Characterization of an antiidiotypic antibody mimicking the actions of estradiol and its interaction with estrogen receptors

Abstract

The ability of a monoclonal antiidiotypic antibody (clone ID5) directed against the binding site of a monoclonal antiestradiol antibody to interact with the estrogen receptor (ER) was investigated. The following lines of evidence indicate that clone ID5 has the capacity of mimicking the actions of estradiol, and recognizes ER: 1) in binding experiments, clone ID5 inhibited the binding of [3H]estradiol to porcine cytosolic 32-kilodalton ER fragment in a dose-dependent manner; irrelevant antibody had no effect; 2) in sucrose gradient density analysis, clone ID5 abolished the specific peak of the [3H] estradiol-ER complex in the 4S region; 3) in immunoprecipitation experiments, clone ID5 interacted with unoccupied ER, but not with estradiol-occupied ER; 4) in direct immunofluorescence studies clone ID5 stained the nuclei of cultured rat epithelial cells and recognized estrogen binding sites in nuclear cryostat sections prepared from human, rat, and mouse estrogen-responsive tissues; and 5) When clone ID5 was injected to immature female rats, it caused 46% increase in uterine creatine kinase activity, suggesting that clone ID5 may possess estrogenic like activity. Under the same experimental conditions, estradiol caused 58% increase in creatine kinase activity. Collectively, these results suggest that clone ID5 interacts with the steroid binding site of ER. Therefore, clone ID5 can serve as a tool in the study of function and structure relationship of ER and to detect changes of ER levels in target cells of various species.