Characterization Of Aire-Expressing Dcs Using A Novel Aire-Reporter Strain

Abstract Aire is predominantly expressed by medullary thymic epithelial cells (mTECs), and it is essential for maintaining self-tolerance by controlling the expression of tissue-restricted self-antigens (TRAs). Besides mTECs, extra-thymic Aire-expressing cells (eTACs) have been reported. However, the exact nature of eTACs has been difficult to study because of the small numbers together with low expression levels of Aire within the cells. We have recently established a novel Aire reporter strain in which endogenous Aire was replaced by the human AIRE-GFP-Flag tag fusion gene (Aire/hAGF-knockin: J. Immunol. 2015). hAGF-reporter protein was efficiently produced and retained within the mTECs as authentic Aire nuclear dot protein. With this high-sensitivity and high-fidelity Aire-reporter strain, we found that DCs in the spleen and lymph nodes expressed Aire although their expression levels were rather low. Aire-expressing DCs showed high levels of MHC-II and CD80/CD86, and half of which expressed CD8. In the thymus, we found that there were two types of DCs expressing Aire: hAGF-low DCs and hAGF-high DCs. Interestingly, hAGF-low DCs had small hAGF dots within the nuclei, whereas hAGF-high DCs retained larger hAGF dots which were mainly present outside the nuclei, suggesting that hAGF-high DCs had acquired hAGF protein from mTECs. Acquisition of hAGF protein by hAGF-high DCs from mTECs was confirmed by the bone-marrow transfer experiment. Mechanisms underlying the transfer of nuclear protein (i.e., hAGF protein) from mTECs to thymic DCs, and immunological consequence of this event are now under investigation.