Microglia and immune activation in Alzheimer's disease.

Although the brain has been traditionally viewed as immunologically privileged, it is now clear that the brain is surveyed by T lymphocytes, that resident brain microglia express immune-related antigens and can function as antigen-presenting cells, and that glial cells can synthesize and respond to cytokines, once viewed as immune system specific regulators. Alzheimer's disease is associated with increased expression of several immune-related markers in brain, including MHC class II antigens, complement factors and their receptors, and acute-phase proteins. Preliminary epidemiological evidence suggests that patients on long-term anti-inflammatory drug therapy for rheumatoid arthritis have an unexpectedly low incidence of Alzheimer's disease.