MPO and type 1 diabetes mellitus: NOD pancreata at 10–12 weeks and T1D onset showed a significant 25- to 29-fold higher frequency of MPO+ islets (52.9% ± 10.4% and 61.4% ± 12.6%, respectively) than control B6SJL islets (2.1% ± 2.1%; Figure 2, A and B); in parallel, 32.5% ± 7.0% (P < 0.05) and 41.1% ± 4.8% (P < 0.01) of islets, respectively, were positive for CitH3+, compared with B6SJL islets in which CitH3 was undetectable (Figure 2C).