C3 and cerebral amyloid angiopathy: Since the activation of the complement cascade by antibody-Aβ immune complexes at sites of cerebral amyloid angiopathy (CAA) may be one possible cause of microhemorrhage, it was of interest to analyze the opsonization of sites of microhemorrhage with C1q and C3 proteolytic fragments, C3b, complement components in mice immunized with mannan-Aβ28.