Suspension culture of separated follicles consisting of differentiated thyroid epithelial cells.

We have prepared thyroid follicles in suspension culture to use as a model system in vitro for investigation of some properties of the thyroid gland. The follicles were free of endothelial cells, fibroblasts, and other nonepithelial cells. They were prepared by collagenase treatment of minced rat thyroid glands followed by differential filtration of the suspension through nylon meshes. Small clusters of principal thyroid epithelial cells were separated from large fragments and single cells. They were cultured in dilute suspension in Coon's modified F-12 medium in dishes coated with agarose to avoid having the cells attach to the dishes. By culture day 3, most of the clusters formed closed follicles containing a periodic acid-Schiff-positive colloid but without a basal lamina. Follicle walls contained an occasional C cell. The epithelium resembled that in the thyroid of a recently hypophysectomized rat, with normal polarity and organelle complement normal with respect to position and abundance, with basally located lysosomes, no pseudopods, and no colloid droplets. The cells were responsive to thyroid-stimulating hormone (thyrotropin) and to dibutyryl cyclic AMP. Thyroid-stimulating hormone at 10 munits/ml resulted in apical migration of lysosomes and formation of pseudopods and colloid droplets within 30 min; longer exposure resulted in depletion of luminal colloid. The results indicate that the suspended follicles resemble follicles in vivo with respect to morphology and responsiveness to thyroid-stimulating hormone in the absence of other cell types.