Aire+ cells were readily identified by immuno-staining in both PN and nPLN sections. Like in mouse, human eTACs were relatively rare but localized outside the B-cell follicles and stained with the hallmark “nuclear speckling” pattern. Furthermore, the eTACs were ubiquitously positive for MHC class II but lacked high expression of CD11c, calling into question their identification as a known resident DC population. Quantitative PCR confirmed the expression of Aire in whole PLN and in sorted CD45+, MHC class II+ populations from fresh human spleen. No difference was found in the relative expression of Aire between T1D, no diabetes, and pre-T1D PLN specimens. However, the expression of ladinin-1, a putative Aire-regulated TSA in mouse eTACS, was positively correlated with Aire expression, suggesting that it might be an Aire-regulated TSA in humans as well.

Overall, our data confirm that Aire is indeed expressed outside the thymus in humans and that human eTACs appear analogous to the more fully characterized murine eTACs. Their potential for promoting peripheral tolerance in a therapeutic setting remains an exciting possibility.