HMOX1 and Alzheimer disease: We next examined whether Aβ, CD11b+ cell density (a marker for infiltrating monocytes), and activated microglia [5, 9, 58, 59] and expression of the anti-oxidant protein heme oxygenase-1 (HO-1) [60], which are associated with neural and vascular inflammation in AD, are greater in parenchyma underlying the collaterals than in the adjacent cortex.