Myeloperoxidase (MPO) staining identified hypochlorous acid-producing neutrophils in the brain, found both within claudin 5-stained vasculature and in the parenchyma, were significantly increased after stroke in old subjects (> 71 years old) compared to young (≤ 71 years old) stroke subjects (Fig. 3a–c). Here, MPO is linked to stroke disorder.