Microglial cells and amyloid β protein (Aβ) deposition: association with Aβ₄₀-plaques

Two distinct species of amyloid protein (A) with different carboxyl termini, A40 and A42(43), are deposited in plaques in the brains of patients with Alzheimer's disease and Down's syndrome. The relationship between these two forms of A and microglial cells was investigated in 16 subjects with Down's syndrome ranging in age from 31 to 64 years. The amount of A40 in plaques was low in persons under 50 years of age, even though high amounts of A42(43) were present, but this former species increased after this age. Microglia were observed most commonly in plaques containing both A40 and A42(43) but less commonly in those with A42(43) alone. The presence of microglial cells in plaques may be associated with the accumulation of A40 and these cells may have a role in the production or processing of this particular molecular species.