[Alzheimer's disease and the immune system response].

Elements that belong to the natural immune system have been identified immunohistochemically in brain of patients with Alzheimer's disease (AD). Senile plaques and ghost tangles appear to be the site of chronic inflammatory response where reactive microglia, the brain resident macrophages, play a major role. Activation of the complement, coagulation and fibrinolysis systems also occur in such lesions. Nevertheless, the accumulation of plaques and tangles in postmortem brain tissue indicates the failure of microglia to phagocytose and degrade these pathological debris. "Frustrated" microglia might elicit the persistent immune responses and cause the neuronal deterioration in AD. The low incidence of AD in rheumatoid arthritis patients, who have received the long-term anti-inflammatory medication, supports this notion.