ABSTRACT
The question of to what extent reactive glial cells contribute to the pathogenesis of neuron damaging brain diseases is a matter of ongoing debate. Microglia as well as astrocytes are the brain endogenous representatives of the general immune system and can be recruited under pathological conditions as immune competent cells. The microglia are highly sensitive sensors for brain insults and, in standby position, are prepared to bring into play the immunological defense mechanisms. The astrocytes stay in the second line for a possible recruitment, if required. Upon activation, the reactive glial cells gain a number of potentially neurotoxic potencies, such as the release of inflammation promoting cytokines and aggressive oxidative radicals. As long as the gradual use of these weapons remains under the strict yin-yang control of a sophisticated intercellular communication network, there is no doubt about the primarily beneficial function of reactive glial cells in defense and repair. However, evidence has accumulated that an escalating pathological glial activation, which involves both microglia and astrocytes, may contribute to secondary nerve cell damage. The latter occurs, for example, after transient brain ischemia, head trauma, and toxic insults and during the course of neurodegenerative diseases.
