Grzegorz Wicher [Public domain] via Wikimedia CommonsMicroglia are the nervous system’s exclusive immune cells. In a resting state, they resemble long-legged spiders, but when confronted with pathogens or injury, they retract their appendages and balloon into round blobs that engulf and remove the pathogens and other cellular debris. They also eliminate damaged synapses. “The idea that [microglia] can clean up brain debris has been well established in studies of brain disease,” Beth Stevens (Boston Children’s Hospital) told New Scientist. “But now, even without damage, we’ve found them to respond to subtle changes in synaptic function.” Stevens led a study in mice that explored more closely the activity of microglia in healthy brain tissue. The results, recently published in (Neuron 74, 691–702; 2012), contradict the notion that microglia are primarily passive immune guardians in the brain.
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