VISUALIZATION OF THE THYROTROPIN RECEPTOR ON THE CELL-SURFACE BY POTENT AUTOANTIBODIES

In autoimmune thyroid disease there are various autoantibodies (Ab) to thyroid cell components. Among the best characterized are those to th yroid peroxidase (TPOAb) and to the thyrotropin receptor (TRAb). While TPOAb were successfully used to visualize TPO in human thyroid cells (HTC) and a rat thyroid cell line (FRTL5) by indirect immunofluorescen ce (IFL), similar attempts with TRAb and thyrotropin receptor (TSHR) f ailed. This could have been due to either relatively low serum levels of TRAb and/or low number of TSHR on thyroid cells. To test these hypo theses, we estimated the number of TSH binding sites on HTC, FRTL5 and Chinese hamster ovary (CHO) cells, transfected with cloned human TSHR (JP-26 cells), and for IFL staining employed 3 sera with the highest potency TRAb in our possession. A clear granular surface staining was detected on all 3 cell types with two sera; with the third, the least potent, no staining was seen. The density of staining paralleled the e stimated number of TSHR per cell, i.e., JP-26 > FRTL5 > HTC. TSHR was also visualized on transiently transfected cells (COS-7-TSHR), facilit ating quantitation of transfection. Our results suggest that the limit ing factor in direct visualization of the TSHR is the TRAb concentrati on.