Intercellular MHC transfer between thymic epithelial and dendritic cells

Thymic dendritic cells (DC) and epithelial cells play a major role in central tolerance but their respective roles are still controversial. Epithelial cells have the unique ability to ectopically express peripheral tissue-restricted antigens conferring self-tolerance to tissues. Paradoxically, while negative selection seems to occur for some of these antigens, epithelial cells, contrary to DC, are poor negative selectors. Using a thymic epithelial cell line, we show the functional intercellular transfer of membrane material, including MHC molecules, occurring between epithelial cells. Using somatic and bone marrow chimeras, we show that this transfer occurs efficiently in vivo between epithelial cells and, in a polarized fashion, from epithelial to DC. This novel mode of transfer of MHC-associated, epithelial cell-derived self-antigens onto DC might participate to the process of negative selection in the thymic medulla.