Although we don't know for certain that new treatments are just over the horizon, here's some potentially exciting news. Scientists at the University of Virginia have discovered previously unknown lymphatic vessels in the outer layers of the brain. These vessels appeared to link the brain and spinal cord with the rest of the body’s immune system. This study used mice and human samples, vessel structure was investigated in the mice, and the observations followed up in the human samples. This was an animal study using mice to investigate the structure and function of lymphatic vessels in the brain. In fact, this story has been circulating for awhile, but recently it's been highlighted in several stories. The good news is that this may mean that the original studies are standing up to scrutiny by other scientists.

The discovery may require a reassessment of our assumptions about lymph drainage in the brain and its role in diseases involving brain inflammation or degeneration, such as Alzheimer’s disease and multiple sclerosis. The study was published in the peer-reviewed scientific journal Nature.

When I was in medical school, we were taught that the central nervous system (brain and spinal cord) did not have a typical lymphatic drainage system. Lymph is the immune fluid that circulates through the body, containing white blood cells to fight infection and destroy abnormal cells. This study aimed to look at the circulation of lymph in the mouse brain, but mice and humans do not have identical biology, so the findings may not be directly applicable. 

The study involved complex laboratory techniques, using a fluorescent antibody to assess the alignment of cells within the brain, examination for markers associated with a lymphatic drainage system and looking at the functional capacity of identified vessels to carry lymphatic fluid to and from the brain. 
Human samples taken from the brain at autopsy were used to investigate any structures found in mice.

The scientists found that the outer protective layers of the mouse brain showed cells that were clearly lined up, which suggested that these were vessels with a unique function. These cells showed the characteristic features of functional lymphatic vessels. These vessels appeared able to carry both fluid and immune cells from the fluid surrounding the brain and spinal cord (the cerebrospinal fluid), and were connected to the lymph nodes in the neck. The location of these vessels may have been the reason they have not been discovered before, thereby causing the belief that there is no lymphatic drainage system in the brain.

This may mean current thinking about how the brain works needs to be reassessed. The researchers go on to say it could be the malfunction of these vessels that could be the cause of a variety of brain disorders, such as multiple sclerosis and Alzheimer’s disease.

Summary: This mouse study has examined the circulation of lymph in the brain. It discovered previously unknown lymphatic vessels in the outer layers of the mouse brain. If accurate, the findings may call for a review of how the immune system in the brain functions, and shed new light on its role in brain diseases involving brain inflammation or degeneration. Though animal research can give a good insight into biological and disease processes, and how they may work in humans, the processes in humans and mice are not identical. Further studies are needed to confirm these findings and to assess whether this knowledge is transferable to humans. As such, it is too early to say whether the findings could one day have any implications for the treatment of degenerative brain conditions such as multiple sclerosis or Alzheimer’s.  

The original article in Nature can be found here.

Tags: lymphatic system, brain, neuroscience, research