Insulin-Like Growth Factor I in Human Thyroid Tissue: Specific Localization by Immunohistochemistry and In Situ Hybridization.

Insulin-like growth factor I and II (IGF-l and IGF-ll) have been implicated in the replication of normal thyroid follicular cells in vitro. This study evaluates the distribution and abundance of immunoreactive IGF-l by histochemical analysis in human thyroid tissue with different histopathologic characteristics. We used two types of highly specific and sensitive polyclonal rabbit anti-IGF-l antibodies and one monoclonal antibody (MAb) with the immunoperoxidase technique on sections of 25 glands harboring adenomatous goiter; 11 glands with follicular adenoma (FA); 45 glands with thyroid carcinoma of papillary, follicular, and undifferentiated types; and 18 glands with Graves' disease. Immunoreactive IGF-l was present in some thyroid follicular cells of all thyroid tissues examined. The percentage of cells staining positively varies among the different processes, being lowest in normal thyroid tissues and highest in all thyroid carcinomas. The cytoplasmic pattern of IGF-l immunoreactivity also varied among the different thyroid conditions. Furthermore, using nonradioactive in situ hybridization (ISH) we detected IGF-l mRNA in the thyroid cells of adenomatous goiter. The expression was higher in the histologically hyperplastic areas. These findings provide further support for an autocrine and/or paracrine role of IGF-l in the function and/or growth of normal thyroid follicular cells and suggest that IGF-l may play a role in the dysfunctional growth of thyroid follicular cells in adenomatous goiter, thyroid carcinoma, and Graves' hyperthyroidism.