Inflammation in neurological disorders: a help or a hindrance?

Inflammation of the central nervous system (CNS) (neuroinflammation) is now recognized to be a feature of all neurological disorders. In multiple sclerosis, there is prominent infiltration of various leukocyte subsets into the CNS. Even when there is no significant inflammatory infiltrates, such as in Parkinson or Alzheimer disease, there is intense activation of microglia with resultant elevation of many inflammatory mediators within the CNS. An extensive dataset describes neuroinflammation to have detrimental consequences, but results emerging largely over the past decade have indicated that aspects of the inflammatory response are beneficial for CNS outcomes. Benefits of neuroinflammation now include neuroprotection, the mobilization of neural precursors for repair, remyelination, and even axonal regeneration. The findings that neuroinflammation can be beneficial should not be surprising as a properly directed inflammatory response in other tissues is a natural healing process after an insult. In this article, we review the data that highlight the dual aspects of neuroinflammation in being a hindrance on the one hand but also a significant help for recovery of the CNS on the other. We consider how the inflammatory response may be beneficial or injurious, and we describe strategies to harness the beneficial aspects of neuroinflammation.