Two types of thyroid function-blocking antibodies in autoimmune atrophic thyroiditis and transient neonatal hypothyroidism due to maternal IgG.

We examined the effects of IgG from four patients with autoimmune atrophic thyroiditis on cAMP responses and iodine metabolism (post-receptor processes), using cultured thyroid cells. We found two types of thyroid function-blocking antibodies: (1) one blocks TSH binding to its receptors and inhibits TSH-stimulated cAMP responses but does not block cAMP-stimulated iodine uptake and organification; (2) the other blocks TSH binding to its receptors, inhibits TSH-stimulated cAMP responses and does block cAMP-stimulated iodine uptake and organification (post-receptor processes). Among the four patients with autoimmune atrophic thyroiditis, three had TSH binding blocking antibodies only and one had antibodies which block post-receptor processes. These antibodies might be responsible for thyroid dysfunction in autoimmune atrophic thyroiditis. The daughter of one of the women with autoimmune atrophic thyroiditis had transient neonatal hypothyroidism and recovered spontaneously from the hypothyroid state with the disappearance of the maternal blocking antibodies.