Specific binding of 17 beta-estradiol in the human thymus

Many observations suggest that estrogenic preparations can depress cell-mediated immune reactions. Since cell-mediated immunity is thymus-dependent, the estrogen-binding properties of human and mouse thymus tissue were studied with the use of an aqueous two-phase separation system. A high-affinity and low-capacity estrogen binding was found in human thymus tissue from six prepubertal children of both sexes and two grown women. A similar specific binding was found in the mouse thymus and in the human uterus. The association constant (Ka) for the binding in the human thymus was 16.01 +/- 8.98 X 10(9)M-1. The human uterus, which is known to possess estrogen receptors, had Ka values in the same range. The binding seems to be located in the reticuloepithelial cells of the thymus. Data suggest that the human thymus is a target organ for estrogens, which may influence lymphocyte function during therapy.