Alzheimer’s disease, multiple sclerosis, autism, schizophrenia and many other neurological and psychiatric conditions have been linked to inflammation in the brain. There’s growing evidence that immune cells and molecules play a key role in normal brain development and function as well. But at the core of the burgeoning field of neuroimmunology lies a mystery: How does the immune system even know what’s happening in the brain? Generations of students have been taught that the brain is immunoprivileged, meaning the immune system largely steers clear of it.
Now, researchers at Washington University School of Medicine in St. Louis believe they have figured out how the immune system keeps tabs on what’s going on in the brain. Immune cells are stationed in the meninges — the tissue that covers the brain and spinal cord — where they sample fluid as it washes out of the brain. If the cells detect signs of infection, disease or injury, they are prepared to initiate an immune response to confront the problem, the researchers said.
The findings, published Jan. 27 in the journal Cell, open up the possibility of targeting immune cells at such surveillance sites as a means of treating conditions driven by brain inflammation.
“Every organ in the body is being surveilled by the immune system,” said senior author Jonathan Kipnis, PhD, the Alan A. and Edith L. Wolff Distinguished Professor of Pathology & Immunology. “If there’s a tumor, an injury, an infection anywhere in the body, the immune system has to know about it. But people say the exception is the brain; if you have a problem in the brain, the immune system just lets it happen. That never made sense to me. What we’ve found is that there is indeed immune surveillance of the brain — it’s just happening outside the brain. Now that we know where it’s happening, that opens up lots of new possibilities for modulating the immune system.”