Immunohistochemical study on the induction of heme oxygenase-1 by traumatic brain injury

We investigated the dynamics of the induction of heme oxygenase-1 (HO-1) in the human brain after death caused by traumatic brain injury (TBI). HO-1 was found to stain neurons and microglia/macrophages in cases with TBI, whereas no positive staining except for a few round cells in the arachnoidal space was observed in control cases. In a case with 7h survival, a considerable number of HO-1 positive neurons and microglia were observed. The number of HO-1 positive cells and level of HO-1 staining gradually increased up to 24h survival. Although HO-1 positive neurons were seldom observed in cases with more than 7-day survival, HO-1 positive microglia were still observed even in cases with 5-month survival. The results indicate that HO-1 may be induced by TBI in human cases, and suggest that prolonged HO-1 induction in microglia might reflect its role in protecting those cells from secondary damage including oxidative stress.