A new study dramatically changes scientific understanding of the brain-immune system connection, with a newly discovered system of lymph vessels in the membranes that line the brain. (See illustration above.)
The discovery could likewise advance understanding of inflammation’s role in neurological conditions such as autism, the study authors say. Their findings appear online this week in the journal Nature.
Lymph vessels carry patrolling immune cells from sites throughout the body to lymph nodes – the “command centers” that direct the immune system to fight perceived threats with inflammation. Previously, it was believed that the brain was largely cut off from the body’s larger immune system. Indeed, the brain has its own distinct immune cells, called glia, which are found nowhere else in the body.
The new discovery suggests that there may be far more interplay between the immune systems of the brain and body than previously thought.
“This adds to the numerous lines of scientific evidence linking brain-immune system interactions to health and well-being and will increase focus on how they relate to autism,” comments neuroscientist Dan Smith, Autism Speaks’ vice president for innovative technologies. (Dr. Smith was not involved in the study.) “Whether we’re looking at genes or environmental risk factors, we repeatedly see that the brain and the immune system are implicated in its causes and symptoms.”
“We believe that for every neurological disease that has an immune component to it, these vessels may play a major role,” says senior study author Jonathan Kipnis, of the University of Virginia’s Center for Brain Immunology and Glia.
The discovery was made by Antoine Louveau, a postdoctoral fellow in Kipnis’ lab. He detected the lymph vessels after developing a method to examine a mouse’s meninges – the membranes covering the brain – as a whole. This enabled him to see vessel-like patterns in the distribution of immune cells on the meninges. Further analysis showed that the immune cells were inside a network of lymphatic vessels.
As to how the brain’s lymphatic vessels managed to escape notice all this time, Kipnis described them as “very well hidden.” They follow blood vessels so closely that they are easy to miss with traditional dissection methods.
Insights into autism, Alzheimer’s and beyond
The newly discovered lymphatic vessels open a new avenue of research into the immune system’s role in brain conditions such as autism, Alzheimer’s, multiple sclerosis and more.
“The promise of these findings is that they will lead to a deeper understanding of how the brain and immune systems interact in autism,” Dr. Smith concludes. “Further study may reveal specific mechanisms that underlie medical or behavioral issues and that might become targets for more effective interventions.”
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