INDUCTION OF TSH BINDING INHIBITORY IMMUNOGLOBULINS WITH THE EXTRACELLULAR DOMAIN OF HUMAN THYROTROPIN RECEPTOR PRODUCED USING BACULOVIRUS EXPRESSION SYSTEM

A cDNA encoding the extracellular domain of human TSHr (ETSHr) was exp ressed in large quantities using the baculovirus expression system. Ma ximum level of protein was produced at 60 hr post-infection and repres ented approximately 20% of the total cellular protein. The identity of the protein as ETSHr was confirmed by Western blot using antibodies t o synthetic peptides derived from the TSHr. The protein has an apparen t molecular weight of 50 kDa and is larger than the predicted size of 44 kDa, suggesting that the protein is glycosylated. Polyclonal antibo dies raised in rabbits against gel purified ETSHr blocked the binding of I-125-TSH to native TSHr in solubilized porcine thyroid membranes i n a radioreceptor assay. The availability of this antigenically active protein will facilitate further characterization of the protein and a nalysis of immune response against TSHr in experimental animals as wel l as in patients with autoimmune Graves' disease.