TTF-1 is predominantly expressed in the epithelial cells of the thyroid gland, lung alveoli, and certain areas of the central nervous system. In histological studies, it is a valuable marker for identifying cells from these tissues. For instance, in the thyroid gland, TTF-1 expression is critical for the synthesis of thyroid hormones. Similarly, in the lungs, it is essential for the development of alveolar cells.
