suggest binding is to a serum protein contaminant present in the mononuclear cell preparation.