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In Alzheimer’s disease, neuritic amyloid-β plaques along with surrounding activated microglia and astrocytes are thought to play an important role in the inflammatory events leading to neurodegeneration. Studies have indicated that amyloid-β can be directly neurotoxic by activating these glial cells to produce oxygen radicals and proinflammatory cytokines. This report shows that, using primary human monocyte-derived macrophages as model cells for microglia, amyloid-β1–42 stimulate these macrophages to the production of superoxide anions and TNF-α. In contrast, astrocytes do not produce both inflammatory mediators when stimulated with amyloid-β1–42. In cocultures with astrocytes and amyloid-β1–42-stimulated macrophages, decreased levels of both superoxide anion and TNF-α were detected. These decreased levels of potential neurotoxins were due to binding of amyloid-β1–42 to astrocytes since FACScan analysis demonstrated binding of FITC-labeled amyloid-β1–42 to astrocytoma cells and pretreatment of astrocytes with amyloid-β1–16 prevented the decrease of superoxide anion in cocultures of human astrocytes and amyloid-β1–42-stimulated macrophages. To elucidate an intracellular pathway involved in TNF-α secretion, the activation state of NF-κB was investigated in macrophages and astrocytoma cells after amyloid-β1–42 treatment. Interestingly, although activation of NF-κB could not be detected in amyloid-β-stimulated macrophages, it was readily detected in astrocytoma cells. These results not only demonstrate that amyloid-β stimulation of astrocytes and macrophages result in different intracellular pathway activation but also indicate that astrocytes attenuate the immune response of macrophages to amyloid-β1–42 by interfering with amyloid-β1–42 binding to macrophages.

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Alzheimer's disease accounts for the majority of dementia in the elderly. Worldwide, approximately 20 million people are suffering from this devastating disease, with no effective treatment currently available. For efficient drug design, it is important to identify the molecular mechanisms underlying the pathology of the disease. An invariant feature in the pathology of Alzheimer's disease is the amyloid-beta peptide. Amyloid-beta is produced by endoproteolytic cleavage of the amyloid precursor protein by beta- and gamma-secretase. In the past 2 years, the protein responsible for beta-secretase activity has been isolated and researchers are close to identifying gamma-secretase. These recent achievements in Alzheimer's disease research have provided helpful tools for the development of therapeutics.

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