ROLE OF THYMIC STROMAL CELLS IN THYMOCYTE EDUCATION - A COMPARITIVE ANALYSIS OF DIFFERENT MODELS

The thymus is the privileged lymphoid organ for T-cell differentiation , including clonal selection. Precursor thymocytes are selected on the basis of their ability to recognize self-major histocompatibility com plex molecules (MHC) that are expressed on thymic stromal cells, inclu ding epithelial cells, macrophages, and interdigitating cells/dendriti c cells (IDCs/DCs). Epithelial cells have been associated with positiv e selection, and dendritic cells with negative selection, but the exac t role played by these stromal elements is still unresolved. This revi ew focuses on the different in vitro and in vivo approaches that have been used to elucidate the role of thymic stromal cell types in thymic function, and on a critical evaluation of these approaches.