In vitro co-culture systems for studying molecular basis of cellular interaction between Aire-expressing medullary thymic epithelial cells and fresh thymocytes

We previously established three mouse cell lines (Aire + TEC1, Aire + TEC2 and Aire + DC) from the medullary thymic epithelial cells (mTECs) and dendritic cells (mDCs). These cells constitutively expressed ‘‘autoimmune regulator (Aire) gene’’ and they exhibited various features of self antigen-presenting cells (self-APCs) present in the thymic medullary region. Here, we confirmed our previous observation that Aire + thymic epithelial cells adhere to fresh thymocytes and kill them by inducing apoptosis, thus potentially reproducing in vitro some aspects of the negative selection of T cells in vivo. In this system, a single Aire + cell appeared able to kill ,30 thymocytes within 24 hrs. Moreover, we observed that ectopic expression of peripheral tissue-specific antigens (TSAs), and expression of several surface markers involved in mTEC development, increased as Aire + cell density increases toward confluency. Thus, these Aire + cells appear to