Article révisé par les pairs
Résumé : Since the binding sites of hormone receptors may be similar to those of antihormone antibodies, we wondered whether the former might not be recognized by the idiotypic network. To test this hypothesis we investigated the interaction of plasma immunoglobulin G (IgG) with the binding sites of estrogen receptors (ER) from uterine or mammary tissue. Using ER isolated from uterine cytosol we found that IgG from normal subjects shifted the position of purified receptor in sucrose gradients and displaced [3H]estradiol (E2) from its receptor-binding sites. Equilibrium studies revealed competitive inhibition by IgG of E2 binding to the ER. IgG isolated by adsorption on a rat uterine cytosol-Blue B matrix gel column also bound to the ER, and this binding was inhibited by an excess of E2. After an 18-h exposure of MCF-7 mammary carcinoma cells in monolayer culture to IgG (2 mg/ml), Scatchard analysis of [3H]E2 binding revealed a reproducible decrease in the available receptor sites from 2.52 +/- 0.56 (+/- SEM) to 0.68 +/- 0.48 fmol/microgram DNA (n = 10). This effect was selective, since enriched anti-ER IgG obtained by adsorption on purified receptor was 20 times more potent than total IgG, whereas IgG identically prepared but not retained by affinity chromatography had no activity. Exposure of the cells to the IgG for 45 min also revealed, as with isolated ER, specific competition of the IgG with E2 for the E2-binding sites; the Kd increased from 10.5 +/- 1.6 to 27.5 +/- 7.2 X 10(-11) M (n = 7). Enriched antireceptor IgG was a 20 times more effective competitor, and the IgG not retained by affinity chromatography had no activity. In conclusion, our observations indicate the presence of ER on the cell surface, interaction of ER with IgG from plasma of normal subjects, and competitive antagonism of these IgG with E2 uptake leading to a decrease in effective ER concentrations.