Control of human thyroid follicular cell proliferation in suspension and monolayer culture.

We have used both suspension and monolayer cultures to investigate the in vitro control of normal human thyroid follicular cell proliferation as assessed by both [3H]TdR incorporation and autoradiography. In suspension cultures, whilst TSH alone produced no effect, inclusion of two permissive factors, namely a supraphysiological concentration of insulin (80 micrograms/ml) and a low concentration of FCS (1%) (which, in the absence of TSH, gave only a weak proliferative response) permitted a highly significant response to TSH at 0.1 mU/ml. A higher concentration of TSH (10 mU/ml) resulted in a reduced response. In monolayer cultures in contrast, insulin and FCS were themselves highly growth stimulatory, with no super-added effect on addition of TSH. Our data indicate that suspension culture provides a more valid in vitro model for the investigation of growth factor control of normal and neoplastic human thyroid epithelium.