APOE and Mental deterioration: Although the primary outcomes of the Phase III pivotal study did not provide evidence that intravenous immunoglobulin (IVIg) was efficacious for treating symptomatic AD (cognitive decline) at the doses tested, IVIg treatment did result in clearing amyloid from the brain, and be efficacious for treating some subgroups of AD patients, particularly among APOE4 carriers, indicating that APOE4 carriers have specific humoral immunity affecting the IgG mediated clearance of Aβ by microglial phagocytosis in the brain [13, 19, 20].