The effects of thyroid-stimulating hormone and thyroid microsomal antibody on thyroid peroxidase activity in human follicular cells: a mini organ culture study.

Thyroid peroxidase (TPO) is an essential enzyme involved in thyroid hormone synthesis and is closely related to the microsomal antigen which is the target of thyroid microsomal antibody. There have been several reports on direct inhibition of peroxidase activity by thyroid microsomal antibody. We prepared a mini organ culture of thyroid glands obtained at operation, and investigated the localization of thyroid peroxidase activity in follicular cells proliferated around the thyroid tissue blocks by electron microscopy. The development of microvilli containing TPO activity on the cell surface facing the culture medium was observed when normal thyroid tissue or Graves' thyroid tissue was incubated with TSH but in the TSH-free group the development of microvilli was poor and TPO activity was very much decreased. After the addition of serum positive for thyroid microsomal antibody, the TPO activity of the microvilli was retained in 4/6 tissue samples, but it disappeared in 2 cases. Our findings suggested that thyroid peroxidase activity is regulated by thyroid stimulating substances such as TSH and by TPO in tissue.