Inflammatory response in Alzheimer's disease.

Microglia belong to the mononuclear phagocyte system. They represent the brain resident tissue macrophages and function as the scavenger cells in brain. In Alzheimer's disease (AD), microglia become activated. Reactive microglia aggregate around senile plaque beta-amyloid and neurofibrillary tangles. Heavy accumulation of these pathological debris in postmortem, however, indicates the failure or, at best, partial success of the removal. It is supposed that continued activation of microglia in these lesions elicits a persistent inflammatory response. In fact, activation fragments of the complement system have been detected in association with beta-amyloid deposits and extracellular ghost tangles. Thrombin, a central serine protease of the coagulation pathway, is also deposited in these pathological debris. Both complements and thrombin could augment the biochemical, synthetic and phagocytic capacities of microglia. Microglia, in turn, might play a major role for the activation of complement and coagulation systems in brain. The available evidence strongly suggests a significant similarity between the chronic inflammation and the tissue response in AD lesions, supporting a notion that the inflammatory process is a part of Alzheimer pathology.