Characterization of Monoclonal Antibodies Raised against Solubilized Thyrotropin Receptors in a Cytochemical Bioassay for Thyroid Stimulators

Selected clones of monoclonal antibodies from mice immunized with solubilized preparations of bovine TSH receptors have been characterized in a cytochemical bioassay (CBA) for thyroid stimulators. This assay is based upon quantification of changes in naphthylamidase activity of sections of guinea pig thyroids with use of a chromogenic substrate. Monoclonal 22A6 is a thyroid-stimulating antibody directed at a site within the TSH receptor. Thus, although it is a weak inhibitor of 125I-TSH binding to thyroid membranes, 22A6 is inhibited from binding to membranes by TSH, exhibits a more than additive agonist effect on adenylate cyclase activity when tested at low TSH concentrations in thyroid cells, and is a competitive antagonist of TSH enhancement of adenylate cyclase activity at high TSH concentrations. In the CBA, 22A6 is a stimulator whose maximal activity is obtained with 77 pg/ml (3-min exposure). Dose-response curves of a long acting thyroid stimulator (LATS)-B standard and 22A6 have slopes which are ...