Immunocytochemical localization of a medullary thymic epithelial glycoprotein.

The thymic microenvironment is known to play a key role in T-cell differentiation, but the exact nature of the interactions between epithelial and lymphoid cells has not been fully elucidated. With a monoclonal antibody to a thymic epithelial glycoprotein, we report the localization of an antigen specific for medullary epithelial cells of the mouse thymus. This antigen is found in the Golgi apparatus of epithelial cells, and on their borders with adjoining lymphocytes. This location is compatible with the previously reported observation that differentiation signals transmitted to thymic lymphocytes by thymic epithelial cells require actual contact between these two cell types.