Conventional wisdom suggests that the brain and the body, while part of the same system, are separate entities. In particular, evidence has long suggested that, because of the brain’s significantly less aggressive immune response, the immune system may not have any brain-body link. However, a new study from the University of Virginia reveals that the immune system does have a presence in the brain that works differently than in the rest of the body. The findings refute previous theories about the brain’s interaction with the immune system and may offer clues to the origin of certain neurological and psychiatric disorders.
The brain has been considered “immunologically privileged” because of its immune response, primarily due to its lack of lymphatic drainage. The lymphatic system is like the networks of arteries and veins that traverse the body. Instead of blood, the lymphatic vessels return intracellular fluid to the blood stream. The lymph nodes throughout the system store immune cells. Previous research into the brain’s connection with the immune system indicated that the lymphatic network was not present in the brain, which meant that the brain had a relatively hospitable response to immunological threats.
For the present study, the researchers used neuroimaging to investigate how lymphatic vessels moved between the brain and body in mice. Their work was based on a previous finding that T-cells, which are present in the meniges (the membranes that surround the brain and spinal cord), were associated with some aspects of cognition.
The researchers discovered that a network of lymphatic vessels inhabits the meniges. The lymphatic vessels in this network transport fluid and immune cells from the cerebrospinal fluid to the neck’s deep cervical lymph nodes. T-cells are present in the lymphatic vessels, but not in the arteries and veins. This confirms that the brain has a lymphatic system that directly connects to the body’s system. The researchers were also able to identify these vessels in human tissue samples, suggesting that the same type of system is present in humans.
This immunological brain-body connection could explain how the immune system contributes to conditions like autism spectrum disorder (ASD) or Alzheimer’s. It may be possible to develop a therapeutic approach to these conditions based on the new information about the immune system.
This research is published in the journal Nature.
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