CYTOCHEMICAL BIOASSAY FOR THYROID-STIMULATING ANTIBODY OF GRAVES-DISEASE - FURTHER EXPERIENCE

The cytochemical assay system for thyroid stimulators has labilization of lysosomal membrane as its end point. TSH and thyroid-stimulating antibody have previously been distinguished by using different times of tissue exposure (7 and 20 min, respectively). To clarify this distinction, serum immunoglobulin G (IgG) from nine patients with clinical Graves' disease were ranked, before being assayed in the cytochemical system, in order of their ability to stimulate cAMP production in the human thyroid. The response to higher concentrations of TSH than those routinely used in the assay was also investigated. All of the IgG tested showed a response at one or more concentrations (1.5 μg to 1.5 mg/ml). The magnitude was dependent on both the duration of exposure and the concentration; 1.5 mg/ml higher ranked IgG showed maximum activity as early as 3 min but no apparent activity at 20 min. With the highest ranked IgG, there was a negative dose-response relationship at both times of exposure and activity was greater at 7 min than at 20 min. Less potent IgG showed biphasic dose-related responses at 20 min (e.g. the response to 0.15 mg/ml was greater than that to either 0.015 or 1.5 mg/ml) and lower activity at one or more concentrations with a 7-min exposure. The two least potent IgG preparations gave responses at 20 min that were not dose related. One IgG preparation was negative in the cAMP assay but showed significant cytochemical responses at three of the concentrations tested with a 20-min exposure of tissue. TSH concentrations of 10 and 1 μU/ml elicited maximum responses at 3 and 6 min, respectively. These data indicate that for each IgG preparation tested by the cytochemical assay system, the concentration of protein is important and a dose-response relationship must be established. To differentiate between TSH and thyroid-stimulating antibody, it is essential that the responses to two dilutions of the test sample are parallel to those of standard TSH before assuming the activity is due to TSH. © 1979 by The Endocrine Society.