There are two types of TSH receptor antibodies (TRAb); thyroid stimulating antibody
(TSAb) and TSH-stimulation blocking antibody (TSBAb). TSAb causes Graves’ hyperthyroidism.
TSBAb causes hypothyroidism. Both TSAb and TSBAb block TSH-binding to thyroid cells
as TSH receptor antibodies (TRAb). TSBAb-positive patients with hypothyroidism and
Graves’ patients with hyperthyroidism may have both TSBAb and TSAb. We studied TSBAb
and TSAb in 43 TSBAb-positive patients with hypothyroidism and in 55 untreated Graves'
patients with hyperthyroidism. TSBAb-activities were expressed as percentage inhibition
of bovine (b) TSH-stimulated cAMP production by test IgG. Two formulas were used to
calculate TSBAb-activities; TSBAb-A (%) = [1 - (c - b)/(a - b)] × 100 and TSBAb-B
(%) = [1 - (c - d)/(a - b)] × 100, where a: cAMP generated in the presence of normal
IgG and bTSH, b: cAMP generated in the presence of normal IgG, c: cAMP generated in
the presence of test IgG and bTSH, and d: cAMP generated in the presence of test IgG.
TSAb (%) = [d/b] × 100. All of the 43 TSBAb-positive patients with hypothyroidism
had strongly positive TSBAb-A and -B. Some of them had weakly positive TSAb (< 240
%). All 55 untreated Graves’ patients had positive TSAb (205 - 2509 %). Some of them
had both TSAb and TSBAb. TSBAb-positive patients with hypothyroidism had a limited
distribution of TSBAb- and TSAb-activities (TSBAb-A + 75 - + 103 %, TSBAb-B + 87 -
+ 106 %, TSAb 92 - 240 %), but Graves' patients with hyperthyroidsim had a wide distribution
of TSAb- and TSBAb-activities (TSAb 205 - 2509 %, TSBAb-A - 158 - + 43 %, TSBAb-B
- 14 - + 164 %). TSBAb-A ignores TSAb activity in serum, and might give low TSBAb
activity. However, TSBAb-A clearly differentiates TSBAb-positive patients with hypothyroidism
from Graves’ patients with hyperthyroidism; thus, we favor TSBAb-A over TSBAb-B. Some
of TSBAb-positive patients with hypothyroidism and Graves' patients with hyperthyroidism
have both TSBAb and TSAb.
Key words:
TSBAb: TSH-Stimulation Blocking Antibody - TSAb: Thyroid Stimulating Antibody - TRAb:
TSH-Receptor Antibody - Graves' Disease - TSBAb-Positive Hypothyroidism - TRAb Disease
References:
in vitro assay for human thyroid stimulator using cultured thyroid cells: effect of sodium
chloride on adenosine 3’,5’-monophosphate increase.
J Clin Endocrinol Metab.
1982;
54
108-114
