Estrophilin: Pro and anti

Antibodies to the estrogen-receptor protein (estrophilin) of calf uterus have been prepared in the rabbit, the goat and two strains of rat. Because these antibodies react with the receptor without preventing or displacing estradiol binding, antibody-antigen interaction is demonstrated and studied conveniently by its effect on the gel filtration and sedimentation properties of estrophilin, using radioactive estradiol as a marker. Antibodies to the nuclear form of calf uterine estrophilin produced in the rabbit and the goat cross react with nuclear as well as extranuclear estradiol-receptor complexes from reproductive tissues of every species tested; antiestrophilin obtained recently in the ACI rat appears similarly cross reactive. In contrast, antiestrophilin generated in the Lewis rat reacted only with receptor from calf uterus. Polyethylene glycol-mediated fusion of spleen cells from the immunized Lewis rat with three different mouse myeloma lines produced viable hybridoma cultures yielding monoclonal hybridoma cell lines secreting either rat IgG or IgM. which react specifically with calf uterine estrophilin. Production and cloning of hybridomas derived from spleen cells of the ACI rat, in an attempt to obtain cross reacting monoclonal antibody, are in progress. This assortment of either cross reacting or species-specific antibodies to estrophilin, especially those produced by monoclonal hybridomas, offers immunochemical approaches to receptor assay and purification as well as novel probes of receptor structure and function, including the question of whether estrophilin is synthesized in target cells by way of a proestrophilin incapable of binding steroid.