The later upregulation of cell cycle proteins is associated with activated microglial/macrophages. The expression of PCNA, cyclin D1 and E was evaluated by immunohistochemistry at 1.5 mm caudal to the epicenter of sham or injured spinal cord at 1 month post-injury. (A-D) PCNA expression was undetectable in sham, but was strongly upregulated in OX42+ microglia/macrophages. (E-H) The membrane bound component of the NADPH oxidase enzyme, p22, co-localized with PCNA+ microglia/macrophages. (I-P) Large numbers of cyclin E+ and D1+ cells in the injured coronal sections were co-labeled with Iba-1+ or OX42+ microglia/macrophages. Scale bars = 500 μm.