Mechanism of the augmentative effect of high polyethylene glycol (PEG) concentrations on the thyroid stimulating activity in TSAb-IgG using a porcine thyroid cell assay

Antibody to immunoglobulin G and polyethylene glycol augment cyclic adenosine monophosphate production by TSH receptor antibody bound to porcine thyroid cells

Anti-immunoglobulin G (IgG) augments cyclic adenosine monophosphate (cAMP) production by thyroid-blocking antibody (TBAb) bound to porcine thyroid cells (PTC). This is described as a conversion phenomenon. We reported the effect of polyethylene glycol (PEG) to augment thyroid-stimulating antibody (TSAb) activity in a PTC assay. In the present experiment we examined the effect of anti-immunoglobulin G (IgG) and PEG on cAMP production from TBAb or TSAb bound to PTC. TBAb bound to PTC was separated from unbound TBAb by centrifugation after a first incubation (0.5 hour at 37 degrees C) of TBAb-IgG with PTC. TBAb bound to PTC were incubated with anti-human (h)IgG or hIgG fragments [F(ab')(2), Fc, Fd, H chain or L-chain] for 4 hours at 37 degrees C in the second incubation. Anti-IgG or anti-IgG fragments increased cAMP production. No conversion was caused by protein A, protein L, or PEG (5%). PEG did not augment cAMP production by these IgG antibodies. PEG augmented cAMP production during incubation of TSAb-IgG bound to PTC, but anti-IgG did not. PEG significantly augmented cAMP production by coincubation of TSAb-IgG bound to PTC and the unbound TSAb-IgG (obtained from the first incubation). A similar augmentative effect of PEG was also observed in experiments using TSAb-F(ab')(2) and TSAb-Fab. cAMP production by PTC bound by both TBAb- and TSAb-IgG was increased by co-incubation with anti-IgG, but was not increased by PEG. In conclusion, anti-IgG specifically increased cAMP production from TBAb bound to PTC (conversion phenomenon) and PEG specifically increased cAMP production by TSAb bound to PTC. Different mechanisms enhance cAMP production by TSAb and conversion of TBAb.

Sensitive thyroid-stimulating antibody assay in whole serum containing five percent polyethylene glycol using porcine thyroid cells

Previously we reported that the amounts of cyclic adenosine monophosphate (cAMP) production by polyethylene glycol (PEG) 22.5% precipitated fraction (PF) (crude immunoglobulin G [IgG]) from thyroid-stimulating antibody (TSAb)-positive serum were higher than those by PEG 12.5% PF, and that PEG (5%) augmented affinity purified TSAb-IgG-stimulated cAMP production in porcine thyroid cells (PTC) assay. In the present work, we studied sensitive TSAb assay using whole sera in the presence of high PEG concentrations in PTC assay. cAMP produced by TSAb-positive serum increased in proportion to serum amounts up to 0.05 mL, but gradually decreased in 0.075 mL. The maximal augmentative effect of PEG on TSAb-positive serum (0.05 mL)-stimulated cAMP production was found in 5% PEG (final). Thus, TSAb assay using whole serum (0.05 mL) in the absence of 5% PEG (serum method) and sensitive TSAb (sTSAb) assay using whole serum (0.05 mL) in the presence of 5% PEG (serum plus 5% PEG method) were performed. The sensitive thyroid-stimulating antibody (sTSAb) activities of Graves' sera showed significantly higher (twofold to sevenfold) compared to simple TSAb activity with sera. sTSAb and TSAb activities were positive in 91% (29/32) and 47% (15/32) of untreated Graves' patients with hyperthyroidism. The sTSAb activities by serum plus 5% PEG method were higher than that by PEG 12.5% precipitated fraction (PF) from test serum (0.2 mL) in many Graves' sera, but lower than that by PEG 22.5% PF from test serum (0.2 mL). PEG (5%) did not augment cAMP produced by high TSH serum (127-210 mU/L) in thyroiditis chronica. sTSAb activity was negative in adenomatous goiter, subacute thyroiditis, and thyroid cancer. sTSAb activity was also negative in TSH stimulation blocking antibody (TSBAb)-positive hypothyroidism (during thyroxine [T4] treatment), but was positive in Graves' sera with coexistence serum of TSAb and TSBAb because of augmentative effect of 5% PEG on TSAb activity. This assay in whole serum (0.05 mL) containing 5% PEG is less sensitive than sensitive TSAb assay using PEG 22.5% PF from test serum (0.2 mL), but this method can be available clinically as routine TSAb assay using whole serum because of the technical simplicity.