NOVEL THYROTROPIN (TSH)-TSH ANTIBODY COMPLEX IN A HEALTHY WOMAN AND HER NEONATES

A novel high-molecular-weight (MW) form of immunoreactive TSH [35,000 Da on Sephacryl S-200HR gel chromatography (S-200 chromatography)] was documented in a 32-year-old healthy woman who delivered two neonates with transient hyperthyrotropinemia. Her TSH levels ranged from 21.2 to 53.9 mU/L on different days or from 11.0 to 48.1 mU/L by the different immunoradiometric assay methods, The IgG fractions showed specific I-125-labeled hTSH binding and inhibited in vitro cAMP increase induced by hTSH but not that induced by bTSH, On protein G Superose HR affinity chromatography (protein G chromatography) equilibrated with 10 mmol/L sodium/potassium phosphate buffer (PB) followed by elution with 0.1mol/L glycine buffer, 95-99% of her TSH immunoreactivity eluted in the latter (bound) fraction while almost all was in the former (unbound) fraction in the control serum containing authentic hTSH, However, after dialysis of this bound fraction overnight with PB adding 0.5 mol/L NaCl (PB/NaCl), which exhibited greater ionic strength than PB, almost all TSH immunoreactivity changed from the bound fraction into the unbound fraction on the protein G chromatography equilibrated with PB/NaCl, These data indicate that the novel immunoreactive TSH was due to hTSH and hTSH-specific antibody complex, and dissociation of the complex may be incomplete on direct S-200, The immunoreactive TSH showed high MW form (35,000 Da), The dissociation may be almost complete during dialysis with greater ionic strength; the native TSH then appeared to be of normal size.