Discovery of hidden structures
One of the principal dogma concerning the central nervous system has just fallen:
brain and immune system are connected by lymphatic vessels.
Until a recent discovery made by researchers at the University of Virginia
school of Medicine and published in the journal
Nature (/documents/import/Louveau_2015.pdf), it was admitted that the lymphatic system was absent in the brain as
it remained unidentified.
By developing a new technique to maintain the integrity of the lymphatic
vessels, easily confoundable with the blood vessels and by visualizing
meninges (the membrane covering the brain) as a whole in mice, Dr Louveau
and his collaborators were able to localize vessels positive for specific
markers of lymphatic endothelial cells surrounded by in a complex network
of immune cells.
Figure 1: Old schematic representation of the lymphatic system (left),
updated map including UVA discovery (right). Picture: Courtesy of the
University of Virginia Health System.
New components of neuroinflammatory diseases
The presence of a functional and classical lymphatic system in the central
nervous system suggests that this structure could carry fluid and immune
cells from the cerebrospinal fluid thus directly impacting the brain microenvironment.
As stated by the authors:” Malfunction of the meningeal lymphatic
vessels could be a root cause of a variety of neurological disorders in
which altered immunity is a fundamental player”.
It is too early to confirm the involvement of the lymphatic drainage system
in the etiology of autism. Nevertheless, this stunning study confirms
the cross-talk existing between the immune system and the brain.
The lymphatic vessels could be a possible vector for the transit of immune
cells thus playing a key role in brain inflammation.