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 ho rmone 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 micros omal antibody. We prepared a mini organ culture of thyroid glands obta ined at operation, and investigated the localization of thyroid peroxi dase activity in follicular cells proliferated around the thyroid tiss ue blocks by electron microscopy. The development of microvilli contai ning TPO activity on the cell surface facing the culture medium was ob served when normal thyroid tissue or Graves' thyroid tissue was incuba ted with TSH but in the TSH-free group the development of microvilli w as poor and TPO activity was very much decreased. After the addition o f 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.