Immunohistochemical studies on the phenotype of murine and human thymic stromal cell lines

Four different murine and human thymic stromal cell (TSC) lines were analyzed by means of indirect immunofluorescence for the presence of tissue specific intermediate filament proteins, extracellular matrix products and thymic hormone. Among these cell lines, only one (IT-45R1) was shown to be epithelial in nature, as revealed by its immunoreactivity with antikeratin antibodies. In addition, IT-45R1 cells (but not the other cell lines) produced thymulin--a well defined thymic hormone--that was detected intracellularly and in the culture medium. Concerning extracellular matrix elements, we noted that all TSC lines were able to produce basement membrane proteins as type IV collagen and fibronectin. Type I collagen however was synthesized by TEPI, HT-5 and HT-7 cells but not by IT-45R1 cells. Our data demonstrate that only the IT-45R1 TSC line is epithelial and active in thymic hormone production. The other three TSC lines are not epithelial in nature, but their definitive phenotypes remain to be determined.