ABSTRACT
Background : Thyroid stimulating antibodies result in the development of hyperthyroidism and goiter in Graves disease. However, thyroid stimulating antibody activities do not correlate with the clinical features in many patients with Graves disease. The purpose of this study is to address this discrepancy between thyroid stimulating antibody activities and clinical features of Graves patients. Methods: We measured thyroid stimulating antibody activities simultaneously using human TSH receptor transfected Chinese hamster(hTSHR-CHO) cells and rat thyroid(FRTL-5) cells in 57 untreated patients with Graves disease, and compared their activities with clinical features including thyroid hormone levels. Results : The detection rate of thyroid stimulating antibody measured by hTSHR-CHO cells was 90% in 57 untreated Graves patients and it was higher than that measured by FRTL-5 cells. Thyroid stimulating antibody activity by hTSHR-CHO cells was significantly correlated with that by FRTL-5 cells(r=0.5, p<0.001), however, 18 of 57(32%) patients showed marked discrepancy of thyroid stimulating antibody activity between in hTSHR-CHO and FRTL-5 systems. Thyroid stimulating antibody activity measured by hTSHR-CHO cells was significantly correlated with serum total T3, free T4 levels, and goiter size but not 99mTc-thyroid uptake. On the other hand, thyroid stimulating antibody activity measured by FRTL-5 cells was significantly correlated with goiter size and 99mTc-thyroid uptake but not thyroid hormone levels. The difference between function and goiter size with respect to thyroid stimulating antibody measurement in two cells system is, nevertheless, particularly evident in the free T4/goiter ratio in patients with high hTSHR-CHO and low FRTL-5 cell assay values. Conclusion: These findings suggest that thyroid stimulating antibodies in Graves disease are heterogeneous population in terms of responses to different origin of cells. Further, thyroid stimulating antibody activities measured by FRTL-5 cells tend to correlate better with goiter size and Tc-thyroid uptake, whereas thyroid stimulating antibody activities measured by hTSH-CHO cells correlate better with thyroid hormone levels.
