Inflammation, a self-defensive reaction against various pathogenic stimuli, may become harmful self-damaging process. Increasing evidence has linked chronic inflammation to a number of neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis. In the central nervous system, microglia, the resident innate immune cells play major role in the inflammatory process. Although they form the first line of defense for the neural parenchyma, uncontrolled activation of microglia may directly toxic to neurons by releasing various substances such as inflammatory cytokines (IL-1beta, TNF-alpha, IL-6), NO, PGE
alpha-Synuclein/physiology ; Signal Transduction ; Parkinson Disease/*etiology/immunology ; Multiple Sclerosis/etiology ; Models, Biological ; Microglia/immunology/metabolism/*physiology ; Metalloproteases/physiology ; Melanins/physiology ; Matrix Metalloproteinase 3 ; Inflammation Mediators/metabolism ; Humans ; Encephalitis/*etiology/immunology ; Cytokines/secretion ; Animals ; Alzheimer Disease/etiology ; AIDS Dementia Complex/etiology