Nature Immunol. 10, 514–523 (2009)

Immune cells can normally penetrate the barrier between the bloodstream and the brain only when the cells along this barrier are inflamed. So how do immune cells enter the brain to initiate the sort of inflammation associated with autoimmune disorders such as multiple sclerosis?

Federica Sallusto of the Institute for Research in Biomedicine, Bellinzona, Switzerland, and her colleagues showed that the cells enter through the choroid plexus, the brain region where cerebrospinal fluid is made. They used a mouse model of multiple sclerosis to show that a subset of T cells gains entry when their CCR6 surface receptors bind to a protein produced by cells of the choroid plexus. Once inside, the immune cells initiate inflammation.

The team also found that this gateway protein is present in the human choroid plexus and that a higher number of T cells from the spinal fluid of patients with multiple sclerosis express the CCR6 receptor.