Phenotypic and functional characterization of human thymic stromal cell lines

To establish new tools for studying human thymic stromal cells, we transfec ted adherent cells from a human postnatal thymus using a plasmid encoding S V40 large T antigen. Among the cell lines obtained, we characterized four e pithelial cell lines (LT-TEC1 to LT-TEC4) and one thymic myoid cell line (M ITC). Several morphological, functional and phenotypic differences were obs erved between these 2 cell types. Epithelial cells were heterogeneous and l arger than myoid cells. Untreated LT-TEC lines expressed MHC class I, ICAM- 1 and LFA-3 antigens and not MHC class II antigens, similarly to primary th ymic epithelial cells (PTEC), while MITC line expressed only class I and LF A-3 antigens. After IFN-gamma treatment, MHC class II and ICAM-1 antigens w ere markedly upregulated in LT-TEC lines but not in MITC, indicating the ab sence or a dysfunction of regulatory factors in MITC line. Myoid cells expr essed mRNA for all the subunits of the acetylcholine receptor (AChR) while epithelial cells expressed only the alpha, beta and epsilon subunits. Strik ingly, LT-TEC produced much more C-C chemokines and IL-6 than MITC cells, w hile these latter produced higher levels of IL-8 and TNF-alpha. Altogether, these results reveal phenotypic and functional differences between these t wo stromal cell types, suggesting a potential involvement of myoid cells in the thymic function.