Thyroid-Stimulating Monoclonal Antibodies

Thyrotropin (TSH) receptor monoclonal antibodies (TSHR mAbs) were obtained from cDNA-immunized NMRI mice. Three mAb immunoglobulin Gs (IgGs) (TSmAbs 1-3) that had distinct V H and V L region sequences stimulated cyclic adenosine monophosphate (cAMP) production in isolated porcine thyroid cells greater than 10× basal and as little as 20 ng/mL (0.13 nmol/L) of TSmAb 1 IgG caused a 2× basal stimulation. TSmAb 1 and 2 Fab fragments were also effective stimulators and thyroid-stimulating activities of the IgGs and Fabs were confirmed using TSHR transfected Chinese hamster ovary (CHO) cells. The TSmAbs also inhibited 125 I-labeled TSH binding to TSHR-coated tubes by 50% or more at concentrations of 1 μg/mL or less and gave 15%-20% inhibition at 20-50 ng/mL. 125 I-labeled TSmAbs bound to TSHR-coated tubes with high affinity (~10 10 L/mol) and this binding was inhibited by TSHR autoantibodies with both TSH agonist and antagonist activities. Inhibition of labeled TSmAb binding by Graves' sera correlated well with inhibition of TSH binding ( r = 0.96; n = 18; p < 0.001 for TSmAb 2). The TSmAbs have considerable potential as (1) new probes for TSHR structure-function studies, (2) reagents for new assays for TSHR autoantibodies, and (3) alternatives to recombinant TSH in various in vivo applications.