In post‐mortem immunohistochemical studies of AD brain, C1q, C4b, C3b/iC3b, and membrane attack complex (MAC) have all been shown to co‐localize with plaques and tangles (Ishii & Haga, 1984; Rogers et al., 1992; Veerhuis et al., 2003). Here, C3 is linked to Alzheimer disease.