Hormones and the lung. II. Immunohistochemical localization of thyroid hormone binding in type II pulmonary epithelial cells clonally-derived from adult rat lung.

The type II pulmonary epithelial cell is the recognized state of surfactant synthesis and storage. Results of recent studies indicate that the thyroid hormones, triiodothyronine (T3) and thyroxine (T4), may be important regulators of surfactant production and/or release. Direct and indirect immunofluorescence techniques were used in an attempt to demonstrate binding of T3 and T4 in monolayer cultures of isolated type II cells. These cultured epithelial cells are clonally-derived from adult rat lung, retain a diploid karyotype through 35 population doublings in vitro, contain granular inclusions (lamellar bodies) in the perinuclear cytoplasm, and synthesize phosphatidylcholine via the CDP-choline pathway. In isolated type II cells, either of two fluorescent patterns was observed: (a) nuclear fluorescence accompanied by a reticular perinuclear network; or (b) diffuse cytoplasmic accumulations with concentrations around perinculear cytoplasmic inclusions. Ultrastructurally these inclusions had the typical appearance of lamellar bodies. Histochemical studies demonstrated that these inclusions contained surfactant-associated nonspecific esterases and stained with Nile blized markers for pulmonary surfactant indicate that these inclusions are indeed lamellar bodies, the putative sites of surfactant synthesis and/or storage. These findings suggest that the type II pulmonary epithelial cell contains specific binding sites for thyroid hormones, and support the hypothesis that thyroid hormones are regulators of surfactant metabolism.