The importance of bioassays measuring stimulating and blocking autoantibodies to the
TSH-receptor (TSH-R) by their effect on cAMP production in CHO cells transfected with
the recombinant TSH-R is increasingly recognized. The standard technique for this
bioassay is cumbersome, as it involves purification of serum IgG with polyethylene
glycol (PEG) and resuspension in hypotonic buffer. We have therefore established a
simpler approach for the detection of stimulating and blocking autoantibodies using
JP09 CHO cells and unfractionated human serum. The cAMP concentration was measured
by a highly sensitive commercial radioimmuno assay. Thyroid stimulating autoantibodies
(TSAb) were present in 107 out of 126 patients with Graves' disease (85%) and in 4
out of 40 patients with Hashimoto's thyroiditis (10%). Specificity was confirmed by
the fact that only 1 patient with insulin dependent diabetes mellitus (IDDM) out of
64 patients with different non-thyroid autoimmune disorders (46 with IDDM, 10 with
stiff man syndrome and 8 with rheumatoid arthrites) and 2 out of 100 healthy controls
(2%) were positive in this assay. In the subgroup of hyperthyroid Graves' disease
patients 76 out of 83 (92%) had TSAb and the same number had TSH binding inhibiting
immunoglobulin (TBII), as assessed by the commercial TRAK assay. Although both antibody
types showed only a weak correlation (r = 0.30), a combination of TSAb and TBII detected
98% of all Graves' patients and 99% of the hyperthyroid subgroup. Thyroid blocking
autoantibodies (TBAb) were measured in 4 out of 24 TSAb negative patients with Graves'
disease (17%), who were hypothyroid and positive for TBII. A comparison of our bioassay
with the standard bioassay using PEG precipitation showed a good correlation (r =
0.76, p < 0.001), demonstrating the feasibility of the simplified assay for the routine
detection of TSAb and TBAb in Graves' disease.
Key words
Graves' disease - cAMP - JP09 - Hypothyroidism - TSH-receptor
