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Table 1 Biological activities of complement activation proteins, with relevance to AD.

From: Using animal models to determine the significance of complement activation in Alzheimer's disease

Name Biological activity
C1q Enhances Aβ aggregation [43,44]; may facilitate Aβ clearance [56]; enhances Aβ-induced cytokine secretion by microglia [49]
C3a Anaphylatoxin (increases capillary permeability) [155] ; protects neurons vs. excitotoxicity [52]
C3b Immune adherence and opsonization [89] (may facilitate Aβ clearance by phagocytic microglia)
C4a Anaphylatoxin (weak) [156]
C5a Anaphylatoxin; protects neurons vs. excitotoxicity [51]; chemotaxic attraction of microglia [46,47]; inhibits apoptosis 54; increases cytokine release from Aβ-primed monocytes [48]
C5b-9 Neurotoxicity [50]; sublytic concentrations may have both pro- and anti- inflammatory activities [157]