Neutrophil activation characteristic of NETosis and inflammation (e.g., neutrophil elastase (NE), myeloperoxidase (MPO), proteinase-3 (PR-3), protein arginine deiminase 4 (PAD4), LL37 and cell-free DNA-histone complexes, and IFN-responsive genes) has been observed in diabetic mice and recent-onset T1D patients (3, 17, 35, 47, 48), with levels of MPO remaining significantly increased relative to healthy controls even in long-term T1D patients (47, 49). Here, PADI4 is linked to type 1 diabetes mellitus.