In the present study, we wanted to investigate whether a global IDO1 defect occurs in NOD pDCs, and more specifically whether the defective, transcriptional response to IFN-γ – which may characterize early insulitis in pre-diabetes – is also associated with a later, IDO1-dependent defect in TGF-β–driven tolerance to auto-antigens in pDCs. This evidence concerns the gene IDO1 and diabetes mellitus.