SHORT‐ AND LONG‐TERM EVALUATION OF NORMAL AND ABNORMAL HUMAN THYROID CELLS IN MONOLAYER CULTURE

We have investigated the TSH responsiveness of normal and abnormal human thyroid cells cultured in the short term with high serum concentrations and for up to 6 months in a low serum, chemically‐defined, medium. Cells from normal human thyroid tissue (n= 9), multinodular goitre (n= 6), benign follicular adenomata (n= 6), and differentiated thyroid carcinoma (n= 3) formed confluent monolayers which were sensitive to bovine TSH (bTSH) in concentrations greater than 25 μU/ml when assessed by the intracellular response of cyclic AMP at 7 d of culture. Such sensitivity was less than that observed with a continuously proliferating thyroid cell line (FRTL‐5) derived from Fisher rat thyroid and which responded to concentrations of bTSH as low as 5–10 μU/ml. Human cells derived from iodine/antithyroid drug treated Graves' thyroid tissue (n= 6) were less sensitive than normal cells requiring up to 500 μU/ml bTSH to increase intracellular cyclic AMP and poorly differentiated thyroid cancer cells (n= 3) failed to respond to bTSH. Long‐term human thyroid cultures of normal and follicular adenoma cells in the chemically‐defined medium used for the FRTL‐5 cells had absent fibroblast growth and continued in monolayer form without significant follicle formation. These cells remained highly sensitive to bTSH stimulation when tested after 4, 13, and 26 weeks of continuous culture. All such cell preparations failed to proliferate under conditions which favoured the rapid growth of the rat thyroid cells. These data demonstrated that while thyroid cell culture conditions described in the literature do not permit proliferation of human thyroid cells, they do allow an assessment of their functional state in vitro which may lead to a further understanding of thyroid cell pathophysiology.