Incidence and Specificities of Labeled Thyrotropic Hormone (TSH) Binding Immunoglobulins (LTB-Igs) in Patients with Graves' Disease and Other Thyroid Disorders

Abstract

Using [125I] bTSH, labeled TSH binding (LTB) in sera from 203 patients with various thyroid disorders was studied. Four of them with known potent anti-TSH antibody showed extremely high LTB, as has been reported previously. Excluding these 4 sera, the mean ± s.d. of serum LTB from 199 patients was calculated to be 8.6 ± 2.1%. LTB exceeding 10.7% (mean + 1 s.d.) was observed in 16 sera; these weretaken as increased. LTB measured by polyethyleneglycol (PEG) precipitation correlated significantly with the serum IgG concentration; however, sera with increased LTB had high values irrespective of the serum IgG concentration. Specificities of increased LTB in 13 sera were further analyzed by means of binding to Protein A-sepharose and displacement studies using bTSH and nonradioactively iodinated bTSH. A significant correlation was observed between the LTB obtained by PEG and those by Protein A-sephrose. BTSH specificity was confirmed in 5 of the 13 sera; 7 of the remaining 8 sera showed displacement only by iodinated bTSH. None of the control Graves' sera showed any significant displacement. Comparisons of the results of measurement of LTB by Protein A-sephrose and those by the displacement studies disclosed that most of displaced sera had increased LTB to the IgG fraction. Disease distributions of 203 overall cases and 20 increased LTB cases revealed that apparently higher incidence (22.9%) of increased LTB in untreated Graves' patients than the others, though some increased LTB cases were also observed in patients with inactive Graves' or other thyroid disorders. In conclusion, increased LTB was observed in sera from approximately 10% of the patients with various thyroid disorders; most of them were found to be specific to either bTSH or iodinated bTSH. A frequent association of increased LTB with active Graves disease suggests a significance of these antibody like products to the disease process.