TSH AND TSH RECEPTOR ANTIBODY-BINDING SITES IN FIBROBLASTS OF PRETIBIAL MYXEDEMA ARE RELATED TO THE EXTRACELLULAR DOMAIN OF ENTIRE TSH RECEPTOR

The role of TSH receptor antibodies in the pathogenesis of pretibial m yxedema is still unclear. This study was designed to determine whether patients with pretibial myxedema had higher serum titers of TSH recep tor antibodies, and whether there were TSH and TSH receptor antibody-b inding sites on plasma membranes of fibroblasts derived from the skin of pretibial myxedema. If there were, were the binding sites similar t o the TSH receptor? The TSH receptor antibodies were determined with r adioreceptor assay in 20 normal subjects, 18 hyperthyroid Graves' dise ase patients without ophthalmopathy, 26 hyperthyroid Graves' disease p atients with ophthalmopathy, and 11 patients with pretibial myxedema a ssociated with Graves' ophthalmopathy. TSH and TSH receptor antibody-b inding sites were studied on plasma membranes of fibroblasts cultured from the skin of pretibial myxedema with radioreceptor assay. RNA was also extracted from the fibroblasts of pretibial myxedema and reverse transcribed using random primers as the primers for cDNA synthesis. Th e resulting cDNAs were subjected to amplification by polymerase chain reaction with the use of a set of primers spanning the 5' region (+256 /+275 and +616/+635) and the 3' region (+1819/+1838 and +2405/+2424) o f the TSH receptor cDNA(+1 transcription start codon). They were furth er identified by Southern blot hybridization, with the probe spanning the 5' region (+272/+612) and the 3' region (+1908/+2268) of the TSH r eceptor cDNA (+1 transcription start codon), and sequencing. The resul ts showed that patients with pretibial myxedema had higher titers of T SH receptor antibodies in the serum. TSH and TSH receptor antibody-bin ding sites were present on plasma membranes of fibroblasts derived fro m the skin of pretibial myxedema patients and related to the extracell ular domain of the TSH receptor. These data suggest a common antigenic site in the skin and in the thyroid as a putative target for TSH rece ptor antibodies or lymphocytes of Graves' disease. (C) 1994 Academic P ress, Inc.