C5 and Alzheimer disease: C4BP is a cofactor for cleavage of C4b by factor I, leading to inactivation of C4b and thus inhibiting classical and alternative pathway C3 and C5 convertase activity, an activity also shared at cell membranes with factor H. C4BP is colocalized with plaques and dead cells (TUNEL staining) in AD brains and binds Aβ in vitro, consistent with a role in reducing a proinflammatory response induced by ongoing complement activation and generation of C5a [196].