Previously, we reported the conversion phenomenon (CP) of thyroid blocking antibody (TBAb) to thyroid
stimulating antibody (TSAb) by induced cAMP production during incubation of TBAb-bound porcine thyroid cells (PTC)
with rabbit anti-IgG Ab. In the present experiment we examined the CP by TBAb-positive sera with high TSH binding
inhibitor immunoglobulin (TBII) activity in primary hypothyroidism. Two patients with extremely high TBII patients;
patient No.1 (35 yo male) with TSH 26.5μU/ml, TSAb negative, TBII 4,600 U/L, TBAb100% and patient No.2 (40 yo
female) with TSH 4.5μU/ml, TSAb negative, TBII 1,620 U/L, TBAb 99.8% were examined. Cyclic AMP production was
examined by 2nd incubation (3h) of anti-IgG Ab with TBAb-bound PTC that was made by 1st incubation (0.5h) of TBAbpositive
serum and PTC. When sera (0.001-0.05 ml) of patient No.1 and No.2 were tested, cAMP production showed 980-
3,700% and 570-3,000% in a dose-dependent manner, respectively. Cyclic AMP production was also observed by anti-
IgG fragments Ab [(Fab’)2, Fab and light chain]. Cyclic AMP production by anti-F(ab’)2 was higher than anti-Fab Ab, and
cAMP by anti-κ Ab was significantly higher (>3 fold) than anti-λ Ab. Cyclic AMP production by TBAb-positive sera
with high TBII activity (35-270 U/L) showed a correlation with serum TBII activity (R=0.76). The fact that all high
TBAb-positive sera show the CP of TBAb to TSAb suggests that TSAb activity may be present in TBAb molecule and
TBAb may be the precursor of TSAb.
Cyclic AMP, Graves’ disease, Primary hypothyroidism, TBAb, TBII, TSAb.
Research Institute for Production Development, 15 Morimoto-cho, Simogamo, Sakyo-ku, Kyoto, 606-0805, Japan.