Scientists have discovered a while new layer of tissues in the brain that acts as a protective barrier and also as a platform from which immune cells monitor the brain for infection and inflammation.
The research, published in the journal Science on Thursday, assessed membranes that encase the brain and keep it bathed in CSF – a colourless body fluid that surrounds the brain and spinal cord, cushioning them from sudden impact or injury.
This sub-arachnoid space is further separated into two compartments by the newly described layer SLYM – Subarachnoidal Lymphatic-like Membrane.
The SLYM, researchers say, is a type of membrane called mesothelium and is known to line other organs in the body, including the lungs and heart.
It is very thin and delicate, consisting of only one or a few cells in thickness, according to the study, and this type of membrane has been shown in previous studies to typically surround and protect organs and harbour immune cells.
The SLYM appears to host its own population of immune cells that use membrane for surveillance at the surface of the brain, allowing them to scan passing brain fluid for signs of infection.
The findings, according to the scientists, suggest that abnormalities in SLYM function might trigger or worsen diseases such as multiple sclerosis, central nervous system infections and Alzheimer’s.
SLYM is also a host for a large population of special cells, whose number increases in response to inflammation and ageing.