The brain immune network in spinal cord injury

Abstract

Diseases or injuries in the central nervous system (CNS) often cause robust immune responses, which significantly affect the recovery process. Here we review recent knowledge about brain-immune system interactions, which occur during degenerative and reparative processes, and focus mainly on spinal cord injury (SCI). Immune system-brain inflammatory responses involve multiple cell types that originate in the bloodstream and reside in the brain. Studies indicate that these cells have bidirectional destructive and supportive effects on the repair of damaged neural tissue after SCI. These opposing roles likely depend on the types of cells and their state of activation. Further detailed investigations on the mechanisms and function of their interactions are required to ultimately reduce the toxicity and enhance the trophic effects of the immune system. This would lead to the development of novel strategies to enhance recovery after SCI. The recent discovery of neural circuits that directly regulate immune responses has further highlighted brain-immune system communication. In this regard, signals from the brain to the immune system should also be considered to understand the whole pathology of SCI. In this review, we aim to emphasize that cell-cell and system-system interactions are important concepts for understanding the complex reactions that occur in the degenerating CNS.