Blocking the brain lymphatics reduces MS-like illness in laboratory model.
Recently, it was shown that lymphatic vessels exist in the brain and may provide one pathway for immune cells to cross into the brain in MS. New research has identified that blocking the function of these lymphatic vessels in the brain lessened disease in a laboratory model of MS.
MS results from an immune attack on the brain and spinal cord, carried out by immune cells which target the myelin coating of nerve fibres. One of the key questions in MS research is how exactly immune cells enter and exit the brain to cause damage.
For a long time, it was thought that the brain was the only organ in the body that was not connected to the drainage vessels of the body, known as the lymphatic system. The lymphatic system, is a network of tubes known as lymph vessels, similar to blood vessels, which carry a fluid known as “lymph” around the body. The lymphatic system is responsible for clearing toxins and providing nutrients to tissues. It also plays an important role in immunity. In 2015, it was found for the first time that lymph vessels did in fact connect to the brain, upending the way researchers thought about the connection between the brain and body. This discovery was of great interest, as it was thought that the lymphatic vessels may provide a way for immune cells to enter the brain and lead to the damage seen in MS.
Back in 2015, a research team that made the discovery of lymphatic vessels in the brain. Now the same team have looked more closely at how these vessels may be involved in MS.
Published in the prestigious journal Nature Neuroscience, the new study shows that the lymph vessels in the brain perform a similar function to the lymph vessels in other parts of the body, draining waste products from the cerebral spinal fluid (the fluid that surrounds the brain and spinal cord) and that the network of vessels extends much further than previously reported, across the protective membranes of both the brain and spinal cord.
The lymph vessels also provide a way for immune cells to carry out surveillance in the brain. The research team showed that using the lymph vessel network, immune cells can travel through the system and exit via lymph nodes located at the top of the spinal cord.
Movement of immune cells throughout the body is controlled by different biological signals and importantly, in this study, the researchers were also able to determine that the immune cells responded to a biological signal known as CCR7 to move through the lymphatic vessels in the brain.
Blocking the drainage function of the lymph vessels in a laboratory model of MS delayed the start of the disease and resulted in less severe symptoms. The disease was not completely stopped, implying that there are other pathways for immune cells to enter the brain and initiate damage.
This work is the first stage in pinpointing the role of the lymphatic system in the brain. It is hoped that a better understanding of the way immune cells interact with the brain, and especially identifying and modifying the pathways involved, may lead to new understandings of the disease mechanisms.