Science Discovers Direct Link Between the Brain and Immune System

There has been a recent discovery out of the University of Virginia that may revolutionize the way we think of neuroimmunology. Neuroimmunology is the study of how the nervous system interacts with the immune system.

What they found was that there is a direct linkage between the immune system and the brain through the lymph vessels. In the past, it was believed that lymph vessels did not reach the brain. Lymph vessels are similar to blood vessels except that, instead of carrying blood, lymph vessels carry lymph fluid, which is part of the immune system.

In the research study, it was discovered that lymph vessels exist underneath the mouse’s skull. This finding could be a link to finding out what causes diseases like Alzheimer’s disease, MS, and autism.

It is now nearly undeniable that the immune system, the brain, and the gut are closely connected. Researchers have found, for example, that autism is linked to the GI tract and possibly to a hyper-responsiveness of the immune system. In addition, other neurological diseases like Alzheimer’s disease and MS are closely linked to alterations in the function of the immune system and that known autoimmune diseases like ulcerative colitis and Crohn’s disease are linked to psychiatric diseases.

Up until now, doctors didn’t know how these types of connections occurred. With the latest research, a link between the gut, the brain, and the immune system has finally been discovered.

The Research

In the research study, it was discovered that the lymph vessels in the mouse model were very close to the meninges of the brain, which is the brain’s protective coverings. They seemed to follow the same pathway as the blood vessels in the brain.

According to the researchers, many neurologic diseases have some kind of immune component affecting them. The discovery of the lymph vessels so near the brain may be a clue as to why this is the case. Lymph vessels contain immune cells and their close association to the brain cannot be ignored.

One example is Alzheimer’s disease. In this condition, there is an accumulation of chunks of protein in brain tissue that may be accumulating because the lymph vessels are not clearing them out to a sufficient degree.

The researchers say that it all makes a lot of sense. The brain should have a direct connection to the immune system. While the brain used to be considered void of surveillance by the immune system, the new research indicates otherwise.

Recent studies have revealed that the brain does indeed interact with the immune system but in ways, you wouldn’t expect. There are immune cells circulating throughout the brain and there are antigens that usually result in an immune response draining from the brain directly into the lymph nodes.

The Brain/Gut Connection

The immune system is not the only part of the body affiliated with the brain. The gut, long known to be related to the immune system, communicates with the brain by means of what researcher’s call the “brain-gut axis.” The wall of the gut itself contains the enteric nervous system, which works alongside the brain and independently of it to control activities within the gut. In a sense, we have two brains—one in the gut and one in the brain itself. The two brains interact with one another so that, if you eat certain foods it affects your emotions and when you’re anxious, you can feel nauseous.

The brain-gut axis seems to go both ways. The brain sends signals to the gastrointestinal system and the immune system that alters the makeup of the microbes within the gut. The microbes themselves make compounds that are neuroactive, including metabolites that act on the brain and neurotransmitters.

The latest research also explains why various alterations in the bacteria in the gut can be linked to disorders of the brain, including depression. The microbes communicate with the brain through the enteric nervous system, which controls the GI tract. The bacteria in the gut also change how the immune system works, which can go on to affect the brain. The substances the gut bacteria make when food is broken down can also play a role in the brain.

When we are under stress or have an infection, the bad bacteria can leak into the blood via a leaky gut, causing the bacteria and the chemicals they produce to make connection to the brain via the cells in the walls of the blood vessels. Bacteria may also be able to make connection to the brain directly, including those areas of the brain that are connected to mood and the stress response.