While this is crucial for defense against pathogens 5-7, misdirected increased MPO activity has been linked to detrimental effects on the host in a large number of diseases including atherosclerosis 8, 9, Alzheimer' disease 10, 11, stroke 12, multiple sclerosis 13, 14, non-alcoholic steatohepatitis 15, and atrial fibrillation 16, among others. Here, MPO is linked to multiple sclerosis.