Lymphatic vessels form a network that includes nearly all of the tissues in the body. This network plays an important role in immune defence and in the removal of larger molecules and fluid from the tissues. Thus far it has been assumed that the central nervous system is not connected to the lymphatic system.
This summer this all changed when the research group led by Academy of Finland Professor Kari Alitalo made a startling discovery.
“We discovered a vessel in the eye that resembled a lymphatic vessel, which led us to examine the potential for lymphatic vessels in the structures around the eye more closely,” explains Aleksanteri Aspelund, one of the researchers in Academy Professor Alitalo’s group.
“Discovering such an extensive lymphatic network next to the brain was a complete surprise,” he notes.
The research group established that the lymphatic nodes in the membranes next to the brain run alongside the major veins, arteries and nerves in the meninges. The fluid and macromolecules in these vessels travel directly to the lymphatic nodes in the neck. This means that even though some textbooks still claim otherwise, the brain is connected to the body’s lymphatic system.
A break-through discovery
The researchers from the University of Helsinki and the Wihuri Research Institute led by Academy Professor Alitalo published their discovery in the June 2015 issue of the Journal of Experimental Medicine. Now the two most esteemed scientific journals, Nature Medicine and Science, have listed the discovery of lymphatic vessels in the brain as one of the most significant scientific discoveries of 2015.
The Finnish researchers lost the scientific race by a nose, as the researchers Antoine Louveau and Jonathan Kipnis had published their observations on the structure of some lymphatic vessels in the meninges only a few weeks before them in Nature.
Hidden in the meninges
It may seem strange that such a groundbreaking observation would only be made in 2015. According to medical researcher Salli Antila, who participated in the research, it is no wonder.
“The lymphatic vessels are very close to the internal structures of the meninges, and they are unlikely to be seen unless researchers are specifically looking for them. Even after we discovered the lymphatic vessels, it took us quite a while before we had developed a decent way of imaging them.”
Both Salli Antila and Aleksanteri Aspelund are working on their dissertations in Kari Alitalo’s group and have important roles in the research.
New perspectives on brain diseases
The lymphatic vessels of the brain are now a very popular topic of research. The discovery opens completely new perspectives on the function of the brain and the mechanisms that underlie many neurological diseases. According to the researchers, it is very possible that the lymphatic system plays an important role in many brain diseases, such as Alzheimer’s disease or strokes.
Researchers from the University of Helsinki and the University of Eastern Finland have joined forces to determine the contribution of the brain’s lymphatic vessels in Alzheimer’s disease, strokes and brain injuries.