Scientists have identified how immune cells bypass the blood-brain barrier to enter the brain, which in turn allows other immune cells to enter the brain and cause disease. The findings, published in Nature Immunology, have implications for our understanding of the autoimmune disease multiple sclerosis (MS).
Controversy surrounded previous work as to which immune cells were responsible for the pathology associated with multiple sclerosis or its mouse model ― experimental autoimmune encephalomyelitis. Federica Sallusto and colleagues resolve much of the controversy by showing two waves of immune cells enter the brain. First, cells expressing the homing receptor CCR6 enter via the choroid plexus ― a blood vessel-rich region that sits above the spinal column ― whose cells function to separate the blood supply from cerebral spinal fluids. Once inside, these immune cells can initiate attack on the brain tissues and trigger changes to the blood-brain barrier, causing it to become leaky and allowing other immune cells to enter the brain and contribute to the pathogenic disease process.
Importantly, the authors show similar findings occur in brain tissues of MS patients. Future work is needed to address whether targeting these CCR6-expressing immune cells might provide therapeutic benefit to MS patients.