K⁺-Channels and Cytokines as Markers for Microglial Activation

Abstract

Activation of brain microglial cells is a key event in neurodegenerative diseases of the Central Nervous System. Microglia are the macrophages of the brain displaying full immunocompetent functions in injury or disease. Although they express many features typical for and indistinguishable from peripheral blood macrophages, there is an increasing body of evidence accentuating special characteristics of microglia that are distinct from peripheral mononuclear cells. Most likely, these features have been imprinted by the special environmental conditions in brain parenchyma, which are e.g. extremely immunosuppressive. Microglial activation stages have been characterized by a variety of morphological and molecular markers, such as retraction of processes, migratory activities, proliferation, cytokine and oxygen radical production and phagocytosis. Evidently, it depends on the nature and strength of stimulus as to which stage is attained and whether or not the cells develop into full-blown macrophages or fall back into quiescence. This report describes some markers which are both useful to characterize earlier and later stages of microglial activation and may be targeted by therapeutic measures in degenerating diseases of the nervous system.