One of the key questions of MS research is how immune cells move into the brain and spinal cord and cause damage. Recently it was discovered that lymphatic vessels, the waste drainage system of the body, do in fact connect to the brain and that this may provide a possible mechanism for immune cells to enter the brain in MS. A new study has shown that lymphatic vessels drain waste products and allow immune cells to move through the system. Blocking the lymphatic vessels delayed and lessened disease in a laboratory model of MS.
MS results from an immune attack on the brain and spinal cord, which is carried out by immune cells that 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 this damage.
Previously, researchers believed the brain was the only organ 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, whilst also playing an important role in immunity. In 2015, it was discovered that lymph vessels did, in fact, connect to the brain, challenging MS researchers’ existing understanding of 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.
Now, the team that discovered these lymphatic vessels in the brain has examined in greater detail 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). It also shows that the network of vessels extends much further than previously reported, stretching 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. In this study, 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. During the study, the team determined 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, in particular, identifying and modifying the pathways involved, may lead to a greater understanding of the disease mechanisms.
With thanks to MS Research Australia – the lead provider of research summaries on our website.