Microglia: The Enemy Within?

摘要

Unlike most other structures in the adult brain, the hippocampus is able to produce new neurons (neu-rogenesis) throughout adult life as it contains a population of neural stem cells. It is believed that neurogenesis contributes to the primary task of the hippocampus, that of coordinating learning and memory. On page 1760 of this issue, Monje, Toda, and Palmer report that in a rat model of brain inflammation, the ability of hip-pocampal neural stem cells to generate new neurons is severely reduced. Intriguingly, the authors were able to restore hippocampal neurogenesis by blocking inflammation with indo-methacin, a common nonsteroidal anti-inflammatory drug. The myriad cognitive functions computed by the brain have been credited in large part to neurons, called those "noble elements" by the father of neuroscience, Ramon y Cajal. Yet brain neurons are vastly outnumbered by other brain cells called glia, which include astrocytes, oligodendrocytes, and microglia. The brain is an im-muno-privileged tissue that exhibits dampened adaptive immunity in response to injury, infection, or tumor formation. However, the brain does exhibit a robust innate immune response thanks to its microglia, which defend against invading microorganisms and clean up by engulfing the debris of dying cells. In addition, the inflammatory mediators released by microglia during an innate immune response strongly influence neurons and their ability to process information.